RESPONSE TO SELECTION FOR LAMB PRODUCTION IN AN INTENSIVE SYSTEM

Selection response achieved for total weight of lamb weaned per ewe pe r year, following approximately two generations of selection is report ed. The study involved approximately two generations of selection in H yfer sheep, which is a new composite breed developed for intensive lam b production. The Hyfer breed was developed crossing selected Poll Dor set (D) ewes with Booroola Merino (B) and Trangie Fertility Merino (T) rams. The two types of progeny were interbred to form a base populati on of 1/2D1/4B1/4T, which was then subject to selection. Ewes are sele cted into the Selection Flock on the basis of their average weight of lamb weaned from three joinings in two years. Rams are selected primar ily on the basis of the performance of their dams. A Control Flock whi ch is representative of the base population is maintained. Unselected ewe progeny from the Selection Flock had 11% higher weight of lamb wea ned than Control Flock ewe progeny (P<0.05) over four cohort groups wh en they were exposed to three joinings at 8-monthly intervals. The res ponse is similar to that predicted from the selection differentials ac hieved and heritability estimated for Hyfer sheep.