Differential expression of HSF1 and HSPA6 genes and physiological responses in Angus and Simmental cattle breeds.

The aim of this study was to identify whether more and less adapted Angus and Simmental cattle differed in physiological responses and expression of the heat shock factor 1 (HSF1) and the heat shock 70 kDa protein 6 (HSPA6), when subjected to heat stress. Thirty bulls (n = 15 ANG; n = 15 SIM), extremes "more adapted" and "less adapted" within each breed were selected to the heat tolerance test. They were selected according to an index based on the average of the respiratory rate obtained on two hot summer days from one hundred bulls. 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 measurements. They were kept in the barn without access to water and shade until 1 p.m. for the afternoon measurements. Respiratory rate in the morning (MRR) and afternoon (ARR), hair coat surface temperature in the morning (MST) and afternoon (AST), rectal temperature in the morning (MRT) and afternoon (ART) were measured and blood samples were collected for expression analysis of the HSF1 and HSPA6 genes. The MIXED procedure of SAS was used for all statistical analysis. The more adapted Simmental group had lesser values of MRR (P = 0.023) and MRT (P = 0.095), but there was no difference within Angus breed. The ARR was greater (P = 0.004) in less adapted animals for both breeds. The ART was lower in the Simmental breed (P < 0.001). Less adapted had greater levels of mRNA of HSF1 (P = 0.06) and HSPA6 (P = 0.09). In conclusion, respiratory rate, rectal temperature and expression of the HSF1 and HSPA6 genes can be indicators of thermotolerance in taurine cattle. Both breeds show physiologically similar responses under heat stress conditions.

Linkage disequilibrium and haplotype block structure in a composite beef cattle breed.

BACKGROUND: The development of linkage disequilibrium (LD) maps and the characterization of haplotype block structure at the population level are useful parameters for guiding genome wide association (GWA) studies, and for understanding the nature of non-linear association between phenotypes and genes. The elucidation of haplotype block structure can reduce the information of several single nucleotide polymorphisms (SNP) into the information of a haplotype block, reducing the number of SNPs in a coherent way for consideration in GWA and genomic selection studies. RESULTS: The maximum average LD, measured by r2 varied between 0.33 to 0.40 at a distance of < 2.5 kb, and the minimum average values of r2 varied between 0.05 to 0.07 at distances ranging from 400 to 500 kb, clearly showing that the average r2 reduced with the increase in SNP pair distances. The persistence of LD phase showed higher values at shorter genomic distances, decreasing with the increase in physical distance, varying from 0.96 at a distance of < 2.5 kb to 0.66 at a distance from 400 to 500 kb. A total of 78% of all SNPs were clustered into haplotype blocks, covering 1,57 Mb of the total autosomal genome size. CONCLUSIONS: This study presented the first high density linkage disequilibrium map and haplotype block structure for a composite beef cattle population, and indicates that the high density SNP panel over 700 k can be used for genomic selection implementation and GWA studies for Canchim beef cattle.