Groups of Bos indicus (Boran) and Bos taurus (Hereford) × Bos indicus steers were kept at constant live weights of 185, 275 and 450 kg for periods of up to 24 weeks. Maintenance of these live weights was achieved by control of the daily ration of a diet having an energy concentration of 10·477 MJ metabolizable energy (ME)/kg d.m. AS time progressed it was noted that less of the diet had to be fed daily to maintain constant live weight. Body composition of steers slaughtered at 0, 12 and 24 weeks showed that the live weights had been maintained by the compensating effect of empty body weight gains and digestive tract content-weight losses.
No significant differences were found between slaughter groups for the energy values of the boneless carcass meat nor the internal deposits of empty digestive tract, omental and mesenteric fat. It was therefore concluded that there had been a progressive increase in the efficiency of energy utilization for the production of edible meat.
The percentage reduction of daily food intake from 3 to 24 weeks necessary to maintain the prescribed live weights ranged from 51·8% for the 185 kg Borans to 17·9% for the 450 kg ¾ Boran × Hereford cross-breds.
Comparison with published estimates for maintenance of live weight showed that after 24 weeks at constant live weight the 185 and 275 kg Borans and the 450 kg ¾ Borans needed 50·5, 37·9 and 34·2% less and the 275 kg Hereford × Boran cross-breds and 450 kg ¾ Herefords 40·8 and 37·9% respectively less food than estimated.
Correction for age effects on the fasting metabolic rates of the 185 and 275 kg weight groups reduced the difference between theoretical and actual maintenance requirements from 50·5, 37·9 and 40·8% to 37·3, 29·3 and 33·8% respectively.
Attention is drawn to the need to differentiate between the live-weight maintenance needs of fast and slow growing animals which may be of similar live weights but differing ages.
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