Proper cold stimulation starting at an earlier age can enhance immunity and improve adaptability to cold stress in broilers

Intermittent and mild cold stimulation enhances immune function of broilers via co-regulation of CIRP and TRPM8 on NF-κB and MAPK signaling pathways

Improving immune function is an important indicator for establishing cold adaptation in broilers. In the study, to explore the effects and molecular mechanisms of intermittent and mild cold stimulation (IMCS) on the immune function of broilers, CIRP and TRPM8, induced by cold stimulation, as well as the NF-κB and MAPK pathways which play an important role in immune response, were selected to investigate. A total of 192 one-day-old broilers (Ross 308) were selected and randomly divided into the control group (CC) and the cold stimulation group (CS). The broilers in CC were raised at normal feeding temperature from d 1 to 43, while the broilers in CS were subjected to cold stimulation from day 15 to 35, with a temperature 3 °C below that of the CC group for 5 h, at 1 d intervals. The results showed that IMCS had little effect on the broiler hearts, and the myocardial structure was not damaged. On d 22, IMCS significantly increased the mRNA levels of CIRP, TRPM8, P65, P38, COX-2, TNF-α, IFN- γ, IL-6, IL-10, and the protein levels of CIRP, P65, P38, IL-1β and iNOS in the hearts, and the levels of CIRP and all cytokines in the serum (P ≤ 0.05). The mRNA and protein levels of IκB-α were significantly reduced (P ≤ 0.05). On d 36, the mRNA levels of TRPM8, P65, ERK, and IL-10 in the hearts and the content of COX-2 in the serum in CS were increased significantly (P ≤ 0.05), while the mRNA levels of IκB-α, P38, and IL-1β were decreased significantly (P ≤ 0.05). On d 43, IMCS significantly upregulated the mRNA levels of TRPM8, IFN- γ, IL-4, IL-6, IL-10, and the protein levels of IκB-α, P38, and the levels of iNOS, TNF-α, IL6 and IL10 in the serum (P ≤ 0.05); whereas it significantly downregulated CIRP, JNK, P38, iNOS, TNF-α mRNA levels, and CIRP, P65, ERK, JNK, IL1β and iNOS protein levels (P ≤ 0.05). Therefore, IMCS can enhance broiler immune function through co-regulation of CIRP and TRPM8 on the NF-κB and MAPK pathways, which facilitate the cold adaptation in broilers.

Unlocking the therapeutic potential of Huoxiang Zhengqi San in cold and high humidity-induced diarrhea: Insights into intestinal microbiota modulation and digestive enzyme activity

Huoxiang Zhengqi San (HXZQS), a traditional Chinese herbal formula, enjoys widespread use in Chinese medicine to treat diarrhea with cold-dampness trapped spleen syndrome (CDSS), which is induced by exposure to cold and high humidity stress. This study aimed to explore its therapeutic mechanisms in mice, particularly focusing on the intestinal microbiota. Forty male SPF-grade KM mice were allocated into two groups: the normal control group (H-Cc, n = 10) and the CDSS group (H-Mc, n = 30). After modeling, H-Mc was subdivided into H-Mc (n = 15) and HXZQS treatment (H-Tc, n = 15) groups. Intestinal samples were analyzed for enzyme activity and microbiota composition. Our findings demonstrated a notable reduction in intestinal lactase activity post-HXZQS treatment (P < 0.05). Lactobacillus johnsonii, Lactobacillus reuteri, and Lactobacillus murinus emerged as the main dominant species across most groups. However, in the H-Mc group, Clostridium sensu stricto 1 was identified as the exclusive dominant bacteria. LEfSe analysis highlighted Clostridiales vadinBB60 group and Corynebacterium as differential bacteria in the H-Tc group, and Cyanobacteria unidentified specie in the H-Mc group. Predicted microbiota functions aligned with changes in abundance, notably in cofactors and vitamins metabolism. The collinear results of the intestinal microbiota interaction network showed that HXZQS restored cooperative interactions among rare bacteria by mitigating their mutual promotion. The HXZQS decoction effectively alleviates diarrhea with CDSS by regulating intestinal microbiota, digestive enzyme activity, and microbiota interaction. Notably, it enhances Clostridium vadinBB60 and suppresses Cyanobacteria unidentified specie, warranting further study.

PI3K/AKT pathway modulation and cold acclimation alleviation concerning apoptosis and necroptosis in broiler thymus

Moderate cold stimulation regulates the thymus's growth and function and facilitates cold acclimatization in broilers. However, the underlying mechanism remains unknown. To explore the possible mechanism of the thymus in cold-acclimated broilers against cold stress, 240 one-day-old Arbor Acres (AA) broilers were assigned to 2 groups randomly. The control group (C) was housed at conventional temperatures. The temperature during the first week was 33°C to 34°C. Between the ages of 8 and 32 d, the temperature was lowered by 1°C every 2 d, i.e., gradually from 32°C to 20°C, and then maintained at 20°C until 42 d of age. The cold-acclimated group (C-3) was housed at the same temperature as C from 1 to 7 d after birth. Between 8 and 42 d, the temperature of C-3 was 3°C colder than C. After 24 h exposure to acute cold stress (ACS) at 42 d, C and C-3 were named as S and S-3. The results showed that ACS was able to induce oxidation stress, modulate PI3K/AKT signal, and cause necroptosis and apoptosis in broiler thymus. By contrast, cold acclimation could alleviate apoptosis and necroptosis induced by cold stress via alleviating oxidative stress, efficiently activating the PI3K/AKT signal, as well as decreasing apoptotic and necrotic genes' levels. This study offers a novel theoretical basis for cold acclimation to improve the body's cold tolerance.

