Phenotypic relationships among early life traits and lifetime ewe production efficiency

In least-squares analyses of variance, 10 ewe lamb traits were used, singly and in various combinations, to predict lifetime production efficiency. Ewes belonged to eight crossbred groups and were raised on two management systems for either 4 or 5 yr of production. Lifetime production efficiency components were total feed and ewe ownership cost, gross income and net revenue. A ewe lamb's type of birth, actual and adjusted weaning weight (WWt and AWWt), postweaning weight (PWWt) and first year gross income (FGROS) were significantly phenotypically related to one or more components of lifetime production efficiency. While triplets were better than either of the other two birth types, single-born ewes were better than twin-born ewes for lifetime production efficiency. Any of the three ewe lamb weights (AWWt, WWt or PWWt) appeared to be an accurate estimator of lifetime production efficiency. The effect of first year productivity was largely a part-whole relationship with lifetime production because the regression coefficients of subsequent lifetime production efficiency (not including first year production) on first year productivity were near zero. Postweaning average daily gain, ewe age at first estrus and date of first lambing (at approximately 12 mo of age) did not have significant relationships with lifetime production efficiency. When type of birth, date of birth, weaning weight and first year gross income were analyzed simultaneously, weaning weight and FGROS had the greatest effect on lifetime production efficiency. When AWWt and type of birth were considered simultaneously, both had significant relationships with lifetime production efficiency.