Comparison of stress biomarkers in laying hens raised under a long-term multiple stress condition

Welfare characteristics of laying hens in aviary and cage systems

Concerns regarding the welfare of laying hens in cage systems (CS) have prompted the development of alternative housing systems, such as aviary systems (AS). However, debate remains about welfare and productivity under both systems. This study compares the welfare and egg quality of laying hens in CS and AS. Hy-Line Brown hens housed in CS (n = 79,500; cage space = 0.075 m2/hen; 6.14 hens/cage) and AS (n = 42,079; floor space = 9 hens/m2) on a single farm were evaluated at 28, 38, and 48 weeks of age. Five evaluators from the Welfare Quality® protocol were used to assess physical conditions (n = 600), and behaviors were assessed through qualitative behavior assessment (n = 15 flocks), avoidance distance test (ADT; n = 315), and novel object test (NOT; n = 15 flocks). Additionally, blood parameters (n = 50), egg quality (n = 50), and serum (n = 50) and egg yolk (n = 90) corticosterone levels were measured. Feather condition in CS hens deteriorated with age, showing higher plumage damage scores than AS hens, though both systems showed increases in comb pecking wounds and feather damage over time. The AS hens showed more positive behaviors, e.g., being active and energetic, while CS hens exhibited more negative behaviors, e.g., fearfulness and depression. In the AS, hens responded more quickly to the observer in the ADT (P < 0.01 for all periods), and more approached the object in the NOT (P < 0.01 at 38 and 48 weeks). The CS hens had higher yolk corticosterone levels (P < 0.05) at 48 weeks but produced heavier eggs consistently across all periods (P < 0.01 for all). In conclusion, this study highlights the importance of evaluating laying hen welfare through a combination of behavioral, physical, and physiological measures. Our findings suggest that the AS provides better welfare outcomes for hens than the CS, offering critical insights for improving both animal welfare and productivity in future housing systems.

Folic acid alleviates the negative effects of dexamethasone induced stress on production performance in Hyline Brown laying hens

Multiple stressors are believed to deteriorate production performance and cause substantial economic losses in commercial poultry farming. Folic acid (FA) is an antioxidant compound that can improve oocyte function and regulate gut microbiota composition. The current study was conducted to investigate the role of FA in alleviating stress and improving production performance. Sixty Hyline Brown laying hens at 21 weeks of age were randomly divided into three groups, with 10 replicates in each group and each replicate containing two chickens. Each group received basic diet and saline injection (Con group), basic diet with dexamethasone (DXM) injection (DXM group), or basic diet supplemented with FA (13 mg/kg in the premix) with DXM injection (FA group). The feeding trial lasted five weeks. Birds in the DXM and FA groups receiving subcutaneous DXM injections at a dosage of 4.50 mg/kg per day during the first seven days of the trial. Results showed that the levels of corticosterone, triglyceride, total cholesterol, and malondialdehyde in serum were significantly increased in the DXM group (P < 0.05), while the concentrations of FA and 5-methyltetrahydrofolate were decreased in the DXM group (P < 0.05). Laying hens in the DXM group had lower laying rates and egg quality, including egg weight, eggshell thickness, eggshell strength, albumen height, and Haugh units (P < 0.05). Conversely, FA alleviated these negative impacts. Through transcriptome analysis, a total of 247 and 151 differentially expressed genes were identified among the three groups, and 32 overlapped genes were further identified. Moreover, 44 and 59 differential metabolites were influenced by DXM and FA, respectively. Kyoto Encyclopedia of Genes and Genomes enrichment from the transcriptome and metabolomics showed that the reduced production performance may be due to the disturbance of oocyte production, calcium metabolism, and oxidative stress. Analysis of 16S rRNA gene amplicon sequences revealed the differential microbial composition and potential functional changes among the different groups. LEfSe analysis showed that Mucispirillum and Nautella were the predominant bacteria in the DXM group, while Clostridium was the predominant bacteria in the FA group. Functional prediction demonstrated that stressors enhanced fatty acid biosynthesis, while betaine biosynthesis and retinol metabolism were elevated in the FA group. Dietary FA reversed the elevated levels of bile acids (BA), including cholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid (P < 0.05). The DXM group showed an overall decrease in short-chain fatty acids (SCFA), but FA restored the concentrations of acetic acid, propionic acid, and isobutyric acid (P < 0.05). In conclusion, this study reveals that dietary FA can alleviate the degradation of production performance caused by stress through improving circulating antioxidant capacity, maintaining intestinal microbiota homeostasis, and regulating SCFA and BA biosynthesis. Thus, highlighting the prominent role of gut microbe-host interactions in alleviating multi-stresses.