Data analytics-based evaluation of blood indices and adaptation of medicated and non-medicated broiler chickens under humid tropical conditions

The growth performance and blood indices of medicated and non-medicated broiler chickens have been the subject of this research coupled with a paucity of comparative information on what can actually happen to broiler chickens if not medicated when reared under humid tropical conditions. One hundred unsexed day-old broilers were randomly and equally allotted into two treatment groups of TM (medicated) and TN (non-medicated) in a completely randomized design each treatment with five replicates having ten birds each. The birds were reared on deep litter system for 56 d which was divided into two phases of 28 d each (starter and finisher), during which data were collected with respect to daily feed intake, final body weight, body weight gained (BWG), mortality rate while blood analysis was carried out on 28th and 56th d for starter and finisher phases, respectively. Non-medicated group served as control. Feed conversion ratio (FCR) and feed conversion efficiency (FCE), were later calculated. Data collected were subjected to analysis of variance statistically. There was no significant difference between the medicated and non-medicated broilers for daily feed intake, final body weight, and BWG and also for the blood parameters investigated at starter phase. However, at finisher phase, no significant difference was observed in the daily feed intake of Tm and Tn but there was significant (P < 0.05) difference in the final body weight, BWG, FCR, FCE, and mortality rate between the two groups. Birds on Tm attained higher weight significantly (P < 0.05) than those on TN. BWG, FCR, and FCE followed the same trend and also the mortality rate. White blood cells count of TN was higher significantly (P < 0.05) than TM while TM birds recorded higher packed cell volume, red blood counts, and hemoglobin concentration (Hb) significantly (P < 0.05) than TM birds. Effect of medication was much noticeable at finisher phase as it improved the growth rate though mortality rate was close to that of TN group. These results suggest that broilers can be produced free of medication with good feeding without loss of birds while the growth rate can be enhanced with the use of prebiotics and prebiotics.

Effects of intermittent cold stimulation on growth performance, meat quality, antioxidant capacity and liver lipid metabolism in broiler chickens

Intermittent cold stimulation (ICS) enhances broilers' resistance to cold stress. Nonetheless, further research is needed to investigate the underlying mechanisms that enhance cold stress resistance. A total of 160 one-day-old male Ross 308 broilers were randomly divided into 2 groups (CC and CS5), with the CC group managing temperature according to the standard for broiler growth stages, while the CS5 group were subjected to cold stimulation at a temperature 3℃ lower than the CC group for 5 h, every 2 d from 15 to 35 d. Sampling was conducted at 36 d (36D), 50 d (50D) and after acute cold stress for 24 h (Y24). First, we examined the effects of ICS on broiler growth performance, meat quality, antioxidant capacity, and lipid metabolism. The results demonstrated that ICS enhanced the performance of broilers to a certain degree. Specifically, the average weight gain in the CS5 group was significantly higher than that of the CC group, and the feed conversion ratio significantly decreased compared to CC at 4 W and 6 W (P ≤ 0.05). Compared with the CC group, cold stimulation significantly reduced drip loss, shearing force, and yellowness (a* value) of chicken meat, while significantly increased redness (b* value) (P ≤ 0.05). At Y24, the levels of T-AOC and GSH-PX in the serum of the CS5 group were significantly higher than those of the CC group, while the level of MDA was significantly lower (P ≤ 0.05). The content of TG, FFA, and VLDL in the serum of the CS5 group was significantly elevated, whereas the level of TC and HDL was significantly lower (P ≤ 0.05). In addition, we further explored whether AMPK-mTOR pathway is involved in the regulation of changes in lipid metabolism and the possible regulatory mechanisms downstream of the signaling pathway. The results showed that ICS significantly upregulated the expression levels of AMPK mRNA and protein in the liver of the CS5 group at 36D and Y24, while significantly down-regulating mTOR (P ≤ 0.05). Compared with the CC group, ICS significantly down-regulated the mRNA expression levels of lipid synthesis and endoplasmic reticulum stress-related genes (SREBP1c, FAS, SCD, ACC, GRP78 and PERK) at 36D and Y24, while significantly up-regulating the mRNA expression levels of lipid decomposition and autophagy-related genes (PPAR and LC3) (P ≤ 0.05). In addition, at Y24, the protein expression levels of endoplasmic reticulum stress-related genes (GRP78) in the CS5 group were significantly lower, while autophagy-related genes (LC3 and ATG7) were significantly higher (P ≤ 0.05). ICS can affect meat quality and lipid metabolism in broilers, and when broilers are subjected to acute cold stress, broilers trained with cold stimulation have stronger lipid metabolism capacity.

The Effects of Housing on Growth, Immune Function and Antioxidant Status of Young Female Lambs in Cold Conditions

Cold conditions in northern China during winter may reduce sheep growth and affect their health, especially if they are young, unless housing is provided. We allocated 45 two-month-old female lambs to be housed in an enclosed building, a polytunnel, or kept outdoors, for 28 days. The daily weight gain and scalp and ear skin temperature of outdoor lambs were less than those of lambs that were housed in either a house or polytunnel; however, rectal temperature was unaffected by treatment. There was a progressive change in blood composition over time, and by the end of the experiment, outdoor lambs had reduced total antioxidant capacity (T-AOC), catalase (CAT), glutathione peroxidase (GSH-Px) and total superoxide dismutase (T-SOD) and increased malondialdehyde compared to those in the house or polytunnel. In relation to immune responses in the lambs' serum, in the polytunnel, immunoglobulin A (IgA), tumor necrosis factor-α (TNF-α) and interleukin-4 (IL-4) were higher and immunoglobulin G (IgG) lower compared with the concentrations in lambs that were outdoors. Over the course of the experiment, genes expressing heat shock proteins and antioxidant enzymes increased in lambs in the outdoor treatment, whereas they decreased in lambs in the indoor treatments. It is concluded that although there were no treatment effects on core body temperature, the trends for progressive changes in blood composition and gene expression indicate that the outdoor lambs were not physiologically stable; hence, they should not be kept outdoors in these environmental conditions for long periods.

Intermittent mild cold stimulation alleviates cold stress-induced pulmonary fibrosis by inhibiting the TGF-β1/Smad signaling pathway in broilers

