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Lactic acid bacterial inoculants and fibrolytic enzymes in forage preservation and degradability



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Several experiments were carried out to determine the effect of high fiber (NDF, ADF) forages on DM intake, digestibility and production using lactating cattle and steers. In vitro and in situ experiments explored the effect of inoculants, inoculant/enzyme, and various combinations of fibrolytic enzymes on DM disappearance, cell wall composition and changes in Cornell carbohydrate and protein degradation fractions. Cell walls of grasses contain high proportions of polysaccharides of low digestive value. The degradation of these cell walls by the rumen microbes is slow and incomplete especially in high fiber forages. Feed additives or processing that facilitate a faster breakdown of the forage cell walls may also increase the rumen turnover rate and the efficiency of feed utilisation through reduced grain supplementation. In the first experiment (chapter three) the feed intake and milk production potential of two napier grass varieties were evaluated. The possibility of using an all crop LAB inoculant in conserving napier grass as silage, was investigated using a late-cut barley silage crop, characterized by high ADF and NDF as a model. The preceding led to the use of a combined LAB inoculant and a fibrolytic enzyme additive on both early and late-cut barley. We also performed several experiments (chapter six and seven) whose main objective was to increase the DM solubility, reduce cell wall fractions and study the effect of enzymes on Cornell carbohydrate and protein fractions in various alfalfa hay, grass hay, barley silage, oat straw and fenugreek hay and straw. Overall the results from all the experiments showed that treating of high fiber (ADF and NDF) forages with inoculants or inoculant/enzyme products did not significantly alter their ensiling or feeding value. Animal performance (DM intake, digestibility and milk yield and composition) was not significantly improved when animals were fed inoculant or inoculant/enzyme treated forages. The use of combinations of various fibrolytic enzymes (additives) reduced the cell wall fractions ADF and NDF in both legume hay, grass hay, cereal silage and legume and cereal straws. These enzymes enhanced more DM disappearance in temperate grasses than in tropical grasses. Fibrolytic enzymes decreased the rapidly degradable protein and unavailable carbohydrate fractions but increased the rapidly degradable and the total available carbohydrate fractions. The causes of the inconsistencies in enzyme treatments on barley silage compared to alfalfa hay or other forages was elucidated by significant shifts in the Cornell carbohydrate and protein degradability fractions of treated forages. The use of fibrolytic enzymes as direct-fed additives or in ensiling forages holds the future for improving both the preservation and digestibility of both tropical and temperate high fiber forages. (Abstract shortened by UMI.)





Doctor of Philosophy (Ph.D.)


Animal and Poultry Science


Animal and Poultry Science



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