New horizons in live and dehydrated black soldier fly larvae usage: Behavioral and welfare implications in "Bianca di Saluzzo" cockerels

The literature on poultry welfare and behavior reports numerous promising effects derived from the administration of live or dehydrated black soldier fly larvae (BSFL) as environmental enrichment; however, their use in slow-growing male chickens has never been evaluated. To fill this gap, we divided a total of 144 Bianca di Saluzzo male chicks aged 39 days old into three experimental groups (six replicates, eight birds/replicate): control (C, no enrichment provided), dehydrated larvae (DL, 4.12% as fed), and live larvae (LL, 15.38% as fed), and reared until 147 days of age. Explorative and aggressive behavior patterns were analyzed, in concomitance with a tonic immobility test and the avoidance distance test, heterophile to lymphocyte -H/L- ratio), and excreta corticosterone metabolites (ECM) matrices. Overall, LL and DL supplementation were both effective at mitigating aggressive interactions among chickens (P < 0.05), while the frequency of indoor explorative behavior was lower in the LL group compared with C and DL (P < 0.01). By contrast, we found no differences in fear reduction during the avoidance distance test in the LL or DL groups compared with C (P < 0.05). We found a trend for the H/L ratio to be C < LL

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MESH Headings

• Animals
• Male
• Chickens/physiology
• Behavior, Animal/physiology
• Larva/physiology
• Animal Welfare
• Corticosterone/metabolism
• Diptera/physiology
• Aggression
• Exploratory Behavior

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Grants

• Prima Programme
• H2020 ERA-NETs

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Affiliation(s)

Valentina Bongiorno Department of Veterinary Sciences, University of Turin, Turin, Italy
Edoardo Fiorilla Department of Veterinary Sciences, University of Turin, Turin, Italy
Marta Gariglio Department of Veterinary Sciences, University of Turin, Turin, Italy
Valeria Zambotto Department of Veterinary Sciences, University of Turin, Turin, Italy
Eleonora Erika Cappone Department of Veterinary Sciences, University of Turin, Turin, Italy
Stefania Bergagna Veterinary Medical Research Institute for Piemonte, Turin, Italy
Isabella Manenti Department of Veterinary Sciences, University of Turin, Turin, Italy
Elisabetta Macchi Department of Veterinary Sciences, University of Turin, Turin, Italy
Francesco Gai Institute of Sciences of Food Production, National Research Council, Turin, Italy
Achille Schiavone Department of Veterinary Sciences, University of Turin, Turin, Italy

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Effect of Stocking Density on Behavioural and Physiological Traits of Laying Hens

This study analysed stocking density as a major stress factor for laying hens and assessed its impact on selected behavioural and physiological traits of the birds. The study population included 142 birds of the Green-legged Partridge breed (12 males and 132 females). The birds were randomly assigned to three experimental groups of standard, low, and high stocking density, and a modified open-field test was conducted to assess their behavioural traits. The following blood parameters were analysed: corticosterone, cortisol, and testosterone. The behavioural test results demonstrated an impact of stocking density on laying hens' behaviour. The birds kept at a low density exhibited the greatest diversity in behaviour as well as the most frequent and longest locomotion. There were no differences between the groups in terms of stress hormone results. All groups showed a significant decrease in testosterone levels compared to the control. This may suggest that, despite differences in stocking, the structure was established quickly, resulting in decreased competition and, consequently, a positive impact on the birds. When kept in lower-stocking-density groups with a stable structure, birds are less competitive; this stable structure improves their well-being to a greater extent than the stocking density.