To investigate the potential protective effect of intermittent cold stimulation on lung tissues of broilers exposed to acute cold stress (ACS). A total of 384 one-day-old broilers were assigned to 4 experimental groups with 6 replicates of 16 birds each: control (CON) and ACS groups were reared at normal feeding temperature from d 1 to 42; cold treatment groups (CS3+ACS and CS9+ACS) were reared, respectively, at 3°C or 9°C for 5 h on alternate days below the CON group from d 15 to 35. Animals in CS3+ACS, CS9+ACS, and ACS groups were exposed at 10°C for 24 h on d 43. Subsequently, lung tissues were collected to perform histopathological examination and measurement of relevant indexes. The results showed that lung tissues in CS9+ACS and ACS groups exhibited increased inflammatory cell infiltrates and collagen deposition compared to the CON group, while this pathological phenomenon was less pronounced in the CS3+ACS group. Compared to CON group, H2O2 and MDA contents were increased, and the activities of antioxidant enzymes (CAT, SOD, GPx, T-AOC) were reduced in CS9+ACS and ACS group (P < 0.05); mRNA and protein levels of inhibitor of NF-κB, Smad7, matrix metallopeptidase (MMP)-2, MMP9, and antioxidant-related genes were downregulated, whereas mRNA and protein levels of genes related to NF-κB/NLRP3 pathway-regulated inflammation and TGF-β1/Smad pathway-regulated fibrosis were upregulated in cold-stressed broilers (P < 0.05). mRNA levels of heme oxygenase-1, NAD(P)H quinone oxidoreductase-1, and MMP9 were increased in CS3+ACS group (P < 0.05). Moreover, the expression of most antioxidant-related genes was increased, and that of inflammation- and fibrosis-related genes was reduced in CS3+ACS group (P < 0.05). Therefore, cold stress caused oxidative stress and inflammation, leading to pulmonary fibrosis in broilers, whereas intermittent mild cold stimulation at 3°C below normal rearing temperature alleviated fibrosis by inhibiting the TGF-β1/Smad pathway modulated by the Nrf2/HO-1 and NF-κB/NLRP3 signaling pathway. This study suggests that intermittent mild cold stimulation can be a potential strategy to reduce ACS-induced lung damage in broilers.

Intermittent cold stimulation affects energy metabolism and improves stress resistance in broiler heart

To investigate the effect of intermittent cold stimulation on cardiac energy metabolism and cold resistance of broilers, 288 broilers were divided into 3 groups: control group (CC) and 2 cold stimulation groups (CS3 and CS9). The CS3 and CS9 groups received cold stimulation at temperatures of 3°C and 9°C lower than CC group for 5 h from d 15 to 35. Three groups were subjected to acute cold stress (ACS) of 10°C for 12 and 24 h at 44 d. Performance, cardiac histopathological changes, heat shock proteins (HSPs), and lipid metabolism levels were measured. Results showed that the performance was not different among groups at 22 and 29 d (P > 0.05), but the mRNA levels of Acyl CoA synthase long-chain family member 1 (ACSL1) and acyl-coenzyme oxidase (ACO) in CS group were upregulated compared to CC group (P < 0.05). At 36 d, the performance of the CS3 group was better than the other 2 groups, myocardial structure was normal and other lipid metabolism indexes, except for peroxisome proliferator-activated receptor coactivator 1α (PGC-1α) levels, were similar to those of CC group (P > 0.05). The myocardial fiber disorder, Triglyceride (TG), and leptin (LEP) contents were significantly lower in CS9 group than in CC and CS3 groups at 36 d (P < 0.05). The HSP protein levels were significantly higher in CS group than in CC group before ACS (P < 0.05). After 24 h of ACS, the mRNA of lipid metabolism genes, the protein levels of HSP40 and HSP60, and the contents of TG and LEP in the CS3 group were upregulated compared to other groups. The CC and CS9 groups showed myocardial structure was destroyed, with lower TG and LEP levels compared to before ACS (P < 0.05). Therefore, cold stimulation at 3°C lower than the normal feeding temperature for 5 h did not impair performance but can increase the resistance of broilers to ACS by promoting lipid metabolism.

Mild Intermittent Cold Stimulation Affects Cardiac Substance Metabolism via the Neuroendocrine Pathway in Broilers

This study aimed to investigate the impact of cold adaptation on the neuroendocrine and cardiac substance metabolism pathways in broilers. The broilers were divided into the control group (CC), cold adaptation group (C3), and cold-stressed group (C9), and experimental period was divided into the training period (d 1-35), recovery period (d 36-43), and cold stress period (d 43-44). During the training period, the CC group was reared at ambient temperature, while C3 and C9 groups were reared at 3 °C and 9 °C lower than the ambient temperature, respectively, for 5 h/d at 1 d intervals. During the recovery period, all the groups were maintained at 20 °C. Lastly, during the cold stress period, the groups were divided into two sub-groups, and each sub-group was placed at 10 °C for 12 h (Y12) or 24 h (Y24) for acute cold stimulation. The blood, hypothalamic, and cardiac tissues samples were obtained from all the groups during the training, recovery, and acute stress periods. The results revealed that the transcription of calcium voltage-gated channel subunit alpha 1 C (CACNAIC) was increased in the hypothalamic tissues of the C3 group (p < 0.05). Moreover, compared to the CC group, the serum norepinephrine (NE) was increased in the C9 group (p < 0.05), but insulin (INS) was decreased in the C9 group (p < 0.05). In addition, the transcription of the phosphoinositide-3 kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR), SREBP1c, FASN, ACC1, and SCD genes was down-regulated in the C3 and C9 groups (p < 0.05); however, their expression increased in the C3 and C9 groups after acute cold stimulation (p < 0.05). Compared to the CC group, the transcription of forkhead box O1 (FoxO1), PEPCK, G6Pase, GLUT1, HK1, PFK, and LDHB genes was up-regulated in the C3 and C9 groups (p < 0.05. Furthermore, compared to the CC and C9 groups, the protein and mRNA expressions of heat shock protein (HSP) 70 and HSP90 were significantly increased in the C3 group (p < 0.05). These results indicate that intermittent cold training can enhance cold stress tolerance in broilers by regulating their neuroendocrine and cardiac substance metabolism pathways.

Effect of Environmental and Farm-Associated Factors on Live Performance Parameters of Broilers Raised under Commercial Tropical Conditions

Although temperature, relative humidity, and farm-associated factors are known to affect broiler live performance, data about the impact of these variables under commercial operations are still scarce. This study aimed to evaluate the effect of temperature, relative humidity, a thermal humidity index, management, and farm-associated factors on BW, BW gain, feed conversion ratio (FCR), and mortality of broilers raised to 35 d under commercial tropical conditions. The data analyzed included performance records of Ross 308 AP broiler flocks placed between 2018 and 2020. Environmental monitoring information was obtained from electronic sensors that captured data hourly from 80 flocks in 29 farms. Farm-associated factors were gathered using a survey of 86 farms. Three data analyses were conducted in parallel. Correlation analyses, one-way ANOVA, and machine learning techniques were employed. Results indicated that BW and BW gain were reduced, and FCR worsened (p < 0.001) up to 21 d when chickens were mainly exposed to temperatures 2.5 °C lower than the recommended optimums for each age period. At the same time, mortality at 28 and 35 d increased. In conclusion, all farm-associated factors affected chicken live performance. Variable importance analysis indicated that performance results at 14 and 21 d were significant to predict BW at 35. At the same time, sex, distance between the hatchery and farm, and farm altitude accounted for the most significant contributions from the farm-associated factors.

