The viability and performance under hot conditions of featherless broilers versus fully feathered broilers

Growth patterns and heat tolerance analysis of dwarf chicken with frizzled feather

Chickens are covered with feathers, lack sweat glands, and are sensitive to the thermal environment. Previously, our group bred a novel dwarf chicken strain with frizzled feather, named as dwarf chicken with frizzled feather (DFC). The cumulative growth of the chicken body weight and size were analyzed with 3 mathematical models. Subsequently, chickens were grouped to investigate the impact of heat stress (HS) on their slaughter performance, histomorphological development and gene mRNA change (HSP70, muscle development and appetite-related factors) using quantitative real-time PCR, tissue sections and Western Blot. In the HS group, chickens were placed at 34 ± 1°C for 8 hours (9:00 am - 17:00 pm) a day and lasted for 2 weeks, while in the control group, chickens were fed at 26 ± 1°C. Chicken tissue samples were collected at the age of 120 days to evaluate production performance, histological changes, and gene expression changes. Our results found that the Gompertz model was the best for fitting the body weight of DFC. The integrity of muscle, liver, spleen, and small intestine tissues was affected under HS conditions. Correspondingly, the length of the ileum was significantly decreased (P < 0.05), the thigh muscle development factor MYOD1 expression was down-regulated (P < 0.05), while the expression of MSTN was up-regulated (P < 0.001). In addition, the jejunum VH / CD was reduced significantly (P < 0.05). The mRNA of appetite-promoting factors AMPKα-1 and AGRP in the gut-brain axis were down-regulated (P < 0.05), while appetite-restrain factors CCK, GHRL, and CART were significantly up-regulated (P < 0.05 or P < 0.01). Moreover, the intestinal transport and absorption factors ZO1, OCLN, PepT1, SGLT1, and CAT1 were up-regulated (P < 0.05 or P < 0.01), and GLUT1 was down-regulated (P < 0.05). These results indicated that HS mainly impacted the appetite of chickens and did not significantly disrupt the nutrient absorption function of these chickens. The DFC appeared to be more tolerant to the hot environments for their frizzled feathers, small body size, and low basal metabolic rate.

Response of broilers to supplementation of Salvia officinalis L. essential oil in hot ambient conditions

Heat stress has various detrimental effects on poultry production. The aim of the study was to alleviate the effects of heat stress in broiler production. For this purpose, 288 one-day-old broiler chicks (Ross 308) were obtained from a commercial hatchery and randomly allocated to one of three treatment groups; CON: corn-soybean meal based commercial diet, SEO100: CON with 100 mg/kg Sage essential oil (SEO) and SEO200: CON with 200 mg/kg SEO with 96 birds in each group (4 replicates each) in a completely randomized design under hot ambient temperatures for 42 days. No differences were observed in the body weight, feed intake, and feed conversion ratio at 42 days of age among groups. However, there was a significant increase in 21-day body weight in SEO200 chicks compared to CON. Furthermore, the addition of SEO significantly decreased the mortality rate under heat stress conditions. The total oxidant status value was lower in broiler chickens in which SEO was added to their diets. While the total antioxidant status value was higher in SEO100 chicks, it did not show a linear increase. Additionally, the results demonstrated that the addition of SEO to broiler diets under heat stress did not have a significant effect on inspected meat quality traits, with the exception of the b*(yellowness) value of breast muscle. In conclusion, the results of this study indicate that 200 mg/kg SEO can be added to diets for the welfare of broiler chickens under heat stress conditions for struggling with oxidants and increasing viability. Further research is needed to investigate the antioxidant activity and meat quality of different levels of SEO in hot ambient conditions.