Effect of dietary supplementation of xylanase alone or combination of xylanase and β-glucanase on growth performance, meat quality, intestinal measurements, and nutrient utilization in broiler chickens

OBJECTIVE

The current study aimed to investigate the effect of dietary supplementation of xylanase alone or combination of xylanase and β-glucanase in high non-starch polysaccharides (NSP) diets with low energy on growth performance, meat quality, intestinal measurements, stress responses, and energy and nutrient utilization in broiler chickens.

METHODS

A total of four hundred 8-d-old Ross 308 broiler chickens were randomly allotted to 1 of 4 treatment groups with 10 replicates. A positive control (PC) diet was formulated with adequate energy and nutrients, whereas a negative control (NC) diet had 100 kcal/kg less nitrogen-corrected apparent metabolizable energy than the PC diet with increasing inclusion of high NSP ingredients. Two additional diets were produced by supplementing 0.1% xylanase alone or 0.1% xylanase and β-glucanase mixture in the NC diet. Experiments lasted for 27 d.

RESULTS

Birds fed PC diets had less (p<0.05) feed conversion ratio (FCR) than those fed NC diets. Birds fed NC diets supplemented with xylanase alone or combination of xylanase and β-glucanase had less (p<0.05) FCR than those fed NC diets. Dietary supplementation of xylanase alone in NC diets exhibited the highest (p<0.05) breast meat pH among dietary treatments. Birds fed PC diets or NC diets supplemented with xylanase and β-glucanase combination exhibited greater (p<0.05) villus height:crypt depth ratio than those fed NC diets. Dietary supplementation of xylanase alone and combination of xylanase and β-glucanase in NC diets decreased (p<0.05) ileal digesta viscosity and increased (p<0.05) xylo-oligosaccharide concentrations in the gastrointestinal tract (GIT) compared with NC diets without affecting energy and nutrient utilization in NC diets.

CONCLUSION

Dietary supplementation of xylanase in high NSP diets with low energy concentrations improves growth performance by decreasing digesta viscosity and increasing concentrations of xylo-oligosaccharides in the GIT of broiler chickens. However, little additional benefits of β-glucanase supplementation in combination with xylanase are identified for broiler chickens.

Effect of increasing supplementation of dietary glycine on growth performance, meat quality, liver characteristics, and intestinal health in broiler chickens raised under heat stress conditions

The current study aimed to investigate the effect of increasing supplementation of dietary glycine (Gly) on growth performance, meat quality, liver characteristics, and intestinal health in broiler chickens raised under heat stress (HS) conditions. A total of one thousand six hundred 25-d-old broiler chickens were randomly allotted to 1 of 5 dietary treatments with 8 replicates. Each replicate comprised 20 male and 20 female birds. A negative control (NC) diet was prepared to meet or exceed energy and nutrient requirement estimates, whereas a positive control (PC) diet was formulated to contain increasing concentrations of AMEn by 50 kcal/kg as well as those of digestible amino acids, total Ca, and available P by 10% compared with the respective concentrations in the NC diet. Three additional diets were prepared by supplementing the NC diet with 0.4, 0.8, or 1.6% Gly. All chickens were raised under cyclic HS conditions at 29°C ± 0.89°C for 10 h/d and 23°C ± 1.45°C for the remaining time over an 18-d feeding trial. Results indicated that broiler chickens fed the NC diet had a greater (P < 0.05) FCR than those fed the PC diet under HS conditions. Increasing supplementation of up to 1.6% Gly in diets decreased (linear, P < 0.001) FCR in broiler chickens. Increasing supplementation of dietary Gly tended to increase (linear, P = 0.070) water holding capacity in the breast meat. Increasing supplementation of dietary Gly decreased (linear, P < 0.05) serum aspartate aminotransferase concentrations and tended to decrease blood heterophil:lymphocyte (linear, P = 0.083) and liver malondialdehyde concentrations (quadratic, P = 0.084). A tendency for increased villus height (linear, P = 0.086) and a significant increase in villus height:crypt depth ratio and goblet cell numbers (linear, P < 0.05) were identified following increasing Gly supplementation. In conclusion, increasing supplementation of dietary Gly improved feed efficiency, meat quality, liver health, and intestinal morphology possibly by mitigating oxidative stress and stress response in broiler chickens raised under HS conditions.