Effects of cold stress on growth performance, carcass traits and tibia attributes in broiler chickens with thiram-induced dyschondroplasia

The objective of this study was to investigate the effect of cold stress (CS) on growth performance and tibia attributes in broiler chickens with thiram-induced dyschondroplasia (TD). Four hundred 10-day-old male broilers were randomly allocated into four groups including, NT0: normal temperature (NT) without thiram; NT50: NT + thiram; CS0: CS without thiram; and CS50: CS + thiram in a completely randomised. The birds in CS groups were placed at a constant temperature of 15 ± 1°C during 11-20 days. Thiram (50 mg/kg) was added to the diet during 11-14 days to induce TD. Results showed that main effects of CS and thiram significantly decreased body weight and daily weight gain during 11-42 days (p < 0.05). Feed intake in the thiram50 group was significantly lower than the group thiram0 during 25-42 days (p < 0.05). Feed conversion ratio in CS birds was significantly more than NT group during 25-42 days (p < 0.05). On day 16, tibia width (TW) and TW to tibia length (TL) ratio were significantly higher in CS chicks compared to the NT group. TW was significantly higher in thiram50 group than thiram0 group (p < 0.05). On day 19, TL in CS chicks was significantly shorter than NT (p < 0.05). On day 23, growth plate width (GPW) in thiram50 group was significantly higher than thiram0 birds. In general, thiram increased tibial GPW and CS decreased TD severity as well as decreased growth performance in broilers.

Heterophil/lymphocyte response of local Spanish breeds of laying hens to cold stress, heat stress, and water restriction

Environmental challenges may adversely affect poultry production. Autochthonous breeds are particularly valuable in a climate change context because of adaptation to the local environment. The objective of the present study was to determine the impact of cold stress, water restriction, and heat stress on the stress response quantified by the heterophil to lymphocyte ratio (H/L) of ten local Spanish breeds of laying hens. Hens of these local breeds were consecutively subjected to three treatments: natural cold stress (2, 4, 6, 7, 9, and 13 °C), water restriction (with a duration of 2.5, 4.5, 7, 10, and 12 h, respectively), and natural heat stress (23, 26, 28, 30, 34, 38, 40, and 42 °C). During cold stress, H/L was higher at 9 and 13 °C than at 2, 4, and 6 °C, and higher at 9 °C than at 7 °C (P < 0.05). H/L values were similar during all water restriction levels. During heat stress, H/L was particularly elevated at temperatures higher than 40 °C (P < 0.05). Overall, Andaluza Azul, Andaluza Perdiz and Prat Codorniz showed lowest resilience to stress based on their H/L response, whereas Pardo de Leon, Villafranquina Roja, and Prat Leonada showed highest resilience.

Heat Shock Protein Response to Stress in Poultry: A Review

Compared to other animal species, production has dramatically increased in the poultry sector. However, in intensive production systems, poultry are subjected to stress conditions that may compromise their well-being. Much like other living organisms, poultry respond to various stressors by synthesising a group of evolutionarily conserved polypeptides named heat shock proteins (HSPs) to maintain homeostasis. These proteins, as chaperones, play a pivotal role in protecting animals against stress by re-establishing normal protein conformation and, thus, cellular homeostasis. In the last few decades, many advances have been made in ascertaining the HSP response to thermal and non-thermal stressors in poultry. The present review focuses on what is currently known about the HSP response to thermal and non-thermal stressors in poultry and discusses the factors that modulate its induction and regulatory mechanisms. The development of practical strategies to alleviate the detrimental effects of environmental stresses on poultry will benefit from detailed studies that describe the mechanisms of stress resilience and enhance our understanding of the nature of heat shock signalling proteins and gene expression.

Appropriate cold stimulation changes energy distribution to improve stress resistance in broilers

Appropriate cold stimulation can improve stress resistance in broilers and alleviate the adverse impacts of a cold environment. To investigate the effects of intermittent mild cold stimulation (IMCS) on energy distribution in the livers of broilers, 96 healthy 1-d-old Ross-308 male broilers were randomly divided into the control group (CC) and the cold stimulation group (H5). The CC group was raised at a normal thermal temperature, i.e., 35 °C until 3 d, after which the temperature was dropped gradually by 0.5 °C/d until 20 °C at 33 d. This temperature was maintained until 49 d. The H5 group was raised at the same temperature as the CC group until 14 d (35 to 29.5 °C) and at 3 °C below the temperature of the CC group starting at 0930 hours for 5 h every other day from 15 to 35 d (26 to 17°C). The temperature was returned to 20 °C at 36 d and maintained until 49 d. At 50 d, all broilers were subjected to acute cold stress (ACS) at 10 °C for 6 and 12 h. We found that IMCS had positive effects on production performance. Using transcriptome sequencing of the broiler livers, 327 differentially expressed genes (DEG) were identified, and highly enriched in fatty acid biosynthesis, fatty acid degradation, and the pyruvate metabolism pathway. When compared to the CC group, the mRNA levels of ACAA1, ACAT2, ACSL1, CPT1A, LDHB, and PCK1 in the H5 group were increased at 22 d (P < 0.05). The LDHB mRNA level was upregulated in the H5 group at 29 d compared to the CC group (P < 0.05). After 21 d of IMCS (at 36 d), the mRNA expression levels of ACAT2 and PCK1 were found to be significantly increased in the H5 group compared to the CC group (P < 0.05). Seven days after the IMCS had ended (at 43 d), the mRNA levels of ACAA1, ACAT2, and LDHB in the H5 group were higher than in the CC group (P < 0.05). The mRNA levels of heat shock protein (HSP) 70, HSP90, and HSP110 in the H5 group were higher than in the CC group after 6 h of ACS (P < 0.05). The protein levels of HSP70 and HSP90 in the H5 group were downregulated after 12 h of ACS, compared to the CC group (P < 0.05). These results indicated that IMCS at 3 °C lower than the normal temperature could improve energy metabolism and stress resistance in the livers of broilers, alleviate the damage of short-term ACS on broilers, help broilers adapt to the low temperature, and maintain stable of energy metabolism in the body.

