Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 1997
Publication Date: N/A
Interpretive Summary: Mastitis and involuntary culling are two major costs to dairy producers. National genetic evaluations for somatic cell score, an indicator of mastitis, and for longevity began in January 1994 for the United States and in January 1996 for Canada. Although USDA bull evaluations for yield traits have included combined (or converted) evaluations for Canadian bulls since January 1993, information was lacking on the best method for combining evaluations for longevity and somatic cell score traits. The relationships between U.S. and Canadian Holstein bull evaluations for longevity (productive life for the United States and herd life for Canada) and somatic cell score were determined, and conversion equations for these traits were developed. These conversion equations will provide guidance for breeders who wish to estimate net merit dollars, a U.S. economic index, for Canadian bulls.
Technical Abstract: For Holstein bulls born in 1975 or later with daughter information from at least 20 herds, reliability of at least 50%, and evaluations in both Canada and the United States, evaluations were compared for longevity measures (433 bulls) and somatic cell score (354 bulls). Number of bulls with longevity evaluations was greater for early years, because longevity information was available from lactation data and daughters were required to be at least 3 years of age for US evaluations; somatic cell score evaluations required additional collection of data and did not have corresponding numbers of bulls until the 1980's. Correlation between longevity measures in the United States (productive life) and Canada (herd life) was .60. This low correlation was expected because U.S. productive life includes yield information, whereas yield is excluded from Canadian herd life. For somatic cell score evaluations, the correlation between the two countries was .82. Estimates of genetic correlations were .69 for longevity as reported, .81 for longevity including yield, and .92 for somatic cell score. Conversion equations for predicting U.S. somatic cell score from Canadian somatic cell score and for predicting U.S. productive life from Canadian herd life and yield evaluations were developed.