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The limiting factor in forage plants which prevents more complete degradation by ruminants is the fiber component. Sometimes called lignocellulose, this fraction is primarily composed of cellulose, hemicellulose, and lignin. Forages are normally high in lignocellulose when compared to cereal grains, therefore they are lower in digestibility, which in turn results in reduced efficiency of animal production. Studies have shown that a small increase in forage digestibility, such as 7 to 12%, can result in increases of 30 to 40% in animal gain. These numbers provide a substantial incentive to further study the factors which limit the degradation of forage with the overall objective of enhancing the efficiency of animal production.
Enzymes produced by microorganisms are solely responsible for degrading forage fiber. The digestive enzymes produced by the animal do not break down fiber. Therefore, it is essential to understand the microorganisms and their interactions, primarily those which occur in the rumen, to improve the degradation process of forage. Approximately 80% of the animal energy is obtained from volatile fatty acids produced by microorganisms in the rumen.
Various studies suggest that the North American buffalo (Bison bison), has a superior ability, when compared with domestic cattle (Bos taurus), to digest low quality forages. Digestion coefficients of all nutrients, including dry matter, crude protein and fiber have been shown to be greater in bison than in Hereford steers. Bison appear to show superior digestibility when poor quality, low protein diets are fed. Explanations offered for the superior digestion coefficients were that a greater recycling of nitrogen to the rumen and a reduced rate of digesta passage occur. Previous studies have not compared the cellulolytic or protozoal populations between bison or domestic cattle. The objective of our studies was to compare cellulose degrading microorganisms and ruminal fermentation parameters between bison, cattle-bison hybrids, and cattle, fed three levels of low quality alfalfa.