Responses to heat stress in commercial and local broiler stocks. 1. Performance traits

Impact of bioclimatic factors on physio-biochemical and molecular response of slow-growing poultry reared in tropics

Most of the climatic studies projected on heat stress have considered heat extremes, but not the humidity. Hence, this work was carried out to evaluate thermotolerance, production performance, physio-biochemical and immunological response of slow-growing poultry towards various temperature-humidity levels in coastal climate. A total of 240 straight run CARI-Debendra birds were reared in three groups based on temperature-humidity indices (THI > 80, = 75-80 and < 75). Significant difference (P < 0.01) in rectal and body surface temperatures was observed among treatment groups. Lowest body weight was observed in THI > 80 group as 1.45 kg at 12 weeks. There was no significant difference in feed intake and FCR; however, total water intake had increased in heat-stressed group. Birds under THI > 80 group had significantly low gizzard weight only at the 12th week compared to other groups. Significant differences (P < 0.05) in relative weight and length of intestine were noticed which was comparable between seasonal control and THI > 80 group but lower than THI < 75 group at the 6th week. However, at the 12th week, intestinal weight varied among the groups (P = 0.08), but intestinal size did not differ. Among immune organs, significant difference (P < 0.05) was noted only in weight of thymus. Except Cl^-, other biochemical indices such as cholesterol, lactate dehydrogenase, creatinine kinase, K⁺ and Na⁺ did not differ among treatment groups. Relative expression of HSP70 gene was differed significantly (P < 0.01) in the liver, intestine and breast muscles under different THI. The changes reported in seasonal control group during month of October to December revealed better thermotolerance capacity and adaptability of CARI-Debendra birds to coastal hot-humid climate. However, response of this breed to heat stress (THI > 80) reported decrease in growth, immune response and mineral balance attributable to heat loss efficacy in high humidity.

Hepatic transcriptome profiling according to growth rate reveals acclimation in metabolic regulatory mechanisms to cyclic heat stress in broiler chickens

Climate change has numerous effects on poultry that result in welfare concerns and economic losses in agricultural industries. However, the mechanisms underlying the acclimation to heat stress in poultry have not been comprehensively defined. Therefore, identifying associated patterns of gene regulation and understanding the molecular mechanisms of acclimation to a warmer environment will provide insights into the acclimation system of broiler chickens. We profiled differentially expressed genes (DEGs) associated with differences in growth performance under heat stress conditions in the liver tissues of broilers based on RNA sequencing data. The DEGs were identified by comparison to the gene expression levels of broilers exhibiting average growth at 28 d of age (D28A) and D36A relative to those at D21A. In D36A, 507 and 312 DEGs were up- and downregulated, respectively, whereas 400 and 156 DEGs were up- and downregulated in D28A, respectively. Pathway enrichment analysis further revealed that “fatty acid degradation” and “heat shock protein expression” were upregulated in broilers exhibiting a higher growth and weight, whereas “cell cycle arrest” and “amino acid metabolism” were downregulated. Transcriptome profiling revealed that the acclimatized group supplied fat and energy from the liver to tissues through the breakdown of fatty acids. Furthermore, homeostasis was maintained via heat shock proteins and antioxidant enzymes. The characterized candidate genes and mechanisms associated with the response to heat stress might serve as a foundation for improving the ability of broilers to acclimatize under heat stress conditions.

A review of heat stress in chickens. Part II: Insights into protein and energy utilization and feeding

With the growing global demand for animal protein and rising temperatures caused by climate change, heat stress (HS) is one of the main emerging environmental challenges for the poultry industry. Commercially-reared birds are particularly sensitive to hot temperatures, so adopting production systems that mitigate the adverse effects of HS on bird performance is essential and requires a holistic approach. Feeding and nutrition can play important roles in limiting the heat load on birds; therefore, this review aims to describe the effects of HS on feed intake (FI) and nutrient digestibility and to highlight feeding strategies and nutritional solutions to potentially mitigate some of the deleterious effects of HS on broiler chickens. The reduction of FI is one of the main behavioral changes induced by hot temperatures as birds attempt to limit heat production associated with the digestion, absorption, and metabolism of nutrients. Although the intensity and length of the heat period influences the type and magnitude of responses, reduced FI explains most of the performance degradation observed in HS broilers, while reduced nutrient digestibility appears to only explain a small proportion of impaired feed efficiency following HS. Targeted feeding strategies, including feed restriction and withdrawal, dual feeding, and wet feeding, have showed some promising results under hot temperatures, but these can be difficult to implement in intensive rearing systems. Concerning diet composition, feeding increased nutrient and energy diets can potentially compensate for decreased FI during HS. Indeed, high energy and high crude protein diets have both been shown to improve bird performance under HS conditions. Specifically, positive results may be obtained with increased added fat concentrations since lipids have a lower thermogenic effect compared to proteins and carbohydrates. Moreover, increased supplementation of some essential amino acids can help support increased amino acid requirements for maintenance functions caused by HS. Further research to better characterize and advance these nutritional strategies will help establish economically viable solutions to enhance productivity, health, welfare, and meat quality of broilers facing HS.

