Residual metabolizable feed consumption as a method of comparing feed efficiency in steers fed silage and silage-grain diets

Sixty crossbred steers averaging 237 +/- 18 kg were randomly allocated in a 2 x 3 factorial arrangement to one of six dietary treatments and were indi vidually fed over 105 days. Dietary treatments were 100% alfalfa (cv. Beave r) silage; 85% alfalfa silage, and 15% barley grain; 70% alfalfa silage and 30% barley grain; 100% fenugreek (Trigonella foenum graecum L.) silage; 85 % fenugreek silage and 15% barley grain; 70% fenugreek silage and 30% barle y grain; all on a dry matter (DM) basis. Individual animal DM intake, weigh t gain. and feed-to-gain ratios were measured or calculated. Residual metab olizable feed consumption (RMFC), calculated as the difference between meta bolizable energy (ME) intake and the predicted ME needed for maintenance an d gain, was compared to feed:gain ratios to determine their relative abilit y to differentiate between efficiency of utilization of the feeds. In spite of an 8% higher ME intake by steers fed alfalfa, there were no differences in DM intake, weight gain, and feed:gain ratios. However, the RMFC of stee rs fed fenugreek was negative compared to those fed alfalfa silage which wa s positive (P < 0.01), indicating that the efficiency of use of ME differed between steers fed fenugreek and alfalfa. We conclude the RMFC concept can be used to detect differences in efficiency of utilization of energy in fe eds. (C) 2001 Elsevier Science B.V. All rights reserved.