Effects of decreasing phosphorus concentrations in diets and phytase supplementation on growth performance, stress response, and intestinal health in broiler chickens

The current study aimed to investigate the effect of decreasing P concentrations in diets and phytase supplementation on growth performance, stress response, and intestinal health in broiler chickens. A total of four hundred 8-d-old Ross broiler chicks were randomly allotted to 1 of 4 dietary treatments with 10 replicates. Three treatment diets were formulated to contain different concentrations of available P (aP): adequate P (0.44 % aP), low P (0.30 % aP), and very low P (0.10 % aP) levels. One additional diet was prepared by supplementing 1,000 FTU/kg phytase in very low-P diets to maintain its aP concentrations equal to those in low-P diets. The experiment lasted for 25 d. It was observed that growth performance and toe ash concentrations were decreased (P < 0.05) in birds fed very low-P diets compared with those fed other treatment diets. Birds fed very low-P diets exhibited a greater (P < 0.05) blood heterophil:lymphocyte ratio than those fed other treatment diets. Jejunal villus height in birds fed adequate P diets or low-P diets was greater (P < 0.05) than those fed very low-P diets or very low-P diets with phytase. The malondialdehyde concentrations in the jejunal mucosa were greater (P < 0.05) for very low-P treatment than for other treatments. The expression levels of IL-4 and OCLN in the jejunal mucosa were less (P < 0.05) for adequate P treatment than for low-P treatment and very low-P with phytase treatment. Expression levels of P transporter genes in the jejunal mucosa were not affected by dietary treatments. In conclusion, feeding very low-P diets impaired growth performance, bone development, and jejunal morphology in broiler chickens with elevated stress response and intestinal lipid peroxidation. However, feeding low-P diets or very low-P diets with phytase maintained bone development, stress response, and antioxidant status in broiler chickens. The gene expression of intestinal P transporters were not influenced by decreasing P concentrations in diets and phytase supplementation in very low-P diets under the current experimental condition.

Increasing concentrations of dietary threonine, tryptophan, and glycine improve growth performance and intestinal health with decreasing stress responses in broiler chickens raised under multiple stress conditions

The current study aimed to compare the effects of increasing concentrations of dietary threonine (Thr), tryptophan (Trp), and glycine (Gly) on growth performance, stress biomarkers, and intestinal function in broiler chickens under multiple stress conditions. Five hundred sixty broiler chickens at 21 d old were randomly allotted to 5 treatments with 8 replicates. Birds in a positive control (PC) treatment were raised under low stock density (16.9 birds/m2 per cage) with recommended environmental conditions, whereas birds in 4 treatments were subjected to multiple stress conditions: a cyclic heat stress of 30 ± 0.3 °C for 10 h and 23 ± 0.2 °C for 14 h per day with high stock density (25.3 birds/m2 per cage). A basal diet was assigned to both PC and negative control (NC) treatments. Three additional diets were individually formulated to contain double concentrations of digestible Thr, Trp, or Gly + Ser compared with their concentrations in the basal diet. The experiment lasted for 14 d. Results showed that NC treatment had less growth performance (P < 0.001), jejunal goblet cell counts (P = 0.018), and trans-epithelial electrical resistance (TEER; P < 0.001), but greater (P = 0.026) feather corticosterone (CORT) concentrations than PC treatment. Thr treatment showed the least (P < 0.001) feed conversion ratio (FCR) among treatments under multiple stress conditions. Thr, Trp, and Gly treatments had less (P = 0.026) feather CORT concentrations, but had greater (P < 0.001) TEER than NC treatment. In conclusion, increasing concentrations of dietary Thr, Trp, or Gly improve the growth performance and intestinal health in broiler chickens with decreasing stress response under multiple stress conditions.

