Single trait selection for yearling fleece weight or liveweight in Romney sheep—direct responses

Abstract

Abstract An experiment was carried out to study the responses to selection for yearling fleece weight and liveweight in Romney sheep. There were two selection lines, one selected for fleece weight (FW) and the other for liveweight (LW), and a control (CO) line was maintained. Data from lambs born 1967–90 were analysed to quantify the direct responses to selection. By 1990 there had been an average of 9 generations of selection with an average generation interval of 2.7 years. Realised heritabilities and selection responses were estimated from the deviation of the selected lines from a control line and by restricted maximum likelihood (REML) techniques. Realised heritabilities were 0.36 ± 0.04 for both fleece weight and liveweight respectively when estimated using the regression of response on selection differential. The corresponding REML estimates of heritabilities were 0.39 ± 0.03 for fleece weight using data from FW + CO and 0.42 ± 0.03 for liveweight using LW + CO. The direct responses to selection, d...