Abstract
A crossbreeding study was used to assess the growth performance of the Outaouais Arcott and Suffolk breeds, their two breed crosses and specific three-breed crosses sired by either Canadian Arcott or Hampshire rams. In a sheep flock maintained under a semi-confinement management system, Suffolk lambs, weighing 3.8 kg at birth, were not significantly heavier than Canadian Arcott- or Hampshire-sired crossbred lambs. Lambs of the Outaouais breed were 26% lighter (P < 0.05) than those of the Suffolk breed, and their two breed crosses had birth weights between the two parental purebreds. The relative ranks among the breeds and their crosses had not changed by 42 d of age with lamb weights ranging from 10.6 to 12.6 kg. By 120 d of age the Canadian Arcott- and Hampshire-sired lambs weighed approximately 28–29 kg and were not significantly different in weight from the Outaouais and Suffolk breeds and their two breed crosses. Additive and maternal genetic effects m the Suffolk breed were significantly greater than in the Outaouais breed for birth weight by 12.9 and 12.6% respectively. By 42 d, no difference was detected between breeds for direct genetic effect. However, the maternal effect favoured the Suffolk breed by 15.8% (P < 0.05). By 120 d, the direct genetic effect was significantly greater in the Outaouais breed by 9.8%, but maternal genetic effects continued to favour the Suffolk breed by 12.5% (P < 0.05). Heterosis effects were generally small (< 3.1%) and not significant for lamb weights. The terminal sire breeds showed no significant difference between Canadian- and Hampshire-sired lamb weights. Generally, results obtained for two analyses (least squares model and multi-trait animal model) of the same data set were consistent. However, the animal model would be preferable when estimating parameters and breeding values from an unbalanced data set with unequal subclass frequencies. Key words: Lambs, weight, genetic effects, heterosis, animal model
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