Breed, heterosis and environmental influences on growth and puberty in ewe lambs.

A study involving 825 spring ewe lambs was conducted to evaluate effects of breed, heterosis, type of birth and rearing, age of dam and preweaning and postweaning growth rate on occurrence of puberty before November 10. Within a breed or breed-cross, preweaning competition among twin and triplet lambs reduced lamb weights by 4 or 5 kg at 70 (weaning), 160 and 230 days of age and by about 3 kg at puberty but delayed puberty only about 1 week. Age of dam strongly influenced preweaning growth of ewe lambs, but did not significantly affect age or weight at puberty. Higher preweaning and 70to 160-day postweaning rate of growth definitely increased percentage of lambs reaching puberty by November 10 and hence reduced mean age at puberty. Percentage reaching puberty by November 10 was far higher for Finn-sired (72 -+ 4%) than for Rambouillet-sired (38 -+ 6%) crosses or purebreds (34 -+ 5%) of the Suffolk, Hampshire, Rambouillet, Dorset, Targhee, Corriedale or Coarse Wool breeds. Finn crosses reached puberty earlier (219 days) and at lighter weight (40 kg) than Rambouillet crosses (238 days and 44 kg) or purebreds (245 days and 45 kg). Domestic breed of dam means ranged from 27 to 57% in estrus before November 10, from 225 to 240 days in expected age at puberty and from 39 to 50 kg in expected weight at puberty. (