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Variance and Covariance Components in Part Lactation Milk and Fat Records

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

The monthly test-day milk and fat records of 1,526 Holstein cows in 232 herds artificially sired by 145 different sires were analyzed to obtain estimates of sire, herd, sire by herd, and error components of variance for the ten test days and for the sum of ten test days and to obtain estimates of sire, herd, sire by herd, and error components of covariance between the monthly records and between the monthly records and the sum of ten test-day records. Although the variances of the estimates of interaction components of variance are not known, the results of the analysis indicate that the sire by herd components of variance are approximately zero. This would suggest that the sire by herd components of covariance are also negligible. It is felt, however, that more data should be analyzed, in order to substantiate or negate these results, since the number of records in the present analysis is small.