Nutritional and physiological responses to dietary phosphorus levels and phytase in pullets and laying hens

The objective of this study was to determine the effects of dietary available phosphorus (P) levels and dietary phytase added into the very low-P diet on the performance, mineral balance, odor emission, and stress responses in growing pullets and laying hens during 13 to 32 wk of age. One hundred sixty-eight pullets (Hy-Line Brown) were randomly assigned into 1 of 4 dietary treatments with 7 replicates of 6 birds each. Experimental diets were formulated to contain 3 graded P levels at 0.25, 0.35, and 0.45% during 13 to 15 wk (phase 1), 0.25, 0.35, and 0.45% during 16 to 18 wk (phase 2), and 0.20, 0.30, and 0.40% during 19 to 32 wk (phase 3). In addition, dietary phytase (500 FTU/kg matrix values) was added into the very low-P diets (0.20% during 13-15 wk, 0.25% during 16-18 wk, and 0.20% during 19-32 wk) to meet the nutritional adequacy with standard P diets. In all phases, decreasing dietary P levels did not affect (P > 0.05) growth, laying performance, and egg qualities. Decreasing dietary P levels linearly increased the relative duodenal and oviduct weights (P < 0.05), and quadratically increased the relative ovary weight in pullets (P = 0.016). Dietary phytase lowered (P = 0.021) the relative duodenal weight compared with the very low-P diet. Tibia breaking strength and tibia Mg contents in pullets were linearly lowered (P < 0.05) as dietary P levels decreased. Dietary phytase tended to increase (P = 0.091) tibia breaking strength and significantly increased (P = 0.025) tibia Mg content compared with the very low-P diet. Dietary P levels and dietary phytase affected (P < 0.05) ileal crypt depth and ileal villus height: crypt depth ratio in pullets. Decreasing dietary P levels linearly decreased (P < 0.01) crude fat digestibility and P excretion in both pullets and laying hens. Dietary phytase reversed (P < 0.05) the very low-P diet-mediated decrease of crude fat digestibility in pullets and laying hens. Dietary P levels and dietary phytase affected (P < 0.05) odor emission including ammonia in pullets and total volatile fatty acids in laying hens. Finally, lowering dietary P levels increased (P < 0.01) yolk corticosterone concentrations and the increased corticosterone concentration by the very low-P diet was reversed by dietary phytase. Collectively, our study shows that decreasing dietary P levels induced nutritional and physiological responses in pullets and laying hens and these P-mediated negative effects were mitigated by dietary phytase.

How does visible light flicker impact laying hen pullet behavior, fear, and stress levels?