Supplementation with artificial sweetener and capsaicin alters metabolic flexibility and performance in heat-stressed and feed-restricted pigs

Substantial economic losses in animal agriculture result from animals experiencing heat stress (HS). Pigs are especially susceptible to HS, resulting in reductions in growth, altered body composition, and compromised substrate metabolism. In this study, an artificial high-intensity sweetener and capsaicin (CAPS-SUC; Pancosma, Switzerland) were supplemented in combination to mitigate the adverse effects of HS on pig performance. Forty cross-bred barrows (16.2 ± 6 kg) were assigned to one of five treatments: thermal neutral controls (TN) (22 ± 1.2 °C; 38%-73% relative humidity) with ad libitum feed, HS conditions with ad libitum feed with (HS+) or without (HS-) supplementation, and pair-fed to HS with (PF+) or without supplementation (PF-). Pigs in heat-stressed treatments were exposed to a cyclical environmental temperature of 12 h at 35 ± 1.2 °C with 27%-45% relative humidity and 12 h at 30 ± 1.1 °C with 24%-35% relative humidity for 21 d. Supplementation (0.1 g/kg feed) began 7 d before and persisted through the duration of environmental or dietary treatments (HS/PF), which lasted for 21 d. Rectal temperatures and respiration rates (RR; breaths/minute) were recorded thrice daily, and feed intake (FI) was recorded daily. Before the start and at the termination of environmental treatments (HS/PF), a muscle biopsy of the longissimus dorsi was taken for metabolic analyses. Blood samples were collected weekly, and animals were weighed every 3 d during treatment. Core temperature (TN 39.2 ± 0.02 °C, HS- 39.6 ± 0.02 °C, and HS+ 39.6 ± 0.02 °C, P < 0.001) and RR (P < 0.001) were increased in both HS- and HS+ groups, but no difference was detected between HS- and HS+. PF- pigs exhibited reduced core temperature (39.1 ± 0.02 °C, P < 0.001), which was restored in PF+ pigs (39.3 ± 0.02 °C) to match TN. Weight gain and feed efficiency were reduced in PF- pigs (P < 0.05) but not in the PF+ or the HS- or HS+ groups. Metabolic flexibility was decreased in the HS- group (-48.4%, P < 0.05) but maintained in the HS+ group. CAPS-SUC did not influence core temperature or weight gain in HS pigs but did restore core temperature, weight gain, and feed efficiency in supplemented PF pigs. In addition, supplementation restored metabolic flexibility during HS and improved weight gain and feed efficiency during PF, highlighting CAPS-SUC's therapeutic metabolic effects.

Chemically Protected Sodium Butyrate Improves Growth Performance and Early Development and Function of Small Intestine in Broilers as One Effective Substitute for Antibiotics

The purpose of this study was to investigate the effects of chemically protected sodium butyrate (CSB) on growth performance and the early development and function of small intestine in broilers as one potential substitute for antibiotics. A total of 192 one-day-old Arbor Acres male broilers were randomly assigned into three dietary treatment groups (eight replicates per treatment): the control (CON) diet; ANT diet, CON diet supplemented with the antibiotics (enramycin, 8 mg/kg and aureomycin, 100 mg/kg); CSB diet, CON diet supplemented with 1000 mg/kg CSB, respectively. The results showed that dietary CSB and antibiotics addition significantly improved the growth performance of broilers by increasing the body weight gain (BWG) and feed conversion ratio (FCR) during different stages (p < 0.05). On day 21, the supplement of CSB in diet improved the structure of small intestine (duodenum, jejunum, and ileum) in broilers by increasing the ratio of villus height to crypt depth (VH/CD) (p < 0.05) and enhanced the butyric acid (BA) (p < 0.05) and total short chain fatty acids (SCFA) concentrations of small intestine (jejunum and ileum) compared with the CON and ANT diets. Besides that, the superoxide dismutase (SOD), total antioxidant capacity (TAC) and TAC to malondialdehyde (TAC/MDA) ratio of the ileal and jejunal mucosa were significantly higher (p < 0.05) in the CSB and ANT than in the CON. In addition, the supplement of CSB in diet markedly significantly enhanced α-amylase, lipase, and trypsin activities of the ileum (p < 0.05) as compared to the ANT diet. 16S rRNA gene sequencing indicated that CSB markedly increased the microbiota diversity of ileum in broilers at 21 days of age as compared to CON and ANT (p < 0.05). Furthermore, we found that Firmicutes was the predominant phyla and Lactobacillus was the major genus in the ileum of broilers. Compared with the ANT diet, the supplement of CSB in diet increased the relative abundance of some genera microbiota (e.g., Candidatus_Arthromitus, Romboutsia) by decreasing the relative abundance of Lactobacillus. Moreover, Akkermansia in the CSB was the highest in comparison to that in the CON and ANT. In addition, Kitasatospora that belongs to the phylum Actinobacteriota was only found in ileum of broilers fed the ANT diet. In summary, the supplement of 1000 mg/kg CSB in the diet improved the growth performance by promoting early development and function of the small intestine, which is associated with the regulation of intestinal flora and reestablishment of micro-ecological balance in broilers. Thus, CSB has great potential value as one of effective substitutes for in-feed antibiotics in the broiler industry.

Thermal stress and high stocking densities in poultry farms: Potential effects and mitigation strategies

Environmental changes pose significant threats to agricultural activities particularly animal production. These changes have induced major concerns which will negatively affect the poultry health and productivity under the current climate changes. Moreover, they also alter the immunological status of the exposed birds and make them susceptible to different diseases. The adverse effects of environmental stress also include poor performance of birds (reduced feed intake, growth, feed efficiency, immunity, and egg production) and inferior product quality. The adverse effect of heat stress on different quail breeds like Japanese quail, bobwhite quail, scaled quail, and Gambel's quail ranged from decreased growth rates (11.0-14.5%), body weight (7.7-13.2%), feed intake (6.1-21.6%), feed efficiency (4.3-8.6%), and egg production (6.6-23.3%). Also, birds reared under heat stress (34 °C) had significantly decreased Haugh units by 10.8% and egg weight by 14.3% in comparison with the control group (reared at 22 °C). On the other hand, increasing stoking density from 30 to 45 kg/m² also negatively affected the feed intake and body weight. Recent studies have focused on evaluating the potential adverse effects of different environmental stresses on poultry performance, behavior, welfare, and reproduction. It is imperative to understand better the interaction of different environmental factors and their subsequent effects on avian physiology, to spotlights on the effective management and nutritional strategies to alleviate the adverse effects of different stresses in poultry. This review aims to present a comprehensive overview of physiological manifestations of major environmental stresses including thermal stress (heat and cold stress) and high stocking densities on poultry health and production. Moreover, we have also critically evaluated the scope and efficacy of some potential strategies to mitigate the influences of these environmental stressors in different poultry species.

