EFFECTS OF AGE AND STAGE OF LACTATION ON TYPE CLASSIFICATION

Classification records on 2,518 Holstein-Friesian cows in 41 Wisconsin herds were used to determine the effects of age, stage of lactation, and age times stage of lactation interaction on type classification. All cows were rescored every 16 months. A total of 4,656 observations was available for the study. The final score, as well as ratings for general appearance, dairy character, body capacity, and mammary system were recorded for each classification. Differences due to age (divided into yearly intervals) and stage of lactation (divided into ten monthly intervals) were highly significant (P < .01) for final score and the four type components. Classification ratings were highest at the beginning and the end of lactation for all ratings, except for dairy character. Dairy character was rated higher at the beginning than at the end of lactation, with the third month being the highest. The interaction of age and stage of lactation was significant (P < .01) only for dairy character. Correction factors were developed to adjust the data for age and stage of lactation. Heritabilities, repeatabilities, phenotypic correlations, and genetic correlations were estimated from the adjusted data. © 1969, American Dairy Science Association. All rights reserved.