Genetics and breeding (online only): Estimation of (Co) Variances of Test Day Yields For First Lactation Holsteins in the United States

摘要

(Co) variance components for milk, fat, and protein yields during first lactation were estimated from data for test days from 23, 029 Holstein cows from 37 herds in Pennsylvania and Wisconsin. Four lactation stages of 75 d were defined, and the test day nearest the center of each interval was used. In four analyses, a lactation stage was added, and observations with missing values were deleted; 17, 190 observations with were available for the final analysis of lactations with test days in all lactation stages.