Effects of Acute Cold Stress after Intermittent Cold Stimulation on Immune-Related Molecules, Intestinal Barrier Genes, and Heat Shock Proteins in Broiler Ileum

Cold stress will have a negative impact on animal welfare and health. In order to explore the effect of intermittent cold stimulation training on the cold resistance of broilers. Immune-related and intestinal barrier genes were detected before and after acute cold stress (ACS), aiming to find an optimal cold stimulation training method. A total of 240 1-day-old Ross broilers (Gallus) were divided into three groups (G1, G2, and G3), each with 5 replicates (16 chickens each replicate). The broilers of G1 were raised at normal temperature, while the broilers of G2 and G3 were treated with cold stimulation at 3 °C lower than the G1 for 3 h and 6 h from 15 to 35 d, respectively, at one-day intervals. At 50 d, the ambient temperature for all groups was reduced to 10 °C for six hours. The results demonstrated that before ACS, IL6, IL17, TLR21, and HSP40 mRNA levels in G3 were apparently down-regulated (p < 0.05), while IL8 and Claudin-1 mRNA levels were significantly up-regulated compared with G1 (p < 0.05). After ACS, IL2, IL6, and IL8 expression levels in G3 were lower than those in G2 (p < 0.05). Compared to G2, Claudin-1, HSP90 mRNA levels, HSP40, and HSP70 protein levels were increased in G3 (p < 0.05). The mRNA levels of TLR5, Mucin2, and Claudin-1 in G2 and IL6, IL8, and TLR4 in G3 were down-regulated after ACS, while IL2, IL6, and IL17 mRNA levels in G2 and HSP40 protein levels in G3 were up-regulated after ACS (p < 0.05). Comprehensive investigation shows that cold stimulation at 3 °C lower than the normal feeding temperature for six hours at one day intervals can enhanced immune function and maintain the stability of intestinal barrier function to lessen the adverse effects on ACS in broilers.

Transport Stress Induced Cardiac NO-NOS Disorder Is Mitigated by Activating Nrf2/HO-1/NQO1 Antioxidant Defense Response in Newly Hatched Chicks

With the development of the intensive poultry industry, the health problems of chickens caused by transportation have attracted more and more attention. Transport stress reduces performance, immune function, and meat quality in chicks, which has become one of the most important factors that endanger the development of the poultry industry. Currently, studies on the effects of transport stress have mainly focused on the performance of livestock and poultry to be slaughtered. However, the effects of transport stress on heart damage and oxidative stress in newborn chicks have not been reported. In this study, we selected newborn chicks as the object. This study was intended to explore the effects of transport stress on the heart damage of newly hatched chicks. The findings suggested that transport stress could cause oxidative stress in the hearts of newly hatched chicks by increasing the levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and decreasing the contents of Total antioxidant capacity (T-AOC), and the activities of antioxidant enzymes (SOD), together with increasing the activities of antioxidant enzymes (Catalase (CAT) and Glutathione S-transferase (GST)). Transport stress disrupted the balance between oxidation and antioxidant systems. The Nrf2 signaling pathway was activated by transport stress and triggered the transcription of antioxidant signaling. In short, transport stress-induced nitric oxide (NO)—nitric oxide synthases (NOS) system metabolic disorders and cardiac oxidative stress are mitigated by activating the nuclear factor-erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1)/NAD(P)H quinone oxidoreductase-1 (NQO1) antioxidant defense response in newly hatched chicks.

Harmful Effects of Inorganic Mercury Exposure on Kidney Cells: Mitochondrial Dynamics Disorder and Excessive Oxidative Stress

Mercury is widely used in industry and has caused global environmental pollution. Inorganic mercury accumulates in the body causes damage to many organs, and the kidney is the most susceptible to the toxic effects of mercury. However, the underlying specific molecular mechanism of renal injury induced by inorganic mercury remains unclear at the cellular level. Therefore, in order to understand its molecular mechanism, we used in vitro method. We established experimental models by treating human embryonic kidney epithelial cell line (HEK-293 T) cells with HgCl₂ (0, 1.25, 5, and 20 µmol/L). We found that HgCl₂ can lead to a decrease in cell viability and oxidative stress of HEK-293 T, which may be mediated by upregulation mitochondrial fission. In addition, HgCl₂ exposure resulted in the mitochondrial disorder of HEK-293 T cells, which was mediated by downregulating the expression of silent information regulator two ortholog 1 (Sirt1)/peroxisome proliferator-activated receptor coactivator-1α (PGC-1α) signaling pathway. In summary, our results suggest that HgCl₂ induces HEK-293 T cell toxicity through promoting Sirt1/PGC-1α axis-mediated mitochondrial dynamics disorder and oxidative stress. Sirt1/PGC-1α may be an appealing pharmaceutical target curing HgCl₂-induced kidney injury.

Effect of inorganic mercury exposure on reproductive system of male mice: Immunosuppression and fibrosis in testis

Mercury as a toxic heavy metal will accumulate in the body and induce various diseases through the food chain. However, it is unknown that the detailed mechanism of reproductive disorder induced by inorganic mercury in male mice to date. This study investigated the toxicological effect of mercuric chloride (HgCl₂ ) exposure on reproductive system in male mice. Male Kunming mice received normal saline daily or HgCl₂ (3 mg/kg bodyweight) by intraperitoneal injection for a week. The reproductive function was evaluated, and the HgCl₂ exposure induced the decline of sperm quality, pregnancy rate, mean litter size, and survival rate. Notably, we firstly found the HgCl₂ -induced immunosuppression and fibrosis in mice testis according to the results of RNA sequencing. Collectively, these findings demonstrate that HgCl₂ exposure disrupts the reproductive system and induces testicular immunosuppression and fibrosis via inhibition of the CD74 signaling pathway in male mice.

