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Effects of Some Genetic and Environmental Factors on Yearling Traits of Navajo and Navajo Crossbred Ewes¹

U. S. Departments of Agriculture and the Interior

Abstract

The effects of differences between breeding groups, age of dam, type of birth and rearing, years, and age of the ewe were studied on 917 yearling ewes. The records were taken during the years 1948, 1949 and 1950 at the Southwestern Range and Sheep Breeding Laboratory, Fort Wingate, New Mexico. The traits included were staple length, grease and clean fleece weights, body weight, type and condition.

The genetic and environmental factors studied accounted for from 33 to 48 percent of the total variation in the six traits. Differences between breeding groups accounted for from 19 to 24 percent of the variation in all of the traits except body weight. In this trait breeding group difference accounted for only 9.4 percent. Although many of the environmental factors had measurable and statistically significant effects, the differences were too small to be practically important.

The estimates of the amount each factor raises or lowers the trait from the flock mean are shown. Ewes born of mature dams had longer staple, produced more grease wool, had heavier body weight and better type and condition scores than ewes born of 2 year old dams. Single ewes were superior to twin ewes in all traits studied. The age of the ewe had an important effect on all traits except type and condition.

¹ The data 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. Department of Agriculture, in cooperation with the Bureau of Indian Affairs, U. S. Department of Interior, and the New Mexico Agricultural Experiment Station.

² Present address, 631 East Ash, Salina, Kansas.

³ Present position, Administrator, Office of Experiment Stations, Agricultural Research Administration, U. S. Department of Agriculture, Washington, D. C.