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Abstract

The main objects of this investigation were to study fat and solids-not-fat levels in cow's milk, the relationship between them and to calculate heritability estimates. During the period of four months in 1955-1956 the milk of twenty Ayrshire cows was sampled and tested for butterfat and solids-not-fat. In the same period of 1956-1957 eighteen Ayrshires and ten Holsteins were similarly tested. Ayrshire cows were used for heritability determinations and represent a group of inbred animals with a high average relationship. A detailed calculation of heritability for fat and solids-not-fat and resultant estimates of 21.2% and 10.9% respectively are presented. Highly significant correlation coefficients between fat and solids-not-fat of + 0.680 in 1955-1956 and + 0.618 in 1956-1957 for Ayrshires and a non-significant value of + 0.570 for Holsteins, were calculated. The question of testing milk for solids-not-fat with respect to achieving genetical improvement is explored and the usefulness of correlation coefficients and regression equations for estimating solids-not-fat is discussed. The effects of mastitis on the level of solids-not-fat are indicated.