Effects of low eggshell temperatures during incubation, in ovo feeding of L-arginine, and post-hatch dietary guanidinoacetic acid on hatching traits, performance, and physiological responses of broilers reared at low ambient temperature

This study aimed to investigate the effect of eggshell temperature (ET) manipulations during incubation, in ovo feeding (IOF) of arginine, and post-hatch dietary supplementation with guanidinoacetic acid (GAA) on hatching traits and subsequent growth and physiological performance of hatched broiler chicks reared under subnormal temperature. In experiment 1, from d 8 of incubation onward, a total of 2,160 hatching eggs were randomly arranged in a 2 × 3 factorial design, in which the eggs were exposed to 2 ET (37.8°C or periodically low ET), and 3 IOF treatments (noninjected, diluent-injected, and 1% arginine solution-injected). In experiment 2, a total of 576 one-day-old male broiler chicks from 2 temperature conditions and 2 IOF treatment groups (noninjected and Arg-injected) were reared for 42 d with or without GAA supplementation in a 2 × 2 × 2 factorial design. Each treatment had 6 replicates with 12 birds each. A subnormal ambient temperature (17°C) was applied from 15 d onward to induce ascites. Results from experiment 1 showed a 2-way interaction between ET and IOF for embryonic mortality rate during 19 to 21 d of incubation and residual yolk weight at hatch (P < 0.05). A periodically low ET significantly increased yolk free body mass, first-grade chicks, and relative heart weight than an ET of 37.8°C. In the second experiment, overall average daily gain (ADG) was increased, but feed conversion ratio (FCR), ascites mortality, and serum thyroid hormones and corticosterone were reduced in the low ET group (P < 0.05). There were also IOF × GAA interactions for ADG and FCR (P < 0.05). IOF of arginine or dietary GAA increased serum nitric oxide concentration and jejunal villus height, but decreased ascites mortality (P < 0.05). In conclusion, a periodically low ET accompanied by IOF of arginine during incubation and posthatch dietary supplementation with GAA could be a useful strategy for improving the chick quality at hatch and subsequent improvements in post-hatch performance and ascites indices in cold-stressed broilers.

Environmental Stress in Chickens and the Potential Effectiveness of Dietary Vitamin Supplementation

Environmental stressors can promote the vulnerability of animals to infections; it is therefore, essential to understand how stressors affect the immune system, the adaptive capacity of animals to respond, and effective techniques in managing stress. This review highlights scientific evidence regarding environmental stress challenge models and the potential effectiveness of vitamin supplementation. The major environmental stressors discussed are heat and cold stress, feed restriction, stocking density, and pollutants. Much work has been done to identify the effects of environmental stress in broilers and layers, while few involved other types of poultry. Studies indicated that chickens' performance, health, and welfare are compromised when challenged with environmental stress. These stressors result in physiological alterations, behavioral changes, decreased egg and meat quality, tissue and intestinal damage, and high mortalities. The application of vitamins with other nutritional approaches can help in combating these environmental stressors in chickens. Poultry birds do not synthesize sufficient vitamins during stressful periods. It is therefore suggested that chicken diets are supplemented with vitamins when subjected to environmental stress. Combination of vitamins are considered more efficient than the use of individual vitamins in alleviating environmental stress in chickens.

Intermittent mild cold stimulation improves the immunity and cold resistance of spleens in broilers

In order to investigate the effect of intermittent mild cold stimulation (IMCS) on immune function of spleens and adaptability to cold stress in broilers, 400 healthy 1-day-old Ross-308 chickens were divided into 5 groups: CC (control) reared in normal thermal environment from 1 to 49 d; CS3, CS4, CS5, and CS6 (treatments) raised at 3°C below the temperature of CC for 3, 4, 5, or 6 h at 1-d intervals from 15 to 35 d, respectively. Subsequently, CS3-6 was raised at 20°C from 36 to 49 d. At 50 d, all groups were exposed to acute cold stress (ACS) for 12 h. The spleen immunity index at 22, 29, 36, 43, and 49 d, expression levels of toll-like receptors (TLRs), cytokines and immunoglobulins at 22, 43, and 49 d and heat shock proteins (HSPs) before and after ACS at 50 d were examined. The spleen index of broilers aged 22 to 49 d did not differ between CS and CC (P > 0.05), and the spleen index of CS5 was higher than that of CS3 at 49 d (P < 0.05). The mRNA levels of TLR5, TLR15, TLR21, and IL-2 in CS3, TLR3, TLR4, TLR15, TLR21, IL-2, IL-6, and IFN-ϒ in CS4, TLR1, TLR3, TLR4, TLR21, IL-2, IFN-a, IFN-ϒ, IgA, and IgG in CS6, but all TLRs, immunoglobulins and cytokines except IFN-ϒ in CS5 differential expressed stably compared with CC at 43 and 49 d (P < 0.05). Compared with Pre-ACS, the mRNA levels of HSP60, HSP70, and HSP90 were upregulated in CS after ACS (P < 0.05). Except for HSP90 mRNA and HSP70 protein in CS6, and HSP90 protein in CS3, the levels of HSPs after ACS in all treatment groups were higher than those in CC (P < 0.05), and the highest HSPs levels after ACS were found in CS5. We concluded that IMCS could enhance immunity of spleens and adaptability to ACS in broilers, besides CS5 was the optimal program.

A protected complex of biofactors and antioxidants improved growth performance and modulated the immunometabolic phenotype of broiler chickens undergoing early life stress

We evaluated the supplementation of a protected complex of biofactors and antioxidants [P(BF+AOx)] on growth performance, antioxidant activity, expression of immune-related genes, and immunometabolic phenotype of broilers submitted to early life stressors. The treatments were a nutritionally complete basal diet supplemented or not with P(BF+AOx) (Jefo Nutrition Inc., Saint-Hyacinthe, QC, Canada) from 1 to 14 d of age. 720 one-day old male Ross 308 chickens were placed into pens of 30 birds (12 replicates/treatment). Birds were double-vaccinated against infectious bronchitis (IB; MILDVAC-Ma5^T) at the hatchery and submitted, on d 3, to an acute reduction on environmental temperature (from 32° C to 20°C) for 48 h. Feed intake (FI), body weight gain (BWG), and feed conversion ratio (FCR) were calculated weekly. On d 7 and 15, samples were collected for expression of immune-related genes and kinome array analysis, and serum to evaluate the antioxidant status. Data were analyzed by ANOVA using SAS (SAS 9.4). From d 1 to 21 and d 1 to 28, the dietary supplementation of P(BF+AOx) significantly increased BWG (P < 0.05) by 3.6 and 3.8%, respectively, and improved FCR (P < 0.05) by 1.2 and 1.8%, respectively. From d 1 to 35, dietary supplementation enhanced BWG (P = 0.03) by 4%. Serum glutathione reductase activity on d 15 was higher in birds fed diets supplemented with P(BF+AOx) compared to the control diet-fed birds (P = 0.04). Dietary supplementation reduced the expression of IL-1β (P = 0.03) in the lungs on d 7. On d 15, dietary supplementation increased the expression of IL-6 (P = 0.02) and IL-10 (P = 0.03) in the liver. It was observed that, via decreased phosphorylation, catalase was activated in the jejunum and liver, and the phosphorylation of immunoregulatory or proinflammatory proteins was decreased. Other important cellular signaling pathways were also changed in the liver and jejunum due to the supplementation. The supplementation of P(BF+AOx) improves growth performance by promoting a general anti-inflammatory and antioxidant response in chickens undergoing early life stress.