Stress and immunity in poultry: light management and nanotechnology as effective immune enhancers to fight stress

The poultry industry plays a significant role in boosting the economy of several countries, particularly developing countries, and acts as a good, cheap, and affordable source of animal protein. A stress-free environment is the main target in poultry production. There are several stressors, such as cold stress, heat stress, high stocking density, and diseases that can affect birds and cause several deleterious changes. Stress reduces feed intake and growth, as well as impairs immune response and function, resulting in high disease susceptibility. These effects are correlated with higher corticosteroid levels that modulate several immune pathways such as cytokine-cytokine receptor interaction and Toll-like receptor signaling along with induction of excessive production of reactive oxygen species (ROS) and thus oxidative stress. Several approaches have been considered to boost bird immunity to overcome stress-associated effects. Of these, dietary supplementation of certain nutrients and management modifications, such as light management, are commonly considered. Dietary supplementations improve bird immunity by improving the development of lymphoid tissues and triggering beneficial immune modulators and responses. Since nano-minerals have higher bioavailability compared to inorganic or organic forms, they are highly recommended to be included in the bird's diet during stress. Additionally, light management is considered a cheap and safe approach to control stress. Changing light from continuous to intermittent and using monochromatic light instead of the normal light improve bird performance and health. Such changes in light management are associated with a reduction of ROS production and increased antioxidant production. In this review, we discuss the impact of stress on the immune system of birds and the transcriptome of oxidative stress and immune-related genes, in addition, how nano-minerals supplementations and light system modulate or mitigate stress-associated effects.

In pursuit of a better broiler: growth, efficiency, and mortality of 16 strains of broiler chickens

To meet the growing consumer demand for chicken meat, the poultry industry has selected broiler chickens for increasing efficiency and breast yield. While this high productivity means affordable and consistent product, it has come at a cost to broiler welfare. There has been increasing advocacy and consumer pressure on primary breeders, producers, processors, and retailers to improve the welfare of the billions of chickens processed annually. Several small-scale studies have reported better welfare outcomes for slower-growing strains compared to fast-growing, conventional strains. However, these studies often housed birds with range access or used strains with vastly different growth rates. Additionally, there may be traits other than growth, such as body conformation, that influence welfare. As the global poultry industries consider the implications of using slower growing strains, there was a need for a comprehensive, multidisciplinary examination of broiler chickens with a wide range of genotypes differing in growth rate and other phenotypic traits. To meet this need, our team designed a study to benchmark data on conventional and slower-growing strains of broiler chickens reared in standardized laboratory conditions. Over a 2-year period, we studied 7,528 broilers from 16 different genetic strains. In this paper, we compare the growth, efficiency, and mortality of broilers to one of two target weights (TW): 2.1 kg (TW1) and 3.2 kg (TW2). We categorized strains by their growth rate to TW2 as conventional (CONV), fastest-slow strains (FAST), moderate-slow strains (MOD), and slowest-slow strains (SLOW). When incubated, hatched, housed, managed, and fed the same, the categories of strains differed in body weights, growth rates, feed intake, and feed efficiency. At 48 d of age, strains in the CONV category were 835 to 1,264 g heavier than strains in the other categories. By TW2, differences in body weights and feed intake resulted in a 22 to 43-point difference in feed conversion ratios. Categories of strains did not differ in their overall mortality rates.

Climate change and heat stress: Impact on production, reproduction and growth performance of poultry and its mitigation using genetic strategies

Heat stress is an important environmental determinant which adversely affects the performance of poultry worldwide. The present communication reviews the impact of heat stress on production, reproduction and growth performance of poultry, and its alleviation using genetic strategies. The adverse effects of high environmental temperature on poultry include decrease in growth rate, body weight, egg production, egg weight, egg quality, meat quality, semen quality, fertility and hatchability, which cause vast financial losses to the poultry industry. High ambient temperature has an antagonistic effect on performance traits of the poultry. Thus, selection of birds for high performance has increased their susceptibility to heat stress. Additionally, heat burden during transportation of birds from one place to another leads to reduced meat quality, increased mortality and welfare issues. Molecular markers are being explored nowadays to recognize the potential candidate genes related to production, reproduction and growth traits for selecting poultry birds to enhance thermo-tolerance and resistance against diseases. In conclusion, there is a critical need of formulating selection strategies based on genetic markers and exploring more genes in addition to HSP25, 70, 90, H1, RB1CC, BAG3, PDK, ID1, Na, F, dw and K responsible for thermoregulation, to improve the overall performance of poultry along with their ability to tolerate heat stress conditions.

Effect of environmental conditions during transport on chick weight loss and mortality

The present study had 2 objectives: the first was to analyze the possible impact of transport on weight loss and mortality during transport, and first-week mortality. The second was to monitor the environmental condition (i.e., temperature, humidity, and so on) variability during transport with an effect on day-old chicks. Probe equipment was installed in a truck of a poultry company from Spain, including a total of 66 journeys made in commercial conditions between May and November 2017. Animal-based measures collected included BW (before and after transport), mortality during transport, mortality during the first week of life, which were contrasted against a series of environmental variables including air temperature, RH, and carbon dioxide (CO₂) atmospheric concentration for every journey, number of day-old chicks (%) per journey, transport duration (h), zones inside the loading area (zone 1, near to the cabin; zone 2, in the central point; and zone 3, close to the back doors), height (1, top; 2, medium; and 3, bottom), mo (May to November), number of stops, type of stop during journey (farm stops and driver stops), time to start the journey, as well as other intrinsic factors of chicks (gender, breed [Ross and Cobb], breeder flock age [wk] and egg storage day). Because the database included random factors, longitudinal data, and repeated measures, a multivariate model was used to analyze the data. The results showed that chick weight loss was positively associated with journey duration and RH. No effect of environmental variables was found on mortality during transport. However, chick mortality during the first week of life was related with the percentage of day-old chicks loaded per journey and chick gender. In conclusion, owing to the environmental heterogeneity during transport and the effect of the environment on chick weight during transport and mortality at first week of life, there is an urgent need to refine the air-conditioning and ventilation systems of day-old chick transport toward a greater environmental homogeneity.

