RESUMO -O manejo do pastejo permite que sistema com base na utilização de pastagem propicie altos rendimentos por animal e por área. Para isto, devem-se utilizar critérios de manejo com intuito de controlar, simultaneamente a qualidade e a quantidade de forragem e manter a sustentabilidade do sistema. A intensidade de pastejo é dinâmica, jamais permanece a mesma, mudando com a taxa de consumo pelos animais e também pelo crescimento das plantas, variando de hora a hora e dia a dia, por isso deve ser controla sistematicamente. Neste cenário, o consumo de forragem parece ser o fator que mais explica as variações no desempenho animal em relação a qualidade da forragem. A suplementação da dieta dos animais em pastejo com concentrado permite aumentar o desempenho de animais, reduzindo a idade de abate ou a da primeira cria. Contudo, as características nutricionais do suplemento devem variar em função da quantidade e da qualidade da forragem ofertada. Ao suplementar a dieta dos animais em pastejo com energia e proteína, pode-se manejar pastos mais baixos em relação a suplementação apenas com sal mineral, sem que ocorra redução da densidade populacional de perfilhos. Estas estratégias de manejo podem reduzir a probabilidade de degradação do pasto. Desta forma, a suplementação da dieta de animais permite aumento na capacidade suporte do pasto. Palavra-chaves: composição química, digestibilidade, gramíneas tropicais, manejo, pastejo, suplementos Supplementation of beef cattle as strategy of pasture managementABSTRACT -The grazing management system based on the intensive pasture utilization result in a high animal and area yield. In order to that to be possible, it should be used a management criteria aiming to control, simultaneously the quality and the amount of forage, maintaining the sustainability of the system. The grazing intensity is dynamic, it never keeps the same status, it can be changed with the animals rate intake, and also by the plants growth, changing every hour and day, due to that, it should be controlled systematically. In this scenery, the forage intake is the main factor which explains the variations in the animal performance in relation to the forage quality. Energy and protein supplementations of the grazing animals increase performance, reducing slaughter and the first birth age. However, the nutritional characteristics of the supplement should vary in function of the amount and quality of the forage allowed. Pastures grazed by supplemented animals can be managed at a lower height, compared to those grazed by animals supplemented with only mineral salt, without reducing the tillers population density. These management strategies can reduce the probability of future pasture degradation. Thus, supplementation of the diet of the grazing animals can increase the pasture carrying capacity.Key Words: chemical composition, digestibility, grazing, management, pasture, supplements IntroduçãoA partir da década de 90 profundas alterações tem ocorrido no cenário mundial da pecuária de corte associada à abertur...

A three-year-long field experiment was conducted in a continuous grazing system with a variable stocking rate to evaluate effects of increasing nitrogen levels in Marandu grass ( Brachiaria brizantha Hochst ex A. Rich Stapf “marandu”) on herbage mass, forage accumulation rate (FAR), forage quality, stocking rate (SR), average daily gain (ADG), gain per hectare (GPH), and gain per kg of applied N. The experimental design was completely randomized with four treatments (control without application of N, and 90, 180, and 270 kg N ha −1 year −1 ) and three replicates (paddocks per treatment); nitrogen was applied in the form of urea. Herbage mass, crude protein (CP), FAR, SR, GPH, and the nitrogen nutrition index increased with increasing nitrogen level (P < 0.05), whereas the neutral detergent fibre (NDF), acid detergent fibre, and nitrogen usage efficiency decreased with increasing nitrogen level (P < 0.01). Crude protein was higher than 12% and NDF lower than 60% in all treatments. Nitrogen application rate affected ADG (P < 0.05) but did not fit any equation. The highest ADG was 90 kg N ha −1 year −1 (985 g animal −1 day −1 ). Increasing the nitrogen level is a promising way to improve Marandu grass production, nutritive value, and animal production.

Two experiments were conducted to determine the effects of grazing height and supplementation levels of Marandu pastures on average daily gain (ADG), gain per hectare (GPH) and methane (CH 4) emissions during the wet season under continuous stocking by Nelore yearling bulls. Exp. 1: three grazing heights were evaluated: 15, 25 and 35 cm, combined with 0.3% of BW of a supplement (161 g crude protein (CP)/kg and 20.1 MJ gross energy (GE)/kg on dry matter basis (DMB)). Experimental design was completely randomized (three paddocks per treatment), and the effects were analyzed by polynomial orthogonal contrasts. Exp. 2: grazing heights were combined with decreasing supplementation levels as grazing heights increased: short height (15 cm) and high supplementation (0.6% of BW of a supplement: 142 g CP/kg and 18.9 MJ GE/kg on DMB) (SHHS); moderate height (25 cm) and moderate supplementation (0.3% of BW of a supplement: 161 g CP/kg and 20.1 MJ GE/kg on DMB) (MHMS) or tall height (35 cm) without supplementation) (THWS). Experimental design was completely randomized (three paddocks per treatment), and treatment means were compared by Tukey test (P < 0.05). In Exp. 1, ADG increased linearly (P = 0.02), and GPH decreased linearly (P = 0.0002) as grazing height increased. Methane emission was not affected (P = 0.64) by grazing height. In Exp. 2, ADG was not influenced (P = 0.14) by treatments. However, GPH was the greatest (P < 0.0001) for the SHHS treatment. In addition, CH 4 emissions were lower (P < 0.0001) in SHHS and MHMS bulls compared to THWS. The SHHS Abbreviations: ADF, acid detergent fiber (expressed inclusive of residual ash); aNDF, neutral detergent fiber (assayed with a heat stable amylase and expressed inclusive of residual ash); ADG, average daily gain; AU, animal unit; BW, body weight; CP, crude protein; DM, dry matter; DMB, dry matter basis; DMI, dry matter intake; GPH, gain per hectare; ha, hectare; GE, gross energy; IVOMD, in vitro organic matter digestibility; IVDMD, in vitro dry matter digestibility; MHMS, moderate height and moderate supplementation; ME, metabolizable energy; OM, organic matter; SHHS, short height and high supplementation; THWS, tall height without supplementation.

