Anticoccidial vaccines for broiler chickens: pathways to success

Prevalence, geographic distribution and risk factors of Eimeria species on commercial broiler farms in Guangdong, China

BACKGROUND

Coccidiosis is one of the most frequently reported diseases in chickens, causing a significant economic impact on the poultry industry. However, there have been no previous studies evaluating the prevalence of this disease in broiler farms in Guangdong province. Therefore, this study aims to conduct an epidemiological investigation into the occurrence of Eimeria species and associated risk factors in intensive management conditions across four regions in Guangdong province, China. A total of 394 fecal samples were collected from 89 broiler farms in Guangdong province. The prevalence of Eimeria species infection was determined using PCR, and the occurrence of Clostridium perfringens type A was assessed using quantitative real-time PCR.

RESULTS

The results showed an overall prevalence of 98.88% (88/89) at the farm level and 87.06% (343/394) at the flock level. All seven Eimeria species were identified, with E. acervulina (72.53%; 64/89), E. tenella (68.54%; 61/89), and E. mitis (66.29%; 59/89) at the farm level, and E. acervulina (36.55%; 144/394), E. mitis (35.28%; 139/394), and E. tenella (34.01%; 134/394) at the flock level. The predominant species combination observed was a co-infection of all seven Eimeria species (6.74%; 6/89), followed by a combination of E. acervulina, E. tenella, E. mitis, E. necatrix, E. brunetti, and E. maxima (5.62%, 5/89). A combination of E. acervulina, E. tenella, E. mitis, E. necatrix, E. brunetti, and E. praecox (4.49%; 4/89) was also observed at the farm level. Furthermore, the study identified several potential risk factors associated with the prevalence of Eimeria species, including farm location, chicken age, drinking water source, control strategy, and the presence of C. perfringens type A were identified as potential risk factors associated with prevalence of Eimeria species. Univariate and multivariate analyses revealed a significant association between E. necatrix infection and both grower chickens (OR = 10.86; 95% CI: 1.92-61.36; p < 0.05) and adult chickens (OR = 24.97; 95% CI: 4.29-145.15; p < 0.001) compared to starter chickens at the farm level. Additionally, farms that used groundwater (OR = 0.27; 95% CI: 0.08-0.94; p < 0.05) were less likely to have E. maxima compared to those that used running water. At the flock level, the prevalence of E. tenella was significantly higher in the Pearl River Delta (OR = 2.48; 95% CI: 1.0-6.15; p = 0.05) compared to eastern Guangdong. Interestingly, flocks with indigenous birds were less likely to have E. brunetti (OR = 0.48; 95% CI: 0.26-0.89; p < 0.05) compared to flocks with indigenous crossbred birds. Furthermore, flocks that used anticoccidial drugs (OR = 0.09; 95% CI: 0.03-0.31; p < 0.001) or a combination of vaccines and anticoccidial drugs (OR = 0.06; 95% CI: 0.01-0.25; p < 0.001) were less likely to be positive for E. tenella compared to flocks that only used vaccines. Finally, flocks with C. perfringens type A infection were significantly more likely to have E. necatrix (OR = 3.26; 95% CI: 1.96-5.43; p < 0.001), E. tenella (OR = 2.14; 95% CI: 1.36-3.36; p < 0.001), E. brunetti (OR = 2.48; 95% CI: 1.45-4.23; p < 0.001), and E. acervulina (OR = 2.62; 95% CI: 1.69-4.06; p < 0.001) compared to flocks without C. perfringens type A.

CONCLUSIONS

This study conducted an investigation on the prevalence, distribution, and risk factors associated with Eimeria species infection in broiler chickens in Guangdong. The farm-level prevalence of Eimeria species was higher than the previous prevalence figures for other areas and countries. E. brunetti was identified at higher prevalence in Guangdong than previously survived prevalence in different regions in China. Farm location, chicken age, drinking water source, control strategy, and the presence of C. perfringens type A were considered as potential risk factors associated with prevalence of Eimeria species. It is imperative to underscore the necessity for further surveys to delve deeper into the occurrence of Eimeria species under intensive management conditions for different flock purposes.

A Study of Cross-Protection between Eimeria maxima Immunovariants

For reasons unknown, Eimeria maxima is unique among Eimeria species infecting chickens in the immunovariability it displays among isolates from different geographical areas. Eimeria maxima oocysts (named EmaxAPU3) were isolated late in grow-out (6 weeks) from litter in a commercial broiler operation that was using Eimeria vaccination as the coccidiosis control program. Cross-protection studies (n = 4) were conducted in immunologically naïve chickens between EmaxAPU3 and two E. maxima lab strains (EmaxAPU1, EmaxAPU2) by immunizing with one E. maxima strain and challenging with either the homologous or heterologous E. maxima. As measured by oocyst output, immunization with EmaxAPU1 protected against homologous challenge (EmaxAPU1) and against heterologous challenge with EmaxAPU3, but not against EmaxAPU2. Similarly, immunization with EmaxAPU3 protected against homologous challenge (EmaxAPU3) and against heterologous challenge with EmaxAPU1, but not against EmaxAPU2. Immunization of chickens with EmaxAPU2 elicited a protective response against homologous challenge (EmaxAPU2), but not against EmaxAPU1 nor EmaxAPU3. The most plausible explanation for the appearance of this immunovariant late in grow-out is that E. maxima APU3 escaped immunity directed to E. maxima antigenic types in the commercial vaccine.

Prevalence and Risk Factors of Eimeria spp. in Broiler Chickens from Pichincha and Santo Domingo de los Tsáchilas, Ecuador

Coccidiosis in chickens is a parasitic disease of economic importance for the poultry industry. In Ecuador, there is limited information regarding the prevalence of Eimeria spp. on commercial broiler farms. Therefore, a total of 155 poultry farms in the provinces of Pichincha and Santo Domingo de los Tsáchilas were surveyed. The analysis of fresh fecal samples was conducted to determine the parasitic load of six of the seven chicken Eimeria species (excluding E. mitis) through multiplex PCR. Additionally, an epidemiological survey was performed to assess the risk factors associated with the infection using a multivariable logistic regression model. All samples tested positive for the presence of Eimeria spp., despite the farmers having implemented prophylactic measures, and no clinical coccidiosis cases were recorded. The parasitic load varied between 25 and 69,900 oocyst per gram. The species prevalence was as follows: Eimeria spp. 100%, E. maxima 80.4%, E. acervulina 70.6%, E. praecox 55.4%, E. tenella 53.6%, E. necatrix 52.2%, and E. brunetti 30.8%. The main species combination was E. cervuline, E. maxima, E. necatrix, and E. praecox (23.90%), followed by E. tenella, as a unique species (10.69%), and then E. acervulina, E. maxima, and E. praecox (8.81%). It was observed that farms operated by independent producers had a higher amount of Eimeria spp. and higher probability of the presence of E. brunetti, E. necatrix, E. praecox, and E. tenella. Poultry houses located below 1300 m above sea level were associated with a higher parasitic load and the presence of E. brunetti. Birds younger than 35 days of age and from open-sided poultry houses (with rudimentary environmental control) had a higher probability of presenting E. maxima. Drinking water from wells increased the risk of E. praecox presence. Research aimed at designing control strategies to improve health management on poultry farms in the region would help minimize the impact of coccidiosis.

Vaccination Against Poultry Parasites

The complexity of parasites and their life cycles makes vaccination against parasitic diseases challenging. This review highlights this by discussing vaccination against four relevant parasites of poultry. Coccidia, i.e., Eimeria spp., are the most important parasites in poultry production, causing multiple billions of dollars of damage worldwide. Due to the trend of antibiotic-free broiler production, use of anticoccidia vaccines in broilers is becoming much more important. As of now, only live vaccines are on the market, almost all of which must be produced in birds. In addition, these live vaccines require extra care in the management of flocks to provide adequate protection and prevent the vaccines from causing damage. Considerable efforts to develop recombinant vaccines and related work to understand the immune response against coccidia have not yet resulted in an alternative. Leucozytozoon caulleryi is a blood parasite that is prevalent in East and South Asia. It is the only poultry parasite for which a recombinant vaccine has been developed and brought to market. Histomonas meleagridis causes typhlohepatitis in chickens and turkeys. The systemic immune response after intramuscular vaccination with inactivated parasites is not protective. The parasite can be grown and attenuated in vitro, but only together with bacteria. This and the necessary intracloacal application make the use of live vaccines difficult. So far, there have been no attempts to develop a recombinant vaccine against H. meleagridis. Inactivated vaccines inducing antibodies against the poultry red mite Dermanyssus gallinae have the potential to control infestations with this parasite. Potential antigens for recombinant vaccines have been identified, but the use of whole-mite extracts yields superior results. In conclusion, while every parasite is unique, development of vaccines against them shares common problems, namely the difficulties of propagating them in vitro and the identification of protective antigens that might be used in recombinant vaccines.

Retrospective Broiler Health Survey: Scope, Parameters, and Overall Trends

A retrospective analysis encompassing 18 yr (1999-2016) of broiler chicken health surveys from broiler production complexes throughout the United States was conducted to identify trends and areas of opportunity. The analysis used necropsy data from 19,577 broiler chickens considered to be "healthy" or "clinically normal" by visual assessment. The very low incidence of dehydrated (0.01%) or undersized (0.02%) broilers is evidence that the objective of examining "healthy" birds was achieved. The results of the correlation analysis were what was expected for "healthy" broilers, with these birds having positive correlations with skin color and size of the bursa of Fabricius. The average age of broilers included in this analysis ranged from 26.2 days in 2008 to 33.7 days in 2013. The percentage of "normal" broilers (those without visible lesions or abnormalities) varied from 5.63% in 2012 to 28.33% in 1999. The results of this study identified four areas of opportunity for improving poultry health: 1) coccidiosis, 2) oral lesions and gizzard erosions, 3) retained yolks, and 4) pododermatitis.

Live attenuated anticoccidial vaccines for chickens

Chicken coccidiosis, caused by infection with single or multiple Eimeria species, results in significant economic losses to the global poultry industry. Over the past decades, considerable efforts have been made to generate attenuated Eimeria strains, and the use of live attenuated anticoccidial vaccines for disease prevention has achieved tremendous success. In this review, we evaluate the advantages and limitations of the methods of attenuation as well as attenuated Eimeria strains in a historical perspective. Also, we summarize the recent exciting research advances in transient/stable transfection systems and clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing developed for Eimeria parasites, and discuss trends and challenges of developing live attenuated anticoccidial vaccines based on transgenesis and genome editing.

