Relationship between United States and Canadian genetic evaluations of longevity and somatic cell score.

Canadian and US evaluations of Holstein bulls were compared for longevity measures (433 bulls) and somatic cell score (354 bulls). Bulls were required to have a birth year of > or = 1975, daughter information from > or = 20 herds, and a reliability of > or = 50% in both Canada and the US. The 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 > or = 3 yr of age for US evaluations; evaluations for somatic cell score required additional collection of data and did not have corresponding numbers of bulls until the 1980s. Correlation between longevity measures in the US (productive life) and Canada (herd life) was 0.60. This low correlation was expected because US productive life includes yield information, but yield is excluded from Canadian herd life. For evaluations for somatic cell score, the correlation between the two countries was 0.82. Genetic correlations with productive life were estimated to be 0.69 for herd life and 0.81 for herd life combined with protein yield. Conversion equations were developed to predict a US evaluation for somatic cell score from a Canadian evaluation for somatic cell score and to predict a US evaluation for productive life from Canadian evaluations for herd life and yield.