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Genetic and Environmental Factors Affecting Type and Condition in Navajo and Navajo Crossbred Weanling Lambs¹

U. S. Departments of Agriculture and the Interior

Abstract

The effects of breeding groups, sex, age of dam, year of birth, type of birth and rearing and age of lambs at weaning on body type and condition scores were studied on 1673 lambs weaned in 1948 and 1949. The average age at weaning was about 120 days.

The advantage of body type scores for single lambs over twin lambs was 0.56. Lambs from 4 to 7 year old dams were superior in type scores to lambs from 2 year old dams, 3 year old dams and dams 8 years and older by 0.24, 0.13 and 0.35, respectively. Differences in body type scores for years and sex were not significantly different.

Ewe lambs were scored better for condition than ram lambs, and single lambs had superior scores to twin lambs or twins raised as singles. Ewes 4 to 7 years of age produced lambs having more condition than either of the other groups studied. Merit in both type and condition scores improved with age at weaning as indicated by regression coefficients.

The factors studied accounted for about 50 percent of the total variance in body type and 35 percent in condition, "or degree of fatness." If the more important differences due to environmental factors are considered in culling lambs, more accurate selection can be made, resulting in more rapid improvement from selection.

¹ The data for this study were collected at the Southwestern Range and Sheep Breeding Laboratory, Fort Wingate, New Mexico, under authority of the Bankhead-Jones Act, by the Bureau of Animal Industry, U.S.D.A. in cooperation with the Bureau of Indian Affairs, U. S. Department of Interior, and the New Mexico Agricultural Experiment Station.

² James O. Grandstaff is an employee of the U. S. Department of the Interior who is also collaborating with the U.S.D.A.