Impacts of phytase and coccidial vaccine on growth performance, nutrient digestibility, bone development, and intestinal gene expression of broilers fed a nutrient reduced diet

An experiment was conducted to evaluate effects of phytase and coccidial vaccine on growth performance, bone ash, bone 3-D microstructure, nutrient digestibility, and gene expression of intestinal biomarkers in broilers fed a regular or nutrient-reduced diet. The experiment was conducted in a 2 × 4 factorial arrangement with 6 replicates per treatment and 10 birds per replicate. Two main factors were coccidial vaccine and dietary treatments. The dietary treatments included: 1) a positive control (PC; normal nutrient levels); 2) a negative control (NC; with a reduction of 0.15% of Ca and avP and 5% of essential amino acid (EAA) and crude protein relative to PC); 3) NC + 500 FTU/kg of phytase; and 4) NC + 1,500 FTU/kg of phytase. No interaction effect of phytase and coccidial vaccine on growth performance, bone ash, and apparent ileal digestibility (AID) was observed. For the main effect, birds fed the NC diet showed lower (P = 0.007) BWG during d 0 to 21 compared to PC birds, whereas supplementing 500 or 1,500 FTU/kg phytase increased BWG to the similar level to the PC. During d 0 to 21, vaccinated birds had a lower (P < 0.001) FI and better (P = 0.045) FCR compared to unvaccinated birds. Birds fed the NC diet resulted a decrease in tibia fat-free dry bone weight (P = 0.012), ash weight (P = 0.005), ash percentage (P < 0.001), and ash concentration (P = 0.019) compared to the PC group at d 21, whereas supplementing phytase at 500 or 1,500 FTU/kg in NC diet was able to improve these bone parameters to the similar level to the PC; however, vaccination did not have any effect on bone ash. Similarly, birds fed with the NC diet showed had significant lower bone microstructure levels including bone volume, bone mineral density, and bone mineral content (P < 0.001), and supplementing phytase at 1,500 FTU/kg improved these parameters. Vaccination improved AID of nitrogen (P < 0.001). Birds from the NC and both phytase supplementation groups had a higher (P = 0.001) AID of Ca compared to the PC. Supplementing phytase at 500 FTU/kg or 1,500 FTU/kg improved (P < 0.001) AID of P compared to the NC. Additionally, the NC had a lower AID of DM than the PC, whereas supplementing phytase at 500 FTU/kg or 1,500 FTU/kg improved DM digestibility (P = 0.0299). In conclusion, supplementation of phytase at 500 or 1,500 FTU/kg improved growth performance, bone mineralization, and nutrient digestibility regardless of vaccination, with a more pronounced effect when supplementing phytase at 1,500 FTU/kg.

Characterization of the novel glucose-methanol-choline (GMC) oxidoreductase EnOXIO1 in Eimeria necatrix

Eimeria species are intracellular obligate parasites, among the most common pathogens affecting the intensive poultry industry. Oxidoreductases are members of a class of proteins with redox activity and are widely found in apicomplexan protozoans. However, there have been few reports related to Eimeria species. In this study, total RNA was extracted from the gametocytes of E. necatrix Yangzhou strain to amplify the EnOXIO1 gene using reverse-transcription polymerase chain reaction. After cloning and sequence analysis, the prokaryotic expression vector pET-28a(+)-EnOXIO1 was constructed and transformed into Escherichia coli BL21(DE3), and the recombinant protein rEnOXIO1 was expressed by induction with isopropyl ß-D-1-thiogalactopyranoside. The full length EnOXIO1 gene was 2535 bp encoding 844 amino acids, and the EnOXIO1 protein had a molecular weight of about 100 kDa and was mainly expressed in inclusion bodies. Western blot analysis indicated that the rEnOXIO1 protein had good antigenicity and cross-reactivity and was specifically recognized by a 6 ×HIS labeled monoclonal antibody, mouse anti-recombinant protein polyclonal antibody, and recovery serum from chickens infected with E. necatrix, E. acervulina, and E. tenella sporulated oocysts. The results of laser confocal immunofluorescence localization showed that the EnOXIO1 protein was mainly located on the wall-forming bodies in gametocytes and played an important role in the formation of the oocyst wall. Quantitative PCR analysis revealed that transcript levels of EnOXIO1 were highest in the gametocyte stage. Protein expression levels of EnOXIO1 were higher in the gametocyte stage than in other developmental stages according to western blot analysis. Vaccination of chickens against E. necatrix was achieved with recombinant protein rEnOXIO1, which triggered humoral immunity and antibody production, increased average body weight gain, reduced oocyst output and alleviated lesions after E. necatrix infection. The highest ACI value (172.36) was observed in chickens that received 200 μg rEnOXIO1 compared with other immunization groups.

Effects of dietary essential oil supplementation on growth performance, carcass yield, meat quality, and intestinal tight junctions of broilers with or without Eimeria challenge

The effects of dietary supplementation of essential oil on growth performance, carcass yield, meat quality, serum antioxidant capacity, and intestinal tight junctions of broilers with or without Eimeria challenge were investigated. A total of 576 one-day-old male broilers were randomly separated into 8 treatments (6 replication floor-pens per treatment, 12 broilers per pen) in a 4 × 2 factorial design. The 4 diets consisted of 1) a corn and soybean meal basal diet, 2) an anticoccidial diet (60 g nicarbazin and 60 g narasin per ton of feed), 3) an oregano oil diet (500 ppm oregano oil), and 4) a clove oil diet (500 ppm clove oil). On d 10, half chicks were challenged with 1 × 104 sporulated oocysts of E. tenella, E. acervulina, and E. maxima per chick, whereas the others were inoculated with an equal amount of dilution (0.5 mL). The Eimeria challenge induced a higher fecal oocyst output on d 18, a lower duodenum Occludin expression level on d 28, a lower serum catalase level, and a higher cook loss and protein loss in thigh muscle on d 42. The anticoccidial diet lowered fecal Eimeria output and increased d 1 to 42 BW gain as compared to the control diet. The clove oil treatment enhanced duodenum ZO-1 expression level in nonchallenged birds, increased BW gain from d 1 to 14 and breast yield on d 42. The oregano oil treatment enhanced ZO-1 expression of challenged birds, reduced feed intake from 15 to 28 d, and helped broilers gain more tender meat. For those Eimeria-challenged broilers, both clove and oregano oil treatments recovered drip loss in breast muscle. Our results suggested that Eimeria challenge in broiler early age could interrupt later serum antioxidant capacity and damage meat quality. The dietary supplementation of clove or oregano essential oils could improve broiler growth performance and partially relieve the coccidial damage in gut integrity and meat quality.

Microbiome of Ceca from Broiler Chicken Vaccinated or Not against Coccidiosis and Fed Berry Pomaces

American cranberry (Vaccinium macrocarpon) and lowbush/wild blueberry (V. angustifolium) pomace are polyphenol-rich products having potentially beneficial effects in broiler chickens. This study investigated the cecal microbiome of broiler-vaccinated or non-vaccinated birds against coccidiosis. Birds in each of the two groups (vaccinated or non-vaccinated) were fed a basal non-supplemented diet (NC), a basal diet supplemented with bacitracin (BAC), American cranberry (CP), and lowbush blueberry (BP) pomace alone or in combination (CP + BP). At 21 days of age, cecal DNA samples were extracted and analyzed using both whole-metagenome shotgun sequencing and targeted-resistome sequencing approaches. Ceca from vaccinated birds showed a lower abundance of Lactobacillus and a higher abundance of Escherichia coli than non-vaccinated birds (p < 0.05). The highest and lowest abundance of L. crispatus and E. coli, respectively, were observed in birds fed CP, BP, and CP + BP compared to those from NC or BAC treatments (p < 0.05). Coccidiosis vaccination affected the abundance of virulence genes (VGs) related to adherence, flagella, iron utilization, and secretion system. Toxin-related genes were observed in vaccinated birds (p < 0.05) in general, with less prevalence in birds fed CP, BP, and CP + BP than NC and BAC (p < 0.05). More than 75 antimicrobial resistance genes (ARGs) detected by the shotgun metagenomics sequencing were impacted by vaccination. Ceca from birds fed CP, BP, and CP + BP showed the lowest (p < 0.05) abundances of ARGs related to multi-drug efflux pumps, modifying/hydrolyzing enzyme and target-mediated mutation, when compared to ceca from birds fed BAC. Targeted metagenomics showed that resistome from BP treatment was distant to other groups for antimicrobials, such as aminoglycosides (p < 0.05). Significant differences in the richness were observed between the vaccinated and non-vaccinated groups for aminoglycosides, β-lactams, lincosamides, and trimethoprim resistance genes (p < 0.05). Overall, this study demonstrated that dietary berry pomaces and coccidiosis vaccination significantly impacted cecal microbiota, virulome, resistome, and metabolic pathways in broiler chickens.

Investigation of a gel-based delivery method for the administration of a live, attenuated Salmonella Typhimurium vaccine

Poultry vaccines are often administered using water as a suspension media and applied using an oral or coarse spray method. Gel-based vaccine diluents have been developed as an alternative vaccine delivery method. Gels are more viscous, and droplets adhere more effectively to feathers giving the vaccine a longer time to be ingested (through preening). Application of gel diluents with live bacterial vaccines, however, is limited. The present study tested a gel diluent prepared in various media, using a live, attenuated Salmonella Typhimurium vaccine, Vaxsafe ST. Reconstitution in gel diluent did not negatively affect vaccine viability or motility. The invasive capacity of vaccine suspended in gel diluent into cultured intestinal epithelial cells was also tested. Results demonstrated that vaccine suspended in gel diluent retained invasiveness. Day old chicks were orally administered with Vaxsafe ST suspended in gel diluent to characterize in vivo colonization capacity of the vaccine. The results revealed that the VaxSafe ST suspended in gel diluent could efficiently colonize the caeca of chicks, which is needed for the development of effective immunity.

