RESUMO
Our objectives were to evaluate strategies to improve productivity and economic returns from beef and dual-purpose cattle systems based on data collected on one dual-purpose (Bos taurus x Bos indicus) and two beef (Nellore) cattle farms in the western Amazon region of Brazil. Forage chemical composition and digestion rates of carbohydrate fractions of grazed Brachiaria decumbens and Brachiaria brizantha cv. Marandu grasses and Pueraria phaseoloides (tropical kudzu) legume were measured monthly during a 9-mo period from the end of one dry season to the end of the subsequent rainy season. Measurements of milk and growth responses to grazing these forages were used to predict animal productivity responses to dietary nutrient availability throughout an annual cycle. The ME available for gain in our simulations was always more limiting than metabolizable protein. The predicted ME available for gain was 0.50 kg/d for steers grazing B. brizantha and 0.40 kg/d for finishing steers grazing B. decumbens. Grasses contained more NDF and neutral detergent insoluble protein and less ME (P < 0.05) in the rainiest months than in the less rainy season, which resulted in 20% less predicted weight gain by growing steers (P < 0.05). Supplementation with sorghum grain was required to increase milk production and growth by 25 or 50% per animal, respectively, but this strategy was less profitable than current forage-only diets. Greater productivity of land and labor from higher stocking indicated greater net margins for beef production, but not for milk. This study suggested that more intensive beef production by judicious fertilization of grass-legume pastures and greater stocking density is the preferable strategy for owners of these cattle systems to improve economic returns under current conditions. It also might help decrease the motivation for additional forest clearing.
Assuntos
Ração Animal/normas , Criação de Animais Domésticos/economia , Criação de Animais Domésticos/métodos , Bovinos/crescimento & desenvolvimento , Leite/metabolismo , Ração Animal/análise , Fenômenos Fisiológicos da Nutrição Animal , Animais , Brasil , Bovinos/fisiologia , Carboidratos da Dieta/administração & dosagem , Carboidratos da Dieta/metabolismo , Fibras na Dieta/administração & dosagem , Fibras na Dieta/metabolismo , Proteínas Alimentares/administração & dosagem , Proteínas Alimentares/metabolismo , Digestão , Feminino , Lactação , Masculino , Valor Nutritivo , Poaceae/química , Densidade Demográfica , Pueraria/química , Estações do Ano , Clima Tropical , Aumento de PesoRESUMO
Objectives of this study were to compare three nutritional management strategies for dual-purpose herds in Venezuela in 1987 using a deterministic, multiperiod linear programming model of a representative farm. The model maximized discounted net margin (total revenues minus variable costs) from the herd for a 3-yr cow replacement cycle partitioned into six periods. The periods accounted for seasonal variation in forage availability and quality, and the model provided information about optimal animal inventories, animal sales, land in forage, and feed supplements. We compared current nutritional management practices and alternatives allowing optimal supplementation with commercial concentrate, molasses, cassava root, and urea. Iteration between the programming model and results from the Cornell Net Carbohydrate and Protein System assured technical coefficients consistent with predicted animal performance. Compared with management practices relying on commercial concentrate, optimal use of molasses and urea permitted increases in the stocking rate. Productivity and profit were restricted primarily by energy intake, which was constrained by intakes of NDF and DM. Alternative management strategies changed the relative importance of nutrient requirements and feed intake constraints. Thus, optimal interventions to alleviate nutritional constraints will vary with current management. Mobilizing adipose and protein tissues during lactation was optimal for most strategies. Supplementing with molasses and urea instead of commercial concentrate was the most profitable strategy, increasing herd net margin by 16% compared to the predominant feeding strategy in the late 1980s.