SELECTION FOR LAMBING RATE AND CLEAN FLEECE WEIGHT IN SHEEP

This study was designed to compare the effectiveness of selection for lambing rate (LB) and clean fleece weight (CFW) separately or by a com bination of both traits at once. Two flocks of approximately 200 weste rn white-faced ewes per flock were maintained at two locations. Each f lock was divided into four equal selection groups of similar initial b irth type and age. The basis of selection in each nock was as follows: Line I, single trait selection for LB; Line II, single trait selectio n for CFW; Line III, multiple trait selection for LB and CFW; and Line IV; visual selection based on conformation and general fleece quality . Repeatability and heritability estimates were .18 and .16 +/- .04, r espectively, for LB and .66 and .60 +/- .09, respectively, for CFW. Th e genetic correlation between LB and CFW was .26 +/- .16. Linear regre ssion coefficients (number born/year) of annual response for LB in Lin es I to IV were .018 +/- .008, .009 +/- .006, .011 +/- .005, and .009 +/- .005 (P > .05). Linear regression coefficients (kg/year) of annual observed response for CFW in lines I to IV were -.001 +/- .006, .027 +/- .009, .019 +/- .006, and .008 +/- .006. Response in Lines II and I II was significant for CFW (P < .05) compared with Lines I and IV. In this study, CFW was increased by selection in white-faced sheep with l ittle effect on lambing rate.