THE EFFECTS OF BREED AND CERTAIN ENVIRONMENTAL FACTORS ON BIRTH AND WEANING TRAITS OF RANGE SHEEP

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Abstract
Data collected during a 4-year period from 830 lambs of the Rambouillet, Romnelet, Canadian Corriedale, and Romeldale breeds were used to estimate the effects of breed and certain environmental factors on birth weight, weaning weight, face cover, conformation, and condition score.Rambouillets ranked first in birth weight and weaning weight, had most wool on the face, and scored poorest in conformation. Romnelets ranked second in weaning weight, had least wool-covering on the face, and were judged superior to the other breeds in conformation and condition. Canadian Corriedales had heavier lambs at birth than Romeldales; however, the Romeldales were more open in the face and scored better in conformation and condition.Year was one of the major sources of variation in weaning weight and conformation. Breed and sex contributed largely to variation in face-cover score. Effects of birth and rearing type (single, twin, or twin raised singly) on birth weight, weaning weight, conformation, and condition were significant (P < 0.01) and accounted for a large part of the total variation in birth weight, weaning weight, and condition score. Age of dam had significant effects on birth weight (P < 0.01) and weaning weight (P < 0.05) but was relatively unimportant as a source of variation. Birth weight increased with advancing date of birth, and weaning weight, body conformation score, and condition score improved with age at weaning.The percentage of total variability (sum of squares) due to the fitting of constants for the factors studied was: birth weight, 47; weaning weight, 47; face cover, 19; conformation, 37; and condition, 24.