Genetic and Environmental Aspects of Udder Infections

Abstract

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. tteritabitities 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 nmnbers 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" approxinmtely .3 with first lactation milk production.

Comparison of Single and Multiple-Trait selected Sires. Response in Mastitis Traits

“…Table 5 gives estimates of means for parities 1 through 3. Means for the clinical mastitis traits agree with (13,18,22,23) indicating lower frequency in first lactations. For example, SUM increased from 2.48 in first lactation to 5.16 in second.…”

“…O'Bleness et al (15) reported a genetic correlation of .44 between milk yield and incidence of clinical mastitis. Wilton et al (23) reported genetic correlations between milk yield in first lactation and mastitis incidence in later lactation that averaged around .30.…”

Differences in mastitis susceptibility between Holstein Friesian, Dutch Friesian and Dutch Red and White cows

“…(2) and Wilton c.s. (12) do not confirm such statements. The present study, also provides evidence of an opposite tendency: more favourable figures with higher production and easier milking ( Table 4).…”

Reviews of the progress of Dairy Science: Mastitis control – progress and prospects

“…Some assessments of the heritability of mastitis susceptibility suggest that progress for breeding more resistant cows is possible(i07, ill). Other researchers have produced low estimates of heritability (233). Part of the discrepancy relates to the difficulty of assessing mastitis susceptibility.…”