Many characteristics of artificial light have been evaluated; however, light-flicker frequency (F) has not been assessed extensively in poultry. Pullets (1,344 per strain [S]; Lohmann Brown-Lite [LB] and LSL-Lite [LW]) were placed into 8 light-tight rooms, containing 6 floor pens (15 pen replicates per F × S for 30 and 250 Hz; 18 pen replicates per F x S for 90 Hz), and assigned 1 of 3 F treatments (30, 90, 250 Hz). The experiment took place over 2 trials (blocks). To evaluate long-term effects of F during rearing, birds were followed through the hen phase. Data were analyzed using Proc Mixed (SAS 9.4). Differences were considered significant when P ≤ 0.05, and behaviors are expressed as percentage of time. Pullets reared under 30 Hz spent more time performing nutritive behaviors (P < 0.01) and as "unidentified" (P = 0.02) than other treatments. Active behavior demonstrated an age x F interaction, with pullets being more active at 16 wk, regardless of F (P < 0.01). Comfort behaviors were higher at 16 wk compared to other ages, regardless of F (P < 0.01). Exploratory behaviors were lowest at 4 wk in pullets under 30 Hz (P < 0.01). Aggressive behaviors (12 wk) were higher in pullets reared under 250 Hz than those under 90 Hz (P < 0.01). Comb score was unaffected by F (P = 0.79) and all birds scored had a full plumage. Heterophil-to-lymphocyte ratio was unaffected by F at 7 or 15 wk (P = 0.85 and P = 0.54, respectively). In trial 1, pullets reared under 90 Hz had higher corticosterone concentrations than those reared under 250 Hz (P = 0.02) and trial 2 there were no effects of F (P = 0.97). For novel object test, LW pullets reared under 90 Hz had a higher latency to peck than LW pullets under 30 Hz or 250 Hz (P = 0.03). Hen behavior (wk 39) and fear tests (36 wk; novel object test (P = 0.86) and tonic immobility (P = 0.37)) were unaffected by F. Overall, minimal effects of F were seen on pullet and hen behavior and stress.

Do flickering lights impact turkey hen behavior, stress, and fear?

Little is known about the effect of light-flicker frequency on poultry, particularly on turkeys. This experiment examined the impact of light-flicker frequency on the behavior, stress, and fear response of Nicholas Select turkey hens reared to 11 wk. The experiment was a randomized complete block design (2 trials), with a one-way factorial analysis evaluating 3 light-flicker frequencies (30, 90, or 195 Hertz; Hz). Birds (n = 3,276 per trial) were housed in 9 individual environmentally controlled rooms (3 replicates per treatment per trial). Data collected included: behavior (4, 8, and 10 wk), incidence of aggressive damage, heterophil-to-lymphocyte ratio, and novel object test (daily d 1-7 and at 4, 8, and 11 wk). Data were analyzed using Proc Mixed (SAS 9.4), with significance declared at P ≤ 0.05. Behavior data are presented as the percentage of time spent performing the behavior. At 4 wk, gentle feather pecking and exploratory behaviors were higher under 195 Hz compared to 30 Hz (P = 0.04 and P = 0.05, respectively). Preening was higher under 90 Hz compared to 30 Hz (P = 0.05). At 8 wk, wing flapping was lowest under 195 Hz (P < 0.01). Gentle feather pecking was higher under 90 and 195 Hz compared to 30 Hz (P = 0.02). Fighting (P = 0.05), aggressive pecking (P = 0.02), and aggressive behaviors (P = 0.01) were lower under 30 Hz compared to 90 Hz. At 10 wk, preening was decreased under 30 Hz (P = 0.03). Incidences of aggressive damage were reduced under 30 Hz compared to 90 Hz (0 d-4 wk; P = 0.01) and under 30 compared to both 90 and 195 Hz (4-8 wk; P = 0.01). At 11 wk, heterophil-to-lymphocyte ratios were lowest under 30 Hz (P = 0.04). The novel object test was unaffected by flicker treatment. In conclusion, many behaviors and the stress and fear responses were unaffected by either visible or non-visible flicker. However, visible flicker (30 Hz) reduced some comfort and exploratory behaviors early in life, and the impact on preening continued to older ages, suggesting minor negative impacts of flicker, particularly early in life.

