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Environmental Factors Affecting Body Size and Conformation in Rambouillet Yearling Ewes¹

University of California²

Abstract

Body measurement data obtained from the University of California purebred Rambouillet flock were studied to learn the importance of known environmental sources of variation, and to find whether a worthwhile gain in accuracy in the use of measurements would be made by adjusting for these effects.

The data include the following measurements on 135 females born from 1936 to 1948, averaging 475 days in age; withers height, depth and width of chest, loin width, heart girth, round measurement and body weight.

It was found that difference in age was an important source of variation in all measurements studied except withers height, in which full growth had apparently been attained. Twins were found to be smaller than singles in all measurements except heart girth and round measurement, while twins from 2-year-old dams were smaller in body weight, heart girth and round than twins from older dams. Damage did not affect other measurements. Combined effects of sires and years were found very important, but these could not be estimated separately. It is concluded that a considerable gain in accuracy for selection purposes can be made by standardizing body measurements with regard to the environmental effects estimated.

¹ This work was supported by the Kellogg Fund for application of genetics to farm mammals.

² Agricultural Experiment Station, Davis.