Two hundred and thirty 5-year-old Romney ewes were synchronised with progestagen intravaginal sponges and injected with dexamethasone 142 or 143 days after the median mating day of the first and second cycles of oestrus. Seventy-one % of the lambs were born 30 to 50 h after injection. The ewes were offered 2 pasture allowances for the last 6 weeks of pregnancy (approximately 6 and 1 kg DM/ewe/d). Lambs were vigour scored (1 to 10) and probed for rectal temperature and ewe lambs were cross-fostered as soon as possible after birth in order to obtain a 2 4 factorial design incorporating birth type (single and twin) rearing types (single and twin), pre-natal nutrition of dam (high and low allowance), and pre-natal nutrition of foster dam (high and low allowance). Lambs born from high allowance ewes had higher rectal temperatures at birth than those born from low allowance ewes, and female lambs had higher rectal temperatures than male lambs. Single-born lambs scored higher on vigour than those born as multiples. Increasing vigour was associated with increasing birth weight for all lambs, but increasing temperature was associated with increasing birth weight only for male lambs. There were no effects of pre-natal nutrition on lamb growth either through the dam or foster dam. The effect of birth type on lamb live weight was significant to 9 weeks of age whereas the effect of rearing type was significant to 33 weeks. There were no significant birth type x rearing type interactions at any age.
Proceedings of the New Zealand Society of Animal Production, Volume 46, , 241-244, 1986
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