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

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Abstract
Estimated somatic cell counts and incidence of clinical mastitis were measured on 163 daughters of 2 groups of bulls selected by 2 alternative criteria. Yield bulls were selected solely on progeny test for milk in the 1st lactation; Merit bulls were selected by independent culling levels on fat-corrected milk yield, percent daughters culled in the 1st lactation and udder type conformation of daughters. Daughters of yield sires exceeded daughters of merit sires by 685 kg milk in the 1st lactation. Groups did not differ significantly in measures of clinical mastitis or in measures of estimated cell counts of milk. Groups did not differ in kilograms of milk discarded because of antibiotic treatment for mastitis despite the large difference in total milk yield. Mean milk discarded per lactation completed was 171 kg, representing 62,243 and 207 kg for parities 1, 2 and 3.