Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: April 12, 2002
Publication Date: N/A
Technical Abstract: Dairy Herd Improvement data with service dates from 2,195,643 Holstein and 171,981 Jersey sire-identified lactations from 1995 through 2000 were used to assess genetic variation in and relationships among fertility traits: days to first service (D1), days to last reported service (DL), nonreturn rate to first service before 70 d (NR), and number of services (NS). Mean NR was calculated by herd-year, and herd-years with NR of <10% or >90% were excluded; NR was not examined for cows that left the herd before 70 d after first insemination or if first service was after September 15, 2000. Phenotypic means for D1, DL, NR, and NS, respectively, were 90 d, 141 d, 55%, and 2.10 services for Holsteins and 83 d, 125 d, 57%, and 1.99 services for Jerseys. Data were adjusted for fixed effects of parity for all fertility traits and also for lactation stage at first service for NR and NS. Adjustment was also made for partial regression of fertility trait on mean of two highest test-day yields of milk, fat, and protein and for deviation of calving age from mean for corresponding parity. Heritabilities and genetic correlations were estimated by multitrait REML with an adjustment for herd-year-season of first service; phenotypic correlations were also estimated. Heritability estimates for Holsteins and Jerseys, respectively, were 0.066 and 0.040 for D1, 0.040 and 0.029 for DL, 0.010 and 0.011 for NR, and 0.018 and 0.022 for NS. Genetic variation for NR is low, but progeny groups can be large. Because DL has a higher heritability than NR and a moderate to high genetic correlation with D1 and NS, it may be the best single criterion of cow fertility of the four traits.