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

Abstract

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 restriction levels 75g DM/kg BW 0.75 or 60g DM/kg BW 0.75 during 58 days (Phase 1) to evaluate the effects of feed restriction on weight gain, feed efficiency, diet digestibility, 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 studying its response to re-alimentation. Average daily gain in the restriction phase reflected different weight gain rates provided by feed levels of 0.288 kg, 0.656 kg, and 1.169 kg, respectively for 60g DM/ BW 0.75 , 75g DM/ BW 0.75 and ad libitum. Feed efficiency increased according to feed intake level 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; however, it differed between phases for the same treatment with 78.8% in Phase 1, and with 68.7% in Phase 2 for the treatment with 60 g DM/BW 0.75 , and 77.8% in Phase 1 and 71.3% in Phase 2 for the treatment with 75 g DM/BW 0.75 . The deposition of empty weight gain, daily water deposition, ether extract, protein, ash, and energy increased with a higher feed intake level in Phase 1. In Phase 2, no difference occurred between the diet intake levels for empty weight gain, chemical components deposition, and retained energy in the gain. Diet digestibility decreased in Nellore steers fed ad libitum after the period of feed restriction, regardless of the previous restriction level to which the animals were submitted.