Genetics: Breeding and Genetics

In broilers, heat stress results in reduced feed intake, digestion inef­ ficiency, impaired metabolism, and death. Our objective was to initiate a study on the effects of heat stress by profiling the transcriptome of a metabolically active organ, the liver, from heat-stressed and non-heat­ stressed broilers. From 21 to 28 d of age, heat-stressed broilers were exposed to daily 7-h cycles of 35°C, while a control group was kept at 25°C throughout this time. Body weight, body temperature, and several blood parameters were measured before the first heat episode began and at the midpoint of the last heat cycle on d 28. Then, liver samples were harvested from 4 sets of full-sibs, with one bird of each pair from the heat-stress treatment and one from the control group. As expected from the small sample size and standard error of the traits, the phenotypes of the birds did not differ significantly (P > 0.05) between the 2 heat treatments. However, 3 traits associated with respiration (HCO3, pCO2, tCO2) differed between heat treatments at 0.08 < P < 0.12, strongly suggesting different physiological responses to heat. This observation was in agreement with the marked panting observed only in the heat-stressed birds during the heat episodes. Ribonucleic acid (mRNA) isolated from the liver samples was used for Illumina Hi-Seq 2000 sequencing. Over 130,000,000 reads, averaging 100 base pairs each, were generated, yielding an average of 1.6 billion bp sequenced per individual bird’s transcriptome. We conclude that the heat-stress treatment was an effective experimental model to generate heat-induced physiological changes, and that high-quality transcriptomic data have been generated to initiate the process of identifying the impact of heat on the liver’s metabolic function. Continuation of this research will help clarify the effects of heat stress on broiler metabolism and thus provide a platform for future investigations into the application of breeding strategies for production of commercial broilers resilient to heat stress.