EFFECT OF REARING TYPE AND PREPARTUM NUTRITION ON THE INTAKE AND PERFORMANCE OF LACTATING GREYFACE EWES AT PASTURE

Eleven single-rearing and 14 twin-rearing Greyface (Border-Leicester .times. Scottish Blackface) ewes which were previously individually-fed indoors on 3 nutritional treatments (treatment 1, adequately nourished; treatment 2, moderately undernourished; treatment 3, severely undernourished) during the final 6 wk of pregnancy, were subsequently grazed with 8 non-lactating Greyface ewes on a ryegrass-white clover pasture for the first 14 wk of lactation. Herbage organic matter (OM) intakes and milk yields of ewes were measured weekly and the herbage OM intakes of lambs, from wk 7 of lactation. Prepartum nutrition had no effect on intake. Maximum intakes were achieved in wk 5 for twin-rearing ewes and wk 4 for single and non-lactating ewes. There were significant differences (P < 0.05) in milk production between single- and twin-rearing ewes in the first 5 wk of lactation. Twin-rearing ewes of prepartum treatment 1 produced consistently more milk in wk 2, 3 and 4 of lactation, while ewes from treatment 3 tended to produce more milk than ewes from the other treatment groups thereafter. Milk intakes of single lambs were always significantly greater than individual twin lambs, and single lambs ate significantly less grass during the herbage OM intake measurement period from wk 7. Their growth rates up to wk 7 were also significantly greater. No differences in the intake or growth rate of lambs could be attributed to the prepartum nutritional treatment of their dams. Ewe maintenance requirements during lactation were estimated to be 242 (.+-. 35.1) kJ ME[metabolizable energy]/kg body weight per day. The efficiency with which ME was used for milk production was 59%. The efficiency with which ME was used for body-weight gain was 53%. Lamb maintenance requirements were estimated to be 427 (.+-. 143) kJ ME/kg W in wk 1 and 2 of lactation and 287 (.+-. 44.2) kJ/kg from wk 7. Efficiency of utilization of energy for body-weight gain in each period was estimated at 71 and 80%, respectively.