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Butterfat Production Per Day of Life as a Criterion of Selection in Dairy Cattle¹

University of Wisconsin, Madison

ABSTRACT

Butterf at production per, day of life was evaluated as a possible selection criterion for genetic improvement of dairy cattle.

The data provided little evidence of heterogeneity of the correlations of production to 36 mo. of age (and 305-day first lactation production) with production to 48, 60, 72 and 84 mo. of age. The predictive values of 36-mo. production and 305-day first lactation production to production at these same ages did not differ significantly.

Age at first calving had significantly less influence on total production to 84 mo. than on total production to 36 mo. of age.

Age at first calving and first 305-day lactation production accounted for 89 percent of the variance in 36-mo. production and 41 percent of the variance in 84-mo. production.

There was no evidence of heritability of production per day of life at any of the ages studied from 36 to 84 mo., nor was age at first calving indicated to be heritable. The estimate of heritability of first lactation butterfat production from these data was 0.30.

¹ Paper no. 465 from the Department of Genetics, University of Wisconsin, Madison. Published with the approval of the Director of the Agricultural Experiment Station.