Comparison of models including cytoplasmic effects for traits of Rambouillet sheep

The objective was to determine appropriate analytical models considering cytoplasmic inheritance for birth weight (BWT, n = 35,604), weaning weight (WWT, n = 34,114), fleece weight (FWT, n = 38,113) and number born (NB, n = 39,029) for Rambouillet sheep. For BWT, models that included dam by year, dam by number born, and sire by dam effects, in addition to direct and maternal effects, were significantly better than the basic maternal effects model. For WWT, variances due to direct, maternal, and maternal permanent environmental effects (0.05 of variance) were not zero. For FWT, heritability was 0.55 for all models, but models with dam by year (0.02), sire by dam (0.05), and sire by cytoplasmic line (0.02) were jointly significantly better than models with permanent environmental effects. For NB, only direct heritability (0.08) and relative permanent environmental variance (0.04) were not zero. No trait showed evidence of variation due to cytoplasmic effects. Adding seldom considered effects to the model did not change estimates of variance due to direct and maternal genetic effects. Variance due to dominance effects may be important for BWT and FWT. The basic direct–maternal effects model seems sufficient for genetic evaluations for WWT and FWT but models for BWT and NB may need to include other effects. Published by Elsevier B.V.