Sex effects on body composition can be viewed using the same concepts of mature weight, mature composition and maturing patterns for individual tissues.
Entire males vs females
Rams and bulls are generally 1.4 times the mature weight of females (i.e. 40% greater). As shown in Table 4.3, mature composition between sexes differs in that males have less fat, more muscle and more bone than females.
In contrast to between breed differences, entire males and females have differences in composition at maturity and there are differences in maturity patterns for the tissues relative to bodyweight (Figure 4.9).
The difference in mature composition and maturing pattern for the various tissues means that the relative composition of rams and ewes changes depending upon the live weight, or stage of maturity at which the comparison is made (Figure 4.10).
Entire males vs castrates
Castration of entire males is commonly undertaken in Australia, Britain and North and South America. This contrasts to much of Europe where entire males are often used for meat production. Historical reasons for castration include the increased fattening ability of the castrate. In addition it was often used as a management aid and allowed for controlled breeding.
Table 4.4 shows that after adjustment for the increased weight of the head and horns and testes in the rams, rams and wethers had a similar mature weight, although there were large differences in mature composition. At maturity rams had less fat and more bone and muscle than wethers. Also there was no difference in maturing patterns for muscle, bone and fat. Because there was no difference in mature size, comparisons were similar whether they were made at the same stage of maturity, or body weight. Rams were leaner than castrates at all stages, with the magnitude of the difference increasing with increased live weight (or stage of maturity).