Resumen La leucaena se puede usar como dieta única para ganado de engorde sin que se presenten problemas nutricionales, resultando en altos aumentos de peso vivo. La alta concentración de proteína cruda en la leucaena sugiere que suplementos energéticos fácilmente fermentados en el rumen podrían ser usados para capturar el exceso de proteína degradable en el rumen y proporcionar más proteína microbiana y energía metabolizable al animal, aumentando aún más la ganancia de peso vivo o la producción de leche. Esta estrategia ha sido probada en sistemas de pastoreo y de corte y acarreo en Australia e Indonesia. En ambos sistemas, la producción (ganancia de peso vivo o producción de leche) aumentó con la adición de suplementos que contenían grandes cantidades de energía metabolizable fermentable. La sustitución de la dieta base (leucaena o leucaena mezclada con pasto o con residuos de cultivos) por el suplemento también significa que se pueden mantener más animales en el sistema por una cantidad o área determinada de leucaena. Los mismos principios se aplicarían a cualquier sistema basado en árboles leguminosos. Los suplementos energéticos pueden ser de muchas formas, tales como almidón fermentable (granos de cereales y yuca), azúcares (melaza), pectinas (cáscaras y pulpa de soya) y fibra (salvado de arroz, bagazo de yuca), pero aún no se han comparado por su eficacia ni por su eventual beneficio económico en estos sistemas.

Abstract Leucaena can be fed as the sole diet to fattening cattle without nutritional problems and it will promote high liveweight gains. The high crude protein concentration in leucaena suggests that energy supplements, which are readily fermented in the rumen, could be used to capture the excess rumen degradable protein and provide more microbial protein and metabolizable energy to the animal, further increasing liveweight gain or milk production. This approach has been tested in grazing cattle and also in cut-and-carry systems in Australia and Indonesia. In both systems, production (liveweight gain or milk production) increased with the addition of supplements containing large amounts of fermentable metabolizable energy. The substitution of the basal diet (leucaena or leucaena mixed with grass or crop residues) by the supplement also means that more animals can be carried in the system for a set amount or area of leucaena. The same principles would apply to any tree legume-based system. Energy supplements can come in many forms, viz. fermentable starch (cereal grains and cassava), sugars (molasses), pectins (soybean hulls and pulps) and fibre (rice bran, cassava bagasse), but they have not been compared for their efficacy nor for their economic benefit, if any, in these systems.

ABSTRACT The live weight gain of cattle on tropical pastures is reviewed and found to be low and dependent on the length of the growing season. Supplements may be added to address the primary limiting nutrient, which, in the dry season, is crude protein. The response relationships of live weight gain to level of supplement (protein or energy) that have been developed for animals on pasture in Brazil and Australia have been compared and found to be very similar. This gives confidence in recommending a supplementation strategy for cattle on tropical pastures. Response in the wet season was very low and likely to be uneconomic compared with dry season supplementation. Supplementation is costly and should only be used as a last resort, but the strategy needs to be viewed in the context of a growth path to a defined market or slaughter weight. In Australia, high inputs in the first dry season are risky as subsequent compensatory growth can reduce or eliminate the weight advantage of a supplement. There is less financial risk in using supplements towards the end of the growth path. Growth paths can follow many forms and there is no need to maximise live weight gain in each period. Targeted supplements in the second dry season, leucaena based systems, other special-purpose pastures or crops, and feedlots offer the most economical way for cattle to meet market targets. The expected annual live weight gain and weaning weight are other major factors which determine the growth path, target market which can be achieved, and the level of intervention (supplements, legumes, feedlots, etc) which are required and when. Some recent results on growth paths in Australia are presented.