Estrus in Range Lambs and Its Relationship to Lifetime Reproductive Performance

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Abstract
The occurrence of estrus in lambs the first winter as related to subsequent lamb production was studied in 2,364 Rambouillet, 1,956 Targhee and 1,350 Columbia ewes. These ewes made one to five lambing records. Twelve percent of the lambs exhibited heat their first winter. The differences among years within breeds were highly significant for each breed. However, the years having a high or low incidence of estrus do not correspond for the three breeds indicating a year-breed interaction. About 60% had one heat period, 25% two heat periods and only 2% had as many as five heat periods. The lambs which came into heat had lower inbreeding coefficients, less face covering, better condition scores, heavier weaning weights, were slightly older and had heavier yearling fall bodyweights than lambs that did not come into heat. The cumulative lamb production was without exception greater for ewes which showed estrus as lambs than for those which did not. The effect was greatest in the Rambouillet breed, being significant for all cumulative lamb production traits but one. Targhee ewes showed an important and significant positive association of estrus and production for the first 3 yr. of production but little association thereafter. The Columbias showed an apparent effect in favor of ewes showing estrus as lambs. However, this was significant only for the lifetime kilograms of lamb weaned per ewe for ewes completing five production records. Rambouillet, Targhee and Columbia ewes showing estrus as lambs accumulated an average of 20.4, 10.9 and 19.1 kg. of lamb more per ewe, respectively, over five production years than those which did not come into heat. There was no significant association of early estrus and lifetime wool production, although in two of the three breeds lifetime grease fleece weights were slightly lower for the groups showing estrus their first winter. Copyright © 1969. American Society of Animal Science. Copyright 1969 by American Society of Animal Science

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