Estimation of the frequency and effects of casual mutations on fertility and production traits in Irish dairy cattle

Abstract

Fertility is a major driver for profitability and sustainability of livestock enterprises. Identifying and estimating the effects of known lethal recessive genetic mutations and genes of major effect on production traits in cattle populations provides additional information to the industry for potential incorporation into breeding programs. Such information may support breeders to make more informed decisions through the identification of carrier animals and the evaluation of potential strategic matings in cases where carrier animals may be of otherwise high genetic merit. This project aims to estimate the frequency and effects of a panel of DNA polymorphisms (n=18) in Irish Holstein Friesian cattle, some of which are validated as causative mutations responsible for lethal recessive disorders (CVM, BLAD, DUMPS and Brachyspina), and some of which have been observed to have major effects on production and functional traits in previous research studies (STAT1, STAT3, STAT5). Genotypes on 21,707 Holstein Friesian dairy cattle were obtained from the ICBF, as were phenotypic data on milk, fertility, carcass and health traits (n=16). Phenotypes, expressed as predicted transmitting abilities (PTAs) were prepared for inclusion in the analysis by removal of parental contributions through a deregression process. Haplotypes were predicted using PHASE for all SNPs with positions on the same chromosome. Subsequently, associations between each SNP/haplotype and PTA were analysed in ASReml using a weighted mixed animal model. Several associations between the genes of major effect and production and functional traits were evident and consistent with previous reports of such associations, for example SNPs within the DGAT and Casein genes were associated with milk composition traits as expected, however, they were also associated with fertility and carcass traits. SNPs within the STAT genes, of which there has not been extensive previous studies on in cattle populations, were associated with both production and functional traits in the population studied. Additionally, a candidate novel lethal recessive mutation in LFNG has been identified. The results from this project will be evaluated by our industry partners, the ICBF, responsible for national genomically assisted breeding programs in Irish cattle