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Association of a SNP in the DGAT1 gene with productive and reproductive performance and profitability in grazing cows milked once and twice a day.

N. Lopez-Villalobos

Abstract:

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Association of a SNP in the DGAT1 gene with productive and reproductive performance and profitability in grazing cows milked once and twice a day.
N. Lopez-Villalobos*1, H. B. P. C. Ariyarathne1, K. Gedye2, M. Correa-Luna1, D. J. Donaghy1. 1School of Agriculture and Environment, Massey University Palmerston North, New Zealand, 2School of Veterinary Sciences, Massey University Palmerston North, New Zealand.

A single nucleotide polymorphism (SNP; rs109421300) of the diacylglycerol acyltransferase 1 (DGAT1, BTA 14) gene has been associated with fat and protein percentages in dairy cows milked twice a day (TAD). This study evaluated the association between rs109421300 genotype with productive and reproductive performance and profitability in grazing cows milked TAD and once a day (OAD) at Massey University, New Zealand. From July 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 with fat percentage (FP), protein percentage (PP), BW, and different fertility measures from the 646 cows in the 2 herds were analyzed with a linear model that included the fixed effects of milking frequency (MF), lactation number (LN), SNP genotype, interactions (MFxSNP, LNxSNP) and covariates for the linear effects of proportion of Holstein-Friesian, heterosis Holstein-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 tonne of 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 with TT cows, the CC cows had significantly higher FP, PP and FY and lower MY in both milking frequencies. The CT cows had values between the TT and CC cows. The combined changes of milk composition, yields and BW resulted in CC cows with the highest MImFC per t DM ($344 � 5.4), followed by CT ($328 � 5.1) and TT ($316 � 7.0) cows in the OAD farm. The respective 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 different between MF. The effects of SNP genotype on the other productive and reproductive traits were not significant. Selecting cows for the C allele of the SNP rs109421300 can be beneficial for New Zealand dairy farmers.

Keywords: milking frequency, SNP genotype, DGAT1.