Computing mating bull fertility from DHI nonreturn data

Animal model methodology was used to compute yearly measures of relative fe rtility of Holstein Al mating bulls based upon 70-d nonreturn of first bree dings as reported to U.S. DHIA from 1988 through 1997. Estimated Relative C onception Rates (ERCR) were computed for bulls with a minimum of 50 first b reedings in a single year using variance ratios 45.5 for mating bull, 45.5 for animal genetic effects, and 31 for permanent environment. The model ass umed repeatability across lactations of 0.05 and included fixed effects of herd-year-month bred and classes of parity, early lactation energy-correcte d milk and days open when bred. Estimates of fertility were greater for bre edings to cows that were young, had low early lactation production, and wer e in late stages of lactation. ERCR were expressed as difference in nonretu rn from the average Al mating bull of herdmates. Values ranged from -18 to +13. For ERCR computed from a minimum of 1000 breedings, 90% were within fo ur units of zero. Early ERCR computed from a few breedings in a single year were tested for ability to predict later ERCR computed from a minimum of 1 000 different breedings. Early ERCR computed from 300 or more matings accur ately predicted later independent ERCR. For yearly estimates each based upo n a minimum of 1000 breedings, 8% changed more than three units, and 4% dec lined more than three units. Correlations between ERCR and predicted transm itting abilities protein and type production index were significant but acc ounted for little variance. Correlations between ERCR and other traits were not significant.