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

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

A Dietary Sugarcane-Derived Polyphenol Mix Reduces the Negative Effects of Cyclic Heat Exposure on Growth Performance, Blood Gas Status, and Meat Quality in Broiler Chickens

Simple Summary

Heat stress is a main reason of systemic oxidative stress, which compromises broiler meat production and quality. To improve the productivity of poultry meat production, studies have investigated different heat stress amelioration strategies. Among these strategies, low-cost feed supplementations are introduced to potentially reduce the negative effects of heat stress. Previous studies have also investigated the effects of different antioxidants on growth performance and meat quality, while a limited number of studies have been made regarding the impacts of the polyphenols at different doses. Polyphenols with antioxidant properties have positive effects against oxidative stress, and are naturally available in high amounts in plants, which makes them a novel feed supplementation for improving meat production as well as meat quality in heat-stressed broiler chickens. Therefore, this study attempted to investigate the effects of different doses of polyphenols supplementation on growth performance, physiological responses, and meat quality in broiler chickens exposed to cyclic heat stress.

Abstract

Heat stress (HS) compromises growth performance and meat quality of broiler chickens by interrupting lipid and protein metabolism, resulting in increased oxidative damages. The experiment attempted to investigate whether dietary polyphenols (Polygain (POL)) could ameliorate the aforementioned adverse effects of HS on performance and meat quality. One hundred and twenty one day-old-male chicks were allocated to two temperature conditions, thermoneutral (TN) or HS, and fed with either a control diet (CON) or the CON plus four different doses of POL (2, 4, 6 and 10 g/kg). Heat stress caused respiratory alkalosis as evidenced by increased rectal temperature (p < 0.001) and respiration rate (p < 0.001) due to increased blood pH (p < 0.001). Heat stress decreased final body weight (p = 0.061) and breast muscle water content (p = 0.013) while POL improved both (p = 0.002 and p = 0.003, respectively). Heat stress amplified muscle damages, indicated by increased thiobarbituric acid reactive substances (p < 0.001) and reduced myofibril fragmentation index (p = 0.006) whereas POL improved both (p = 0.037 and p = 0.092, respectively). Heat stress impaired meat tenderness (p < 0.001) while POL improved it (p = 0.003). In conclusion, HS impaired growth performance and meat quality whereas POL ameliorated these responses in a dose-dependent manner, and effects of POL were evident under both temperature conditions.

Effects of heat stress on animal physiology, metabolism, and meat quality: A review

Heat stress is one of the most stressful events in the life of livestock with harmful consequences for animal health, productivity and product quality. Ruminants, pigs and poultry are susceptible to heat stress due to their rapid metabolic rate and growth, high level of production, and species-specific characteristics such as rumen fermentation, sweating impairment, and skin insulation. Acute heat stress immediately before slaughter stimulates muscle glycogenolysis and can result in pale, soft and exudative (PSE) meat characterized by low water holding capacity (WHC). By contrast, animals subjected to chronic heat stress, have reduced muscle glycogen stores resulting in dark, firm and dry (DFD) meat with high ultimate pH and high WHC. Furthermore, heat stress leads to oxidative stress, lipid and protein oxidation, and reduced shelf life and food safety due to bacterial growth and shedding. This review discusses the scientific evidence regarding the effects of heat stress on livestock physiology and metabolism, and their consequences for meat quality and safety.

Effects of environmental temperature and dietary zinc on egg production performance, egg quality and antioxidant status and expression of heat-shock proteins in tissues of broiler breeders

To investigate the effects of environmental temperature and dietary Zn on egg production performance, egg quality and antioxidant status, as well as expression of heat-shock proteins (HSP) in tissues, of laying broiler breeders, we used a completely randomised design with a 2×3 factorial arrangement of treatments. The two environmental temperatures were normal (21±1°C, NT) and high (32±1°C, HT). The three dietary Zn sources were a Zn-unsupplemented basal diet (CON), and the basal diet supplemented with 110 mg Zn/kg as either the inorganic Zn sulphate (iZn) or the organic Zn proteinate with a moderate chelation strength (oZn). HT decreased (P<0·002) egg weight, laying rate, eggshell strength, thickness and weight, but increased (P≤0·05) rectal temperature, broken egg rate, misshapen egg rate, feed:egg ratio, Cu Zn superoxide dismutase activities in liver and pancreas, as well as metallothionein (MT) level in pancreas, and HSP70 mRNA levels in liver and pancreas of laying broiler breeders. Broiler breeders fed the oZn diet had higher (P<0·04) Zn content in the liver, as well as MT levels in the liver and pancreas, compared with those fed the CON diet. Under HT, broiler breeders fed the oZn diet had higher (P<0·05) Zn content in the pancreas compared with those fed the iZn and CON diets. The results from this study indicated that HT impaired egg production performance and eggshell quality possibly because of the disturbed redox balance and HSP homoeostasis, whereas the oZn is more available than the iZn for pancreatic Zn of heat-stressed laying broiler breeders.

Heat stress management in poultry farms: A comprehensive overview

Heat stress causes significant economic losses in poultry production, especially in tropical and arid regions of the world. Several studies have investigated the effects of heat stress on the welfare and productivity of poultry. The harmful impacts of heat stress on different poultry types include decreased growth rates, appetites, feed utilization and laying and impaired meat and egg qualities. Recent studies have focused on the deleterious influences of heat stress on bird behaviour, welfare and reproduction. The primary strategies for mitigating heat stress in poultry farms have included feed supplements and management, but the results have not been consistent. This review article discusses the physiological effects of heat stress on poultry health and production and various management and nutritional approaches to cope with it.

