Applications of the in vitro gas method in the evaluation of feed resources, and enhancement of nutritional value of tannin-rich tree/browse leaves and agro-industrial by-products

A major constraint to increasing livestock productivity in developing countries is the scarcity and fluctuating quantity and quality of the year-round supply of conventional feeds. In order to meet the projected high demand of livestock products, and to fulfil the future hopes of feeding the millions and safeguarding their food security, the better utilisation of non-conventional feed resources which do not compete with human food is imperative. There is also a need to identify and introduce new and lesser known food and feed crops capable of growing in poor soils, which can play a vital role in control of soil erosion, bring economic benefits to farmers, enhance biodiversity, create jobs and bridge the wide gap between supply and demand for animal feeds. This paper highlights the potential of a novel approach using an in vitro rumen fermentation technique for evaluation of nutritional quality of non-conventional feed resources; many of the considerations discussed also apply to conventional feeds. This technique enables selection of a feed for high efficiency of microbial protein synthesis in the rumen along with high dry matter digestibility, and provides a basis for development of feeding strategies to better synchronise energy and nutrient release to maximise substrate fixation into microbial cells. This could lead to increase in the supply of protein to intestine and reduce methane production from ruminants. Tannins are the most widely occurring anti-nutritional factor in non-conventional feeds. General approaches for detanninification and increasing nutritional value of tannin-rich feed resources are also discussed. (author)