Selenomethionine ameliorates LPS-induced intestinal immune dysfunction in chicken jejunum

Selenomethionine (SeMet) is a widely used food supplement. However, the research on the effect of SeMet on intestinal immune function is not enough. Therefore, in this experiment, SeMet was added to the diet of chickens, and lipopolysaccharide (LPS) was used as harmful stimulation to study the effect of SeMet on intestinal immune function in chickens. We chose chicken jejunum as the research object. The results showed that LPS treatment decreased the expressions of selenoproteins and induced inflammatory reaction, cytokine disorder, decreases of immunoglobulin levels, heat shock protein expression disorder, and decreases of defensin expression levels in jejunum. However, dietary SeMet can effectively alleviate the above injury caused by LPS. Our results showed that SeMet could improve the intestinal immunity in chickens, and feeding SeMet could alleviate the intestinal immune dysfunction caused by LPS. The application range of SeMet in feed can be roughly given through our experiment; i.e. 0.35-0.5 mg/kg SeMet was effective. We speculated that dietary SeMet could effectively alleviate the intestinal immune dysfunction caused by harmful stimulation and help to resist the further damage caused by harmful stimulation.

Hexavalent chromium induced heart dysfunction via Sesn2-mediated impairment of mitochondrial function and energy supply

Hexavalent chromium (Cr(VI)), the most toxic valence state of chromium, is widely present in industrial effluents and wastes. Although previous study has reported that Cr(VI) can cause cytomembrane structure impairment by aggravating lipid peroxidation in the heart, the detailed mechanism of Cr(VI)-induced heart dysfunction is still unclear. Sesn2, a novel antioxidant and stress-inducible molecule, is evidenced to protect against various cardiometabolic diseases such as atherosclerosis and cardiomyopathy. To define the potential mechanism of heart dysfunction induced by chronic Cr(VI) exposure, Wistar rats were intraperitoneal injected with potassium dichromate (K₂Cr₂O₇) for 35 d in the present study. The data showed that chronic K₂Cr₂O₇ exposure caused dose-dependently hematological variations, oxidative stress, dysfunction, and disorganized structure of heart, cardiomyocyte apoptosis, ATP depletion, and mitochondria impairment in rats. In addition, the expressions of Drp1 and Bax were increased by K₂Cr₂O₇. However, the suppression of Mfn2, PGC-1α, Sesn2, nuclear Nrf2, HO-1, and NQO1 protein levels was observed in K₂Cr₂O₇-treated rat hearts. In conclusion, these results demonstrate that chronic K₂Cr₂O₇ exposure dose-dependently causes heart dysfunction, and the molecular mechanism of this event is associated with the loss of Sesn2 mediated mitochondrial function and energy supply impairment.

Mixed plasticizers aggravated apoptosis by NOD2-RIP2-NF-κB pathway in grass carp hepatocytes

The wide application of plastics led to the wide exposure of plasticizers to the environment. As a new environmental pollutant, plasticizers' toxicity researches were far from enough in fish. To further explore these mechanisms, we used two common plasticizers (Diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP) expose to grass carp hepatocytes (L8824). The results showed that the mRNA levels of NOD2-RIP2-NF-κB signal pathway and its downstream inflammatory genes were significantly increased compared to those in control group. Then, the levels of mRNAs and proteins of apoptosis markers were changed, and hepatocytes apoptosis was induced. After DBP and DEHP exposure together, there were higher levels of inflammatory factors and the proportion of apoptotic cells. After NOD2 inhibitor treatment, the phenomena mentioned above were obviously alleviated. We conclude that DBP and DEHP exposure at least partially activated the NOD2-RIP2-NF-κB signal pathway in grass carp hepatocytes, and caused inflammation and apoptosis. In terms of hepatotoxicity, there was synergistic relationship between DBP and DEHP. In addition, we put forward new views on the use of plasticizers: select low toxicity plasticizers, then reduce the types of plasticizers used and reduce the high toxicity level of mixed plasticizers.

Exploring the liver fibrosis induced by deltamethrin exposure in quails and elucidating the protective mechanism of resveratrol

Deltamethrin (DLM) is widely used in agriculture and the prevention of human insect-borne diseases. However, the molecular mechanism of DLM induced liver injury remains unclear to date. This study investigated the potential molecular mechanism that DLM induced liver fibrosis in quails. Japanese quails received resveratrol (500 mg/kg) daily with or without DLM (45 mg/kg) exposure for 12 weeks. Histopathology, transmission electron microscopy, biochemical indexes, TUNEL, quantitative real-time PCR, and western blot analysis were performed. DLM exposure induced hepatic steatosis, oxidative stress, inflammation, and apoptosis. Most importantly, the Nrf2/TGF-β1/Smad3 signaling pathway played an important role on DLM-induced liver fibrosis in quails. Interestingly, the addition of resveratrol, an Nrf2 activator, alleviates oxidative stress and inflammation response by activating Nrf2, thereby inhibits the liver fibrosis induced by DLM in quails. Collectively, these findings demonstrate that chronic exposure to DLM induces oxidative stress via the Nrf2 expression inhibition and apoptosis, and then results in liver fibrosis in quails by the activation of NF-κB/TNF-α and TGF-β1/Smad3 signaling pathway.

