Monitoring and significance of the recessive genetic defect AH1 of Ayrshire cattle

Modern dairy farming is characterised by high selection intensity and the use of a limited number of bulls-producers. This increases the likelihood of widespread genetic defects in livestock populations. Genome-wide studies have identified DNA loci associated with the disruption of foetal embryonic development and its death, which have been called "fertility haplotypes". The aim of this study is to analyse the occurrence of АН1 haplotype or rs475678587 in Ayrshire bulls (n = 186) used in the artificial insemination system of Russia and to evaluate the reproductive and productive qualities of their daughters. The proportion of genetic defect carrier bulls in the analysed sample cohort was 16.66%. Analysis of the proportion of carriers of unwanted haplotype depending on the place of birth of the bull for service showed that the highest frequency was observed in bulls of Canadian origin (26.66%). Based on data on 97 478 cow and heifer calvings, stillbirth and abortion rates were analysed and cow reproduction rates were based on an AH1 status for the bull-father and bull for service. We observed a significant increase (P < 0.05 and P < 0.001) in the incidence of stillbirths when crossing the daughters of AH1-C bulls with AH1-C bulls. There was no negative association of abortion rates and reproductive qualities with AH1 haplotype. The high incidence of AH1 haplotype among animals of Ayrshire breed requires regular screening for the carriers of this haplotype not only among bulls, but also in cows.