Determining effects of monensin on energy value of corn silage diets for beef cattle by linear or semi-log methods.

An energy balance experiment was conducted to examine the effects of monensin on energy partitioning of cattle fed corn silage diets. One hundred and thirty Hereford steer feeder calves (average initial weight 247 kg) were used. Cattle were fed ad libitum for 211 days or limit-fed for 253 days. Carcass specific gravity was measured on all cattle for calculation of energy and tissue retention conclusions on energy utilization were based on linear regressions of energy retention on metabolizable energy and dry matter intake above maintenance, with comparisons to semilog calculations evaluated. Rates of live weight gain for ad libitum-fed cattle were similar with and without monensin (920 vs 923 g/day), while dry matter consumption was significantly reduced (5.91%) with monensin. Feed conversion was improved (5.84%) with monensin. Terminal body composition an total energy retained were not significantly altered by monensin. Limiting energy intake reduced daily rates of fat deposition more (-47.3%) than it reduced protein (-25.1%). Limit-fed steers had 10% less fat than ad libitum fed steers at equal empty body weights. Monensin tended to increase rates of protein and decrease rates of fat deposition in limit-fed cattle, and it induced a change (P < .08) in composition of growth. Monensin increased the apparent efficiency of energy use for maintenance by 5.7% but did not alter the efficiency of energy use for growth. Dry matter needed for maintenance was reduced by 5.4% with monensin. These data indicate that monensin may decrease maintenance requirements and (or) increase efficiency of diet energy use for maintenance.