Volume 16, Issue 4 (12-2025)
Res Anim Prod 2025, 16(4): 86-103 |
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Sedghi M, Ghasemi R, Abbasi M, Sarrami Z, Mohammadi I. (2025). The Effect of Heat Stress and Density per Unit Area on Performance, Immunological Response, Meat Quality, and Intestinal Morphology in Arian Broiler Chickens. Res Anim Prod. 16(4), 86-103. doi:10.61882/rap.2025.1419
URL: http://rap.sanru.ac.ir/article-1-1419-en.html
URL: http://rap.sanru.ac.ir/article-1-1419-en.html
1- Department of Animal Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran
Abstract: (1183 Views)
Extended Abstract
Background: In the poultry industry, enhancing production efficiency, reducing production costs, and maximizing economic performance are fundamental objectives. However, these objectives can be achieved only when environmental, managerial, and nutritional factors are maintained at optimal levels. Any deviation from proper management practices results in environmental stress, which adversely affects the growth performance, health, and welfare of broiler chickens. Among undesirable environmental factors, high ambient temperature and excessive stocking density are recognized as major stressors, whose influence has recently received greater attention due to the global rise in temperature, and producers’ common tendency to use higher densities to increase profitability. Heat stress is considered one of the most challenging issues in poultry production because birds lack efficient thermoregulatory mechanisms, such as sweat glands, and are therefore highly sensitive to thermal changes. Exposure to high temperatures disrupts heat-dissipation mechanisms, elevates body temperature, induces metabolic disturbances, reduces feed intake, suppresses growth, and weakens the immune response. On the other hand, high stocking density is widely practiced to increase meat production and economic efficiency, especially during the growth period. While greater density can elevate total meat yield, inadequate ventilation, limited space for movement, and non-uniform access to feed and water result in increased physiological stress, reduced welfare, and negative impacts on growth and health metrics. Furthermore, overcrowding hampers air exchange and restricts effective dissipation of body heat, thereby exacerbating the effects of heat stress. Considering the importance of the combined effects of ambient temperature and stocking density in industrial poultry production systems, investigating these two factors simultaneously appears essential. Furthermore, evaluating their impacts on various productive and physiological aspects, such as growth performance, blood biochemistry, immune function, meat quality, and intestinal morphology, can provide a more comprehensive scientific perspective for optimizing management strategies. Therefore, this study aimed to evaluate the interaction between heat stress and stocking density on productive performance, biochemical blood indices, immune responses, meat quality, and intestinal morphological parameters in Arian broiler chickens.
Methods: For this purpose, 868 one-day-old mixed sex Arian broiler chicks were allocated to a 2 × 2 factorial arrangement consisting of four treatments with seven replicates. Experimental groups included two stocking densities (14 and 17 birds per square meter from the beginning of the rearing period) and two temperature regimes (standard temperature and heat stress during the last 2 weeks of rearing). Productive parameters, including weight gain, feed intake, and feed conversion ratio, were recorded weekly. The weights of lymphoid organs (bursa of Fabricius, thymus, and spleen), liver, heart, breast, thighs, and abdominal fat were measured at the end of the trial. The thickness of the right and left ventricular walls was also evaluated. Blood samples were collected for hematological traits, biochemical parameters, and liver enzyme assessment. Immune response was assessed by measuring antibody titers against sheep red blood cells (SRBC) and the Newcastle disease virus. To assess intestinal morphology, jejunum samples were used to determine villus height and width, crypt depth, villus height-to-crypt depth ratio, and muscular layer thickness. For meat quality evaluation, breast muscle samples were collected after slaughter and analyzed for pH, dry matter, crude fat, crude protein, color, and textural properties, including cooking loss and water-holding capacity. Data were analyzed using SAS software, and means were compared by Tukey’s test at a significance level of P < 0.05.
Results: Productive parameters throughout the experimental period were influenced by the treatments, with daily weight gain significantly higher under standard temperature and normal density. Increased stocking density led to a significant elevation in feed conversion ratio, indicating reduced feed efficiency under dense rearing conditions. The weights of the bursa of Fabricius, thymus, and spleen were higher at standard temperature with both densities (14 and 17 birds), indicating better immune function in the absence of heat stress. Furthermore, elevated temperature affected the cardiac structure and increased the right ventricular diameter. Hematological findings showed that heat stress reduced lymphocyte count while increasing heterophil numbers. The primary antibody titer against SRBC decreased under heat stress treatments; moreover, both heat stress and increased stocking density elevated serum alanine transaminase and malondialdehyde concentrations. Meat quality assessment revealed that heat stress and high stocking density reduced meat quality. Evaluation of intestinal morphology demonstrated that structural indices, including villus height, crypt depth, muscular layer thickness, and absorptive surface area, increased in broilers raised under standard stocking density.
