Correlated responses in greasy fleece weight in Border Leicester and Coopworth sheep breeds selected for lean tissue growth rate

Abstract

Correlated responses in greasy fleece weight were estimated from data of two breeds; Border Leicester ( n=608 and 462 for rams and ewes, respectively) and Coopworth ( n=1711 and 2024 for rams and ewes, respectively) of 11–13 months of age recorded for a period of nine years at Lincoln University in New Zealand. These flocks were selected for lean tissue growth rate without taking into consideration the production of greasy fleece weight, which is of major economic importance in New Zealand. Therefore, the aim of this study was to estimate the genetic and phenotypic parameters for the selection index component traits (liveweight, fat and muscle depths) and greasy fleece, and correlated responses in greasy fleece weight in Border Leicester and Coopworth breeds selected for lean tissue growth rate. Results showed that there were non-genetic effects viz birth rank, age of dam, year and age at measurement which affected greasy fleece weight production. The results also showed that the estimates of genetic and phenotypic parameters for the selection index component traits (liveweight, fat and muscle depths) and greasy fleece were moderate (0.12–0.30) to high (>0.30). Genetic and phenotypic correlations were low (0.20–0.40) to moderately high (0.40–0.60) for liveweight and greasy fleece weight, and very low (−0.20 to 0.20) to low for greasy fleece weight and fat and muscle depths. An indication that favourable correlated responses in greasy fleece weight would be observed when selecting for lean tissue growth rate in these breeds. Correlated responses in greasy fleece weight were all desirable, i.e. an average increase of 12.99±4.01 g/year giving average relative response rates of 0.46±0.14% per year. These correlated responses were not significantly different ( P>0.05) between sexes and breeds. Therefore, selection for lean tissue growth rate produced a positive effect on greasy fleece weight.