Foram avaliados os efeitos da suplementação com diferentes relações proteína: carboidrato sobre a composição corporal, características de carcaça e eficiência de deposição de proteína e energia em tourinhos. Utilizou-se 24 bezerros Nelore (132,5 ± 5,5 kg e 90-150 dias de idade) em pastagem por um período experimental de 430 dias. Os tratamentos foram: Controle = mistura mineral ; HPHC = suplemento com alta proteína e alto carboidrato; HPLC = suplemento com alta proteína e baixo carboidrato; LPHC = suplemento com baixa proteína e alto carboidrato; LPLC = suplemento com baixa proteína e baixo carboidrato. foram abatidos quatro animais no início do experimento e 20 animais no final do experimento para avaliar a composição da carcaça. Os tourinhos controle apresentaram o menor (p < 0,05) consumo de EM (9,8 Mcal dia-1) não havendo diferenças (p > 0,05) entre os tourinhos suplementados (13 Mcal dia-1). Embora os tourinhos não suplementados tivessem menor (p <0,05) proteína retida, energia retida (ER), ganho de peso e rendimento de carcaça que os animais suplementados, não foram observado diferenças (p > 0,05) entre os touros suplementados. Suplementos com alto carboidrato foram associados com maior (p < 0,05) ER (596,2 Mcal) do que os suplementos de baixo carboidrato (515,5 Mcal). Não houve diferenças (p > 0,05) na eficiência energética entre os grupos. Portanto, a suplementação aumenta a ingestão e retenção de proteína e energia, sem alterar a eficiência de retenção.

The effects of supplementation with different protein: carbohydrate ratios on body composition, carcass characteristics and protein and energy deposition efficiency of young were assessed. Twenty-four Nellore calves (132.5 ± 5.5 kg and 90-150 days of age) were kept on pasture for a 430 day experimental period. The treatments were: Control = mineral mixture only; HPHC = high-protein and high-carbohydrate supplement; HPLC = high-protein and low-carbohydrate supplement; LPHC = low-protein and high-carbohydrate supplement; LPLC = low-protein and low-carbohydrate supplement. Four animals at begning and 20 animal at end of experiment were slaughtered to evaluate the carcass composition. Control bulls had the lowest (p < 0.05) intake of ME (9.8 Mcal day-1) with no difference (p > 0.05) between supplemented bulls (13 Mcal day-1). Although non-supplemented bulls had less (p < 0.05) retained protein, retained energy (RE), body weight gain and dressing percentage, differences were not observed (p > 0.05) between supplemented bulls. High-carbohydrate supplements were associated with more (p < 0.05) RE (596.2 Mcal) than low-carbohydrate supplements (515.5 Mcal). Differences were not found (p > 0.05) in the energy efficiency between the groups. Therefore, supplementation increases the intake and retention of protein and energy without changing the retention efficiency.

Objetivou-se estimar as exigências de proteína e energia de bovinos de corte em pastagens tropicais dos 4 até 18 meses de idade. Foram utilizados 46 bezerros Nelore (138,3 ± 3,4 kg e 90-150 dias de idade) em pastagem, distribuídos em um grupo de mantença (alimentação restrita) ou em planos nutricionais, recebendo suplemento com diferentes quantidades de proteína e carboidrato, ou não suplementados. A exigência de energia líquida para ganho de peso (ELg) foi obtida por regressão linear do logaritmo da energia retida em função do logaritmo do ganho de peso corporal vazio. A exigência de energia líquida para mantença (ELm) foi estimada pela relação exponencial entre a produção de calor e consumo de energia metabolizável. A exigência líquida de proteína para ganho de peso (PR) foi estimada pela regressão linear múltipla da proteína retida no ganho de peso de corpo vazio (GPCVZ) e da energia retida. A eficiência de uso da energia metabolizável (EM) para mantença foi de 0,55 e para o ganho de peso foi de 0,26. A exigência de EM para mantença foi de 124 kcal PCVZ-0,75. A PR diminuiu com o aumento do peso corporal. O ELg e PR podem ser obtidos por meio das equações: ELg (Mcal kg-1) = 0,044 x PCVZ0,75 x GPCVZ1,1302, PR (g dia-1) = -31,45 + 229,69 x GPCVZ - 8,75 x ER, respectivamente.

Protein and energy requirements of beef cattle, aged between 4 and 18 months old, on tropical pastures, were estimated. Forty-six Nellore calves (138.3 ± 3.4 kg BW and 90-150 days old), kept on pasture, were distributed in a maintenance group (restricted feeding) or in nutritional plans, receiving a supplements with different amounts of protein and carbohydrate or non-supplemented. The net energy requirement for weight gain (NEg) was obtained by linear regression of logarithm of retained energy as a function of logarithm of empty body weight gain. The net energy requirement for maintenance (NEm) was estimated by the exponential relation between heat production and metabolizable energy intake. Net protein requirement for weight gain (RP) was estimated by multiple linear regression of retained protein in the weight gain of empty body (EBWG) and retained energy. The efficiency of metabolizable energy (ME) used for maintenance and for weight gain was 0.55 and 0.26, respectively. The ME requirement for maintenance was 124 kcal EBW-0.75. RP decreased in proportion to body weight increase. NEg and RP may be obtained by equations: RE (Mcal kg-1) = 0.044 x EBW0.75 x EBWG1.1302 and RP (g day-1) = -31.45 + 229.69 x EBWG - 8.75 x RE, respectively.

