- Genetic analysis of body weight at different ages in the Grootfontein Merino stud
Genetic analysis of body weight at different ages in the Grootfontein
K.R. Nemutandani1,2, M.A. Snyman1, W.J. Olivier1 & C. Visser2
1Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900, South Africa
2Department of Animal & Wildlife Sciences, Faculty of Natural & Agricultural Sciences, University of Pretoria, 0002, South Africa
# Corresponding author: Khetho Nemutandani
The implementation of genomic selection in the South African Merino sheep breed is dependent on the most accurate model being used when breeding values (EBVs) are estimated for animals in the reference population, as it will have an influence on the accuracy of determining marker effects. The aim of this study is to determine the most suitable statistical models and procedures for the estimation of breeding values for body weight to be used in a genomic selection program for South African Merino sheep. The aim of this part of the study reported here was to determine the most suitable model for the analysis of body weights, as well as to estimate genetic parameters among body weights at different ages, employing restricted maximum likelihood procedures. Data recorded on progeny born in the Grootfontein Merino stud from 1968 to 2012 were included in the analysis. The traits that were included are birth weight (BW), weight at 42 day (W42), weaning weight (WW), body weight at 6 months (BW6), 8 months (BW8), 12 months (BW12) and 15 months (BW15) of age. The fixed effects tested using the GLM-procedures of SAS included year-season, sex, birth status, rearing status, damage and their interactions. The estimation of the genetic parameters was done with ASREML by fitting single-trait animal models. Direct additive and maternal additive genetic effects, with or without a covariance between them, and maternal permanent environmental effects were tested for all traits in different combinations. For BW and W42, the most suitable model included all the random effects, while for WW the covariance between the additive and maternal effects were excluded. For BW6 and BW8, the most suitable model also included all the random effects. The most suitable model for BW12 included only the direct effect, while for BW15, direct and maternal effects were included. The direct additive heritability (h2a ± s.e.), maternal heritability (h2m ± s.e.) and the maternal permanent environmental effect (c2mpe ± s.e.) for birth weight were 0.20 ± 0.26, 0.11 ± 0.02 and 0.12 ± 0.01 respectively and for weaning weight these were 0.20 ± 0.02, 0.05 ± 0.01, 0.09 ± 0.01. The direct additive heritability, maternal heritability and the maternal permanent environmental effect for weight at 6 months were 0.54 ± 0.15, 0.29 ± 0.17 and 0.15 ± 0.49. For weight at 8 months these were 0.43 ± 0.11, 0.18 ± 0.08 and 0.21 ± 0.04. For weight at 12 months the direct additive heritability was 0.42 ± 0.05, while the direct additive heritability and maternal heritability for weight at 15 months were 0.51 ± 0.04 and 0.08 ± 0.02. The results correspond with the parameter estimates and models reported in other studies for the traits considered. Several analyses still need to be done before the most suitable statistical models and procedures for the estimation of breeding values for body weight to be used in a genomic selection program for South African Merino sheep could be identified. These included the multivariate analyses with restricted maximum likelihood procedures, random regression and repeatability procedures, as well as the estimation and comparison of breeding values with each procedure.
Proceedings 47th SASAS congress, Pretoria