Location: Dale Bumpers Small Farms Research CenterTitle: Variance components for direct and maternal effects on body weights of Katahdin lambs
|NGERE, LAURETTA - Orise Fellow|
|NOTTER, DAVID - Virginia Tech|
|MORGAN, JAMES - Katahdin Hair Sheep International|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2017
Publication Date: 8/1/2017
Citation: Ngere, L., Burke, J.M., Notter, D.R., Morgan, J.L. 2017. Variance components for direct and maternal effects on body weights of Katahdin lambs. Journal of Animal Science. 95(8):3396-3405. https://doi.org/10.2527/jas.2017.1596.
Interpretive Summary: Selection for heavier body weights (BW) in lambs is desirable to achieve acceptable carcass weights. Statistical models have estimated variance components in several sheep breeds, but data is limited in the fast growing Katahdin breed and information on sources of variation for post-weaning gains is missing. Scientists from the Oakridge Institute for Science and Education, the Agricultural Research Service - Booneville, AR, Virginia Tech, and Katahdin Hair Sheep International determined that both direct and maternal effects have an important impact on BW in Katahdin lambs, and more accurate estimates of breeding values can be achieved, which will result in better selection decisions. This information is important to sheep producers, scientists, veterinarians, and extension specialists aiming to improve genetic parameters in sheep.
Technical Abstract: The aim of this study was to estimate genetic parameters for BW in Katahdin lambs. Six animal models were used to study direct and maternal effects on birth (BWT), weaning (WWT) and postweaning (PWWT) weights using 41,066 BWT, 33,980 WWT, and 22,793 PWWT records collected over 17 yr in 100 flocks. Fixed effects of management group, dam age, type of birth (for BWT) or type of birth and rearing (for WWT and PWWT), and lamb age at weighing (fitted as a covariate for WWT and PWWT) were defined variation in BW (P < 0.05). Variance components for random effects were estimated in sequentially more complex models and tested for significance with likelihood-ratio tests. A model that fitted only an additive genetic animal effect overestimated additive variance for all BW, resulting in larger estimates of direct heritability than models that included maternal effects. Maternal effects explained variation (P < 0.05) in all BW. Heritability estimates for the best-fit models were 0.15 for BWT, 0.18 for WWT, and 0.20 for PWWT. Estimates of maternal heritabilities were 0.14 for BWT, 0.10 for WWT, and 0.06 for PWWT. Permanent environmental maternal effects explained 4 to 6% of the total phenotypic variances for these BW. Litter effects included temporary environmental effects common to littermates and a proportion of the dominance genetic variance and accounted for an additional 16 to 19% of phenotypic variance. Correlations between additive direct and maternal genetic effects were -0.14 for BWT, -0.23 for WWT, and -0.04 for PWWT but differed from zero (P < 0.05) only for WWT. Total heritability predicted the total response in direct and maternal genetic effects from mass selection and ranged from 0.20 to 0.23 for BWT, 0.18 to 0.22 for WWT, and 0.22 to 0.25 for PWWT. Direct and maternal additive, maternal permanent environmental, residual, and phenotypic correlations between BWT and WWT were 0.53, 0.58, 0.51, 0.39, and 0.44, respectively; those between BWT and PWWT were 0.45, 0.58, 0.36, 0.33, and 0.37 respectively, and those between WWT and PWWT were 0.85, 0.99, 0.92, 0.77, and 0.81, respectively. This study demonstrated that both direct and maternal effects have an important impact on BW in Katahdin lambs. Models that include both additive and permanent environmental maternal effects as well as a temporary environmental litter effect would be expected to result in more accurate estimates of breeding values and better selection decisions.