Expression of genes related to heat stress in taurine cattle with different levels of adaptability

Abstract

Identification of genes related to heat tolerance in bovine may allow advantageous selection of animals avoiding productivity decrease caused by heat stress. The aim of this study was to identify whether Angus and Simme ntal cattle and, if more and least adapted animals within these breeds, differed in respiratory rate, coat surface and rectal temperature, and expression of the HSF1 and HSPA6 genes when subjected to heat stress. One hundred animals were classified by level of adaptation, according to an index based on the average of the respiratory rate obtained on two hot summer days. Of these, 30 bulls (n = 15 Ang us and n = 15 Simmental), extreme “most adapted" and "least adapted" of each breed were selected to the heat tolerance test. In the day before the heat tolerance test day, animals were taken to a paddock with water, grass and shade until 7 a.m. of the following day for morning (M) measurements. The animals were then kept in the barn without access to water and shade until 1 p.m., when the afternoon (A) measurements were performed. Respiratory rate in the morning (MRR) and afternoon (ARR), surface temperature in the morning (MST) and afternoon (AST), rectal temperature in the morning (MRT) and afternoon (ART) were measured and blood samples were c ollected for expression analysis of the HSF1 and HSPA6 genes. The MIXED procedure of SAS (SAS Inst., Inc., Cary, NC) was used for all statistical analysis. There was interaction of breed and level of adaptation for MRR (P = 0.023) and MRT (P = 0.095). For Simmental, the least adapted animals had greater values of MRR; however, within the Angus breed there was no difference between high and least adapted. The high adapted Simmental group had lesser values of MRR and MRT. The ARR was greater (P = 0.004) in least adapted then in high adapted animals. The ART was lesser in the Simmental breed (P<0.001). Least adapted had greater levels of mRNA of HSF1 (P = 0.06) and HSPA6 (P = 0.09) than high adapted animals. In conclusion, respiratory rate and rectal temperature and expression of the HSF1 and HSPA6 genes can be indicators of least adapted animals. The Simmental breed is more resistant than the Angus breed in a thermal comfort condition, but both have similar behavior under heat stress.