Conclusion: Overall, the findings of this study demonstrate that rearing broiler chickens under heat stress and high stocking density results in reduced growth performance, weakened immune system, elevated oxidative stress-related enzymes, decreased meat quality, and unfavorable changes in intestinal structure. Therefore, maintaining optimal ambient temperature and proper stocking density are essential requirements in commercial broiler production, playing a crucial role in promoting bird health, improving performance, and enhancing final product quality.
Background: In the poultry industry, enhancing production efficiency, reducing production costs, and maximizing economic performance are fundamental objectives. However, these objectives can be achieved only when environmental, managerial, and nutritional factors are maintained at optimal levels. Any deviation from proper management practices results in environmental stress, which adversely affects the growth performance, health, and welfare of broiler chickens. Among undesirable environmental factors, high ambient temperature and excessive stocking density are recognized as major stressors, whose influence has recently received greater attention due to the global rise in temperature, and producers’ common tendency to use higher densities to increase profitability. Heat stress is considered one of the most challenging issues in poultry production because birds lack efficient thermoregulatory mechanisms, such as sweat glands, and are therefore highly sensitive to thermal changes. Exposure to high temperatures disrupts heat-dissipation mechanisms, elevates body temperature, induces metabolic disturbances, reduces feed intake, suppresses growth, and weakens the immune response. On the other hand, high stocking density is widely practiced to increase meat production and economic efficiency, especially during the growth period. While greater density can elevate total meat yield, inadequate ventilation, limited space for movement, and non-uniform access to feed and water result in increased physiological stress, reduced welfare, and negative impacts on growth and health metrics. Furthermore, overcrowding hampers air exchange and restricts effective dissipation of body heat, thereby exacerbating the effects of heat stress. Considering the importance of the combined effects of ambient temperature and stocking density in industrial poultry production systems, investigating these two factors simultaneously appears essential. Furthermore, evaluating their impacts on various productive and physiological aspects, such as growth performance, blood biochemistry, immune function, meat quality, and intestinal morphology, can provide a more comprehensive scientific perspective for optimizing management strategies. Therefore, this study aimed to evaluate the interaction between heat stress and stocking density on productive performance, biochemical blood indices, immune responses, meat quality, and intestinal morphological parameters in Arian broiler chickens.
Methods: For this purpose, 868 one-day-old mixed sex Arian broiler chicks were allocated to a 2 × 2 factorial arrangement consisting of four treatments with seven replicates. Experimental groups included two stocking densities (14 and 17 birds per square meter from the beginning of the rearing period) and two temperature regimes (standard temperature and heat stress during the last 2 weeks of rearing). Productive parameters, including weight gain, feed intake, and feed conversion ratio, were recorded weekly. The weights of lymphoid organs (bursa of Fabricius, thymus, and spleen), liver, heart, breast, thighs, and abdominal fat were measured at the end of the trial. The thickness of the right and left ventricular walls was also evaluated. Blood samples were collected for hematological traits, biochemical parameters, and liver enzyme assessment. Immune response was assessed by measuring antibody titers against sheep red blood cells (SRBC) and the Newcastle disease virus. To assess intestinal morphology, jejunum samples were used to determine villus height and width, crypt depth, villus height-to-crypt depth ratio, and muscular layer thickness. For meat quality evaluation, breast muscle samples were collected after slaughter and analyzed for pH, dry matter, crude fat, crude protein, color, and textural properties, including cooking loss and water-holding capacity. Data were analyzed using SAS software, and means were compared by Tukey’s test at a significance level of P < 0.05.
Results: Productive parameters throughout the experimental period were influenced by the treatments, with daily weight gain significantly higher under standard temperature and normal density. Increased stocking density led to a significant elevation in feed conversion ratio, indicating reduced feed efficiency under dense rearing conditions. The weights of the bursa of Fabricius, thymus, and spleen were higher at standard temperature with both densities (14 and 17 birds), indicating better immune function in the absence of heat stress. Furthermore, elevated temperature affected the cardiac structure and increased the right ventricular diameter. Hematological findings showed that heat stress reduced lymphocyte count while increasing heterophil numbers. The primary antibody titer against SRBC decreased under heat stress treatments; moreover, both heat stress and increased stocking density elevated serum alanine transaminase and malondialdehyde concentrations. Meat quality assessment revealed that heat stress and high stocking density reduced meat quality. Evaluation of intestinal morphology demonstrated that structural indices, including villus height, crypt depth, muscular layer thickness, and absorptive surface area, increased in broilers raised under standard stocking density.
Conclusion: Overall, the findings of this study demonstrate that rearing broiler chickens under heat stress and high stocking density results in reduced growth performance, weakened immune system, elevated oxidative stress-related enzymes, decreased meat quality, and unfavorable changes in intestinal structure. Therefore, maintaining optimal ambient temperature and proper stocking density are essential requirements in commercial broiler production, playing a crucial role in promoting bird health, improving performance, and enhancing final product quality.
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