Effect of maize grain and herbage allowance on estimated metabolizable energy intake and animal performance in beef cattle finishing systems

This study investigated the effects of levels of supplementation with maize grain and herbage allowance (HA) on grass herbage and maize intake, animal performance and grazing behaviour in two replicated grazing experiments with Angus beef cattle in Argentina. In Experiment 1, the response to increasing HA (2.5, 5.0 and 7.5 kg DM herbage 100 kg -1 live weight (LW) d -1 with and without 0.5 kg DM maize grain 100 kg -1 LW d -1) was investigated. In Experiment 2, the responses to level of maize grain offered (0, 0.5 and 1.0 kg DM maize grain 100 kg -1 LW d -1) at an HA of 2.5 kg DM herbage 100 kg -1 LW d -1 and an HA of 5.0 kg 100 kg -1 LW d -1 without maize grain were assessed. In Experiment 2, soyabean meal was added to control the crude protein concentration in the diet. Two methods were used for intake estimates: pre- and post-feeding herbage mass difference, and the use of the n-alkane and 13C technique. The latter predicted most accurately the metabolizable energy requirements calculated from live weights and liveweight gain of beef cattle attained in each treatment in both experiments. Increasing HA significantly increased herbage intake and liveweight gain (P < 0.01), and general quadratic relationships between these variables could be fitted across experiments despite differences in animal and pasture characteristics. Increasing the amount of maize grain offered significantly reduced herbage intake and grazing time, but increased liveweight gain and digestibility of the diet. Substitution rate increased with increasing HA in Experiment 1 but was not affected by level of maize supplementation in Experiment 2. These relationships will aid the development of grazing management models for Argentinean conditions. © 2006 The Authors.