Components of Variance Associated with Service Sire for Milk Yield and Reproductive Traits

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The association of service sire or sire of fetus with three milk yield traits and two reproductive intervals were investigated. Two procedures for estimation of variance components, Henderson's Method 1 and Method 3, were applied to a model of herd-year-season, sire of cow, and service sire. Analyses were for sire of calf born to initiate second lactation and service sire of the cow in second lactation. About 11,000second lactation records on Holstein cows were available after editing for breeding and calving dates. Service sires and sires of cows were required to be in artificial insemination. Estimates by Method 1 for gestation length and days open were 6.0% and −.2% of total variance for sire of calf and 1.0% and 5.4% for service sire in second lactation. Method 1 estimates were consistently larger than Method 3 for milk yield. Variance components expressed as percent of total variance for mature equivalent milk yield in 305 days, 150-day milk yield, and milk yield in remaining days of lactation were 2.7%, 3.1%, and 1.7% for sire of calf and 2.7%, 3.8%, and 1.3% for service sire in second lactation. These same components from Method 3 were .8%, .4%, .8%, and 1.0%, 1.6%, .6%. The differences in estimates may reflect nonrandom use of service sires across herd-year-seasons and sires of cows. About 1% of variance in milk yield was associated with service sires.