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Crossbreeding in Sheep with Evaluation of Combining Ability, Heterosis and Recombination Effects for Lamb Growth^1,2,

University of Minnesota, St. Paul 55108

Abstract

The relative merit of Columbia, Suffolk and Targhee breeds were examined in straightbred and two- and three-breed combinations. Lamb performance traits studied were birth weight, preweaning average daily gain, weaning weight at 70 d of age, postweaning average daily gain and age at market weight (50 to 55 kg). Pure-bred Suffolk lambs excelled other straightbreds in all traits and reached market weight 18 and 25 d earlier than Targhee and Columbia lambs, respectively. Differences in general combining ability were significant only for postweaning average daily gain and age at market weight. Three-way cross lambs were superior in performance followed by two-way crosses. Differences among three-breed crosses were significant for all traits except age at market weight. This suggests that the manner in which breeds are combined in a three-way cross is important and should be considered in the design of breeding programs. Three-breed cross lambs born to Suffolk dams were superior in preweaning average daily gain, weaning weight and age at market. Lambs from Targhee-Suffolk sires and Columbia dams excelled in postweaning average daily gain. Based on both straight-bred and crossbred lamb performance, ranking of the three breeds of dams in descending order of merit was Suffolk, Targhee and Columbia. Significant individual heterosis (h^I) was observed only for birth weight (4.6%). Mean estimates of maternal heterosis (h^M) were small and varied rather widely, from .7% for birth weight to –4.6% for postweaning average daily gain. Recombination effects were small but favorable; the mean values ranged from 1.4% for birth weight to 5.7% for preweaning average daily gain.

¹ Paper No. 11,564. Scientific Journal Ser. of the Minnesota Agr. Exp. Sta. in cooperation with ARS, USDA as a contribution to the Regional Project NC-111.

² This study was supported by a grant from the Louis W. and Maud Hill Family Foundation.

³ Present address: Dept. of Livestock Sci., Faculty of Agriculture, Univ. of the West Indies, St. Augustine, Trinidad, West Indies.