Effect of General Combining Ability and Maternal Ability of Oxford, Suffolk and North Country Cheviot Breeds of Sheep on Growth Performance of Lambs

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Abstract
A crossbreeding experiment was undertaken with the Oxford, Suffolk and North Country Cheviot breeds of sheep. Four different mating systems were involved. Purebred progeny were available only in the Oxford and Suffolk breeds. Two-breed cross, backcross and 3-breed cross progeny were produced from the three breeds. Birthweight, 28-day weight, weaning weight adjusted to 120 days of age and average daily gain from birth to weaning were the traits studied. Analyses were conducted on the data from 1,449 lambs born and 1,169 lambs weaned between 1956 and 1964. Appropriate models were fitted to the data to obtain estimates of the effects due to year, sex, type of birth and rearing, age of dam, mating system, general combining ability and maternal ability of the breeds. The estimates for the additive genetic effects showed that the Suffolks were significantly superior to the Oxfords and Cheviots for bodyweight at 120 days of age. A statistically significant interaction between mating system and maternal ability of the breeds was obtained for all variables except birthweight. Separate analyses of each mating system indicated that the Suffolk breed was the most outstanding in terms of mothering ability except in the backcross mating system. The estimates for the type of dam effect (purebred vs. crossbred) showed that the crossbred ewe was superior to the purebred ewe, especially in the backcross mating system. Results from this study clearly indicate that considerable improvement of bodyweight and gain in weight is obtained by crossing breeds in sheep to produce 2-breed crosses and 3-bred crosses. Crosses should be made among the best breeds, since most of the differences between the breeding groups within a mating system could be explained on the basis of the additive genetic and maternal effects of the breeds. Using crossbred ewes provided an additional advantage in the growth performance of lambs.

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