The objective of this study was to estimate requirements of energy, protein and macrominerals of young Nellore/Holstein crossbreds bulls supplemented on pastures of Brachiaria decumbens Stapf. Thirty-five young bulls, at 8.53±0.18 months of age and with initial body weight of 230.6±6.1 kg were used. Ten animals were slaughtered as reference, in different weight range, and the other animals were slaughtered at the end of the experimental period. For estimate of net energy requirements for weight, a regression equation between log of retained energy (RE) and log of empty body weight gain (EBWG) was constructed. Net requirements of Ca, P, Mg, Na and K were determined by the equation Y' = a.b.Xb-1, in which a and b represent the intercept and the coefficient of equation of prediction of macrominerals in body content, respectively. Requirements of metabolizable energy for maintenance (MEm) were obtained from retained energy in function of metabolizable energy intake (MEI). The requirements of MEm of Nellore/Holstein crossbreds young bulls on pasture was 125 kcal/EBW0.75/day. The efficiency of ME utilization for maintenance (k) of grazing Nellore/Holstein crossbred young mbulls was 0.58 and 0.24 for gain. The total metabolizable protein requirements for an animal with 400 kg and with average daily gain of 1.0 kg, were 638.36 g/day. The dietetic requirements of Ca and P for an animal with 400 kg BW were 0.49 and 0.21% of DM, respectively. Daily metabolizable energy requirement for maintenance of grazing Nellore/Holstein crossbred young bulls was 11.6% greater than the values found for cattle in feedlot in Brazil (112 kcal/kg EBW0.75).

The study assessed performance, microbial protein synthesis, intake and digestibility of nutrients by beef heifers receiving levels of multiple supplements or nitrogen salt, in a self-controlled intake, on pasture, during the dry season. Thirty-five beef heifers, from 6 to 9 months of age and average initial body weight of 203.4 + 4.5 kg, were used. Study factors were: control - mineral mixture; nitrogen salt - 50% of urea + mineral mixture, at proportion of 1:1, and 50% of corn (75% of crude protein); levels of multiple supplementation - multiple supplements with different percentages of intake controller mixture (urea + mineral mixture, at the proportion of 1:1), corn and soybean meal (45% of crude protein). Supplement consumptions observed were: 115, 173, 572 and 1214 g/animal/day for animals fed on nitrogen salt, low, medium and high levels of multiple supplement, respectively. Supplemented animals had greater average daily gain, evidencing the positive linear effect of the levels of multiple supplementation on average daily gain. Overall, there were no significant differences between average daily gain of animals fed on multiple supplements or nitrogen salt. Supplementation increased the intake and digestibility of nutrients, except for digestibility of neutral detergent fiber, although the intake of digested neutral detergent fiber increased. Supplementation increased the production of microbial nitrogen as well as nitrogen losses in urine, although the quantity of nitrogen assimilated by bacteria, proportionally to intake, was higher. Supplementation improves nutritional parameters and weight gain.

Objetivou-se avaliar o desempenho produtivo, o consumo e a digestibilidade aparente na recria de novilhas de corte em pastagem de Brachiaria decumbens Stapf, sob suplementação com fontes de energia amilácea ou fibrosa durante o período da seca. Foram utilizadas 40 novilhas (20 da raça Nelore e 20 mestiças), recém-desmamadas, com 8,5 meses de idade e peso inicial de 197,9 ± 3,74 kg. Foram formulados dois suplementos: o primeiro à base de fubá de milho e farelo de soja (rico em amido) e o segundo, à base de farelo de trigo (rico em fibra), que foram ofertados nas quantidades de 0,5 ou 1,0 kg/animal/dia, em comparação à oferta de apenas mistura mineral (controle). Os animais foram distribuídos segundo delineamento de blocos completos casualizados em esquema fatorial 2 × 2 + 1, com duas fontes de energia e dois níveis de suplementação mais o controle; o grupo genético foi adotado como medida de controle local. O ganho médio diário de peso foi maior nos animais sob suplementação que naqueles que receberam apenas mistura mineral (0,198 vs 0,077 kg/animal/dia). Além disso, o desempenho dos animais sob suplementação com fonte amilácea de energia foi maior em relação aos daqueles que receberam suplemento à base de farelo de trigo (0,232 vs 0,163 kg/animal/dia). O consumo de matéria seca de pasto foi menor no grupo que recebeu o maior nível de suplementação. A suplementação de novilhas de corte sob pastejo durante o período da seca possibilita aumentar o desempenho produtivo. Em comparação ao farelo de trigo, a utilização da mistura milho/farelo de soja como base da mistura múltipla melhora o desempenho produtivo das novilhas.

This experiment aimed at evaluating the productive performance, intake and the apparent digestibility in the raising of beef heifers on Brachiaria decumbens Stapf. pastures under supplementation with starch or fibrous energy sources during the dry season. It was used 40 newly weaned heifers (20 Nellore and 20 crossbreed), at 8.5 months of age and 197.9 ± 3.74 kg initial weight. Two supplements were formulated: the first was corn meal- and soybean meal-based diet (high in starch) and the second was based on wheat meal (high in fiber), which were given at the quantities of 0.5 or 1.0 kg/animal/day, compared to the offer of only mineral mixture (control). The animals were distributed according to a complete randomized block design in a 2 × 2 + 1 factorial arrangement with two sources of energy and two levels of supplementation plus the control treatment; the genetic group was used as a measure of local control. The average daily weight gain was higher for the animals under supplementation than those fed only mineral mixture (0.198 vs. 0.077 kg/animal/day). Moreover, performance of the animals under supplementation with starch energy source was higher than those fed wheat meal-based supplement (0.232 vs. 0.163 kg/animal/day). The intake of pasture dry matter was lower for the group given the highest supplementation level. The supplementation of beef heifers under pasture makes it possible to improve the productive performance. Compared to wheat meal, the use of the corn/soybean mixture meal as the basis of multiple mixture improves the productive performance of the heifers.