Stress-Related Gene Expression in Liver Tissues from Laying Hens Housed in Conventional Cage and Cage-Free Systems in the Tropics

Global egg production is mainly based on cage systems, which have been associated with negative effects on the welfare of birds. Stress factors in restrictive production systems can lead to changes in gene transcription and protein synthesis, ultimately impacting the quality of poultry products. The liver serves various metabolic functions, such as glycogen storage, and plays a crucial role in animals' adaptation to environmental changes. Consequently, both internal and external conditions can influence liver functions. The aim of this study was to evaluate the gene expression of AGP, CRP, NOX4, SOD1, CAT, GPX1, SREBF1, and FXR in the liver of laying hens under two different production systems. Liver tissues from Hy-Line Brown hens housed in conventional cage and cage-free egg production systems at 60 and 80 weeks of production were used. mRNA transcript levels were determined by qPCR using the relative quantification method and ACTB as the reference gene. AGP, SOD1, and SREBF1 gene expressions were significantly higher in the conventional cage group at the 60 weeks of production. Furthermore, the mRNA levels of transcripts related to oxidative stress and lipid metabolism were higher in the group of laying hens housed in conventional cages compared to those in cage-free systems. These results suggest differential gene expression of genes related to oxidative stress in liver tissues from hens housed in conventional cages compared to cage-free systems. The conditions of the egg production system can impact the gene expression of oxidative stress and lipid synthesis genes, potentially leading to changes in the metabolism and performance of hens, including egg quality.

Effect of dietary glycine supplementation on productive performance, egg quality, stress response, and fatty liver incidence in laying hens raised under heat stress conditions

The current experiment aimed to investigate the effect of dietary glycine (Gly) supplementation on productive performance, egg quality, stress response, and fatty liver incidence in laying hens raised under heat stress (HS) conditions. A total of two hundred eighty 24-wk-old Lohmann Brown-Lite laying hens were randomly allotted to 1 of 4 dietary treatments with 7 replicates. The negative control (NC) diet was prepared to meet or exceed the nutrient and energy requirement for Lohmann Brown laying hens, whereas the positive control (PC) diet was formulated to increase AMEn by 100 kcal/kg compared with the NC diet. Two additional diets were prepared by supplementing 0.341% and 0.683% Gly to the NC diet. All hens were exposed to cyclic HS at 31.4 ± 1.17°C for 8 h/d and 26.7 ± 1.10°C for the remaining time for a 12-wk trial. Results indicated that increasing supplementation of Gly in diets tended (linear, P = 0.088) to decrease the FCR of laying hens. Increasing supplementation of Gly in diets increased (linear, P < 0.05) eggshell lightness and decreased (linear, P < 0.05) egg yolk color. Moreover, a tendency for a quadratic association (P < 0.10) of serum aspartate aminotransferase and alanine aminotransferase concentrations with increasing supplementation of Gly was observed. Increasing supplementation of Gly in diets decreased (linear, P < 0.05) blood heterophil:lymphocyte ratio of laying hens. Hens fed the NC diet showed higher fatty liver incidence (P < 0.05) than those fed the PC diet, but increasing supplementation of Gly decreased (linear, P < 0.05) fatty liver incidence of laying hens. In conclusion, increasing supplementation of Gly up to 0.683% in diets decreases FCR, stress response, and fatty liver incidence in laying hens raised under HS conditions.

Heat stress and poultry production: a comprehensive review

The impact of global warming on poultry production has gained significant attention over the years. However, our current knowledge and understanding of the mechanisms through which heat stress (HS) resulting from global warming affects the welfare, behavior, immune response, production performance, and even transgenerational effects in poultry are still incomplete. Further research is needed to delve deeper into these mechanisms to gain a comprehensive understanding. Numerous studies have investigated various biomarkers of stress in poultry, aiming to identify reliable markers that can accurately assess the physiological status and well-being of birds. However, there is a significant amount of variation and inconsistency in the results reported across different studies. This inconsistency highlights the need for more standardized methods and assays and a clearer understanding of the factors that influence these biomarkers in poultry. This review article specifically focuses on 3 main aspects: 1) the neuroendocrine and behavioral responses of poultry to HS, 2) the biomarkers of HS and 3) the impact of HS on poultry production that have been studied in poultry. By examining the neuroendocrine and behavioral changes exhibited by poultry under HS, we aim to gain insights into the physiological impact of elevated temperatures in poultry.