Using microsphere or fluorescein tracers and total oocyst output to measure ingestion of material following live coccidiosis vaccinations

One method of prevention of coccidiosis in broiler chickens raised without antibiotics relies on coccidiosis vaccination. Live-coccidiosis vaccines carry the risk for pathogenic effects if the Eimeria species overcycle. However, all chicks must receive an appropriate dose of Eimeria oocysts to induce immunity and reduce the risk of adverse effects. At the hatchery, coccidiosis vaccines are administered topically to boxes of chicks by spray or gel-droplet application. Determining the volume of vaccine ingested by individual chicks could provide a means of evaluating the success of different application methods. For each of 2 mass application methods (spray, gel-droplet), we used 3 quantification methodologies to determine the amount of vaccine material ingested by chicks: total oocyst counts from feces collected 5- to 8-days postvaccination; and counts of either microsphere or fluorescein tracers recovered from the gastrointestinal tract 30-min postvaccination. For each quantification methodology, chicks vaccinated via spray or gel-droplet application were compared to chicks vaccinated via oral gavage using the same concentration of oocysts per mL for all groups. Chicks vaccinated via gel-droplet application shed 10-fold more oocysts than those vaccinated by spray application. Individual chick consumption of vaccine material using tracers also revealed that chicks ingested more material following gel-droplet application than spray application, although the magnitude of the difference varied based on quantification methodology. The results of this study suggest that all 3 quantification methodologies can be used to help validate and improve mass vaccine application methods to ensure optimal ingestion, and therefore, coccidiosis vaccination success.

Protective efficacy induced by Eimeria maxima rhomboid-like protein 1 against homologous infection

Introduction

Avian coccidiosis, caused by apicomplexan protozoa belonging to the Eimeria genus, is considered one of the most important diseases in the intensive poultry industry worldwide. Due to the shortcomings of live anticoccidial vaccines and drugs, the development of novel anticoccidial vaccines is increasingly urgent.

Methods

Eimeria maxima rhomboid-like protein 1 (EmROM1), an invasion-related molecule, was selected as a candidate antigen to evaluate its protective efficacy against E. maxima in chickens. Firstly, the prokaryotic recombinant plasmid pET-32a-EmROM1 was constructed to prepare EmROM1 recombinant protein (rEmROM1), which was used as a subunit vaccine. The eukaryotic recombinant plasmid pVAX1.0-EmROM1 (pEmROM1) was constructed as a DNA vaccine. Subsequently, 2-week-old chicks were separately vaccinated with the rEmROM1 and pEmROM1 twice every 7 days. One week post the booster vaccination, induced cellular immune responses were determined by evaluating the mRNA level of cytokines including IL-2, IFN-γ, IL-4, IL-10, TGF-β, IL-17, and TNFSF15, as well as the percentages of CD4⁺ and CD8⁺ T cells from spleens of vaccinated chickens. Specific serum antibody level in the vaccinated chickens was determined to assess induced humoral immune responses. Finally, the protective efficacy of EmROM1 was evaluated by a vaccination-challenge trial.

Results

EmROM1 vaccination significantly upregulated the cytokine transcription levels and CD4⁺/CD8⁺ T cell percentages in vaccinated chickens compared with control groups, and also significantly increased the levels of serum-specific antibodies in vaccinated chickens. The animal trial showed that EmROM1 vaccination significantly reduced oocyst shedding, enteric lesions, and weight loss of infected birds compared with the controls. The anticoccidial index (ACI) from the rEmROM-vaccination group and pEmROM1-vaccination group were 174.11 and 163.37, respectively, showing moderate protection against E. maxima infection.

Discussion

EmROM1 is an effective candidate antigen for developing DNA or subunit vaccines against avian coccidiosis.

Impact of Dietary Supplementation with Sodium Butyrate Protected by Medium-Chain Fatty Acid Salts on Gut Health of Broiler Chickens

Simple Summary

Nutritional strategies to improve gut health are under research to reduce antibiotic use in poultry production. This study investigated the effect of dietary supplementation with sodium butyrate protected by sodium salts of medium-chain fatty acids as a feed additive on broiler gut health. A first trial was conducted to assess the effectiveness of this feed additive supplemented at a dose range of 0.5, 1, and 2 kg/t to promote a good health status on broilers raised under optimal conditions. Supplementation at 0.5 and 1 kg/t maintained the number of mucin-secretory cells contained in the gut barrier of young chickens, and the use of 1 kg/t improved the intestinal immune system of aged broilers. However, the beneficial effects of some feed additives are not detected under non-challenged conditions. Therefore, the second experiment was performed to evaluate the effect of the feed additive at 1 kg/t in coccidiosis-challenged broilers. In this context, sodium butyrate protected by sodium salts of medium-chain fatty acids restored the number of mucin-secretory cells as well as impacted on the intestinal morphometry and microbiota. The results of the present study suggest that this feed additive could be a useful strategy to reinforce the gut barrier, especially for birds with coccidiosis.

Abstract

Nutritional strategies to improve gut health of broilers are under research. This study investigated the effect of dietary supplementation with sodium butyrate protected by sodium salts of medium-chain fatty acids as a feed additive on broiler gut health. The first experiment was conducted to evaluate the effect of supplementing at 0.5, 1, and 2 kg/t in broilers housed under optimal conditions. Supplementation at 0.5 and 1 kg/t maintained goblet cell counts at 10 days of age (p ≤ 0.05), and supplementation at 1 kg/t decreased intraepithelial lymphocyte counts compared to 2 kg/t at 39 days (p ≤ 0.10). Abdominal fat pad levels of lauric and myristic acids were gradually increased by supplement dose (p ≤ 0.05). In the second experiment, the feed additive at 1 kg/t was evaluated in coccidiosis-challenged broilers. Experimental treatments were as follows: non-challenged, control-challenged, and supplemented-challenged treatments. Coccidiosis negatively impact performance and modify histomorphometry and microbiota (p ≤ 0.05). The feed additive increased crypt depth at 7 days post-inoculation and goblet cell count at 14 days post-inoculation (p ≤ 0.05). Further, supplementation interacted with the microbiota modification led by the coccidiosis (p ≤ 0.05). These results suggest that this feed additive could be a useful strategy to reinforce the gut barrier, especially for birds under coccidiosis-challenge treatments.

Effects of phytase and coccidial vaccine on growth performance, nutrient digestibility, bone mineralization, and intestinal gene expression of broilers

A study was conducted to evaluate effects of phytase and coccidial vaccine on growth performance, bone mineralization, nutrient digestibility, and intestinal gene expression of broiler chickens. The experiment was conducted in a 2 × 4 completely randomized factorial arrangement with 6 replicates per treatment and 10 birds each. Applications of coccidiosis vaccine and different dietary treatments were the 2 main factors in the current study. The dietary treatments included 1) a positive control (PC; 0.90% Ca and 0.45% available P: avP); 2) a negative control (NC; 0.75% Ca and 0.30% AvP); 3) NC + 500 FTU/kg of phytase (NC + 500PHY); and 4) NC + 1500 FTU/kg of phytase (NC + 1500PHY). Data were analyzed using SAS by 2-way ANOVA via GLM procedure. The statistical significance was set at P ≤ 0.05, and means were further separated using Tukey's Test. The results indicated that vaccination had no effect on growth performance except for feed intake from 0 to 14 d but negatively (P < 0.05) regulated bone ash and Ca digestibility. Birds fed with the Ca and P-reduced diet (NC) showed a lower BWG and bone ash compared to birds fed with the normal diet (PC), but supplementing phytase mitigated the negative effects on those birds. Broilers fed the NC diet had higher (P < 0.05) total Ca and P digestibility, and phytate degradation; supplementing phytase further increased P digestibility and phytate degradation of the broilers. A significant interaction (P < 0.05) between phytase and vaccination was observed, suggesting the vaccinated birds fed the PC diet and the unvaccinated birds fed the NC + 1500PHY increased calcium-sensing receptor gene expression compared with the unvaccinated birds fed the PC diet. In conclusion, in spite of coccidiosis vaccine, supplementing phytase at 1,500 FTU/kg alleviated the negative effects on growth performance, bone mineralization, and apparent ileal digestibility of P and phytate.

Epidemiological investigation and drug resistance of Eimeria species in Korean chicken farms

Background

Coccidiosis is a poultry disease that occurs worldwide and is caused by Eimeria species. The infection is associated with reduced feed efficiency, body weight gain, and egg production. This study aimed to investigate the current status of coccidiosis and anticoccidial resistance to anticoccidial drugs used as part of control strategies for this disease in Korean chicken farms.

Results

An overall prevalence of 75% (291/388) was found. Positive farms contained several Eimeria species (mean = 4.2). Of the positive samples, E. acervulina (98.6%), E. maxima (84.8%), and E. tenella (82.8%) were the most prevalent species. Compared with cage-fed chickens, broilers and native chickens reared in free-range management were more at risk of acquiring an Eimeria infection. Sensitivities to six anticoccidial drugs (clopidol, diclazuril, maduramycin, monensin, salinomycin, and toltrazuril) were tested using nine field samples. Compared with untreated healthy control chickens, the body weight gains of infected chickens and treated/infected chickens were significantly reduced in all groups. Fecal oocyst shedding was significantly reduced in four clopidol-treated/infected groups, three diclazuril-treated/infected groups, two toltrazuril-treated/infected groups, one monensin-treated/infected group, and one salinomycin-treated/infected group, compared with the respective untreated/infected control groups. Intestinal lesion scores were also reduced in three clopidol-treated/infected groups, one monensin-treated/infected group, and one toltrazuril-treated/infected group. However, an overall assessment using the anticoccidial index, percent optimum anticoccidial activity, relative oocyst production, and reduced lesion score index found that all field samples had strong resistance to all tested anticoccidial drugs.

Conclusion

The results of this large-scale epidemiological investigation and anticoccidial sensitivity testing showed a high prevalence of coccidiosis and the presence of severe drug resistant Eimeria species in the field. These findings will be useful for optimizing the control of coccidiosis in the poultry industry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03369-3.

Anticoccidial Vaccination Is Associated with Improved Intestinal Health in Organic Chickens

Simple Summary

In recent years, the number of organic chicken farms has increased. Chickens can be infected by single-cell parasites, coccidia, which cause lesions in the lining of the intestine leading to poor growth and sometimes death (coccidiosis). This infection can also lead to overgrowth in the intestine of a bacterium, Clostridium perfringens, that may cause further damage (necrotic enteritis). Prevention is often achieved by adding substances in the feed that will slow down the development of parasites and bacteria, but this is not allowed in organic farming. The aim of this study was to investigate if vaccination against coccidia can prevent these diseases in organic chickens. Vaccinated chickens developed milder gut lesions, had fewer and less damaging C. perfringens, and had similar or higher body weight compared to unvaccinated chickens six weeks after vaccination. No deaths from coccidiosis or necrotic enteritis occurred among vaccinated chickens while some unvaccinated chickens died from these diseases. We conclude that vaccination against coccidia benefits organic chickens. This study provides knowledge supporting further development of the organic chicken industry. The results are also of relevance to the management of coccidiosis and necrotic enteritis in conventional broilers.

