Records on feed efficiency, feed intake, milk yield, fat plus protein yield and mean liveweight from a dairy herd, fed ad libitum, were analysed by Restricted Maximum Likelihood fitting an Animal model, with repeat lactations as an additional random effect. Univariate analyses were done after approximate canonical transformation of the traits. Heritability estimates for feed efficiency and feed intake were 0.13±0.09 and 0.37±0.11 for 26-week and 0.13±0.12 and 0.52±0.14 for 38-week lactation periods respectively. Over the same periods, estimates for milk yield were 0.20±0.08 and 0.20±0.11 respectively. Genetic correlations between milk production traits and efficiency ranged from 0.44 to 0.61 and those between milk production traits and feed intake from 0.32 to 0.74. In both cases lower correlations were obtained for the longer period. Genetic correlations between mean liveweight and efficiency were -0.81 and -0.82, and those between liveweight and feed intake, 0.34 and 0.45 for the 26- and 38- week period, respectively. The results indicate that when selection is on yield, the correlated responses in efficiency may be smaller under ad libitum feeding, compared with published values where cows were fed according to yield. Higher responses in efficiency could be obtained by selecting on an index of yield and liveweight. In MOET nucleus schemes it may be worthwhile to select directly for efficiency.

P. Persaud, G. Simm, William G Hill

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XIV. Dairy cattle genetics and breeding, adaptation and conservation., , 237–240, 1990
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