Metabolic and endocrine changes induced by chronic heatexposure in broiler chickens : biological and endocrinological variables

Genomic Analyses Reveal Adaptation to Hot Arid and Harsh Environments in Native Chickens of China

The acute thermal response has been extensively studied in commercial chickens because of the adverse effects of heat stress on poultry production worldwide. Here, we performed whole-genome resequencing of autochthonous Niya chicken breed native to the Taklimakan Desert region as well as of 11 native chicken breeds that are widely distributed and reared under native humid and temperate areas. We used combined statistical analysis to search for putative genes that might be related to the adaptation of hot arid and harsh environment in Niya chickens. We obtained a list of intersected candidate genes with log2 θπ ratio, FST and XP-CLR (including 123 regions of 21 chromosomes with the average length of 54.4 kb) involved in different molecular processes and pathways implied complex genetic mechanisms of adaptation of native chickens to hot arid and harsh environments. We identified several selective regions containing genes that were associated with the circulatory system and blood vessel development (BVES, SMYD1, IL18, PDGFRA, NRP1, and CORIN), related to central nervous system development (SIM2 and NALCN), related to apoptosis (CLPTM1L, APP, CRADD, and PARK2) responded to stimuli (AHR, ESRRG FAS, and UBE4B) and involved in fatty acid metabolism (FABP1). Our findings provided the genomic evidence of the complex genetic mechanisms of adaptation to hot arid and harsh environments in chickens. These results may improve our understanding of thermal, drought, and harsh environment acclimation in chickens and may serve as a valuable resource for developing new biotechnological tools to breed stress-tolerant chicken lines and or breeds in the future.

Histologic Effects of Concurrent Heat Stress and Coccidial Infection on the Lymphoid Tissues of Broiler Chickens

We characterized the histologic effects of two stressors (heat and coccidial infection) alone or in combination on bursa of Fabricius, thymus, and spleen in broiler chickens. Four hundred and eighty Cobb500 male chicks at 14 days of age were randomly assigned to two treatments in a 2×2 factorial design, with 15 replicates per treatment and eight birds per replicate. The treatment factors were temperature (25 and 35 C) and a mixed culture of 2.5 × 10⁵ sporulated Eimeria acervulina and Eimeria maxima oocysts (infection or no infection). Histologic lesion severity was scored in these tissues at different ages. At 21 and 28 days of age, bursal and thymic tissues from birds raised at 35 C exhibited significant increases in lymphoid depletion severity compared with those raised at 25 C. No significant differences were detected in the lymphoid depletion severity of birds infected with Eimeria when compared with uninfected birds. These results indicate that continuous exposure to heat stress-inducing temperatures results in lymphoid depletion of the bursa and thymus in broiler chickens, a potential histologic marker for the immunologic changes known to arise as a result of heat stress. Bursal and thymic atrophy are thought to contribute to immunologic changes that underlie the negative effects of heat stress on poultry production characteristics.