Abstract

Eimeria spp. and Clostridium perfringens (CP) are pathogens associated with coccidiosis and necrotic enteritis (NE) in broiler chickens. In this study we evaluated the effect of anticoccidial vaccination on intestinal health in clinically healthy organic Ross 308 chickens. On each of two farms, one unvaccinated flock (A1 and B1) was compared to one vaccinated flock (A2 and B2) until ten weeks of age (WOA). Faecal oocysts were counted weekly, and species were identified by PCR (ITS-1 gene). Lesion scoring, CP quantification and PCR targeting the CP NetB toxin gene were performed at three, four, and six WOA and chickens were weighed. Necropsies were performed on randomly selected chickens to identify coccidiosis/NE. Oocyst shedding peaked at three WOA in all flocks. Later oocyst shedding (E. tenella/E. maxima) in unvaccinated flocks at 5–7 WOA coincided with coccidiosis/NE. Although results differed somewhat between farms, vaccination was associated with lower intestinal lesion scores, reduced caecal CP counts, lower proportions of netB-positive CP, lower body weight at three–four WOA, and similar or slightly increased body weight at six WOA. In conclusion, the intestinal health of organic broilers can benefit from anticoccidial vaccination when oocyst exposure levels are high.

Research Note:Effects of different anticoccidial regimens on the growth performance, hematological parameters, immune response, and intestinal coccidial lesion scores of yellow-feathered broilers

Yellow-feathered broiler chickens generally have a longer growth cycle than white broilers and therefore face different coccidiosis challenges. General single vaccine and drug regimens struggle to prevent coccidiosis for yellow broilers. In this study, a single vaccine, and a combination of coccidiostat regimens was employed to explore the preventative and control effects of different pilot regimens on coccidiosis in yellow-feathered broilers. A total of 2,000 one day old Chinese Huang Youma female broilers were allocated into 4 experimental groups, each with 5 replicates. All birds were fed the same starter feed from Days 1 to 25, and all groups were inoculated with a vaccine on Day 4. After Day 26, the groups were then fed as follows: (1) Negative control group: basal diet + vaccine (NC); (2) NC + maduramycin (NCMD); (3) NC + narasin (NCNR); and (4) NC + salinomycin (NCSL). From Days 26 to 75, the NCNR group had a lower FCR than the other groups. The 75-d BW was higher in the NCNR group than in the NCSL group but was not significantly higher than that in the NC and NCMD groups. The growth performance followed the same trend during the whole experiment (Days 1–75). Compared to the NC group, the NCNR and NCSL groups had higher intestinal mucosa SIgA concentrations at Day 40 and Day 60 (P < 0.001); however the NCMD group had lower IgG levels at Day 40 and Day 60 (P = 0.036, P = 0.006 respectively). The combination groups had significantly reduced AKP levels and urine acid concentrations at Day 60 in comparison to those of the NC group (P = 0.004). The NCNR and NCMD groups had less severe intestinal coccidiosis lesion scores than the NC and NCSL groups in older birds. Thus, a single vaccine and/or combinations with different coccidiostats had different effects on broilers. The NCNR group showed comparatively better growth performance, blood biochemical indices, immune response, and coccidiosis lesion scores.

Standardized ileal digestibility of amino acids in broiler chickens fed single or mixture of feed ingredients-based diets with or without Eimeria challenge

The effect of Eimeria challenge on standardized ileal digestibility (SID) of amino acids (AA) in major poultry feed ingredients fed to broiler chickens was determined. A total of 840 male 9-day-old Ross 708 chicks were placed in 84 cages (10 birds/cage) and allocated to either a nitrogen-free diet (NFD) or one of the 6 test diets based on a single or mixture of feed ingredients as the sole source of AA (n = 12). Test diets were: 1) corn, 2) wheat, 3) soybean meal (SBM), 4) pork meal (PM), 5) corn, SBM, and PM (CSP), and 6) wheat, SBM, and PM (WSP). On d 10, birds in 6 cages/diet were orally gavaged with 1 mL of E. acervulina and E. maxima mixture and the other 6 cages with sham. On d 15, birds were bled for plasma AA and necropsied for intestinal lesion scores and ileal digesta samples. Challenge decreased (P < 0.05) plasma concentration of Arg, His, Thr, Asp, Gln, and Tyr and increased concentration of Lys, Ile, Leu, and Val. There was a diet by challenge interaction (P < 0.05) on intestinal lesion scores with birds fed mixed diets exhibiting more severe lesions than birds fed single ingredient diets. Diet by challenge interacted (P < 0.05) on ileal total endogenous flow (ITEF) of AA except for Arg, Met, Ala, Asp, and Cys, such that challenged birds fed the mixed, particularly WSP, had higher ITEF of AA compared to single ingredients birds. Diet and challenge interaction (P < 0.05) was observed for SID of Arg, Thr, Val, Glu, and Gly. Challenge decreased (P < 0.05) SID of most AA except for Met, Asp, and Cys with the largest impact seen on Lys, His, Ser, and Thr. With exception of Arg, Thr, Asp, and Cys, birds fed mixed diets had higher (P < 0.05) SID values compared to birds fed single ingredients. In conclusion, Eimeria reduced plasma availability and ileal digestibility of most AA. However, challenge interaction with diet composition on SID of some AA warrants further investigations.

PLGA Nanospheres as Delivery Platforms for Eimeria mitis 1a Protein: A Novel Strategy to Improve Specific Immunity

The infections of chicken coccidiosis impact the welfare of chickens and the economical production of poultry. Eimeria mitis is ubiquitous in chicken coccidiosis, and E. mitis infection can significantly affect the productivity of birds. Up to now, few efficient vaccines against E. mitis have been reported, whereas the recombinant subunit vaccines delivered by nanomaterials may elicit an encouraging outcome. Thus, in this study, we chose E. mitis 1a (Em1a) protein as the candidate antigen to generate Em1a preparations. The recombinant Em1a (rEm1a) protein was encapsulated with poly lactic-co-glycolic acid (PLGA) and chitosan (CS) nanospheres. The physical characterization of the rEm1a-PLGA and rEm1a-CS nanospheres was investigated, and the resulting nanospheres were proven to be nontoxic. The protective efficacy of rEm1a-PLGA and rEm1a-CS preparations was evaluated in E. mitis-challenged birds in comparison with two preparations containing rEm1a antigen emulsified in commercially available adjuvants. ELISA assay, flow cytometry analysis, and quantitative real-time PCR (qPCR) analysis indicated that vaccination with rEm1a-loaded nanospheres significantly upregulated the secretions of antibodies and cytokines and proportions of CD4⁺ and CD8⁺ T lymphocytes. Compared with the other three preparations, rEm1a-PLGA nanosphere was more effective in improving growth performance and inhibiting oocyst output in feces, indicating that the PLGA nanosphere was associated with optimal protection against E. mitis. Collectively, our results highlighted the advantages of nanovaccine in eliciting protective immunity and may provide a new perspective for developing effective vaccines against chicken coccidiosis.

Precision intestinal nutrition: knowledge and gaps regarding the role of amino acids during an enteric challenge

Poultry nutritionists continually strive for more “precision” nutritional programs that provide the exact balance of nutrients that maximize broiler growth performance without economically and environmentally costly excesses. Many factors affect the precise amount and balance of nutrients needed by the broiler, including genetics, age, sex, and environment. Furthermore, broilers in intensive rearing environments will almost always be subjected to some degree of enteric stress that can alter nutrient needs. Exposure to enteric pathogens such as Eimeria spp., the intestinal parasites that cause avian coccidiosis, induces physical damage to the intestinal epithelium and activates immune responses, ultimately resulting in the repartitioning of amino acids (AA) in response to these prioritized demands. Even without any pathogenic challenge, the intestine has an already high demand for many AA, with 30 to 100% of dietary AA extracted during first pass intestinal metabolism. In many cases, increasing dietary protein from intact proteins has been shown to be a viable option to ameliorate impaired AA digestion and absorption and heightened need for certain AA of birds under an enteric stress. However, increasing dietary protein often results in concomitant increases in indigestible protein and carbohydrates that can stimulate the overgrowth of pathogenic bacteria (i.e., Clostridium perfringens). Alternative options to increase dietary AA levels are to increase all feed-grade, free AA (e.g., Met, Lys, Thr, Val), or specific individual feed-grade AA. Therefore, the objectives of this paper are to discuss precision nutrition, the dietary AA demands of the intestine, consequences of coccidiosis on AA needs of the intestine, and formulation approaches to meet these altered needs. In summary, increased dietary protein met by intact proteins has consistently demonstrated its benefits during an Eimeria spp. infection; however, to further the goal of precision nutritional programs, feeding higher levels of a specific AA to support desired functions such as intestinal recovery or immune function for birds experiencing an enteric stress still require further evaluation.

Efficacy of an attenuated vaccine against avian coccidiosis in combination with feed additives based on organic acids and essential oils on production performance and intestinal lesions in broilers experimentally challenged with necrotic enteritis

Several factors predisposing to necrotic enteritis (NE) have been identified, including diet and Eimeria spp. infestations. Coccidiosis vaccines are indicated to decrease the intestinal lesions caused by specific Eimeria species that are a known predisposing factor to NE and, consequently, these vaccines could be a holistic approach to the control of NE disease and an alternative solution to coccidiostats. Besides, feed additives have also gained special attention from the poultry industry as an alternative solution to antibiotics to prevent NE as well as other bacterial enteritis.

Then, the combination of vaccination against coccidiosis and the supplementation of the diet with feed additives could be a composite approach to the control of NE problems triggered by Eimeria spp. infestation. The objective of this study was to test the efficacy of an attenuated coccidiosis vaccine (EVANT) in combination with different feed additives to prevent the loss of production performance and intestinal lesions in broilers challenged with NE.

Healthy day-old broilers (n = 960) were randomly allocated to 6 groups (8 cages/group). Groups 1–2 were left unvaccinated. Groups 3–6 were vaccinated following the manufacturer's instructions. Chickens were grown using a diet favoring the intestinal proliferation of Clostridium perfringens. Moreover, the diets of groups 4–6 were supplemented with medium chain fatty acids (MCFA), butyric acid or phytogenic feed additives (PFA), respectively. A NE infection model was used to challenge groups 2–6; chickens were orally infected with Eimeria maxima (4,500 oocysts) and then C. perfringens (10⁸ CFU) at 15 and 20 d, respectively. Birds were monitored and productive parameters recorded until 42 d; intestinal lesions were scored.

Results showed that coccidiosis vaccination, with or without the addition of feed additives, decreased intestinal lesions associated with NE and improved the performance of the birds. Besides, the addition of MCFA to the diet decreased intestinal lesions associated to NE in vaccinated animals compared to all treatment groups. Moreover, the same additive improved the feed conversion rate. Therefore, vaccination with a live attenuated coccidiosis vaccine together with in-feed inclusion of MCFA might be a solution to reduce NE in broilers raised antimicrobial- and coccidiostat-free.

