Abstract

One hundred and four ewe lambs born in 1980 to either ewes that had been immunised against steroid hormones or untreated control ewes were retained for study of their subsequent growth and reproductive performance. There was no significant effect of dam immunisation on growth rate or reproductive performance as hoggets, 2-tooths or 4- tooths. Dam breed (Coopworth or Romney) was the major factor influencing reproductive performance. Mean lamb birth weight was 3.7 kg, weaning weight 18.7 kg, hogget mating weight 40.0 kg, 2-tooth mating weight 54.4 kg and 4-tooth mating weight 60.4 kg. At 9 months of age 83% had exhibited oestrus and their ovulation rate was 1.08, as 2- tooths, 96% mated in the first cycle with an ovulation rate of 1.68 and a conception rate of 80% to first service. They had a lamb drop of 1.49 lambs born/ewe joined and weaned 1.35 lambs/ewe joined. The respective figures as 4-tooths were 98%, 1.8, 85%, 1.43 and 1.34. These data indicate that immunisation of ewes against steroid hormones has no adverse effects on the performance of their progeny.

KP, McNatty, D Heath, S Lun, KM Henderson, N Hudson, M Gibb, J McDiarmid, GW Montgomery, and DC Thurley

Proceedings of the New Zealand Society of Animal Production, Volume 44, , 19-20, 1984