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Observed growth of cattle during the postweaning period reflects the genetic potential for growth as modified by the environment. Various breeds or breed crosses of cattle have been characterized for postweaning liveweight gain under ad libitum feeding conditions. Previous results showed calves by Simmental males had greater rates of postweaning gain than those sired by Hereford males. Simmental-sired steers were more efficient during a weight-constant interval, of equal efficiency during a time-constant interval and less efficient to a fat-constant end point than Hereford-sired steers. Differences among breeds in efficiencies of energy utilization for maintenance and gain have been reported. Similarly, differences among sexes (or sex condition) in growth rate and carcass characteristics have been documented. Efficiencies of energy utilization for maintenance and gain of castrate males have been reported to be similar to those of females. However, other results have suggested that intact males had higher maintenance requirements than castrate males.
This paper describes the accretion of total empty body weight, water, fat, protein, and energy by Hereford and Simmental males and females in response to differing rates of metabolic energy (ME) intake. Estimates of breed and sex effects on ME requirements for maintenance and efficiencies of utilization of ME for maintenance and gain are reported.