Eleven single-rearing and 14 twin-rearing Greyface (Border-Leicester × Scottish Blackface) ewes which had previously been individually fed indoors on three nutritional treatments (treatment 1, adequately nourished; treatment 2, moderately undernourished; treatment 3, severely undernourished) during the final 6 weeks of pregnancy, were subsequently grazed with eight non-lactating Greyface ewes on a ryegrass–white clover pasture for the first 14 weeks of lactation.
Herbage organic matter (OM) intakes and milk yields of ewes were measured weekly and the herbage OM intakes of lambs from week 7 of lactation.
Mean daily OM intakes were 36·6 (± 1·09), 38·9 (± 0·99) and 26·4 (± 0·93) g OM/kg body-weight for single- and twin-rearing, and non-lactating ewes respectively. Prepartum nutrition had no effect on intake. Maximum intakes were achieved in week 5 for twin-rearing ewes (53 g OM/kg) and week 4 for single and non-lactating ewes (54 and 38 g OM/kg respectively).
Mean daily weight gains over the period for single-, twin-rearing and non-lactating ewes were 89 (±22·2), 73 (±16·1) and 182 (±22·5)g respectively. There were no differences due to prepartum treatment.
There were significant differences (P < 0·05) in milk production between singleand twin-rearing ewes in the first 5 weeks of lactation. Twin-rearing ewes of prepartum treatment 1 produced consistently more milk in weeks 2, 3 and 4 of lactation, whereas 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 week 7; their growth rates up to week 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/kg body weight/day; the efficiency with which ME was used for milk production to be 59%; and the efficiency with which ME was used for body-weight gain, 53%.
Lamb maintenance requirements were estimated to be 427 (± 143) kJ ME/kg W in weeks 1 and 2 of lactation and 287 (± 44·2) kJ/kg from week 7. Efficiency of utilization of energy for body-weight gain in each period was estimated to be 71 and 80% respectively.