Alleviating heat stress effects in poultry: updates on methods and mechanisms of actions

Heat stress is a threat that can lead to significant financial losses in the production of poultry in the world's tropical and arid regions. The degree of heat stress (mild, moderate, severe) experienced by poultry depends mainly on thermal radiation, humidity, the animal's thermoregulatory ability, metabolic rate, age, intensity, and duration of the heat stress. Contemporary commercial broiler chickens have a rapid metabolism, which makes them produce higher heat and be prone to heat stress. The negative effect of heat stress on poultry birds' physiology, health, production, welfare, and behaviors are reviewed in detail in this work. The appropriate mitigation strategies for heat stress in poultry are equally explored in this review. Interestingly, each of these strategies finds its applicability at different stages of a poultry's lifecycle. For instance, gene mapping prior to breeding and genetic selection during breeding are promising tools for developing heat-resistant breeds. Thermal conditioning during embryonic development or early life enhances the ability of birds to tolerate heat during their adult life. Nutritional management such as dietary manipulations, nighttime feeding, and wet feeding often, applied with timely and effective correction of environmental conditions have been proven to ameliorate the effect of heat stress in chicks and adult birds. As long as the climatic crises persist, heat stress may continue to require considerable attention; thus, it is imperative to explore the current happenings and pay attention to the future trajectory of heat stress effects on poultry production.

Effects of Cyclic Thermal Stress at Later Age on Production Performance and Meat Quality of Fast-Growing, Medium-Growing and Thai Native Chickens

The present study aimed at assessing the impact of cyclic thermal stress on production performance and meat quality of commercial broilers (BRs), Thai native chickens (NT) and the hybrids between BR and NT (H75; crossbreed 25% NT). At the age of 3, 5 and 9 weeks for BR, H75 and NT, respectively, each strain was equally divided (n = 50) into control and treatment groups. The controls were raised at a constant 26 ± 1 °C, while the treatments were subjected to thermal stress (35 ± 1 °C, 6 h daily) for 3 weeks. The results indicated that final weight and average daily gain of BR and NT treated groups were significantly lower than those of their control counterparts. Reduced body weight gain of BR and H75, as well as feed intake of H75, was observed in the treatment groups (p < 0.05). The stressed BR breasts showed decreased moisture, fat and carbohydrate, accompanied by increased protein, ash, L *-value, b*-value and shear force (p < 0.05). No significant effects (p ≥ 0.05) of the thermal stress on meat quality indices were found for H75 and NT breast samples. Pectoral myopathies were observed in BR and H75 chickens, but the numbers of cases were decreased in the thermally treated groups.

The genetic basis and robustness of naked neck mutation in chicken

Chicken is a homeothermic animal; consequently, regardless of fluctuation in weather conditions, it maintains constant body temperature. However, in hot regions and seasons, chickens suffer from heat stress. To dissipate excess heat, besides modifying the environment, which is costly, however, chickens with efficient heat dissipation capacity might be utilized. Naked neck chickens have a higher capacity for heat loss attributable to reduced feather mass. The naked neck mutation (Na) was originated from a large insertion (~ 180 bp) integrated ~ 260-kb downstream of a protein-coding gene-GDF7 (Growth Differentiation Factor 7). Na possesses a cis-regulatory function and upregulates the expression of GDF7-a gene that exhibits a tissue-specific effect by the sensitizing action of retinoic acid. Na suppresses the development of feathers in the neck and vent. Na shows autosomal incomplete dominance and regulates several developmental processes. Na usually segregates at low frequency, which might be attributed to limited socio-cultural preferences. Specifically, in hot and humid regions, although to a varying extent, Na enhances performance, immunocompetence, and resilience to disease both in the homozygous and heterozygous state. Occasionally, naked neck chickens (especially the homozygous ones) lose comparative advantage in cool environments. Homozygous Na also results in high embryo death and reduced hatchability and diminishes floating and flying capacity. Nevertheless, selective breeding of naked neck chickens for fertility traits enhances the performance and welfare of chickens in hot and humid regions. The comparative advantage of Na needs to be studied not only from a temperature perspective and under controlled experiment but also from humidity, body weight, feed intake (absolute and relative to body weight), age, agroecology insights, and under field condition. Due to the incomplete dominant expression pattern of Na, studies need to separately report their findings for homozygous and heterozygous naked neck chicken.

Emerging Genetic Tools to Investigate Molecular Pathways Related to Heat Stress in Chickens: A Review

Simple Summary

New genomic tools have been used as an instrument in order to assess the molecular pathway involved in heat stress resistance. Local chicken breeds have a better attitude to face heat stress. This review aims to summarize studies linked to chickens, heat stress, and heat shock protein.

