Effect of breed of dam and lamb, and of lamb sex on efficiency of conversion of food to lamb and wool in Merino and first-cross Merino ewes

Abstract

The effects of breed of dam (Merino (M), Border Leicester x Merino (BL x M) and Poll Dorset x Merino (PD x M)), breed of lamb (Suffolk sired (S)) and sex of lamb (castrate male, female) on the efficiency of the ewe (organic matter intake per unit metabolic weight and clean wool weight per unit intake) and on the efficiency of the ewe-lamb unit (liveweight and carcass weight per unit intake) were examined. The effects of breed of dam and breed of lamb were differentiated by a system of cross-mothering of all lambs at birth. Each lamb was slaughtered at = 35 kg liveweight. The two crossbred types ate less organic matter per unit metabolic weight than did M dams during late pregnancy, but there were no differences during lactation. Compared with the absolute intake of M dams, PD x M and BL x M ewes ate 11 and 18 % more throughout the experimental period (224 days). The conversion efficiencies of food to wool of PD x M and BL x M dams were 59 and 66 % of that of Merinos. There were no significant differences between breeds of lamb or between lamb sexes for either intake per unit metabolic weight or clean wool growth per unit intake of the ewe. There were no significant differences between breeds of dam or between lamb sexes for either lamb liveweight or carcass weight per unit intake. This applied whether the lambs were at the same age or at the same liveweight. Ewes rearing S x (PD x M) and S x (BL x M) lambs had higher carcass weights per unit intake than did those rearing S x M lambs.