Osmoregulatory function of betaine in alleviating heat stress in poultry

This review focuses on the osmoregulatory function of betaine and its effect in terms of alleviating heat stress in poultry. Poultry appear to be particularly sensitive to temperature-associated environmental challenges, especially heat stress. High ambient temperatures are deleterious to productive performance in poultry, including broilers, laying hens, quails and turkeys, resulting in considerable economic losses. Heat stress impairs overall poultry production by decreasing feed intake and negatively affecting intestinal development, leading to reduced nutrient digestibility. Apart from inducing a high mortality rate, heat stress is known to depress growth rate and reduce meat yield in broilers. In layers, lower feed intake impairs ovarian function, leading to decreased feed efficiency, egg production and egg quality. In addition, reduced immune functions, such as thyroid activity and antibody production, are evident in poultry exposed to heat stress. Heat stress increases the production of oxidants, causing oxidative stress and lipid peroxidation of cell membranes. Poultry respond physiologically and behaviourally when encountering the negative effects of heat stress, attempting to return the body to homeostasis. This requires energy at the expense of weight gain or egg production. Due to its zwitterionic structure, betaine has osmoprotective properties that aid in protecting intestinal cell proteins and enzymes from environmental stress, including high ambient temperature, thereby counteracting performance losses. Betaine also exerts an osmoregulatory role in cells, regulating water balance, and this results in more stable tissue metabolism. Inclusion of betaine in the diet may be beneficial for alleviating physical reactions to heat stress, as indicated by increases in nutrient digestibility. In broilers, betaine supplementation increases weight gain and breast muscle yield, while improving feed conversion. In layers, betaine supplementation improves egg production, egg quality traits and immune indices. In conclusion, due to its osmoregulatory functions, betaine plays an important role in alleviating heat stress in poultry.

Physiological responses to heat stress in two genetically distinct chicken inbred lines

High ambient temperature is one of the most important environmental factors negatively impacting poultry production and health. Genetics is an important contributor in mitigating the stress response to heat. Two genetically distinct highly inbred lines of similar body size (Leghorn and Fayoumi) were characterized for phenotypic differences in response to heat. At 14 days of age, birds were exposed to 38°C with 50% humidity for 4 hours, then 35°C until the conclusion of the experiment. Non-treated individuals were kept at 29.4°C for the first week and then 25°C throughout the experiment. Birds in the heat-stress group were inoculated at day (d) 21 with Newcastle disease virus (NDV) La Sota strain to investigate the effects of heat stress and NDV infection. Thirteen blood parameters were measured using the iSTAT blood analyzer at three stages: 4 h, 6 d, and 9 d post heat-stress treatment, representing acute heat (AH) exposure, chronic heat (CH1) exposure, and chronic heat exposure after virus infection (CH2), respectively. Most blood parameters were significantly changed with heat stress in Leghorns at AH and in Fayoumis at CH1 and CH2. The Leghorn line had significant acute responses with disrupted acid-base balance and metabolic disorders. The heat-resilient Fayoumis maintained a relatively well-balanced acid-base balance. The current study provides the comprehensive profile of biomarker signatures in blood associated with heat tolerance and suggests that PO2, TCO2, HCO3, and base excess can be served as potential biomarkers that can be used to genetically improve heat tolerance in poultry.

Capsaicinoids improve egg production by regulating ovary nuclear transcription factors against heat stress in quail

1. To examine the molecular mechanism of capsaicinoid supplementation from capsicum extract, laying Japanese quail (n = 180, 5 weeks old) were reared either at 22°C for 24 h/d (thermoneutral, TN) or at 34°C for 8 h/d (heat stress, HS) and fed on one of three diets containing 0, 25 or 50 mg of capsaicinoids per kilogram for 12 weeks (2 × 3 factorial arrangement). 2. The results revealed that exposure to HS decreased feed consumption by 10.7% and egg production by 13.6%, increased serum and ovary malondialdehyde (MDA) levels by 66.9% and 88.1%, respectively, and reduced ovary superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) activities by 28.3%, 48.7% and 43.8%, respectively. 3. There were magnifications in the ovary nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) levels by 42.4% and suppressions in nuclear factor (erythroid-derived 2)-like 2 (Nrf2), protein kinase B (Akt) and haem-oxygenase 1 (HO-1) levels by 29.2%, 38.2% and 30.7%, respectively, in heat-stressed quail. 4. With increasing supplemental capsaicinoids, there were linear increases in egg production, antioxidant enzyme activity, linear decreases in ovary MDA and NF-κB levels and linear increases in ovary Nrf2, Akt and HO-1 levels at a greater extent in quail reared under TN condition than those reared under HS condition. Two-way treatment interactions showed that the degree of restorations in all response variables was more notable under the HS environment than under the TN environment as supplemental capsaicinoid level was increased. 5. In conclusion, capsaicinoid supplementation alleviates oxidative stress through regulating the ovary nuclear transcription factors in heat-stressed quail.

Selection in the presence of a genotype by environment interaction: response in environmental sensitivity

The effect of selection for high phenotypic value in the presence of a genotype by environment interaction (G ✕ E, i.e. genetic variation for environmental sensitivity) and an improving environment was studied in a simulation. Environmental sensitivity was evaluated by using reaction norms, which describe the phenotype expressed by a genotype as a function of the environment. Three types of reaction norms (linear, quadratic and sigmoid), and two selection schemes (mass selection and progeny test selection) were studied. Environmental sensitivity was measured as the weighted average of the absolute value of the first derivative of the reaction norm function. Results showed that environmental sensitivity increased in response to selection for high phenotypic value in the presence of G ✕ E and an improving environment when reaction norms were linear or quadratic. For sigmoid reaction norms, approximating threshold characters, environmental sensitivity increased within the environmental range encompassing the threshold. With mass selection and/or non-linear reaction norms, environmental sensitivity increased even without environmental change.

