Breeding and Genetics

摘要

A single nucleotide polymorphism (SNP; rs109421300) of the diacylglycerolacyltransferase 1 (DGAT1, BTA 14) gene has been associated with fatand protein percentages in dairy cows milked twice a day (TAD). This studyevaluated the association between rs109421300 genotype with productiveand reproductive performance and profitability in grazing cows milkedTAD and once a day (OAD) at Massey University, New Zealand. FromJuly 2017 to May 2018, 161 cows (32 TT, 65 CT and 64 CC genotypes)were milked OAD and 485 cows (91 TT, 254 CT and 140 CC genotypes)were milked TAD. Yields of milk (MY), fat (FY), protein (PY), along withfat percentage (FP), protein percentage (PP), BW, and different fertilitymeasures from the 646 cows in the 2 herds were analyzed with a linearmodel that included the fixed effects of milking frequency (MF), lactationnumber (LN), SNP genotype, interactions (MFxSNP, LNxSNP) and covariatesfor the linear effects of proportion of Holstein-Friesian, heterosisHolstein-Friesian x Jersey, and deviation from herd median calving date.DM intake was derived from estimations of metabolizable energy requirements.Milk income minus feed cost (MImCF) was expressed per tonneof predicted DM intake. Milk income was based on the milk payment system;$7.141 × kg FY + $6.156 × kg PY - $0.033 × kg MY. Compared withTT cows, the CC cows had significantly higher FP, PP and FY and lowerMY in both milking frequencies. The CT cows had values between the TTand CC cows. The combined changes of milk composition, yields and BWresulted in CC cows with the highest MImFC per t DM ($344 ± 5.4), followedby CT ($328 ± 5.1) and TT ($316 ± 7.0) cows in the OAD farm. Therespective values in the TAD farm were $381 ± 4.2, $365 ± 3.2 and $348 ±4.7. The allele substitution effect for MImFC was not significantly differentbetween MF. The effects of SNP genotype on the other productive andreproductive traits were not significant. Selecting cows for the C allele ofthe SNP rs109421300 can be beneficial for New Zealand dairy farmers.