Genetic and phenotypic parameter estimates were derived from performance data collected over nine years for the Lincoln University Dorset Down flock. Data were for animals born each spring and run at pasture. Ewes (n=922) were measured in autumn and rams (n=819) in winter. Measurements were live weight and in vivo fat and muscle depths. Genetic and phenotypic parameters were estimated using multi-variate AIREML analyses by fitting an individual animal model with animal as a random effect, birth rank, age of dam and year of birth as fixed effects and age at measurement as a covariate. Multi-variate heritability estimates (± s.e.) for live weight, fat and muscle depths were 0.42 (±0.04), and 0.30(±0.05) for rams and 0.26(±0.01), 0.20(±0.05) and 0.13(±0.03) for ewes respectively. Estimates of genetic correlations were generally moderate to high for the two sexes. The genetic correlation between live weight and fat depth was significantly different for the two sexes, with rams (0.42±0.10) having a higher value than ewes (0.24±0.02). Phenotypic correlations differed between the sexes, with estimates for ewes being slightly higher. For both sexes, parameter estimates were different from those used to derive the indices used to select for lean tissue growth, ram estimates being consistently higher while those for ewes were more equivocal.
Proceedings of the New Zealand Society of Animal Production, Volume 54, , 251-254, 1994
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