Effect of Energy Intake Level and Influence of Breed and Sex on the Physical Composition of the Carcass of Cattle

Abstract

The physical composition (muscle, fat, bone and tendon) of the right side of the carcass was determined in 141 animals slaughtered at weights ranging from 121 to 706 kilograms. Bulls, steers and heifers of the Holstein and Angus breeds were fed at two energy levels: ad libitum and 65 to 70% ad libitum. The equation Y = aX^b was used to study the effect of energy intake and the influence of breed and sex on the growth rates of muscle, fat and bone plus tendon (BTN) relative to the carcass side and to muscle plus BTN. In Angus cattle, irrespective of the level of energy intake, sex did not influence the growth rate of muscle, fat and BTN relative to the carcass side or muscle plus BTN. However, in Holsteins, the expression of a sex influence on the growth rates depended on die level of energy intake considered: a sex influence was detected (P<.05) only in the high energy intake animals. No genetic influence on the growth rate of fat relative to carcass side or muscle plus BTN were observed; with one exception: for the low intake group, the growth rate of fat relative to muscle plus BTN was larger (P<.05) in the Holstein steers and heifers than in Angus cattle of the same sex. Furthermore, breed generally did not influence (P>.05) the growth rates of muscle and BTN. The level of energy intake altered (P<.05) the growth rates of the various carcass tissues. However, the magnitude of the response depended on the breed and sex considered. In all three sexes of Angus, the growth rate of fat relative to the carcass side or muscle plus BTN was larger (P<.05) in the high energy group than in the low energy group, whereas in all three sexes of Holsteins, the growth rate of fat was not altered (P>.05) by the level of energy intake.