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Intensification of tropical grassland can be a strategy to increase beef production, but methods for achieving this should maintain or reduce its environmental impact and should not compromise future food-producing capacity. The objective of this review was to discuss the aspects of grassland management, animal supplementation, the environment, and the socioeconomics of grassland intensification. Reducing environmental impact in the form of, for example, greenhouse gas (GHG) emissions is particularly important in Brazil, which is the second-largest beef producer in the world. Most Brazilian pastures, however, are degraded, representing a considerable opportunity for the mitigation and increase of beef-cattle production, and consequently increasing global protein supply. Moreover, in Brazil, forage production is necessary for seasonal feeding strategies that maintain animal performance during periods of forage scarcity. There are many options to achieve this objective that can be adopted alone or in association. These options include improving grassland management, pasture fertilization, and animal supplementation. Improving grazing management has the potential to mitigate GHG emissions through the reduction of the intensity of CO2 emissions, as well as the preservation of natural areas by reducing the need for expanding pastureland. Limitations to farmers adopting intensification strategies include cultural aspects and the lack of financial resources and technical assistance.

RESUMO -Avaliaram-se as características morfogênicas e estruturais do dossel de Brachiaria brizantha, cv. Marandu, sob pastejo intermitente no período chuvoso, em diferentes ofertas de forragem e ciclos de pastejo. O delineamento experimental foi em blocos ao acaso, em esquema de parcelas subdivididas, com três repetições. Nas parcelas, avaliou-se o efeito das ofertas de forragem (4, 7, 10 e 13% do PV/dia) e, nas subparcelas, o efeito dos ciclos de pastejo. Todas as variáveis diferiram entre os ciclos de pastejo, comprovando grande influência das condições ambientais sobre as características avaliadas. A taxa de alongamento do colmo e a altura do dossel responderam linear e positivamente ao aumento da oferta de forragem. O número de perfilhos vegetativos nos piquetes com a menor oferta permaneceu constante ao longo de todo o período experimental, no entanto, nos piquetes com as demais ofertas, atingiu valores mais elevados nos ciclos intermediários. A densidade de perfilhos reprodutivos e totais ajustou-se ao modelo quadrático de acordo com a oferta de forragem. Pastos manejados com ofertas de forragem próximas a 4% PV/dia têm menor alongamento de colmos e tendem a reduzir as perdas por senescência. As variáveis ambientais exercem maior influência sobre as características morfogênicas e estruturais em comparação a ações de manejo como a oferta de forragem. block experimental design was used in a split-plot scheme with three replicates. It was evaluated in the plots the plots, the effects of forage supplies (4,7, 10 and 13% BW/day) and in the subplots, the effects of grazing cycles were evaluated. All the variables differed among grazing cycles, proving the great influence of environmental conditions on the evaluated characteristics. Stem elongation rate and canopy height showed linear and positive responses to the increase on forage supply. Number of vegetative tillers in the plots with the lowest supply was constant over the whole experimental period, however, in the plots with the other supplies, tillers reached highest values in the intermediate cycles. Density of total and reproductive tillers was fitted to the quadratic model accordingly to the forage supply. Pastures managed with forage supplies close to 4% BW/day showed lower stem elongation and they tend to reduce loses caused by senescence.Environmental variables affect morphogenetic and structural characteristics more than management with forage supply does.Key Words: Brachiaria brizantha, canopy height, grazing cycles, grazing intensity, morphogenesis, stem elongation IntroduçãoNa busca pela correta condução dos animais em pastejo, é de grande importância o conhecimento do processo de transformação da forragem em produto animal e, principalmente, da dinâmica dos processos de crescimento e desenvolvimento das plantas que compõem a pastagem e suas respostas morfofisiológicas aos fatores interferentes. Entre esses fatores, destaca-se a intensidade de pastejo, que afeta diretamente as taxa de acúmulo de forragem (Parsons et al., 1983).As gramíneas tropica...

O manejo do pastejo e a suplementação estratégica permitem maximizar a produção de carne bovina em pastagens de forma sustentável. A intensidade de pastejo influencia diretamente o crescimento individual, taxas de aparecimento e mortalidade de perfilhos, a determinar o acúmulo de forragem e a estrutura do dossel. Dessa forma, nas águas, é função do manejo do pastejo adequar a frequência e intensidade de desfolhação para que o animal possa colher forragem com idade fisiológica e valor nutritivo adequados. A idade e tamanho dos perfilhos determinam a proporção de tecidos de suporte lignificados que reduzem a digestibilidade da forragem. No período seco, o manejo do pasto e a estratégia de diferimento, ao final do período das águas, são determinantes na obtenção de forragem de melhor valor nutritivo. Assim, o manejo das pastagens visa, primeiramente, à produção de forragens com altos teores de fibra potencialmente digestíveis. A partir de então, a caracterização da quantidade e qualidade da forragem são primordiais à adequação dos nutrientes fornecidos, via suplementos, para otimizar a utilização dos recursos forrageiros basais. A suplementação da dieta dos animais em pastejo, com concentrado, permite aumentar o desempenho dos animais, o que reduz a idade de abate e melhora a qualidade da carcaça e da carne obtida, além dos benefícios na preparação dos animais terminados em confinamento. Portanto, o manejo do pastejo e a suplementação da dieta dos animais permitem aumento de produtividade e maior qualidade dos produtos.

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