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Thirty-six Nellore steers at 20 months of age on average and initial body weight of 360 kg were fed ad libitum for 78 days and two levels of feed restriction for 58 days and posterior ad libitum feeding for 78 days were used to estimate body composition using the methods of indirect deuterium oxide or the 9th-10th-11th ribs cut. The body water content was calculated with equations established for Nellore steers. The chemical body composition was different for the ether extract content. The animals subjected to feed restriction presented higher body fat content when estimated by deuterium than by the rib cut. The deuterium oxide or 9th-10th-11th ribs cut methods used for body composition determination were effective to estimate body contents for animals fed ad libitum, however, not for animals on feed restriction. Comparatively, the indirect method of deuterium oxide was better than the 9th-10th-11th ribs cut method to estimate body composition in Nellore steers submitted to feed restriction; however, both methods were similar in animals fed ad libitum.

The aim of this study was determine the energy and protein requirements for maintenance and gain of Nellore steers. Thirty six Nellore steers with a average weight and age of 359±13 kg and 20 months at the beginning of the trial were individually fed for 56. The steers were fed the same diet (76.43% TDN and 13.62% CP) in three levels of dry matter (DM) intake, ad libitum, 75 g DM/kg BW0.75 and 60 g DM/kg BW0.75. The initial and final body composition was estimated with the marker deuterium oxide that allowed repeated water estimate in the same animal. Deuterium in blood samples was analyzed by mass spectrometry. The effects of intake levels, comparison of intercept and slope among feeding level, and equations were evaluated by the analysis of variance, adopting P

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.

Blood parameters of 18 Nellore steers submitted to high concentrate diet in two sequential feeding regimes (Phase 1: restriction and Phase 2: ad libitum feed) were evaluated. In the first phase, steers were fed during 56 days in three intake levels of dry matter (ad libitum, 75 g dry matter (DM)/kg metabolic body weight (BW0.75) or 60 g DM/kg BW0.75. In the second phase, from the 57th day of confinement, animals fed 60 g DM/kg BW0.75 and 75 g DM/kg BW0.75 received feed ad libitum until the 136th day. In the 8th, 27th, 55th (first phase), 71st, 84th, 112th and 132nd (second phase day of experimental period, blood samples were collected and insulin-like growth factor I (IGF-I), triiodothyronine (T3), thyroxine (T4), glucose, plasma ureic nitrogen (PUN) and total protein (TP) were determined. In the first phase IGF-I, T4, glucose and total protein concentration was not different among treatments (P>0.05) and there was no interaction between treatment and time (P>0.05). There was an interaction among treatments and time on T3 and plasma ureic nitrogen (P0.05). For plasma ureic nitrogen concentration there was an interaction among treatments and time (P=0.02). Lower levels of diet intake can be used to improve animal performance in feedlot.

The aim of this study was determine the energy and protein requirements for maintenance and gain of Nellore steers. Thirty six Nellore steers with a average weight and age of 359±13 kg and 20 months at the beginning of the trial were individually fed for 56. The steers were fed the same diet (76.43% TDN and 13.62% CP) in three levels of dry matter (DM) intake, ad libitum, 75 g DM/kg BW0.75 and 60 g DM/kg BW0.75. The initial and final body composition was estimated with the marker deuterium oxide that allowed repeated water estimate in the same animal. Deuterium in blood samples was analyzed by mass spectrometry. The effects of intake levels, comparison of intercept and slope among feeding level, and equations were evaluated by the analysis of variance, adopting P

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.