Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2007
Publication Date: May 1, 2007
Citation: Cole, J.B., Wiggans, G.R., Van Raden, P.M., Miller, R.H. 2007. Stillbirth (co)variance components for a sire-maternal grandsire threshold model and development of a calving ability index for sire selection. Journal of Dairy Science. 90(5):2489-2496. Interpretive Summary: Producers are concerned about stillbirth rates in Holsteins. Accurate (co)variance components are needed for implementation of a national genetic evaluation. Gibbs sampling and quasi-REML procedures were used to estimate (co)variance components using six samples from the national calving ease database. All samples produced similar results, but the quasi-REML approach was faster. Results were comparable with literature estimates. Mean Gibbs sampling (co)variances were selected for use in the national evaluation model. Direct and maternal heritabilities were 3.0% and 5.8%, respectively, and the genetic correlation was 0.02. A sub-index including stillbirth and calving ease was developed for inclusion in Lifetime Net Merit.
Technical Abstract: (Co)variance components for stillbirth in US Holsteins were estimated under a sire-maternal grandsire threshold model using subsets of data from the national calving ease database, which includes over 7 million calving records with associated stillbirth scores. Stillbirth was coded as a binomial trait indicating whether the calf was alive 48 h postpartum. Records were selected for calves whose sire and maternal grandsire (MGS) were among the 2,600 most-frequently appearing bulls (2,578 sires and 2,586 MGS). Herd-years were required to contain at least 20 records and only single births were used. After edits, the dataset included 2,083,979 calving records from 5,765 herds and 33,304 herd-years. Six sample datasets of approximately 250,000 records each were created by randomly selecting herd codes. Quasi-REML and Gibbs sampling approaches were used to estimate (co)variance components from each sample. The model included fixed year-season, parity-sex, birth year group of sire, and birth year group of MGS effects and random herd-year, sire, MGS, and residual effects. Quasi-REML and Gibbs sampling produced similar results, although the Gibbs sampling estimates were slightly larger. Marginal posterior means (and standard deviations) from Gibbs Sampling averaged 0.0085 (0.0015), 0.0181 (0.0020), 0.0872 (0.0538), and 0.00410 (0.0001) for sire, MGS, and herd-year variances and the sire-MGS covariance, respectively. Mean direct and maternal heritabilities were 0.030 (0.003) and 0.058 (0.005), respectively, and the mean genetic correlation between the two effects was –0. 02 (0.16). A calving ability index combining stillbirth (SB) and calving ease (CE) was developed for inclusion in the Lifetime Net Merit $ index. The index is calculated as: –4(sire CE) – 3(daughter CE) – 4(sire SB) – 8(daughter SB).