Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: March 23, 2004
Publication Date: July 25, 2004
Citation: VanRaden, P.M., Tooker, M.E., Cole, J.B. 2004. Heterosis and breed differences for daughter pregnancy rate in crossbred dairy cows [abstract]. Journal of Dairy Science. 87(Suppl. 1):284. Technical Abstract: Crossbred and purebred dairy cows were compared for the fertility trait daughter pregnancy rate (DPR) as defined and introduced in February 2003. Heterosis and breed differences were estimated from first lactation records of 11,708 F1 crossbred cows and 195,123 purebred contemporaries born after 1987 in 5775 herds. A second analysis of lactations 1 to 5 included 485,297 records. Lactations were required to be >250 days in milk. Records with >250 days open were set to 250 days open and records with <50 days open were set to 50 days open. Numbers of purebred contemporaries were 1679 Ayrshires (AY), 1259 Brown Swiss (BS), 1926 Guernseys (GU), 191,872 Holsteins (HO), 8812 Jerseys (JE), and 396 Milking Shorthorns (MS). The most numerous F1 cross was 5563 progeny of JE sires mated to HO dams. Days open records were converted to DPR by the linear approximation DPR = .25 (233 - days open). To compare base cows born in 2000, sire predicted transmitting abilities for DPR were adjusted to the 2000 genetic base and subtracted from DPR records. The model for adjusted DPR included linear and quadratic effects of age at first calving, herd-year-season of calving with three seasons per year, lactation number, heterosis, and breed effects as compared to purebred HO. Estimates of heterosis for DPR were +2.4 +-0.6 for first lactation and +1.8 +-0.5 for all lactations. Within herd-year-season estimates of breed differences and standard errors were AY +0.9 +-0.9, BS +0.9 +-0.8, GU +2.2 +-1.2, JE +3.9 +-0.5, MS +4.5 +-1.8 for first lactations and AY +1.8 +-0.5, BS +0.1 +-0.4, GU +2.0 +-0.7, JE +4.6 +-0.3, MS +4.3 +-1.0 for all lactations. These estimates are similar to differences obtained from national breed averages for first lactation DPR, which were AY 22.8, BS 21.9, GU 21.3, HO 22.3, JE 27.0, and MS 26.0 for cows born in 2000. JE x HO crossbreds are as fertile as purebred JE, and heterosis for DPR is about 10% of mean DPR. Crossbred cows have significant advantages over their purebred parents for daughter fertility.