Coccidiosis: Recent Progress in Host Immunity and Alternatives to Antibiotic Strategies

Coccidiosis is an avian intestinal disease caused by several distinct species of Eimeria parasites that damage the host’s intestinal system, resulting in poor nutrition absorption, reduced growth, and often death. Increasing evidence from recent studies indicates that immune-based strategies such as the use of recombinant vaccines and various dietary immunomodulating feed additives can improve host defense against intracellular parasitism and reduce intestinal damage due to inflammatory responses induced by parasites. Therefore, a comprehensive understanding of the complex interactions between the host immune system, gut microbiota, enteroendocrine system, and parasites that contribute to the outcome of coccidiosis is necessary to develop logical strategies to control coccidiosis in the post-antibiotic era. Most important for vaccine development is the need to understand the protective role of the local intestinal immune response and the identification of various effector molecules which mediate anti-coccidial activity against intracellular parasites. This review summarizes the current understanding of the host immune response to coccidiosis in poultry and discusses various non-antibiotic strategies which are being developed for coccidiosis control. A better understanding of the basic immunobiology of pertinent host–parasite interactions in avian coccidiosis will facilitate the development of effective anti-Eimeria strategies to mitigate the negative effects of coccidiosis.

Quantifying the effect of coccidiosis on broiler performance and infection outcomes in the presence and absence of control methods

A systematic review and meta-analysis was conducted to investigate the role of Eimeria species, dose and inoculation time, on performance and infection outcomes of different broiler strains infected for different study durations. The meta-analysis addressed E. acervulina, E. maxima, E. tenella, and mixed species infections, and involved data from 72 peer-reviewed articles, corresponding to 521 treatments performed on 20,756 broilers. A secondary objective was to investigate the effects of synthetic anticoccidials, ionophores, and vaccination against Eimeria on the above outcomes. Performance during infection was scaled (%) to that of the uninfected birds. Infection reduced scaled ADFI and ADG (P < 0.001) and increased feed conversion ratio (FCR; P < 0.05); there was a significant interaction between dose and species on scaled ADFI and ADG, suggesting that different species affected these variables to different extents (P < 0.001). There was a tendency for an interaction between dose and broiler strain on scaled ADFI (P = 0.079), and a significant interaction between these variables on scaled ADG (P < 0.01). A tendency for an interaction between oocyst dose and Eimeria species (P = 0.067) on maximum number of oocysts excreted was observed. Lesion scores were significantly affected by dose, species, and their interaction (P < 0.05), the latter caused by an increase in the lesion scores during E. maxima and E. tenella infections. Control methods significantly affected scaled ADG and FCR (P < 0.05) and there was an interaction between dose and control methods on ADFI (P < 0.001). Synthetic anticoccidial use improved scaled ADG (P < 0.01), whereas ionophores improved FCR compared with untreated birds (P < 0.01). An interaction between dose and control method on scaled ADFI was caused by the higher ADFI of vaccinated compared to untreated birds, as dose increased. There was a significant effect of control methods on lesion scores (P < 0.01). All findings advance our understanding of the factors that influence the impact of coccidiosis and its controls in broilers.

Eimeria maxima Rhomboid-like Protein 5 Provided Partial Protection against Homologous Challenge in Forms of Recombinant Protein and DNA Plasmid in Chickens

Eimeria maxima (E. maxima) is one of the most prevalent species that causes chicken coccidiosis on chicken farms. During apicomplexan protozoa invasion, rhomboid-like proteins (ROMs) cleave microneme proteins (MICs), allowing the parasites to fully enter the host cells, which suggests that ROMs have the potential to be candidate antigens for the development of subunit or DNA vaccines against coccidiosis. In this study, a recombinant protein of E. maxima ROM5 (rEmROM5) was expressed and purified and was used as a subunit vaccine. The eukaryotic expression plasmid of pVAX-EmROM5 was constructed and was used as a DNA vaccine. Chickens who were two weeks old were vaccinated with the rEmROM5 and pVAX-EmROM5 vaccines twice, with a one-week interval separating the vaccination periods. The transcription and expression of pVAX-EmROM5 in the injected sites were detected through reverse transcription PCR (RT-PCR) and Western blot (WB) assays. The cellular and humoral immune responses that were induced by EmROM5 were determined by detecting the proportion of CD4⁺ and CD8⁺ T lymphocytes, the cytokine levels, and the serum antibody levels. Finally, vaccination-challenge trials were conducted to evaluate the protective efficacy of EmROM5 in forms of the recombinant protein (rEmROM5) and in the DNA plasmid (pVAX-EmROM5) separately. The results showed that rEmROM5 was about 53.64 kDa, which was well purified and recognized by the His-Tag Mouse Monoclonal antibody and the chicken serum against E. maxima separately. After vaccination, pVAX-EmROM5 was successfully transcribed and expressed in the injected sites of the chickens. Vaccination with rEmROM5 or pVAX-EmROM5 significantly promoted the proportion of CD4⁺/CD3⁺ and CD8⁺/CD3⁺ T lymphocytes, the mRNA levels of the cytokines IFN-γ, IL-2, IL-4, IL-17, TNF SF15, and IL-10, and specific IgG antibody levels compared to the control groups. The immunization also significantly reduced the weight loss, oocyst production, and intestinal lesions that are caused by E. maxima infection. The anticoccidial index (ACI)s of the vaccinated groups were beyond 160, showing moderate protection against E. maxima infection. In summary, EmROM5 was able to induce a robust immune response and effective protection against E. maxima in chickens in the form of both a recombinant protein and DNA plasmid. Hence, EmROM5 could be used as a candidate antigen for DNA vaccines and subunit vaccines against avian coccidiosis.

Chicken Coccidiosis: From the Parasite Lifecycle to Control of the Disease

The poultry industry is one of the main providers of protein for the world's population, but it faces great challenges including coccidiosis, one of the diseases with the most impact on productive performance. Coccidiosis is caused by protozoan parasites of the genus Eimeria, which are a group of monoxenous obligate intracellular parasites. Seven species of this genus can affect chickens (Gallus gallus), each with different pathogenic characteristics and targeting a specific intestinal location. Eimeria alters the function of the intestinal tract, generating deficiencies in the absorption of nutrients and lowering productive performance, leading to economic losses. The objective of this manuscript is to review basic concepts of coccidiosis, the different Eimeria species that infect chickens, their life cycle, and the most sustainable and holistic methods available to control the disease.

CircNFIC Balances Inflammation and Apoptosis by Sponging miR-30e-3p and Regulating DENND1B Expression

Disordered inflammation and apoptosis are closely related to diseases, and inflammation can also promote cell apoptosis, where growing evidence has shown that circular RNAs (circRNAs) play important roles. Lipopolysaccharide (LPS) is the main component of the cytoderm of gram-negative bacterium, which can cause inflammatory responses in macrophages. We constructed an inflammatory model by exposing chicken macrophage cell lines (also known as HD11) to LPS for in vitro experiments. In this study, we validated a novel circRNA-circNFIC-which was dramatically up-regulated in tissues infected by coccidia and cells exposed to LPS. Besides, circNFIC could significantly promote the expression levels of pro-inflammation factors, including (IL-1β, TNFα, and IFNγ) and pro-apoptosis maker genes (caspase 3 and caspase 8) in HD11 exposed to LPS or not. In terms of mechanism, circNFIC exerted notable effects on DENND1B to regulate cell inflammation and apoptosis by sponging miR-30e-3p. The molecular functions played by miR-30e-3p and DENND1B have been explored, respectively. In addition, the effects of circNFIC knockdown suppressing the expression of pro-inflammatory and pro-apoptosis functions could be reversed by a miR-30e-3p inhibitor. On the whole, circNFIC promoted cell inflammation and apoptosis via the miR-30e-3p/DENND1B axis.

The Impact of Tributyrin on Performance and Intestinal Health of Broiler Chickens Post Coccidiosis Vaccination

Coccidiosis is a major intestinal disease affecting broiler chickens. Tributyrin (TB) is a valid alternative to butyrate acid, which was associated with the improvement of performance and attenuation of intestinal inflammation in animal production. However, there are few reports on TB as a prophylactic treatment against coccidiosis in broilers. The aim of the study was to investigate the effects of TB supplementation on performance and intestinal health of broiler chickens post coccidiosis vaccination with a mixed-species Eimeria. In the first experiment, 612 broiler chicks were randomly assigned to two treatments with six replicates. Treatments included no TB supplementation and coccidiosis vaccination (CV1), or TB supplementation (400 mg/kg) and coccidiosis vaccination (TBCV1). On day 5, all broilers received a single vaccine dose. Performance, intestinal histopathology, clinical severity, and fecal oocyst counts were evaluated from day 1 to day 63. TB supplementation resulted in a nonsignificant effect on body weight gain (BWG), feed intake (FI), and mortality-corrected feed conversion ratio (FCR), except in increased FI on days 22-42 (P < 0.05). The TBCV1 group had increased (P < 0.05) villi heights in the duodenum and increased (P < 0.05) villi widths in the ileum on day 63 of age and reduced oocyst shedding on days 19-26 compared to CV1(P < 0.05). The route of administration in the second experiment was different from the first experiment in which the seeder birds (half of birds from each pen) received a tenfold dose on day 5. TB supplementation in broilers resulted in increased (P < 0.05) BWG and reduced (P < 0.05) FCR on days 22-42, and increased (P < 0.05) villi heights in the duodenum and increased (P < 0.05) villi widths in the ileum on day 63 of age, as well as a lower frequency (P < 0.05) of intestinal hemorrhage on days 13-62 and reduced (P < 0.001) oocyst shedding on day 5 post-Eimeria challenge. In conclusion, the study demonstrated that TB can be considered as a feed additive for protecting broilers from coccidiosis on days 22-42.

