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Genetic and Environmental Changes Possible in Milk Composition

Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst 01002

ABSTRACT

The possibility of changing milk constituent percentages in lactation records through environment is small. Fat percentage can be reduced by feeding high-concentrate low-roughage rations, low-fiber feeds, pellets, etc.

Changes in milk composition are possible through breeding, as heritabilities for yields are around .25, percentages .50 to .60, and ratios .60, but gains in protein and solids-not-fat (SNF) percentages would be less than fat gains because of their smaller variation. Genetic correlations among yields are highly positive, .9; between percentages, .3 to .9%; and between yields and percentages generally negative, — .2 to — .4.

Selection for protein or SNF percentage alone would be effective but would result in a correlated loss in milk (75 to 100 kg per generation) with small gains in protein or SNF yields. Selection for milk would generally result in a correlated increase in protein yield, which is about 90% as effective as direct selection for protein yield but would decrease protein percent slightly. However, selection for protein yield gives about 70% as great an increase in milk yield as selection for milk alone and increases protein percent about 20% as much as selection for protein only. Selection indices have been constructed so as to maintain the percentages while improving milk yield. In practice, Holstein dairymen in this country and in Holland have increased fat percent and milk yield.