Effect of Supplementing Organic Forms of Zinc, Selenium and Chromium on Performance, Anti-Oxidant and Immune Responses in Broiler Chicken Reared in Tropical Summer

Two experiments were conducted to study the effect of supplementing organic forms of zinc (Zn), selenium (Se) and chromium (Cr) on performance, anti-oxidant activities and immune responses in broiler chickens from 1 to 21 days of age, which were reared in cyclic heat-stressed condition under tropical summer in open-sided poultry house. A total of 200 (experiment I) and 450-day-old (experiment II) broiler male chicks (Cobb 400) were randomly distributed in stainless steel battery brooders (610 mm × 762 mm × 475 mm) at the rate of five birds per pen. A maize-soybean meal-based control diet (CD) containing recommended (Vencobb 400, Broiler Management Guide) concentrations of inorganic trace minerals and other nutrients was prepared. The CD was supplemented individually with organic form of selenium (Se, 0.30 mg/kg), chromium (Cr, 2 mg/kg) and zinc (Zn, 40 mg/kg) in experiment I. In experiment II, two concentrations of each Zn (20 and 40 mg/kg), Se (0.15 and 0.30 mg/kg) and Cr (1 and 2 mg/kg) were supplemented to the basal diet in 2 × 2 × 2 factorial design. A group without supplementing inorganic trace minerals was maintained as control group in both experiments. Each diet was allotted randomly to ten replicates in both experiments and fed ad libitum from 1 to 21 days of age. At 19th day of age, blood samples were collected for estimation of anti-oxidant and immune responses. Supplementation of Se, Cr and Zn increased (P < 0.05) body mass gain (BMG) and feed intake compared to those fed the CD in experiment I. The feed efficiency (FE) in Cr-fed group was higher (P < 0.05) compared to the CD-fed group. Se or Cr supplementation reduced lipid peroxidation (LP) compared to broilers fed the CD. In experiment II, BMG was not affected (P > 0.05) by the interaction between levels of Zn, Se and Cr in broiler diet. The FE improved (P < 0.05) with supplementation of the trace minerals tested at both concentrations except in group fed 40 mg Zn, 0.5 mg Se and 1 mg Cr/kg. Reduction in lipid peroxidation (LP, P < 0.05) and increased (P < 0.05) activity of superoxide dismutase were observed in broiler fed organic Zn, Se and Cr compared to the CD-fed group. The dietary concentrations of Zn, Se and Cr did not influence (P > 0.05) the immune responses (Newcastle disease titre and cell-mediated immune response to phytohaemagglutinin-P) in both the experiments. Based on the results, it is concluded that supplementation of organic form of Se, Cr and Zn (0.30, 2 and 40 mg/kg, respectively) either alone or in combination significantly improved performance and anti-oxidant responses (reduced LP and increased superoxide dismutase) in commercial broiler chicks (21 days of age) reared in cyclic heat stress conditions in open-sided poultry house during summer.

Effects of thermal manipulations during embryogenesis of broiler chickens on developmental stability, hatchability and chick quality

Stress based on high temperature and humidity reduces the production performance of fast-growing broilers and causes high mortality. Temperatures higher than optimum have been applied to broilers in the embryonic period in order to overcome thermal stress. This study was conducted to investigate the effects of exposure to two long-term high-thermal environments on the developmental stability of embryonic growth, hatchability and chick quality. For this purpose, 600 broiler eggs were incubated. Treatments consisted of eggs incubated at 37.8°C at 55% relative humidity throughout (control), heated to 39.6°C at 60% relative humidity for 6 h daily from 0 to 8th day, and heated to 39.6°C at 60% relative humidity for 6 h daily from the 10 to 18th day. Embryo weights and lengths of face, wing, femur, tibia and metatarsus were measured daily between the 10th and 21st day of the experiment. Daily relative asymmetry values of bilateral traits were estimated. The hatchability, the weight of the 1-day-old chicks and chick quality were determined. In conclusion, no negative effects of the treatments of the long-term high-thermal environment in the early and late stages of incubation for epigenetic adaptation were determined on the embryo morphology, development stability and weight of the chick. Moreover, regressed hatchability of embryos that were exposed to a long-term high-thermal environment was detected. Especially between the 10 and 18th day, the thermal manipulation considerably reduced the quality of the chicks. Acclimation treatments of high temperature on the eggs from cross-breeding flocks should not be made long term; instead, short-term treatments should be made by determining the stage that generates epigenetic adaptation.

Effects of different heat stress periods on various blood and meat quality parameters in young Arbor Acer broiler chickens

Tang, S., Yu, J., Zhang, M. and Bao, E. 2013. Effects of different heat stress periods on various blood and meat quality parameters in young Arbor Acer broiler chickens. Can. J. Anim. Sci. 93: 453–460. Heat stress can influence muscle metabolism and meat quality in animals reared for food production. From a commercial perspective, understanding the mechanism of this effect is clearly necessary. The aim of this study was to investigate the effects of different heat stress periods on serum metabolites and chicken meat quality (n=120). Plasma indicators creatine kinase (CK), glutamic-pyruvic transaminase (GPT), glutamic-oxaloacetic transaminase (GOT), insulin and glucagon and meat quality (pH, expressible moisture, cooking losses, shear force values) were evaluated. Compared with controls, the concentrations of CK and GPT increased (P<0.01) after 2 and 3 h of heat stress, respectively, whereas plasma insulin and glucagon decreased after 1 and 5 h of heat stress, respectively. The immediate pH (pHi) and ultimate pH (pHu) of the pectoralis muscles decreased (P<0.01) after 1 and 2 h of exposure to heat stress, respectively. Cooking loss, expressible moisture and shear force value increased (P<0.01) after 3, 2, and 1 h of heat stress, respectively. These data indicate that elevated plasma concentrations of CK and GPT can be used as parameters for assessing the stress level to which broilers are exposed before slaughter. The preslaughter exposure of broiler chickens to heat stress can alter muscle metabolism and membrane integrity, leading to undesirable meat characteristics. Thus, a clear understanding of the mechanisms underlying these processes will contribute to the determination of prevention strategies and the avoidance of the associated economic losses.