The Influence of Heat Stress on Chicken Immune System and Mitigation of Negative Impacts by Baicalin and Baicalein

Heat stress (HS) in poultry husbandry is an important stressor and with increasing global temperatures its importance will increase. The negative effects of stress on the quality and quantity of poultry production are described in a range of research studies. However, a lack of attention is devoted to the impacts of HS on individual chicken immune cells and whole lymphoid tissue in birds. Oxidative stress and increased inflammation are accompanying processes of HS, but with deleterious effects on the whole organism. They play a key role in the inflammation and oxidative stress of the chicken immune system. There are a range of strategies that can help mitigate the adverse effects of HS in poultry. Phytochemicals are well studied and some of them report promising results to mitigate oxidative stress and inflammation, a major consequence of HS. Current studies revealed that mitigating these two main impacts of HS will be a key factor in solving the problem of increasing temperatures in poultry production. Improved function of the chicken immune system is another benefit of using phytochemicals in poultry due to the importance of poultry health management in today's post pandemic world. Based on the current literature, baicalin and baicalein have proven to have strong anti-inflammatory and antioxidative effects in mammalian and avian models. Taken together, this review is dedicated to collecting the literature about the known effects of HS on chicken immune cells and lymphoid tissue. The second part of the review is dedicated to the potential use of baicalin and baicalein in poultry to mitigate the negative impacts of HS on poultry production.

Effect of individual or combination of dietary betaine and glycine on productive performance, stress response, liver health, and intestinal barrier function in broiler chickens raised under heat stress conditions

The current experiment was conducted to investigate the effect of individual or combination of dietary betaine (Bet) and glycine (Gly) on productive performance, stress response, liver health, and intestinal barrier function in broiler chickens raised under heat stress (HS) conditions. A total of four hundred twenty 21-d-old Ross 308 broiler chickens were randomly allotted to 1 of 5 dietary treatments with 7 replicates. Birds in treatment 1 were raised under the thermoneutral condition (TN; 23 ± 0.6°C). Birds in other 4 treatment groups were subjected to a cyclic HS by exposing them to 32 ± 0.9°C for 8 h/d (from 09:00 to 17:00 h) and 28 ± 1.2°C for the remaining time for 14 d. Birds were fed a basal diet in TN condition (TN-C) and one group in HS conditions (HS-C), whereas other birds raised under HS conditions were fed the basal diet supplemented with 0.20% Bet (HS-Bet), 0.79% Gly (HS-Gly), or their combination (0.20% Bet + 0.79% Gly; HS-Bet+Gly). Results indicated that birds in HS-Bet, HS-Gly, or HS-Bet+Gly treatment had higher (P < 0.05) final BW and BW gain, but lower (P < 0.05) feed conversion ratio (FCR) than those in HS-C treatment. However, values for improved final BW, BW gain, and FCR by dietary treatments were lower (P < 0.05) than those measured in TN-C treatment. Under HS conditions, birds in HS-Bet, HS-Gly, or HS-Bet+Gly treatment had lower (P < 0.05) heterophil to lymphocyte ratio than those in HS-C treatment. Birds in HS-Gly or HS-Bet+Gly treatment had higher (P < 0.05) villus height and goblet cell number than birds in HS-C treatment. Intestinal permeability was higher (P < 0.05) in all HS-treatment groups than in TN-C treatment, but it was not affected by dietary treatment. In conclusion, individual supplementation of 0.20% Bet or 0.79% Gly in diets alleviates the negative effect of HS in broiler chickens. However, the synergistic effect of the combination of 0.20% Bet and 0.79% Gly in broiler diets seems lower than expected.