Energy values of corn, bird-resistant and non-bird-resistant sorghum grain in rations fed to steers

Three Aberdeen-Angus bullocks were used in a Latin square design to estimate metabolisable energy (ME) and digestibility of maize, bird-resistant (BR) and non-resistant (NBR) sorghums. The diets had 78% of the grains, 16.5% forage sorghum silage and 5% of a supplement consisting of soya bean oilmeal 76%, urea 7% and minerals, vitamins, antibiotic and trace elements. Cattle in the metabolism phase of the experiment were rotated to new rations every 19 days, allowing 14 days for adjustment and 5 days for collection. Production of methane and its energy content were measured. In the feedlot phase, 54 bullocks were fed to appetite or restricted to allow about half the daily gain with feeding to appetite. From each of the 6 groups 1 bullock was killed at the start. The remainder were given 36 mg diethylstilboestrol. The cattle were fed for 128 days. Tannins were estimated in the diets.Bullocks on the restricted amounts of maize, NBR and BR gained 62, 66 and 67% of gain with feeding to appetite. The maize, NBR and BR sorghum had 3.21, 2.63 and 2.49 Mcal ME/kg DM. Net energy for maintenance was 2.40, 1.98 and 1.78 Mcal/kg and for gain (NEg) was 1.49, 1.15 and 0.73 Mcal/kg DM when cattle were fed to appetite. Gross energy (GE), ME, NEm and NEg were used to predict gains, using the NRC (NAR 41, 1510) and ARC (NAR 36, 5513) systems and values were compared with actual gains. Predicted daily gains by the NRC system for bullocks fed to appetite agreed within 0.08 kg and by the ARC system were within 0.01, 0.23 and 0.12 kg of actual gains with maize, NBR and BR. When NRC NEm and NEg values for sorghum grain were used for BR, predicted daily gains were 0.45 kg greater than actual gain