Nutritive Value And Manure Quality In Supplemented Maize Stover And Grass Hay Diets For Ruminants.
Production of ruminants is highly dependent on utilization of roughages. In tropical regions, particularly Sub-Saharan Africa, the roughages are predominantly of poor quality due to high fibre and low protein content. For these reasons supplementation with protein sources and other feeds with high degradability is essential. Maize is an important cereal in the world, and in Africa it produces the highest amount of crop residue. The stovers left after harvesting maize grain are potentially an important feed resource. The overall goal of this study was to identify nutritive attributes of diets comprised of maize stovers or grass hay and their mixtures with different protein supplements for ruminant production, and to determine the influence of the diets on manure quality. There were three different roughages and three different protein supplements used in the study. The roughages were grass hay and maize stovers harvested when the grain was at milk stage or when the grain was dry (approximately 80% DM content).The roughages were characterized by high fibre and low protein content. The protein supplements included lucerne, Sericea lespedeza and sunflower oil cake. Although lucerne has been widely used as a model protein source for ruminant production there are agronomic and climatic limitations which constrain its widespread use, particularly in smallholder systems. Hence there is a need for alternative protein sources such as those included in the present evaluation. There were three sets of investigations carried out: The first set involved laboratory chemical composition and in vitro rumen fermentation of feeds using automated gas production technique (IVGPT). Over forty feed rations were evaluated. Multivariate cluster analysis was performed to create clusters of diets exhibiting homogeneous nutritive characteristics from IVGPT measurements. The diets were grouped into three different clusters. Ten diets were selected, with each cluster represented, and tested in a second set of investigations. These investigations involved conducting feeding trials using Damara rams. Data collected included intake, digestibility, weight gain and manure (faeces) production. The third set of in investigations involved manure quality analyses. This was done by determining the mineral composition and nutrient release, particularly nitrogen mineralization. The relationships among chemical composition, IVGPT, in vivo and manure quality measurements were determined. Models to predict in vivo performance from chemical composition and IVGPT measurements were derived. Maturity stage influenced the nutritive characteristics of the forages whereby both maize stovers and lespedeza depreciated in quality with age, but the effect was small in the stovers with regard to degradability. The stovers harvested at grain milk, stage showed superior nutritive quality over stovers harvested at dry stage by having higher soluble carbohydrate, lower fibre content and shorter lag time (time taken for microbes to colonize and begin fermenting the substrate) under in vitro fermentation. The positive effects of supplementation with lespedeza included enhancing fermentation of fibre fraction of and decreasing lag time. However, increasing the ratio of lespedeza caused a decrease in degradability, and this was attributed to the presence of tannins in lespedeza. In vitro gas production technique (IVGPT) is currently one of the most widely used methods in ruminant feed evaluation. It measures the gas production arising from fermentation of feeds, and the degradability can be measured by weighing the residues left at the end of incubation. Gas production profile from IVGPT can be fitted in models to derive parameters of fermentation kinetics. Although IVGPT can give several nutritive measurements to help in understanding the fate of substrates in the rumen, this study obtained inconsistent and confounding results in some parameters. These included gas volume, microbial yield