J. B. Cole and A. H. Sanders
Animal Improvement Programs Laboratory ,
Agricultural Research Service,
USDA, Beltsville, MD 20705-2350
Termination codes are reported at the end of lactation in the U.S. These codes indicate a routine lactation or one of several reasons for culling, including low production, poor reproduction, and mastitis/high somatic cell count. Cases of clinical mastitis (CM) are recorded in on-farm record systems, but are not stored in a national database for use in genetic improvement. The objective of this research was to determine the feasibility of using the mastitis termination code (TC7) as a proxy for sire evaluation of clinical mastitis. Data consisted of terminal lactations from 40,106 Holstein cows calving between January 1, 1998 and January 1, 2004; cows with TC7 were assumed to have CM. (Co)variance components were estimated using a threshold animal model that included terminal lactation number, random herd-year-season and animal effects, and days open. Correlations among sire PTA for CM and yield traits, somatic cell score (SCS), daughter pregnancy rate, and productive life (PL) were estimated using sires with 50 or more daughters. Heritability of CM was 0.02, which is consistent with literature estimates. Correlations between PTA for CM and SCS and CM and PL were 0.35 and -0.09, respectively; all other correlations were non-significant (P < 0.05). The correlation between CM and SCS is lower than reported by participants in Interbull CM evaluations.