Variance and Covariance Components in Part Lactation Milk and Fat Records

Abstract

The monthly test day milk and fat records of 1526 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 10 test days and for the sum of 10 test days and to obtain estimates of sire, herd, sire by herd, and error components of covariance between monthly records and sum of ten test day records. Although the variances of estimates of interaction components of variance are not known, 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 to substantiate or negate these results since the number of records in the present analysis is small.