Effect of organic acids on growth performance, intestinal morphology, and immunity of broiler chickens with and without coccidial challenge

A total of 360-day-old broiler chicks were allocated into six groups in 2 (Coccidial challenge or not) × 3 (dietary treatments) factorial design. Three dietary treatments including: basic diet, basic diet plus organic acids (OAs) in drinking water, and basic diet plus OAs in the feed with and without coccidial challenge. The OAs in water or feed improved (P < 0.01) average body weight (ABW), average body weight gain (ABWG), and feed conversion ratio (FCR) as compared with the control diet during starter, grower, and whole experimental period. Coccidial challenge decreased BW, ABWG, and average feed intake (AFI), as well as resulted in poor FCR during the starter and whole experimental period (P < 0.05). Though there was no interaction between OAs supplementation and coccidial challenge, the OAs supplementation improved the overall performance with and without coccidial challenge birds on 21 d and 35 d. IgG was found higher (P = 0.03) in broilers fed OAs in feed without the coccidial challenge group. On 18 d, OAs supplementation in feed increased TNF-γ (P = 0.006), whereas the coccidial challenge decreases TNF-γ (P = 0.01) and IL-10 (P =  < .0001), and increases IgM (P = 0.03), IgG (P = 0.04) and IgA (P = 0.02). On 29 d, the coccidial challenge increases IgM and IgA. On 18 d, jejunal lesion score was found significantly higher in the coccidial challenged group as compared to OAs supplementation with coccidial challenged groups on 18 d (P < 0.0001) and 29 d (P = 0.03). Crypt depth was higher, and Villus-height to Crypt depth ratio was lower in the coccidial challenge group on 18 and 29 d. The Goblet cells were found higher in the non-coccidial challenge on 18 d. After 18 d, 16S rDNA gene sequence analysis of ileal chyme has shown that coccidial challenge decreases Lactobacillus_reuteri species as compared to the non-challenged group (P = 0.02). After 29, Cyanobacteria abundance reduced (P = 0.014) in the challenged group than the non-challenged group at the phylum level. At the genus level, Lactobacillus (P = 0.036) and unidentified Cyanobacteria (P = 0.01) were found higher in the non-challenged group than the coccidial challenge group. The results indicate that the OAs supplementation showed improved responses in a pattern similar to the non-challenged control group by neutralizing the negative effects of the coccidial challenge.

Survey of coccidia on commercial broiler farms in Colombia: frequency of Eimeria species, anticoccidial sensitivity, and histopathology

Avian coccidiosis continues to be one of the costliest diseases of commercial poultry. Understanding the epidemiology of Eimeria species in poultry flocks and the resistance profile to common anticoccidials is important to design effective disease prevention and control strategies. This study examined litter samples to estimate the prevalence and distribution of Eimeria species among broiler farms in 4 geographic regions of Colombia. A total of 245 litter samples were collected from 194 broiler farms across representative regions of poultry production between March and August 2019. The litter samples were processed for oocysts enumeration and speciation after sporulation. End-point polymerase chain reaction (PCR) analysis was conducted to confirm the presence of Eimeria species. Anticoccidial sensitivity was determined with 160 Ross AP males in 5 treatment groups: noninfected, nonmedicated control (NNC), infected, nonmedicated control (INC), infected salinomycin treated (SAL, dose: 66 ppm), infected diclazuril treated (DIC, dose: 1 ppm), and infected methylbenzocuate-Clopidol treated (MET.CLO, dose: 100 ppm), All birds were orally inoculated with 1 × 106 sporulated oocysts using a 1 mL syringe, except for the NNC- group who received 1ml of water.Eimeria spp. were found in 236 (96.3%) out of 245 individual houses, representing 180 (92.8%) out of 194 farms. Eimeria acervulina was the most prevalent species (35.0%) followed by Eimeria tenella (30.9%), Eimeria maxima (20.4%), and other Eimeria spp. (13.6%). However, mixed species infections were common, with the most prevalent combination being mixtures of E. acervulina, E. maxima, E. tenella, and other species in 31.4% of the Eimeria-positive samples. PCR analysis identified E. acervulina, E. maxima, E. tenella, Eimeria necatrix, Eimeria mitis, and Eimeria praecox with variable prevalence across farms and regions. Anticoccidial sensitivity testing of strains of Eimeria isolated from 1 region, no treatment difference (P > 0.05) was observed in final weight (BW), weight gain (BWG) or feed conversion (FCR). For the global resistance index (GI) classified SAL and MET.CLO as good efficacy (85.79 and 85.49, respectively) and DIC as limited efficacy (74.52%). These results demonstrate the ubiquitous nature of Eimeria spp. and identifies the current state of sensitivity to commonly used anticoccidials in a region of poultry importance for Colombia.

Effect of Replacing In-Feed Antibiotics with Synergistic Organic Acids, with or without Trace Mineral and/or Water Acidification, on Growth Performance and Health of Broiler Chickens Under a Clostridium perfringens Type A Challenge

This study investigated the effects of a proprietary commercial feed additive (FA) comprised of a blend of fatty acids, organic acids, and phytochemicals; a hydroxychloride copper (MA); as well as a water acidification product (WA), alone and in combination, on growth performance in nonvaccinated broiler chickens raised in an antibiotic-free production system. The test treatments were FA; WA; FA and WA combined (FA + WA); and FA, WA, and MA combined (FA + WA + MA). The efficacy of these treatments was compared with a negative control (CON) and a medicated feeding program (bacitracin, antibiotic growth promoter [AGP]). Ross 708 cockerels (n = 2376) were subject to a 3-phase commercial feeding program, namely, starter (0-20 days), grower (21-28 days), and finisher (28-35 days), with no coccidiostats or additional medications added to the feed. On day 14, birds were subjected to an in-feed Clostridium perfringens challenge and a subset of animals were euthanized and the ileal digesta was collected for C. perfringens enumeration. Prior to pathogen challenge (day 14), birds fed the FA + WA and F + WA + MA treatments had significantly higher body weights (+2.6%-3.5%) than those fed CON and similar body weights to birds fed the AGP. These early growth advantages were not sustained postchallenge. Clostridia counts in ileal digesta were dramatically reduced in birds fed the AGP compared with all treatments. The FA (-2.5 log), FA + WA (-2.0 log), and FA + WA + MA (-2.3 log) treatments had significantly lower clostridia counts than the CON treatment. Together, these findings support the use of combined in-feed and in-water strategies for reducing clostridia, while maintaining growth, in antibiotic-free production systems.

Evaluation of a subunit vaccine candidate (Biotech Vac Cox) against Eimeria spp. in broiler chickens

This study evaluated growth performance and cross-protection against Eimeria spp. using a subunit coccidia vaccine in 2 independent challenge experiments. In both trials, chickens were challenged with E. acervulina, E. maxima, and E. tenella oocysts. In Exp 1, 1000-day-old chickens were allocated in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 35, and 42. On d 34, coccidia lesions were scored. Oocysts per gram of feces (OPG) were evaluated on d 28, 35, and 42. In Exp 2, 900-day-old chickens were assigned in one of 2 treatments 1) Control group; 2) Biotech Vac Cox group. The vaccine was orally gavaged on d 2 and 16 of life and coccidia challenge was on d 21. Performance parameters were evaluated on d 21, 27, 35, and 42, and lesion scores and OPG at d 27. In Exp 1, chickens vaccinated had significantly lower feed intake (FI) at d 21 and feed conversion ratio (FCR) at d 35 compared to control chickens (P < 0.05). Vaccinated chickens showed a significant reduction (P ≤ 0.05) in OPG for E. maxima to nondetectable levels and for all coccidian species at d 42 compared to control chickens. In Exp 2, the chickens vaccinated showed a significant increase in BW, BW gain (BWG) and reduction in FCR on d 27, 35, and 42 (P ≤ 0.05). Vaccinated chickens had significantly lower (P ≤ 0.05) lesion scores for all 3 Eimeria species. Moreover, vaccinated chickens had a reduction in total OPG of 35.50% (P = 0.0739). Studies to evaluate the serological and mucosal immune response are currently being evaluated. This inactivated, orally delivered subunit vaccine offers significant cross-protection to Eimeria spp. and eliminates the needs to treat broilers with live oocysts, enhanced ease of use, and greater biosecurity to producers.

Recent achievements and doors opened for coccidian parasite research and development through transcriptomics of enteric sexual stages

The Coccidia is the largest group of parasites within the Apicomplexa, a phylum of unicellular, obligate parasites characterized by the possession of an apical complex of organelles and structures in the asexual stages of their life cycles, as well as by a sexual reproductive phase that occurs enterically in host animals. Coccidian sexual reproduction involves morphologically distinct microgametes and macrogametes that combine to form a diploid zygote and, ultimately, following meiosis and mitosis, haploid, infectious sporozoites, inside sporocysts within an oocyst. Recent transcriptomic analyses have identified genes involved in coccidian sexual stage development and reproduction, including genes encoding for microgamete- and macrogamete-specific proteins with roles in gamete motility, fusion and fertilization, and in the formation of the resilient oocyst wall that allows coccidians to persist for long periods in the environment. Transcriptomics has also provided important clues about the regulation of gene expression in the transformation of parasites from one developmental stage to the next, a complex sequence of events that may involve transcription factors such as the apicomplexan Apetala2 (ApiAP2) family, alternative splicing, regulatory RNAs and MORC (a microrchida homologue and regulator of sexual stage development in Toxoplasma gondii). The molecular dissection of coccidian sexual development and reproduction by transcriptomic analyses may lead to the development of novel transmission-blocking strategies.

Effects of riboflavin and Bacillus subtilis on internal organ development and intestinal health of Ross 708 male broilers with or without coccidial challenge

In a companion study, we found that inclusion of different doses of riboflavin affected growth performance of Ross 708 male broilers' responses to coccidial challenge (by 5 Eimeria spp on day 14 of age) and dietary Bacillus subtilis (B. subtilis) supplementation. The current study was conducted to further test whether supplementation of B. subtilis and riboflavin will reduce negative impact and inflammation caused by Eimeria spp proliferation and help proper function of internal organs. A total of 1,248 Ross × Ross 708 male broiler chicks were randomly placed in 96 floor pens (8 blocks, 12 treatments). Treatments were arranged in a 3 (riboflavin) × 2 (B. subtilis) × 2 (Coccidial challenge) factorial arrangement in a randomized complete block design. Coccidial challenge reduced the weight of sampled birds on day 27 and day 36 and increased the relative weights of the internal organs of proventriculus, duodenum, jejunum, ileum, and spleen to BW on day 27, which may be because of inflammation caused by proliferation of Eimeria spp. The increased relative weights of duodenum, jejunum, ileum, and spleen on coccidial challenged birds were lost on day 36. Correlation analysis also indicated that the jejunum weight was positively related to villus height, Eimeria acervulina, and Eimeria maxima on day 27 but was not on day 36. The loss of the positive relationships may be because of recovery of the birds from coccidiosis on day 36. Even though the coccidial challenge and riboflavin interactively affected feed conversion ratio and BW gain and supplementation of dietary B. subtilis reduced mortality from day 35 to 42 in the companion study, the same response of internal organs was not observed in the current study. Coccidial challenge compromised development of internal organs of Ross 708 male broilers at an early age, but the negative effects subsided with age of birds rather than supplementation of riboflavin and B. subtilis at current tested levels under our experimental set up.

