Single Nucleotide Polymorphisms in the Signal Transducer and Regulator of Transcription (STAT) Genes Are Associated with Milk Production, Milk Composition and Fertility Traits in Holstein Friesian Cattle

Signal transducer and activator of transcription (STAT) genes encode for a family of proteins that are involved in pre- and post-natal growth and development. In cattle, variants in these genes have been associated with economically important traits including milk production and embryonic survival. The objective of this study was to estimate the effects of polymorphisms in the STAT1, STAT3, and STAT5 genes on milk production, composition, and fertility traits in Holstein Friesian dairy cattle. STAT genotypes (n=8) on 10,707 dairy cattle were obtained through the Irish Cattle Breeding Federation (ICBF). The phenotypes (n=16) for milk production, milk composition and fertility traits also were obtained from the ICBF and expressed as predicted transmitting abilities (PTAs). The association between each SNP and deregressed PTA was analysed in ASREML using a weighted mixed animal model. The association analysis included n=6876 for milk yield and composition traits. The analysis for fertility traits included n = 1193, 264, 4566, 8564, 152, and 2380 cows for calving interval, survival, calving difficulty, gestation length, calf mortality, and maternal calving difficulty, respectively. In the analysis of the STAT variants with milk traits (milk protein concentration, milk fat concentration, milk yield, milk fat yield, milk protein yield) a significant association (p<0.05) was observed between STAT3 (25042) and STAT5 variants (12195, 13244, 13319, 13516) and milk protein percentage. STAT3 variants (19069, 25042) were associated (p<0.001) with milk fat percentage, additionally STAT5 variants (13244, 13516) were also found to be associated (p<0.05) with this trait. The G allele of STAT3 (25042) was also associated with increased milk yield (17.01 kg, s.e. 6.708, p<0.05). No associations were observed between STAT1 and the remaining polymorphisms analysed in either STAT3 or STAT5 with the milk production and milk composition traits examined. Associations were observed between STAT3 (19069) and gestation length (0.11 days, s.e. 0.056, p<0.05) and STAT5 (12195) with calf mortality (2.04, s.e. 1.017, p<0.05). None of the six remaining polymorphisms considered in this study within the STAT genes were associated with any of the aforementioned fertility traits. These results support a multifaceted role of the STAT family in milk production, composition, and fertility which warrants further functional analysis and consideration for incorporation into genetic evaluation programs for maximising the rate of genetic gain.