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Information on the presence or absence of bacterial infections and abnormal secretions in each quarter of cows in their initial survey on the New York State Veterinary College Mastitis Program was used to obtain several criteria of udder infection. Year-season and stage of lactation effects were statistically significant for several criteria of infection in first, second, and later lactation groups but did not explain much of the variation in any infection criterion. Age within first and second lactation group also accounted for little of the variation in infection although age within later lactations accounted for up to 5% of the variation in some criteria.
Heritabilities from sire components of variance were all low for first, second, and later lactation cows. Heritabilities from daughter-dam regression were low for first and second lactation cows but moderately high for later lactation cows. Regression of second lactation infections on first lactation infections, later lactation infections on first lactation infections, and later lactation infections on second lactation infections were moderately high. Heritabilities from sire components of variance were not increased by using two surveys per cow, by using only herds with high incidence of infections, or by using only sires with large numbers of daughters. Phenotypic relationships between milk yield and infections were all low. Some of the overall measurements of infection on later lactation cows had genetic correlations of approximately .3 with first lactation milk production.