Restoration of the sensitivity of Eimeria acervulina to anticoccidial drugs in the chicken following use of a live coccidiosis vaccine

The efficacy of the anticoccidial drugs amprolium, clopidol, diclazuril, monensin, monensin + nicarbazin, narasin, narasin + nicarbazin, and salinomycin against field isolates of Eimeria acervulina obtained from a commercial broiler enterprise before and after immunization with a coccidiosis vaccine was investigated. Evaluated by weight gain, feed conversion, and lesion score following challenge, the isolate obtained before vaccination was resistant to all the drugs tested. By contrast, after vaccination the isolate was sensitive to all drugs evaluated by weight gain, and to most drugs judged by feed conversion and lesion score. It is concluded that vaccination had resulted in the restoration of sensitivity to these drugs.

Evaluation of immunoprotective effects of recombinant protein and DNA vaccine based on Eimeria tenella surface antigen 16 and 22 in vivo

Coccidiosis triggered by Eimeria tenella is accompanied by haemorrhagic caecum and high morbidity. Vaccines are preferable choices to replace chemical drugs against coccidiosis. Surface antigens of apicomplexan parasites can adhere to host cells during the infection process. Therefore, truncated fragments coding E. tenella surface antigen 16 (EtSAG16) and 22 (EtSAG22) were cloned into pET-28a prokaryotic vector to express recombinant protein 16 (rEtSAG16) and 22 (rEtSAG22), respectively. Likewise, pEGFP-N1-EtSAG16 and pEGFP-N1-EtSAG22 plasmids were constructed using pEGFP-N1 eukaryotic vector. Further, pEGFP-N1-EtSAG4-16-22 multiple gene plasmid carrying EtSAG4, 16 and 22 were designed as cocktail vaccines to study integral immunoprotective effects. Western blot and RT-PCR (reverse transcription) assay were performed to verify expressions of EtSAG16 and 22 genes. Immunoprotective effects of recombinant protein or DNA vaccine were evaluated using different doses (50 or 100 μg) in vivo. All chickens in the vaccination group showed higher cytokine concentration (IFN-γ and IL-17), raised IgY antibody level, increased weight gain, lower caecum lesion score and reduced oocyst shedding compared with infection control groups (p < 0.05). The highest anticoccidial index (ACI) value 173.11 was from the pEGFP-N1-EtSAG4-16-22 plasmid (50 μg) group. In conclusion, EtSAG16 and 22 might be alternative candidate genes for generating vaccines against E. tenella infection.

Coccidia Vaccine Challenge and Exogenous Enzyme Supplementation in Broiler Chicken 1. Effect on Digesta Viscosity, Diet Energy Utilization, and Apparent Metabolizable Energy Value of Wheat

This study examined the effect of exogenous mixed-enzyme supplementation (xylanase, β-glucanase, and pectinase) to a corn-SBM (CS) and a wheat-CS-based (WCS) diet in birds challenged with coccidia vaccine (Coccivac B-52™). The WCS-based diet was produced by replacing 30% of the energy-yielding portions of the CS-based diet with wheat. On day 14, 448 (n = 7) Cobb by-product breeder male broilers were assigned to a 2 (diet types) × 2 (with or without enzyme supplementation) × 2 (0 or 20 × coccidia vaccine challenge; CVC) factorial arrangement of treatments in a completely randomized design for the determination of the apparent metabolizable energy (AME) value of wheat. Treatment effects on jejunum digesta viscosity and AME corrected for nitrogen (AMEn) of the diets were evaluated within each diet type as a 2 × 2 factorial arrangement of treatments, 7- and 14-day post-challenge. Seven-day post-challenge (day 21), dry matter (DM) and energy utilization, AME, and AMEn of the CS- and WCS-based diets decreased (p < 0.05) with CVC. Both AME and AMEn of wheat decreased (p < 0.05) by about a 20% in CVC-birds 7-day post-challenge. Enzyme and CVC resulted in a decrease (p < 0.05) in jejunal digesta viscosity in birds fed the CS-based diets, while there was an interaction (p < 0.05) between CVC and enzyme, with enzyme lowering (p < 0.05) the viscosity of digesta 7-day post-challenge. Results from this study showed that CVC resulted in a 20% decrease in AMEn 7-day post-challenge, while the interaction between exogenous enzyme supplementation and CVC resulted in an improvement in nitrogen utilization (~6%) in CVC birds fed the corn-SBM-based diet 7-days post challenge.

Network meta-analysis comparing the effectiveness of anticoccidial drugs and anticoccidial vaccination in broiler chickens

With the trend to organic production and concerns about using antibiotic feed additives, the control of infections with Eimeria spp. in broiler flocks has become more difficult. Vaccination against coccidia is an alternative, but there are concerns that the live vaccines used might have negative effects on production parameters and intestinal health. Reports of experiments directly comparing anticoccidial drugs and anticoccidial vaccines are rare. This network meta-analysis (NMA) identified and analyzed 61 articles reporting 63 experiments testing anticoccidial drugs and anticoccidial vaccines under conditions resembling commercial broiler production. The effect sizes were mean differences in body weight/body weight gain (BW/BWG) and feed conversion rate (FCR) between the 175 included groups. The results show that groups vaccinated against coccidia have a similar BW/BWG and FCR at processing age compared to groups given anticoccidial drugs. However, the results tended to be more favorable for anticoccidial drugs than for vaccines. The analysis of eight subsets, containing only groups (1) groups that had not received an AGP in addition to an anticoccidial drug, (2) groups that had not received ionophores, (3) groups that had not received chemicals, (4) groups that had not received an attenuated vaccine, (5) groups that had not received a fully virulent vaccine, (6) groups that were not additionally challenged with bacteria or not challenged, (7) groups that had received a severe challenge as defined by a total infection dose of more than 100,000 oocysts or were not challenged, (8) groups that were challenged on day 15 or earlier or not challenged brought similar results and confirmed the robustness of the NMA. In addition, the analysis exposes unnecessary, as well as inherent, problems with data quality, which every researcher working with coccidia should carefully consider, and identifies under-researched areas that should be addressed in future research.

Effects of administration of an in ovo coccidiosis vaccine at different embryonic ages on vaccine cycling and performance of broiler chickens,. Poult Sci 2020;100:100914. [PMID: 33518328 PMCID: PMC7936202 DOI: 10.1016/j.psj.2020.11.078]

Use of a live coccidiosis vaccine has become an increasingly common method to control coccidiosis, especially in antibiotic-free broiler production. The Inovocox EM1 vaccine (EM1) is recommended for the vaccination of embryonated broiler hatching eggs between 18.0 and 19.0 d of incubation (doi). This allows for earlier acquisition of immunity to wild-type coccidia. However, it is unclear whether the difference in embryo age at the time of in ovo injection can influence the effect of the vaccine during grow-out as well as if the growth performance of broiler chickens is affected. Therefore, the objective of the study was to evaluate the effects of 2 injection ages (18.5 and 19.0 doi) and 3 injection types (noninjected, diluent, and vaccine) in a 3 × 2 factorial design, consisting of 10 replicates per treatment (60 treatment-replicate groups). There was a significant effect of injection age on BW at 0, 14, and 35 d after hatch, with a difference in the BW of birds belonging to the 18.5 and 19.0 doi groups up to day 35 after hatch. There was a significant effect of injection type on BW gain, feed intake, and FCR between 0 and 28 d after hatch. Between 0 and 35 d, FCR was lower in the vaccine-injected group in comparison with the noninjected and diluent control groups. Furthermore, total intestine coccidia and lesion indices were higher in the vaccine-18.5 treatment group in comparison with the diluent-18.5 treatment group at 28 d. In conclusion, hatchling weight was affected by injection age, and this subsequently affected growth performance. Furthermore, intestinal coccidia cycling peaked at 28 d, resulting in a reduction in growth performance through 28 d and subsequent compensatory growth by 35 d. There was no significant difference in coccidiosis cycling between the vaccine-18.5 and vaccine-19.0 doi treatment combination groups.

Evaluation of 4 merozoite antigens as candidate vaccines against Eimeria tenella infection

Coccidiosis, caused by parasites of the genus Eimeria, is one of the most widespread and economically detrimental diseases in the global poultry industry. Because the merozoite stage of Eimeria tenella is immunologically vulnerable, motile, and functionally important for the parasites, the proteins expressed in these stages are considered to be potentially immunoprotective antigens, especially the secreted antigens and surface antigens. Here, we detected a previously unidentified MIC2-associated protein (Et-M2AP) from E. tenella and determined its localization. An immunofluorescence assay revealed that Et-M2AP was distributed in the apical part of second generation merozoites and sporozoites. In addition, an expression profile analysis revealed that the transcriptional level of Et-M2AP is significantly higher in the merozoite stage. To assess the potential of Et-M2AP protein as a coccidiosis vaccine, we expressed recombinant Et-M2AP (rEt-M2AP) and compared the immune protective efficacy of rEt-M2AP with 3 surface antigens that are highly expressed by merozoites (rEt-SAG23, rEt-SAG16, and rEt-SAG2 proteins). The immune protective efficacy of these vaccine candidates was assessed based on survival rate, lesion score, BW gain, relative BW gain, and oocyst output. The results show that the survival rate was 90%, which are significantly higher than those in the challenge control group. The BW gain rate was 42% (P < 0.001) in rEt-M2AP-immunized chickens, which are significantly higher than those in the challenge control group and rEt-SAG23, rEt-SAG16, and rEt-SAG2 proteins-immunized chickens. In addition, chickens immunized with rEt-M2AP (88% oocyst output decrease rate, P < 0.001) had the least oocyst output, compared with those immunized with rEt-SAG16 (59.2% oocyst output decrease rate, P < 0.001), rEt-SAG23 (22% oocyst output decrease rate), and rEt-SAG2 (1.36% oocyst output decrease rate). These results demonstrate that rEt-M2AP provided effective protection against challenge with E. tenella, suggesting that rEt-M2AP is a promising candidate antigen gene for development as a coccidiosis vaccine.

