The aim of this study was to estimate genetic parameters for milk urea (MU), yields of milk (MY), fat (FY), crude protein (CPY) and lactose (LY), concentrations of fat (FP), crude protein (CPP) and lactose (LP) and efficiency of crude protein utilisation (ECPU) in grazing dairy cows. Data consisted of 1284 herd-test records of milk traits and MU from 468 mixed-breed cows in two herds. Univariate and bivariate repeatability animal models were used to estimate heritabilities (h2) and genetic (rG) and phenotypic (rP) correlations among the traits. Estimates of h2 for MU and ECPU were 0.24 and 0.11, whereas h2 estimates for MY, FY, CPY and LY ranged from 0.10 to 0.20. Estimates of h2 for FP, CPP and LP were 0.37, 0.59 and 0.19, respectively. The estimates of rP for MU with other traits were near zero. The rG of MU with MY (0.38), and of MU with LY (0.31) were positive and significant (P<0.01) whereas the rG of MU with FP (-0.80), CPP (-0.66) and LP (-0.76) were negative and significant (P<0.01). The rG between MU and ECPU was -0.09. These estimates of genetic parameters can be used to predict genetic responses to selection for reduction of MU.
Proceedings of the New Zealand Society of Animal Production, Volume 78, Lincoln, 56-61, 2018
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