Effects of Some Environmental Factors on Weanling Traits of Range Rambouillet Lambs

Abstract

The effects of sex, age of dam, year, breeding group, type of birth, age at weaning and percent inbreeding were studied on 2183 range Rambouillet lambs born in 1941 and 1942. The average age at weaning was 123.8 ± 11.1 days. Differences in weaning weight between ram lambs and ewe lambs, single lambs and twin lambs, and lambs from mature ewes and those from 2-year-old ewes were 8.3, 9.2, and 6.1 pounds, respectively. Ewe lambs, single lambs, and lambs from mature ewes had higher body type and condition scores than the contrasting groups. Ram lambs had more neck folds and more wool on their faces than ewe lambs. Weaning weight, staple length, and body type and condition scores improved with age at weaning and became poorer with increased inbreeding, as shown by regression coefficients. The factors studied had the greatest influence on weaning weight and the least on face covering, accounting for 49.5 and 5.6 percent, respectively, of the variance in these traits. It is suggested that the more important differences be considered in culling lambs, thereby increasing the improvement expected from selection. This can be accomplished by sorting the lambs into groups according to sex, type of birth, age of dam, etc., or by adjusting weanling records. Progeny test comparisons, particularly with small numbers of offspring, can be made more accurately after adjusting for the important factors.