Composition of weight gain in Nellore steers at different levels of feed intake

Thirty six Nellore steers, with an average initial age and weight of 20 months and 360 kg, were fed the same diet in three levels of dry matter intake: ad libitum or in two quantitative restriction levels 75g DM/kg BW0.75 or 60g DM/kg BW0.75 during 58 days (Phase 1) to evaluate the effects of feed restriction on performance and composition of weight gain in restriction and re-alimentation phases. All steers were fed ad libitum for 78 days (Phase 2). Body composition was estimated with the marker deuterium oxide, which allowed repeated measurements of the same animal and to study of its response to re-alimentation. Average daily gain in restriction phase reflected different weight gain rates provided by feed levels, being them 0.288 kg, 0.656 kg and 1.169 kg, respectively for 60g DM/ BW0.75, 75g DM/ BW0.75 and ad libitum. Feed efficiency raised according to level of feed intake in Phase 1 and no differences between treatments were observed in Phase 2. Dry matter digestibility did not differ between treatments in both Phase 1 and Phase 2, but was different between Phases for the same treatment with 78.8% in Phase 1 and 68.7% in Phase 2 for the treatment 60 g DM/BW0.75 and 77.8% in Phase 1 and 71.3% in Phase 2 for treatment 75 g DM/BW0.75. The empty weight gain, the daily deposition of water, ether extract, protein, ash and energy had an increase in their deposition according to the elevation of the level of feed intake in Phase 1. In Phase 2 there was no difference between the levels of diet intake for empty weight gain, chemical components deposition and retained energy in the gain. A short period of quantitative feed restriction imposed to Nellore steers could be used in beef cattle production system.