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Selecting for Weight and Rate of Gain in Noninbred Lambs

U.S. Department of Agriculture,¹ Dubois, Idaho 83423

Abstract

Eight hundred and seven crossbred, 502 Rambouillet, 703 Targhee and 516 Columbia ewe lambs were weighed at birth in April, weaning in August and at approximately monthly intervals thereafter through shearing in May. Postweaning gains were calculated for feeding periods from October through December on mature, dry, fall range forage and for January through April on high quality alfalfa hay pellets. Gains were almost negligible in the October through December period but averaged about 0.09 kg per day during the later period. Distinct trends were evident in magnitudes of heritabilities and correlations involving body weights. Heritabilities tended to increase with time from weaning. Both genetic and phenotypic correlations tended to decrease with time between observations on correlated variables. Heritabilities of gain under a good nutritive environment were typically at least double those under the less favorable environment during October through December. Genetic variation in gains was distinctly higher under the better environment. Indices, incorporating various practical selection criteria, were calculated which would lead to the maximum rate of progress in improving weaning and yearling weights and postweaning gains. The data showed no evidence of serious genetic antagonisms among weights and gains.

¹ From the U.S. Sheep Experiment Station, Sheep and Fur Animal Research Branch, Animal Science Research Division, A.R.S., Dubois, Idaho in cooperation with the University of Idaho, Moscow, Idaho.