Berberis vulgaris root extract alleviates the adverse effects of heat stress via modulating hepatic nuclear transcription factors in quails

To evaluate the action mode of Berberis vulgaris root extract in the alleviation of oxidative stress, female Japanese quails (n 180, aged 5 weeks) were reared, either at 22°C for 24 h/d (thermoneutral, TN) or 34°C for 8 h/d (heat stress, HS), and fed one of three diets: diets containing 0, 100 or 200 mg of B. vulgaris root extract per kg for 12 weeks. Exposure to HS depressed feed intake by 8·5 % and egg production by 12·1 %, increased hepatic malondialdehyde (MDA) level by 98·0 % and decreased hepatic superoxide dismutase, catalase and glutathione peroxidase activities by 23·5, 35·4 and 55·7 %, respectively (P< 0·001 for all). There were also aggravations in expressions of hepatic NF-κB and heat-shock protein 70 (HSP70) by 42 and 43 %, respectively and suppressions in expressions of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and haeme-oxygenase 1 (HO-1) by 57 and 61 %, respectively, in heat-stressed quails (P< 0·001 for all). As supplemental B. vulgaris extract increased, there were linear increases in performance parameters, activities of antioxidant enzymes and hepatic Nrf2 and HO-1 expressions (P< 0·001 for all) and linear decreases in hepatic MDA level and NF-κB and HSP70 expressions at a greater extent in quails reared under TN condition and those reared under HS condition. In conclusion, dietary supplementation of B. vulgaris root extract to quails reduces the detrimental effects of oxidative stress and lipid peroxidation resulting from HS via activating the host defence system at the cellular level.

Cool perch availability improves the performance and welfare status of broiler chickens in hot weather

A study was conducted to determine whether water-cooled perches would be preferred by commercial broilers exposed to a hot ambient environment, and subsequently, whether utilization of these perches would improve performance and the well-being of birds, beyond those provided by normal perches. Four hundred and thirty-two 14-d-old male chickens from a commercial fast-growing strain (Arbor Acres) were housed in the following conditions: 1) cool perches, 2) normal perches, and 3) control pens with no perches. The results showed that there was greater use of cool perches than normal perches for broiler chickens during summer (F1, 4=125, P=0.0004). Cool perches increased BW gain (F2, 6=5.44, P=0.0449) and breast (F2, 24=3.31, P=0.0539) and thigh muscle yields (F2, 24=6.29, P=0.0063), while decreasing abdominal fat deposition (F2, 24=7.57, P=0.0028), cooking loss (pectoralis major, F2, 24=3.30, P=0.0542; biceps femoris, F2, 24=3.42, P=0.0493), percentage of panting birds (F2, 6=102, P<0.0001), and scores of footpad (F2, 6=122, P<0.0001) and hock (F2, 6=68.2, P<0.0001) burn, and abdominal plumage condition (F2, 6=52.0, P=0.0002), particularly toward the end of the rearing period. In contrast, normal perches hardly affected growth performance, carcass composition, meat quality and behavioral patterns, and appeared to worsen the welfare status, including footpad and hock burns and abdominal plumage condition, due to a lower occupancy rate. Cool perches offer a thermoregulatory and performance advantage to broilers exposed to a hot environment and appear to be a management strategy for improving the production and well-being of commercial broilers.

Effects of dietary dried fermented ginger on growth performance, carcass quality, and intestinal histology of heat-stressed broilers

Khonyoung, D., Yamauchi, K., Buwjoom, T., Maneewan, B. and Thongwittaya, N. 2012. Effects of dietary dried fermented ginger on growth performance, carcass quality, and intestinal histology of heat- stressed broilers. Can. J. Anim. Sci. 92: 307–317. To investigate the effects of a dried fermented ginger product (DFG) on growth performance, carcass quality, and intestinal histology of heat-stressed broiler, at 7 d of age, 200 male broilers were divided into 0% (control), 0.25% (0.25 S+F), 0.5% (0.5 S+F) and 1% (1 S+F) dietary DFG groups fed from 7 to 49 d of age (starter+finisher groups, S+F). Another group of chicks was fed the basal diet until 21 d of age. At 22 d of age, 150 birds from this group showing almost similar body weight were divided into 0.25% (0.25 F), 0.5% (0.5 F) and 1% (1 F) dietary DFG groups fed from 22 to 49 d of age (finisher groups, F); the control group was common for the S+F and F groups. The average temperature was around 31°C (23.2–38.6°C) throughout the trial. Compared with the control, the experimental DFG groups were not different in feed intake, body weight gain, feed efficiency and carcass quality. However, abdominal fat of the 1 S+F, 0.5 F, and 1 F groups decreased (P<0.05). Cell mitosis numbers in the duodenum tended to increase in the 1 S+F group (P<0.1). Epithelial cells on the jejunal villus apical surface of the control were mainly flat, and desquamations were observed. Desquamation was reduced with increasing DFG, and in the 1% DFG groups, many protuberant cells and cell clusters were present. The present results suggest that under high ambient temperature 1% dietary DFG from 7 to 49 d of age can decrease abdominal fat, and that jejunal villus apex was desquamated with heat stress, but desquamations were reduced with increasing DFG, and disappeared in 1% DFG groups.

