Records from an unselected flock of Morada Nova sheep collected over an 11-year period (1981 to 1991) were used to evaluate environmental sources of variation affecting growth traits. The effects of year of birth to yearling (A), sex of lamb (S), type of birth (T), and weigth of ewe at lambing (P) were important sources of variation to explain differences in weigth at birth (PN), weaning (PD), six- months (PM6) and 12 months (PM12) of age. Males were heavier than female lambs at all ages. Single lambs born and raised as singles (SS) weighed more at all ages than twins raised as singles (GS) or twins raised as twins (GG). Age of ewe at lambing (I) had a significant effect on PN, PD, and PM6. Results suggest that nutritional management should be improved to reduce the environmental effects such as year of birth, type of birth and weight of ewe lambing. Adjustment factors for sex of lamb, type of birth/rearing and age of ewe at lambing need to be estimated and considered in selection programs to improve growth performance of Morada Nova lambs.
hair sheep; growth traits; environmental factors
