INFLUENCE OF FEED ALLOWANCE DURING PREGNANCY ON REPRODUCTIVE PERFORMANCE OF EWES AND GROWTH OF SUCKLED AND ARTIFICIALLY REARED LAMBS

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Abstract
Eighty mature ewes (Rambouillet × Columbia type) were allocated on the basis of initial weight among four pregnancy treatments: (T1) fed a maintenance level throughout; (T2) fed the same total as T1 but distributed so as to increase exponentially from 15% below maintenance post-mating to 57% above maintenance by parturition; (T3) fed 80% of maintenance throughout; (T4) the same as T3 except ewes were resheared after mating. At lambing each treatment group was subdivided so that half the ewes reared their lambs, while those from the other half were reared, from within 16 h of birth, on milk replacer to 7 wk of age. Postpartum feed allowances for the ewes were ad libitum for the first 35 days, after which those not lactating were reduced to maintenance while those suckling lambs were given a recommended allowance for lactation. From 9 to 12 wk, all were fed a maintenance level. All ewes lost weight from conception to immediate postpartum but there were highly significant differences between treatments, with treatment 2 losing the least (4.5%) and treatment 4 losing the most (25%). Lamb birth weights were also significantly different, with treatment 2 heavier and treatments 3 and 4 lighter than treatment 1. Among suckled lambs, survival was 100% on treatments 1 and 2 but only 67 and 44%, respectively, on treatments 3 and 4. With artificial rearing, survival on treatments 1 to 4, respectively, was 45, 80, 56 and 30%. Birth weight did not influence survival among artificially reared lambs but suckled lamb survivors were approximately 50% heavier at birth than those which died. Suckled lambs were 33% heavier at 12 wk than artificially reared lambs, partly through faster early growth but mainly through a growth check in the latter following termination of milk replacer at 7 wk.

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