Effects of cold stress on growth performance, serum biochemistry, intestinal barrier molecules, and adenosine monophosphate-activated protein kinase in broilers

The homeostasis dysfunctions caused by cold stress remain a threat to intestinal health, particularly for young broiler chickens. We hypothesized that adenosine monophosphate-activated protein kinase (AMPK) was involved in the regulation of cold stress on intestinal health. This study aimed to examine the effect of cold stress for 72 h on growth performance, serum biochemistry, intestinal barrier molecules, and AMPK in broilers. A total of 144 10-day-old male Arbor Acres broilers were subjected to temperature treatments (control 28  ± 1 °C vs cold stress 16 ± 1 °C) for 72 h. Growth performance was monitored, serum was collected for the analysis of physiological parameters, and jejunal mucosa was sampled for the determination of tight junction (TJ) proteins, heat shock proteins, and AMPK signaling molecules. Results showed that 72 h cold treatment reduced average BW gain and increased the feed conversion ratio of the broilers (P < 0.05). Cold stress for 72 h increased blood endotoxin, aspartate aminotransferase, glucose, and low-density lipoprotein cholesterol levels (P < 0.05). Moreover, 72 h cold treatment up-regulated jejunal Occludin, zonula occludin 1, inducible nitric oxide synthase, heat shock factor 1, and AMPKα1 gene expression (P < 0.05) but had no obvious effect on total AMPK protein expression (P > 0.05). In conclusion, cold stress significantly reduced the growth performance of broiler chickens. The intestinal barrier function might be impaired, and enhanced bacterial translocation might occur. The unregulated gene expression of TJ proteins implied the remodeling of intestinal barrier. The change of AMPK suggested the possible relationship between intestinal energy metabolism and barrier function under cold stress.

Selenium Prevents Lead-Induced Necroptosis by Restoring Antioxidant Functions and Blocking MAPK/NF-κB Pathway in Chicken Lymphocytes

Recent studies have identified a new existence of a genetically programmed and regulated cell death characterized by necrotic cell death morphology, termed necroptosis. Lead (Pb) is a ubiquitously distributed environmental pollutant that is highly toxic to animals and human beings. However, no detailed report has been conducted on the necroptosis in lymphocytes caused by Pb. Selenium (Se), a trace element in the body, has been shown to exert cytoprotective effect in numerous pathological injury caused by heavy metals. Here, lymphocytes isolated from chicken spleen were divided into four groups, control group, Se group, Pb group, and Pb + Se co-treatment group to investigate the potential mechanism in the necroptosis triggered by Pb and in the antagonistic effect of Se on Pb toxicity. Flow cytometry analysis and AO/EB staining showed Pb caused typical necrosis characteristics in the lymphocytes. The expression of RIP1, RIP3, and MLKL was increased, whereas the level of caspase 8 was declined in Pb group, which proved the occurrence of necroptosis. Meanwhile, Pb exposure disrupted the antioxidant enzyme (SOD, GSH-Px, and CAT) balance, promoted the expression of MAPK/NF-κB pathway factors (ERK, JNK, p38, NF-κB, and TNF-α), and activated HSPs (HSP27, HSP40, HSP60, HSP70, and HSP90). However, those Pb-induced changes were significantly alleviated in Se + Pb group. Our study revealed that Pb could trigger lymphocyte necroptosis through MAPK/NF-κB pathway activated by oxidative stress and that Se could antagonize Pb-induced necroptosis in chicken lymphocytes.

Hexavalent chromium induces renal apoptosis and autophagy via disordering the balance of mitochondrial dynamics in rats

The use of hexavalent chromium (Cr(VI)) in many industrial processes has resulted in serious environmental pollution problems. Cr(VI) causes organ toxicity in animals after ingestion or inhalation. However, the exact mechanism by which Cr(VI) produces kidney damage remains elusive. Herein, we investigated whether Cr(VI)-induced kidney damage is related to the disorder of mitochondrial dynamics. In this study, 28 male rats were divided into four groups and intraperitoneally injected with 0, 2, 4, and 6 mg/kg body weight potassium dichromate for 5 weeks. Experiment included analysis of renal histopathology and ultrastructure, determination of biochemical indicators, and measurement of related protein content. The results showed that Cr(VI) induced kidney injury through promotion of oxidative stress, apoptosis, and disorder of mitochondrial dynamics in a dose-dependent manner. The protein levels of the silent information regulator two ortholog 1 (Sirt1), peroxisome proliferation-activated receptor-g coactivator-1a (PGC-1a), and autophagy-related proteins were significantly decreased after Cr(VI) exposure. These findings suggest that Cr(VI) leads to the disorder of mitochondrial dynamics by inhibiting the Sirt1/PGC-1a pathway, which leads to renal apoptosis and autophagy in rats.

Effects of Intermittent Mild Cold Stimulation on mRNA Expression of Immunoglobulins, Cytokines, and Toll-Like Receptors in the Small Intestine of Broilers

Simple Summary

Cold stress has been associated with adverse effects on health and welfare of broilers. Whilst several studies have shown that long-term sustained and mild cold stimulation can improve immune function, little is known of the effects of intermittent cold stimulation on immune modulation in broilers. In this study, broilers were submitted to cold stimulation of 3 °C below than the usual rearing temperature during 3 and 6 h every two days during 43 days to explore its effect on the intestinal immunity. The findings confirm that appropriate mild cold stimulation has an overall positive influence on the intestinal immunity of broilers. The mild cold stimulation tested in this study is cost-effective and likely enhances overall health of broilers.

Abstract

Appropriate cold stimulation can improve immune function and stress tolerance in broilers. In order to investigate the effect of intermittent mild cold stimulation on the intestinal immunity of broilers, 240 healthy one-day-old Ross 308 chickens were randomly divided into three groups: the control group (CC) housed in climatic chambers under usual rearing ambient temperature with a gradual 3.5 °C decrease per week; group II (C3) and group III (C6) to which cold stimulation at 3 °C below the temperature used in CC was applied every two days for 3 and 6 h, respectively, from day 15 to 35, and at the same temperature used in CC from day 35 to 43. The mRNA expression levels of immunoglobulins (IgA and IgG), cytokines (IL2, IL6, IL8, IL17, and IFNγ), and Toll-like receptors (TLR2, TLR4, TLR5, TLR7, and TLR21) were investigated in duodenum, jejunum, and ileum tissue samples on days 22, 29, 35, and 43. From day 15 to 35, mRNA expression of IL2 and IFNγ was increased in the intestine of broilers. After one week of cold stimulation on day 43, mRNA levels of immunoglobulins, cytokines, and Toll-like receptors (TLRs) stabilized. Collectively, the findings indicate that cold stimulation at 3 °C below the usual rearing temperature had a positive impact on intestinal immunity of broilers.