The effects of early-age thermal manipulation and daily short-term fasting on performance and body temperatures in broiler exposed to heat stress

This study was conducted to investigate the effects of thermal manipulation at 5 days of age and short-term fasting during the warmest part of the day on responses to prolonged heat stress of broilers. A total of 240-day-old Ross 308 female broiler chicks were divided into three groups: control, thermal manipulation (chicks were exposed to 36 °C for 24 h at 5 days of age) and short-term fasting during the warmest part of the day (10.00-17.00 h). Prolonged heat stress was induced daily from 28 to 42 days by heating until the ambient temperature reached 32-35 °C between 10.00 and 17.00 h. Both thermal manipulation and short-term fasting resulted in a decrease in rectal temperatures and haematocrit values at 35 and 41 days of age. Thermal manipulation improved body weight, feed consumption and feed conversion. However, short-term fasting caused a reduction in body weight and a deterioration in feed conversion. Short-term fasting lowered the percentages of carcass, whereas thermal manipulation highered breast yield. Both thermal manipulation and short-term fasting decreased heart mass and abdominal fat.

Dietary magnesium sulfate supplementation protects heat stress-induced oxidative damage by restoring the activities of anti-oxidative enzymes in broilers

The purpose of this study was to investigate the effect of dietary magnesium sulfate supplementation on heat stress-induced oxidative damage in broilers. One hundred twenty 14-day-old broilers were randomly assigned into four treatment groups with three replicates of ten birds each. The broilers were reared under normal ambient temperature (24 ± 1°C) fed with a basal (control) diet or reared under high ambient temperature (35 ± 1°C between 1000 and 1800 h, 8 h each day) fed with a basal diet supplemented with magnesium sulfate (0, 2.5 or 5.0 mg/kg of diet) from 14 to 42 days of age. Growth performance and oxidative damage were evaluated in each treatment group. Our results demonstrated that dietary magnesium sulfate supplementation significantly prevented heat stress-induced oxidative damage and improved growth performance in broilers compared with that of control. Mechanistically, this beneficial effect was mediated, at least partly, by restoring the activity of anti-oxidative enzymes. This finding suggests that magnesium sulfate supplementation might be a potential strategy to attenuate heat stress-induced detrimental effects in broilers raised in summer season or tropical areas.

Role of dietary zinc in heat-stressed poultry: a review

High ambient temperatures compromise performance and productivity through reducing feed intake and decreasing nutrient utilization, growth rate, egg production, egg quality, and feed efficiency, which lead to economic losses in poultry. Environmental stress also leads to oxidative stress associated with a reduced antioxidant status in the bird in vivo, as reflected by increased oxidative damage and lowered plasma concentrations of antioxidant vitamins (e.g., vitamins E, A, and C) and minerals (e.g., Zn). Zinc has an important role in numerous biological processes in avian and mammalian species. For instance, Zn is an essential component of many enzymes, and it has both structural and catalytic functions in metalloenzymes. Furthermore, dietary Zn is required for normal immune function as well as proper skeletal development and maintenance. One of the most important functions of Zn is related to its antioxidant role and its participation in the antioxidant defense system. This work compiles past and present information about the role of Zn in heat-stressed poultry health.

The effect of the Naked Neck genotype (Nana), feeding and outdoor rearing on growth and carcass characteristics of free range broilers in a hot climate

Alternative poultry production with special reference to free range broilers has increased significantly since the nineties in many regions of the world. Numerous factors influence the productive performance of this type of broilers: genotype (namely the use of naked neck animals), feeding and access to an outdoor area. The aim of this paper is to study the influence of each of these factors on the productive performance of free range broilers under commercial rearing conditions. A total of 3200, day old chicks of both sexes from naked neck and normally feathered genotypes were used in this trial. After a joint initiation phase, animals were divided into four different treatments with the combination of two concentrates (high vs low energy content) and management (access to outside park or not). Experiment lasted a total of 12 weeks. Live weight date was recorded weekly and a samples of animals from the trial were sacrificed at the age of 8, 10 and 12 weeks, when carcass characteristics were determined. Besides sex, the only factor that seems to affect growth characteristics was genotype as naked neck animals had poorer growth rates than normally feathered. No effect was detected on carcass yields and percentages of carcass components for any of the variables. From the data presented in this trial the practises associated with free range production are of relative inconsequence to the technical animal production parameters and can only be justified by a pressing need to differentiate these products from standard poultry products in what concerns both welfare issues and meat characteristics. The results also indicate that genetic material from alternative poultry production in Europe can be a useful option in poultry production development projects in the tropics.

Effect of chronic heat exposure on fat deposition and meat quality in two genetic types of chicken

The effects of chronic heat stress on growth, proportion of carcass and fat deposition, and meat quality were investigated in 2 genetic types of chickens. One hundred and eight 5-wk-old male chickens from a commercially fast-growing strain (Arbor Acres, AA) and a locally slow-growing species (Beijing You chicken, BJY) were kept in the following conditions: constant optimal ambient temperature at 21 degrees C and ad libitum feeding (21AL), constant high ambient temperature at 34 degrees C and ad libitum feeding (34AL), and constant optimal ambient temperature 21 degrees C and pair-fed to the 34AL chickens (21PF). The results showed that feed intakes were decreased by heat exposure in both type of chickens at 8 wk of age (P<0.001). At 34 degrees C, AA broilers exhibited greatly decreased weight gain (22.38 vs. 61.45 g/d for 21AL) and lower breast proportion compared with 21AL, while the relevant indices of BJY chickens were not affected in hot condition. Abdominal fat deposition of BJY chickens was enhanced by heat exposure (P<0.05). Fat deposition of AA broilers was decreased in heat-exposed and pair-fed chickens. Abdominal and intermuscular fat deposition in 34AL birds, however, were enhanced compared with 21PF birds (P<0.01). The L* values, drip loss, initial pH, and shear force of breast meat in BJY chickens were not affected by treatments. In AA birds, chronic heat stress increased L* values and drip loss compared with 21AL, but pH and shear force were not affected by treatments. The results from this study indicated that the impact of heat stress was breed dependent and that BJY chickens showed higher resistance to high ambient temperature, which could be related to their increased feed efficiency and deposition of abdominal fat under heat exposure.