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Byproduct as whole cottonseed (WCS) and soybean hulls are quite used in finishing diets to feedlot lambs and WCS is a potential source to be included in lambs diet when prices are advantageous. The most part of the studies with WCS is used as a replacement of cereals as corn. Thus, this study was conducted to evaluate the effect of replacing a fibrous byproduct (soybean hulls) with increasing levels of WCS (0, 10 and 20%) on the performance, carcass traits and meat quality of feedlot lambs. Thirty crossbred lambs (15 males and 15 females, 20±1.6 kg) were fed 1 of 3 high concentration diets: CTL (without WCS), WCS10 (with 10% WCS), and WCS20 (with 20% WCS) in a block design (sex) for 56 days. Feeding 10 or 20% WCS significantly (P=0.013) improved the feed conversion without affecting the final weight gain, average daily gain or dry matter intake in kg/d. However, the DMI (in %) of live weight was affected by treatments (P<0.0001): lambs fed the CTL and the WCS10 diet consumed more DMI than the lambs from WCS20 diet (4.19, 4.03 and 3.6%, respectively). The hot carcass weight, dressing percentage, longissimus muscle area and fat thickness were not affected by the WCS levels. The shear force and meat colour were similar among treatments. These results suggested that fattening lambs may benefit from an increase in feed efficiency from 10% WCS up to 20% without negatively impacting carcass and meat quality.

Thirty-six Nellore steers at 20 months of age on average and initial body weight of 360 kg, 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 9 th -10 th -11 th 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 9 th -10 th -11 th 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 9 th -10 th -11 th ribs cut method to estimate body composition in Nellore steers submitted to feed restriction; however, both methods were similar in animals fed ad libitum.

Blood parameters of 18 Nellore steers submitted to high concentrate diet in two sequential feeding regimes (phase 1: restriction and phase 2: ad libitum feeding) were evaluated. In the first phase, steers were fed for 56 days three intake levels of dry matter (ad libitum, 75 g dry matter (DM)/kg metabolic body weight (BW 0.75) or 60 g DM/kg BW 0.75. In the second phase, from the 57 th day on feed, animals fed 60 g DM/kg BW 0.75 and 75 g DM/kg BW 0.75 were fed ad libitum until the 136 th day. In the 8 th , 27 th , 55 th (first phase), 71 st , 84 th , 112 th and 132 nd (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 (P<0.01). In the second phase IGF-I, T3, T4, glucose and total protein concentration was not different among treatments and there was no interaction between treatment and time (P>0.05). 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.

Dietary protein adjustments can reduce environmental impact and economic losses in production systems. However, we lack information regarding nitrogen (N) metabolism and protein requirements for maintenance of crossbred animals such as Red Norte breed, precluding a precise dietary management. The objective was to evaluate the effect of increasing dietary CP levels (9%, 11%, 13%, 15% and 17%) on intake, digestibility and N balance, as well as to estimate the metabolizable protein requirements for maintenance (MPm) of growing Red Norte bulls. Thirty five animals averaging 280 ± 4.0 kg BW were fed during 45 days in a 60 : 40 forage : concentrate ratio diet in which the last 5 days were used for the digestibility trial. Intakes of CP and non-fibrous carbohydrates (NFCs) and feed efficiency linearly increased (P < 0.05) as CP levels increased, while DM, NDF, nitrogen efficiency use and ether extract were not influenced by CP levels (P > 0.05). Digestibilities of DM, organic matter, ether extract, NFC and CP as well as metabolizable energy intake linearly increased (P < 0.05), and true digestibility of CP was not affected (P > 0.05) by treatments. Urinary N and retained N linearly increased (P < 0.05) with the increase in dietary N. The MPm were estimated as 4.46 g/BW0.75 and the efficiency of use of MPm was 0.673. In conclusion, obtained MPm requirements of growing Red Norte bulls are greater than the values reported in literature for Zebu cattle and dietary CP levels of 15% and 17% exhibited great responses for growing Red Norte cattle. However, a cost-benefit evaluation should be done before its use.

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.