A pooled afternoon and morning milk sample was obtained from each of 3,789 cows of known pedigree during a standard herd-test carried out in 21 North Island spring-calving herds between November and February. The cows were all sired by one of 11 Holstein-Friesian bulls, in a sampling design intended to sample milk from many daughters per sire, for segregation studies. Routine herd-test data consisted of 24 hour milk yield, protein %, fat % and somatic cell count. Samples were measured at Ruakura for fatty acid composition, fat melting point, and the concentrations of the following components, lactoferrin, β-lactoglobulin, β-casein, κ-casein, and total carotenoids. After liaison between AgResearch Ruakura staff and each dairy farmer a variate describing the current grazing groups of cows were included in analyses. Coefficients of variation were calculated for each milk component, and ranged from 0.04 to 0.35. Phenotypic correlations among components were estimated. The correlations were negative between the percentage of mono-unsaturated fatty acids present in milkfat and both the protein % (-0.26 ± 0.03 (standard error)) and fat % (-0.38 ± 0.02) of the milk. Some implications of selection mainly for yield from cows at pasture are discussed in terms of likely effects on milk composition.
Proceedings of the New Zealand Society of Animal Production, Volume 72, Christchurch, 58-62, 2012
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