Response of broiler chickens fed diets supplemented with a bioactive olive pomace extract from Olea europaea to an experimental coccidial vaccine challenge

This study aimed to investigate an experimental procedure of coccidial challenge in battery cages and the anticoccidial effect of a bioactive olive pomace extract from Olea europaea (OE) in broiler chickens. To this end, four hundred 1-day-old male chicks were randomly assigned to 5 experimental treatments (10 cages/treatment; 8 birds/cage). One group was fed the control diet without any additives and not challenged (NCU). The other 4 groups were challenged and fed the control diet with no additives (NCC) or supplemented with 500 ppm of coccidiostat or with 500 or 1,500 ppm of OE. At 0, 7, and 14 d, all challenged birds, except the NCC group, were orally gavaged with a live Eimeria spp. oocyst vaccine at 1x, 4x, and 16x of the manufacturer's recommended dose, respectively. Feed intake (FI), body weight gain (BWG), and feed conversion ratio (FCR) were determined at 7, 14, 20, and 28 d. At 20 d of age, 1 bird per cage was euthanized to analyze duodenum and jejunum morphology, ileal mucosa gene expression, and plasma cytokine, alpha-1-acid glycoprotein, and carotenoid (CAR) concentrations. Coccidial vaccine challenge lowered BW (P < 0.05) throughout the trial, and reduced FI and BWG, except from 20 to 28d, and increased FCR from 0 to 7, 0 to 14, and 0 to 20 d. Birds in the NCC group had higher (P < 0.05) oocyst counts and lower (P < 0.05) CAR and villus height to crypt depth ratios compared with NCU birds. Overall, coccidia challenge caused the expected reductions in growth performance and gut integrity. While the coccidiostat reduced oocysts excretion, dietary OE or coccidiostat had no effects on performance or gut integrity. The attenuated inflammatory response observed for all the treatments following the third infection can be attributed to the adaptation or immunization to the repetitive exposure to Eimeria spp.

Bacillus subtilis delivery route: effect on growth performance, intestinal morphology, cecal short-chain fatty acid concentration, and cecal microbiota in broiler chickens

As the poultry industry recedes from the use of antibiotic growth promoters, the need to evaluate the efficacy of possible alternatives and the delivery method that maximizes their effectiveness arises. This study aimed at expounding knowledge on the effect of the delivery method of a probiotic product (Bacillus subtilis fermentation extract) on performance and gut parameters in broiler chickens. A total of 450 fertile eggs sourced from Cobb 500 broiler breeders were randomly allotted to 3 groups: in ovo probiotic (n = 66), in ovo saline (n = 66), and noninjection (n = 200) and incubated for 21 d. On day 18.5 of incubation, 200 μL of either probiotic (10 × 10⁶ cfu) or saline was injected into the amnion. At hatch, chicks were reallotted to 6 new treatment groups: in ovo probiotic, in ovo saline, in-feed antibiotics, in-water probiotic, in-feed probiotics, and control (corn-wheat-soybean diet) in 6 replicate cages and raised for 28 d. Of all hatch parameters evaluated, only percentage pipped eggs was found significant (P < 0.05) with the noninjection group having higher percentage pipped eggs than the other groups. Treatments did not affect the incidence of necrotic enteritis on day 28 (P > 0.05). Irrespective of the delivery method, the probiotic treatments had no significant effect on growth performance. The ileum villus width of the in ovo probiotic treatment was 18% higher than the in ovo saline group (P = 0.05) but not statistically higher than other groups. The jejunum villus height was 23% higher (P = 0.000) in the in ovo probiotic group than in the control group. There was no effect of treatment on total cecal short-chain fatty acid concentration and cecal gut microbiota composition and diversity (P > 0.05), although few unique bacteria differential abundance were recorded per treatment. Conclusively, although probiotic treatments (irrespective of the delivery route) did not affect growth performance, in ovo delivery of the probiotic product enhanced intestinal morphology, without compromising hatch performance and gut homeostasis.

Monitoring coccidia in commercial broiler chicken flocks in Ontario: comparing oocyst cycling patterns in flocks using anticoccidial medications or live vaccination

Coccidiosis, the parasitic disease caused by Eimeria spp., is controlled during broiler chicken production through the inclusion of in-feed anticoccidial medications. Live-coccidiosis vaccination has become an increasingly common alternative to these medications. Monitoring infections with Eimeria spp. in flocks can be accomplished through determining the concentration of oocysts excreted in the fecal material (i.e., oocysts per gram; OPG). The purpose of our study was to sample commercial Ontario broiler chicken flocks at various times of the year to determine weekly OPG counts for flocks that use either an in-feed anticoccidial medication or a live-coccidiosis vaccine. Weekly sampling of 95 flocks from placement to market permitted documentation of oocyst cycling patterns typical of conventional and antibiotic-free flocks, and variation of these patterns in summer and winter. Medicated flocks had higher and later peak oocyst shedding compared with vaccinated flocks. Flocks reared in the summer peaked in oocyst shedding earlier than flocks reared in the winter. Despite what appears to be poorer coccidiosis control in the medicated flocks, the performance data were similar for these flocks compared with vaccinated flocks. This is the first study describing typical patterns of parasite shedding in Ontarian commercial broiler chicken flocks; these data will provide a baseline of expected Eimeria spp. infections in Canadian broiler chicken flocks to ensure optimal coccidiosis prevention.

Avian Pathogenic Escherichia coli and Clostridium perfringens: Challenges in No Antibiotics Ever Broiler Production and Potential Solutions

United States is the largest producer and the second largest exporter of broiler meat in the world. In the US, broiler production is largely converting to antibiotic-free programs which has caused an increase in morbidity and mortality within broiler farms. Escherichia coli and Clostridium perfringens are two important pathogenic bacteria readily found in the broiler environment and result in annual billion-dollar losses from colibacillosis, gangrenous dermatitis, and necrotic enteritis. The broiler industry is in search of non-antibiotic alternatives including novel vaccines, prebiotics, probiotics, and housing management strategies to mitigate production losses due to these diseases. This review provides an overview of the broiler industry and antibiotic free production, current challenges, and emerging research on antibiotic alternatives to reduce pathogenic microbial presence and improve bird health.

Mucosal Delivery of a Self-destructing Salmonella-Based Vaccine Inducing Immunity Against Eimeria

A programmed self-destructive Salmonella vaccine delivery system was developed to facilitate efficient colonization in host tissues that allows release of the bacterial cell contents after lysis to stimulate mucosal, systemic, and cellular immunities against a diversity of pathogens. Adoption and modification of these technological improvements could form part of an integrated strategy for cost-effective control and prevention of infectious diseases, including those caused by parasitic pathogens. Avian coccidiosis is a common poultry disease caused by Eimeria. Coccidiosis has been controlled by medicating feed with anticoccidial drugs or administering vaccines containing low doses of virulent or attenuated Eimeria oocysts. Problems of drug resistance and nonuniform administration of these Eimeria resulting in variable immunity are prompting efforts to develop recombinant Eimeria vaccines. In this study, we designed, constructed, and evaluated a self-destructing recombinant attenuated Salmonella vaccine (RASV) lysis strain synthesizing the Eimeria tenella SO7 antigen. We showed that the RASV lysis strain χ11791(pYA5293) with a ΔsifA mutation enabling escape from the Salmonella-containing vesicle (or endosome) successfully colonized chicken lymphoid tissues and induced strong mucosal and cell-mediated immunities, which are critically important for protection against Eimeria challenge. The results from animal clinical trials show that this vaccine strain significantly increased food conversion efficiency and protection against weight gain depression after challenge with 105E. tenella oocysts with concomitant decreased oocyst output. More importantly, the programmed regulated lysis feature designed into this RASV strain promotes bacterial self-clearance from the host, lessening persistence of vaccine strains in vivo and survival if excreted, which is a critically important advantage in a vaccine for livestock animals. Our approach should provide a safe, cost-effective, and efficacious vaccine to control coccidiosis upon addition of additional protective Eimeria antigens. These improved RASVs can also be modified for use to control other parasitic diseases infecting other animal species.

A Novel Rhoptry Protein as Candidate Vaccine against Eimeria tenella Infection

Eimeria tenella (E. tenella) is a highly pathogenic and prevalent species of Eimeria that infects chickens, and it causes a considerable disease burden worldwide. The secreted proteins and surface antigens of E. tenella at the sporozoite stage play an essential role in the host–parasite interaction, which involves attachment and invasion, and these interactions are considered vaccine candidates based on the strategy of cutting off the invasion pathway to interrupt infection. We selected two highly expressed surface antigens (SAGs; Et-SAG13 and Et-SAG) and two highly expressed secreted antigens (rhoptry kinases Eten5-A, Et-ROPK-Eten5-A and dense granule 12, Et-GRA12) at the sporozoite stage. Et-ROPK-Eten5-A and Et-GRA12 were two unexplored proteins. Et-ROPK-Eten5-A was an E. tenella-specific rhoptry (ROP) protein and distributed in the apical pole of sporozoites and merozoites. Et-GRA12 was scattered in granular form at the sporozoite stage. To evaluate the potential of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG proteins as a coccidiosis vaccine, the protective efficacy was examined based on survival rate, lesion score, body weight gain, relative body weight gain and oocyst output. The survival rate was significantly improved in rEt-ROPK-Eten5-A (100%) and rEt-GRA12 (100%) immune chickens compared to the challenged control group (40%). The average body weight gains of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG immunized chickens were significantly higher than those of unimmunized chickens. The mean lesion score and oocyst output of the rEt-ROPK-Eten5-A immunized chickens were significantly reduced compared to unimmunized challenged chickens. These results suggest that the rEt-ROPK-Eten5-A protein effectively triggered protection against E. tenella in chickens and provides a useful foundation for future work developing anticoccidial vaccines.

Molecular characterization of 60S ribosomal protein L12 of E. tenella

This study analyzed the large-subunit (60S) ribosomal protein L12 of Eimeria tenella (Et60s-RPL12). A full-length cDNA was cloned, and the recombinant protein was expressed in E. coli BL21 and inoculated in rabbits to produce the polyclonal antibody. Quantitative real-time polymerase chain reaction and western blotting were used to analyze the transcription levels of Et60s-RPL12 and translation levels in different developmental stages of E. tenella. The results showed that the mRNA transcription level of Et60s-RPL12 was highest in second-generation merozoites, whereas the translation level was highest in unsporulated oocysts. Indirect immunofluorescence showed that Et60s-RPL12 was localized to the anterior region and surface of sporozoites, except for the two refractile bodies. As the invasion of DF-1 cells progressed, fluorescence intensity was increased, and Et60s-RPL12 was localized to the parasitophorous vacuole membrane (PVM). The secretion assay results using staurosporine indicated that this protein was secreted, but not from micronemes. The role of Et60s-RPL12 in invasion was evaluated in vitro. The results of the invasion assay showed that polyclonal antibody inhibited host cell invasion by the parasite, which reached about 12%. However, the rate of invasion was not correlated with the concentration of IgG.