Abstract

Chicken products are the most consumed animal-sourced foods at a global level across greatly diverse cultures, traditions, and religions. The consumption of chicken meat has increased rapidly in the past few decades and chicken meat is the main animal protein source in developing countries. Heat stress is one of the environmental factors which decreases the productive performance of poultry and meat quality. Heat stress produces the over-expression of heat shock factors and heat shock proteins in chicken tissues. Heat shock proteins regulate several molecular pathways in cells in response to stress conditions, changing the homeostasis of cells and tissues. These changes can affect the physiology of the tissue and hence the production ability of chickens. Indeed, commercial chicken strains can reach a high production level, but their body metabolism, being comparatively accelerated, has poor thermoregulation. In contrast, native backyard chickens are more adapted to the environments in which they live, with a robustness that allows them to survive and reproduce constantly. In the past few years, new molecular tools have been developed, such as RNA-Seq, Single Nucleotide Polymorphisms (SNPs), and bioinformatics approaches such as Genome-Wide Association Study (GWAS). Based on these genetic tools, many studies have detected the main pathways involved in cellular response mechanisms. In this context, it is necessary to clarify all the genetic and molecular mechanisms involved in heat stress response. Hence, this paper aims to review the ability of the new generation of genetic tools to clarify the molecular pathways associated with heat stress in chickens, offering new perspectives for the use of these findings in the animal breeding field.

Impact of Heat Stress on Poultry Health and Performances, and Potential Mitigation Strategies

Heat stress is one of the major environmental stressors in the poultry industry resulting in substantial economic loss. Heat stress causes several physiological changes, such as oxidative stress, acid-base imbalance, and suppressed immunocompetence, which leads to increased mortality and reduced feed efficiency, body weight, feed intake, and egg production, and also affects meat and egg quality. Several strategies, with a variable degree of effectiveness, have been implemented to attenuate heat stress in poultry. Nutritional strategies, such as restricting the feed, wet or dual feeding, adding fat in diets, supplementing vitamins, minerals, osmolytes, and phytochemicals, have been widely studied and found to reduce the deleterious effects of heat stress. Furthermore, the use of naked neck (Na) and frizzle (F) genes in certain breed lines have also gained massive attention in recent times. However, only a few of these strategies have been widely used in the poultry industry. Therefore, developing heat-tolerant breed lines along with proper management and nutritional approach needs to be considered for solving this problem. Thus, this review highlights the scientific evidence regarding the effects of heat stress on poultry health and performances, and potential mitigation strategies against heat stress in broiler chickens and laying hens.

The effect of intermittent feeding and cold water on performance and carcass traits of broilers reared under daily heat stress

Objective

This study aimed to determine the effect of intermittent feeding and cold water on performance and carcass traits in broiler chickens between 4 to 6 wk of age exposed to daily high temperature.

Methods

Broilers were assigned to four treatment groups according to a 2×2 factorial design between 22 to 42 d of age (80 broilers per treatment, 4 replications). Broilers were divided into two main groups as feeding type (ad-libitum [AL] and intermittent [IF] for 6 h daily) and sub-groups as water temperature (normal [NW], 24.9°C and cold [CW], 16.4°C). Heat treatment was applied between 11.00 to 17.00 h daily between 22 to 42 d of age.

Results

Live weight at 6th wk was not affected by feeding type and water temperature, but the live weight was significantly higher in IF chickens at the 5th wk (p<0.05). Average weekly gain of IF broiler chickens were higher compared to AL group at 4, 5, and 6 wk of age (p< 0.05). Although feeding type did not affect feed intake in 4 and 5th wk, feed intake was higher in IF chickens at 6th wk (p<0.01). In addition, feeding type and water temperature did not affect feed conversion ratio and interactions were not significant (p>0.05). Water temperature had no significant effect on heart, liver, gizzard, and abdominal fat percentages (p>0.05).

Conclusion

It is concluded that IF increased the average weekly gain in chickens reared under daily heat stress for 6 h between 22 to 42 d of age. IF in hot environmental conditions slightly increased performance without adversely affecting health, welfare, and physiological traits, whereas CW implementation had no significant effect on performance. It can also be said that IF suppresses a sudden increase in body temperature depending on age and live weight.

