Association analysis of HSP70A1A haplotypes with heat tolerance in Chinese Holstein cattle

Single-nucleotide polymorphisms (SNPs) in the coding and untranslated regions of heat shock 70 kDa protein 1A (HSP70A1A), an inducible molecular chaperone that is responsible for cellular protection against heat stress, have been reported as being associated with heat tolerance. A fragment of the HSP70A1A gene was amplified in Chinese Holstein cattle and eight novel mutations were found. We performed comprehensive linkage disequilibrium (LD) and haplotype analyses of the eight SNPs of the HSP70A1A gene and examined their involvement in heat resistance in 600 Chinese Holstein cattle. Our results revealed the presence of significant differences between individuals carrying haplotype 1 and those without haplotype 1 for most of the heat-tolerance traits. Haplotype 1 increased the risk of heat stress; however, association analysis of its combination with haplotype 2 showed the lowest rectal temperature and red blood cell K(+) level, moderate respiratory rate, and the highest red blood cell NKA level, suggesting a heterozygote advantage in the penetration of the phenotype. Protein expression levels in white blood cells among haplotype combinations further confirmed the hypothesis that heterozygotes for haplotypes 1 and 2 are more sensitive to heat stress. We presume that these mutations may be useful in the future as molecular genetic markers to assist selection for heat tolerance in cattle.