Evaluations for service-sire conception rate for heifer and cow inseminations with conventional and sexed semen

Service-sire conception rate (SCR), a phenotypic fertility evaluation based on conventional (nonsexed) inseminations from parities 1 through 5, was implemented for the United States in August 2008. The SCR model contains the categorical fixed effects of parity for lactations 1 to 5; state-year-month of insemination group; 6 standardized milk yield groups; service number for inseminations 1 to 7; cow age; and herd-year-season-parity-registry status class. Covariate effects for service-sire and mating inbreeding coefficients were linear regressions fit as deviations from the overall mean. Random effects included service-sire age group; AI organization-insemination year group; individual service sire; cow's genetic ability to conceive; cow's permanent environmental effect; and residual. Using insemination data from 2005 through 2009, the SCR procedure was applied separately for nulliparous heifer inseminations with conventional semen (SCRHconv), cow inseminations with conventional semen (SCRCconv), nulliparous heifer inseminations with sexed semen (SCRHsexed), and cow inseminations with sexed semen (SCRCsexed). Holstein and Jersey bulls with ≥300 and ≥200 artificial inseminations, respectively, in ≥10 herds and with ≥100 breedings during the 12 mo before evaluation were examined. The number of bulls evaluated for SCR in January 2010 was 270 Holsteins and 16 Jerseys for SCRHconv, 2,309 Holsteins and 214 Jerseys for SCRCconv, 114 Holsteins and 6 Jerseys for SCRHsexed, and 25 Holsteins and 7 Jerseys for SCRCsexed. The mean SCR for each evaluation category was set to 0; Holstein standard deviations were 2.55% for SCRHconv, 2.21% for SCRCconv, 4.29% for SCRHsexed, and 2.39% for SCRCsexed. The mean Holstein reliabilities were 82, 79, 75, and 73%, respectively. Correlations for Holstein SCR between conventional and sexed semen averaged near zero (−0.21 to 0.18). Predicted correlations between true SCR were −0.27 to 0.24. In contrast, correlations between Holstein heifers and cows were high (0.66 to 0.76), and predicted true correlations averaged near 1.0 (0.82 to 1.03). Correlations for Jerseys were often larger, although based on fewer inseminations and service sires compared with Holsteins. Some rankings for SCR could benefit from combining cow and heifer data but should be kept separate for conventional and sexed semen inseminations.