REPRODUCTIVE EFFICIENCE AND IDENTIFICATION OF SINGLE NUCLEOTIDE POLYMORPHISMS IN THERMOTOLERANT HOLSTEIN COWS

Abstract

The aim of this study was to identify novel SNPs in thermotolerant Holstein cows and to evaluate the reproduction of these animals. Vaginal temperatures of 110 Holstein animals were measured with an automatic thermometer during the summer. Animals were classified as thermotolerant (TT), animals in which no temperature event (at least 30 min) occurred above 39 °C; intermediate (INT), animals in which one or more half-hour temperature events occurred between 39.1 and 39.5 °C; and thermosensitive/heat stressed (HS), animals in which the temperature exceeded 39.5 °C in at least one half-hour event. Tail hair was collected for DNA extraction, PCR, and DNA sequencing. Primers from ATP1A1 gene and HSP90AB1 gene were used to detect polymorphism. Temperature [mean, maximum, and coefficient of variance (CV)], milk production data, and number of artificial inseminations required for pregnancy were analyzed using the GLM procedure and PDIFF of SAS. Seventy-one cows were placed in the HS group, 14 in the INT group, and 25 in the TT group. Mean, maximum and CV temperatures were higher in animals in the HS group (P <.01). Milk production was not different within the groups. The number of inseminations required for the cow to become pregnant was higher (P = 0.05) in the HS group. There was a moderate and positive correlation (0.33; P < 0.004) between temperature CV and number of inseminations. One SNP was identified in the gene ATP1A1; this mutation represents a change from aspartate to asparagine. Four SNPs were identified in the HSP90AB1 gene. In summary, animals that can maintain a lower body temperature under heat stress have better fertility because they require less artificial insemination to become pregnant, regardless of milk production. Novel SNPS have been found in both ATP1A1 and HSP90AB1 genes, but further studies are needed to link them to thermoregulation.