Single nucleotide polymorphisms associated with thermoregulation in lactating dairy cows exposed to heat stress

<jats:title>Summary</jats:title><jats:p>Dairy cows with increased rectal temperature experience lower milk yield and fertility. Rectal temperature during heat stress is heritable, so genetic selection for body temperature regulation could reduce effects of heat stress on production. One aim of the study was to validate the relationship between genotype and heat tolerance for single nucleotide polymorphisms (<jats:styled-content style="fixed-case">SNP</jats:styled-content>s) previously associated with resistance to heat stress. A second aim was to identify new <jats:styled-content style="fixed-case">SNP</jats:styled-content>s associated with heat stress resistance. Thermotolerance was assessed in lactating Holsteins during the summer by measuring rectal temperature (a direct measurement of body temperature regulation; <jats:italic>n</jats:italic> = 435), respiration rate (an indirect measurement of body temperature regulation, <jats:italic>n</jats:italic> = 450) and sweating rate (the major evaporative cooling mechanism in cattle, <jats:italic>n</jats:italic> = 455). The association between genotype and thermotolerance was evaluated for 19 <jats:styled-content style="fixed-case">SNP</jats:styled-content>s previously associated with rectal temperature from a genomewide analysis study (<jats:styled-content style="fixed-case">GWAS</jats:styled-content>), four <jats:styled-content style="fixed-case">SNP</jats:styled-content>s previously associated with change in milk yield during heat stress from <jats:styled-content style="fixed-case">GWAS</jats:styled-content>, 2 candidate gene <jats:styled-content style="fixed-case">SNP</jats:styled-content>s previously associated with rectal temperature and respiration rate during heat stress (<jats:italic><jats:styled-content style="fixed-case">ATPA</jats:styled-content>1A</jats:italic> and <jats:italic><jats:styled-content style="fixed-case">HSP</jats:styled-content>70A</jats:italic>) and 66 <jats:styled-content style="fixed-case">SNP</jats:styled-content>s in genes previously shown to be associated with reproduction, production or health traits in Holsteins. For <jats:styled-content style="fixed-case">SNP</jats:styled-content>s previously associated with heat tolerance, regions of <jats:styled-content style="fixed-case">BTA</jats:styled-content>4, <jats:styled-content style="fixed-case">BTA</jats:styled-content>6 and <jats:styled-content style="fixed-case">BTA</jats:styled-content>24 were associated with rectal temperature; regions of <jats:styled-content style="fixed-case">BTA</jats:styled-content>6 and <jats:styled-content style="fixed-case">BTA</jats:styled-content>24 were associated with respiration rate; and regions of <jats:styled-content style="fixed-case">BTA</jats:styled-content>5, <jats:styled-content style="fixed-case">BTA</jats:styled-content>26 and <jats:styled-content style="fixed-case">BTA</jats:styled-content>29 were associated with sweating rate. New <jats:styled-content style="fixed-case">SNP</jats:styled-content>s were identified for rectal temperature (<jats:italic>n</jats:italic> = 12), respiration rate (<jats:italic>n</jats:italic> = 8) and sweating rate (<jats:italic>n</jats:italic> = 3) from among those previously associated with production, reproduction or health traits. The <jats:styled-content style="fixed-case">SNP</jats:styled-content> that explained the most variation were <jats:italic><jats:styled-content style="fixed-case">PGR</jats:styled-content></jats:italic> and <jats:italic><jats:styled-content style="fixed-case">ASL</jats:styled-content></jats:italic> for rectal temperature, <jats:italic><jats:styled-content style="fixed-case">ACAT</jats:styled-content>2</jats:italic> and <jats:italic><jats:styled-content style="fixed-case">HSD</jats:styled-content>17<jats:styled-content style="fixed-case">B</jats:styled-content>7</jats:italic> for respiration rate, and <jats:italic><jats:styled-content style="fixed-case">ARL</jats:styled-content>6<jats:styled-content style="fixed-case">IP</jats:styled-content>1</jats:italic> and <jats:italic><jats:styled-content style="fixed-case">SERPINE</jats:styled-content>2</jats:italic> for sweating rate. <jats:italic><jats:styled-content style="fixed-case">ARL</jats:styled-content>6<jats:styled-content style="fixed-case">IP</jats:styled-content>1</jats:italic> was associated with all three thermotolerance traits. In conclusion, specific genetic markers responsible for genetic variation in thermoregulation during heat stress in Holsteins were identified. These markers may prove useful in genetic selection for heat tolerance in Holstein cattle.</jats:p>