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

Correlated responses in greasy fleece weight were estimated from data of tw o 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 mo nths of age recorded for a period of nine years at Lincoln University in Ne w Zealand. These flocks were selected for lean tissue growth rate without t aking into consideration the production of greasy fleece weight, which is o f major economic importance in New Zealand. Therefore, the aim of this stud y was to estimate the genetic and phenotypic parameters for the selection i ndex 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 als o showed that the estimates of genetic and phenotypic parameters for the se lection index component traits (liveweight, fat and muscle depths) and grea sy 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 livew eight and greasy fleece weight, and very low (-0.20 to 0.20) to low for gre asy fleece weight and fat and muscle depths. An indication that favourable correlated responses in greasy fleece weight would be observed when selecti ng for lean tissue growth rate :in these breeds. Correlated responses in gr easy 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) betw een sexes and breeds. Therefore, selection for lean tissue growth rate prod uced a positive effect on greasy fleece weight. (C) 1999 Elsevier Science B .V. All rights reserved.