Genomic regions and pathways associated with thermotolerance in layer-type strain Taiwan indigenous chickens

This study aimed to investigate genetic markers and candidate genes associated with thermotolerance in a layer-type strain Taiwan indigenous chickens exposed to acute heat stress. One hundred and ninety-two 30-week-old roosters were subjected to acute heat stress. Changes in body temperature (BT, ΔT) were calculated by measuring the difference between the initial BT and the highest BT during heat stress and the results were categorized into dead, susceptible, tolerant, and intermediate groups depending on their survival and ΔT values at the end of the experiment. A genome-wide association study on survival and ΔT values was conducted using the Cochran-Armitage trend test and Fisher's exact test. Association analyses identified 80 significant SNPs being annotated to 23 candidate genes, 440 SNPs to 71 candidate genes, 64 SNPs to 25 candidate genes, and 378 SNPs to 78 candidate genes in the dead versus survivor, tolerant versus susceptible, intermediate versus tolerant, and intermediate versus susceptible groups, respectively. The annotated genes were associated with apoptosis, cellular stress responses, DNA repair, and metabolic oxidative stress. In conclusion, the identified SNPs of candidate genes provide insights into the potential mechanisms underlying physiological responses to acute heat stress in chickens.

High fidelity CRISPR/Cas9 increases precise monoallelic and biallelic editing events in primordial germ cells

Primordial germ cells (PGCs), the embryonic precursors of the sperm and egg, are used for the introduction of genetic modifications into avian genome. Introduction of small defined sequences using genome editing has not been demonstrated in bird species. Here, we compared oligonucleotide-mediated HDR using wild type SpCas9 (SpCas9-WT) and high fidelity SpCas9-HF1 in PGCs and show that many loci in chicken PGCs can be precise edited using donors containing CRISPR/Cas9-blocking mutations positioned in the protospacer adjacent motif (PAM). However, targeting was more efficient using SpCas9-HF1 when mutations were introduced only into the gRNA target sequence. We subsequently employed an eGFP-to-BFP conversion assay, to directly compare HDR mediated by SpCas9-WT and SpCas9-HF1 and discovered that SpCas9-HF1 increases HDR while reducing INDEL formation. Furthermore, SpCas9-HF1 increases the frequency of single allele editing in comparison to SpCas9-WT. We used SpCas9-HF1 to demonstrate the introduction of monoallelic and biallelic point mutations into the FGF20 gene and generate clonal populations of edited PGCs with defined homozygous and heterozygous genotypes. Our results demonstrate the use of oligonucleotide donors and high fidelity CRISPR/Cas9 variants to perform precise genome editing with high efficiency in PGCs.

Daily variations in the thermoregulatory behaviors of naked neck broilers in an equatorial semi-arid environment

The aim of this study was to evaluate the daily variations in the thermoregulatory behavior of 4- to 6-week-old naked neck broilers (Label Rouge) in an equatorial semi-arid environment. A total of 220 birds were monitored for 5 days starting at 0600 hours and ending at 1800 hours. The period of observation was divided into classes of hours (C H). The observed behaviors were as follows: feed and water intake, wing-spreading, sitting or lying, and beak-opening. A total of 14,300 behavioral data values were registered. In C H 2 (0900 hours to 1100 hours) and 3 (1200 hours to 1500 hours), the greatest average body surface temperature was recorded (34.67 ± 0.25 °C and 35.12 ± 0.22 °C, respectively). The C H had an effect on the exhibition of all behaviors with the exception of the water intake behavior. Feed intake was more frequent in C H 1 (0600 hours to 0800 hours) and 4 (1600 hours to 1800 hours). In C H 2 and 3, the highest frequency of sitting or lying behavior was observed. Beak-opening and wing-spreading behaviors occurred more frequently in C H 3 where the body surface temperature (35.12 ± 0.22 °C), radiant heat load (519.38 ± 2.22 W m(-2)), and enthalpy (82.74 ± 0.36 kJ kg(-1) of dry air) reached maximum recorded averages. Thus, it can be concluded that naked neck broilers adjust their behavior in response to daily variations in the thermal environment. Wing-spreading and beak-opening behaviors are important adaptive responses to the thermal challenges posed by the equatorial semi-arid environment.

