The Influence Of Sexual Dimorphism On The Feed Efficiency Of Lamb Production

A review of the literature reporting mature weights of ewes and rams from the same flock revealed that the range of sexual dimorphism (ram/ewe weight) varies between 1.0 (no difference between rams and ewes) and 1.5 (rams 50% heavier than ewes). Furthermore, Gudex et al. (2009) demonstrated that it is possible to alter the magnitude of sexual dimorphism in sheep via genetic selection. Studies in other species have shown that sexual dimorphism can alter the feed efficiency of meat production systems. Jaap (1969) found that the use of a known recessive, sex linked dwarfism gene in chickens reduced the size of female parents by 30% and their feed requirements by 33%. Roux et al. (1992) found that bulls 60% larger than cows could increase feed efficiency by up to 16% depending on the percentage of heifers required as replacements. No such studies have been conducted in sheep. This study evaluates the effect that genetic selection on sexual dimorphism could have on the feed efficiency of lamb production by comparing the nutritional requirements of each sex in the presence of sexual dimorphism varying between 1.0 and 1.5.