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For Economically Important Traits of Sheep¹

Western Sheep Breeding Laboratory

Abstract

A study was made of the amount of selection practiced and of the gains made from selection for certain traits of economic importance in a flock of range Rambouillet sheep to determine if this selection has been effective in producing genetic improvement in each of the various traits and in overall merit.

Fleece and body records were studied for 8,274 lambs, 1,215 yearling rams and 3,150 yearling ewes born from 1938 through 1948 in inbred Rambouillet lines. Selection differentials, or the difference between the average records of the parents and the average records of the entire population from which they were selected, were obtained for sires of lambs born from 1943 through 1948 and for dams of lambs born from 1946 through 1948.

Selection differentials were nearly all positive. Those for sires generally increased from 1943 to 1948 for staple length, type, face covering and weanling index. This appears to be due partly to increased accuracy of selection and partly to a decreasing generation length for sires.

¹ Abstract of paper presented at the meetings of the American Society of Animal Production, Chicago, Ill., November 25, 1949.