Effect of incorporation of thermo-regulatory genes into exotic layers on egg production and quality under tropical environment

A breed development strategy aimed at making exotic layers (Lohmann Brown) more productive under tropical environment using thermo-regulatory genes is underway at Akate Farms in Kumasi, Ghana. The present experiment was carried out to find out the effect of the genes on egg production in hot and humid environments. Three genetic groups comprising naked-neck, frizzle and their normally feathered sibs were obtained after successive generations of crossing between naked-neck and frizzle cocks and Lohmann brown hens. A total of 270 18-week-old pullets, 90 each of the 3 groups, were selected randomly and assigned to a completely randomized design experiment with 3 replicates, with 30 birds in each replicate group and kept up to a period of 72 weeks. The birds were kept in a partitioned open-sided deep-litter house constructed with sandcrete blocks with 30 pullets in each compartment. They were fed ad libitum with layer diets containing 18 % crude protein and 2,800 kcal ME/kg. Results obtained showed that the crossbred naked-neck and frizzle phenotypes produced eggs at a significantly (P < 0.05) higher rates than their normally feathered sibs and also out-performed their normally feathered sibs in other egg production parameters measured, even though they all segregated from similar parents. This is an indication of the favourable effect of the genes on egg production under hot and humid environments.

Changes in body temperature during growth and in response to fasting in growing modern meat type chickens

1. Rectal or core body temperature was determined in a study to examine the effects of fasting in modern meat type broilers at three stages of growth, namely d 19, 33 and 47. 2. There were two treatment groups: fed with feed available ad libitum and fasted. Rectal temperatures were determined at noon (1200 h). At that time, feed was removed from the fasted group. The body temperatures were then determined again after 6, 12, 18 and 24 h. 3. Core body temperatures decreased with fasting. The decrease was evident after as little as 6 h of fasting with a further decline evident by 12 h. 4. Accompanying the decrease in body temperature with fasting there were decreases in the venous concentrations of carbon dioxide in the blood and sodium in the plasma. 5. The decrease in both body temperature and carbon dioxide presumably reflects depressed metabolic rate. 6. Unexpectedly, the core body temperature increased progressively with age in the control fed group (d 19 = 41·04 ± 0·02°C, d 33 = 41·65 ± 0·05°C, d 47 = 42·21 ± 0·12°C). 7. In the fed control group, core body temperatures were reduced at night, when feeding activity would be anticipated to be greatly reduced.

Genome-wide SNP scan of pooled DNA reveals nonsense mutation in FGF20 in the scaleless line of featherless chickens

Background

Scaleless (sc/sc) chickens carry a single recessive mutation that causes a lack of almost all body feathers, as well as foot scales and spurs, due to a failure of skin patterning during embryogenesis. This spontaneous mutant line, first described in the 1950s, has been used extensively to explore the tissue interactions involved in ectodermal appendage formation in embryonic skin. Moreover, the trait is potentially useful in tropical agriculture due to the ability of featherless chickens to tolerate heat, which is at present a major constraint to efficient poultry meat production in hot climates. In the interests of enhancing our understanding of feather placode development, and to provide the poultry industry with a strategy to breed heat-tolerant meat-type chickens (broilers), we mapped and identified the sc mutation.

Results

Through a cost-effective and labour-efficient SNP array mapping approach using DNA from sc/sc and sc/+ blood sample pools, we map the sc trait to chromosome 4 and show that a nonsense mutation in FGF20 is completely associated with the sc/sc phenotype. This mutation, common to all sc/sc individuals and absent from wild type, is predicted to lead to loss of a highly conserved region of the FGF20 protein important for FGF signalling. In situ hybridisation and quantitative RT-PCR studies reveal that FGF20 is epidermally expressed during the early stages of feather placode patterning. In addition, we describe a dCAPS genotyping assay based on the mutation, developed to facilitate discrimination between wild type and sc alleles.

Conclusions

This work represents the first loss of function genetic evidence supporting a role for FGF ligand signalling in feather development, and suggests FGF20 as a novel central player in the development of vertebrate skin appendages, including hair follicles and exocrine glands. In addition, this is to our knowledge the first report describing the use of the chicken SNP array to map genes based on genotyping of DNA samples from pooled whole blood. The identification of the sc mutation has important implications for the future breeding of this potentially useful trait for the poultry industry, and our genotyping assay can facilitate its rapid introgression into production lines.