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Waste is produced in large quantities in cattle feedlots, and this is a potential environmental pollutant. Recycling of feedlot waste as livestock feed has been investigated extensively as one means of lowering the disposable waste load. Refeeding fresh manure will only partially alleviate waste disposal problems. In one study, only about one-half of the manure collected daily could be refed, and the remainder was discarded.
Currently, there is increased interest in the development of a microbial process for recycling and utilizing feedlot wastes. Commercial digestors are in operation. In some of these systems, the potential exists for capturing methane as a product of fermentation and recovering a biomass product which has potential feed value. Because of high capital costs associated with the equipment, labor, etc., necessary for the fermentation process, preliminary economic analyses indicate that, for the fermentation system to be profitable at moderate feedlot sizes, the operation must show a reasonable return for the feeding value of the fermentor effluent biomass. Based on its nutrient content (particularly total nitrogen, amino acids, and some essential minerals), fermentor effluent should be a good dietary supplement for ruminant livestock.
Thermophilic (high temperature) anaerobic fermentation of livestock manures has several advantages that make it attractive for more detailed investigation. Thermophilic fermentation has the potential for higher methane production rates, and minimizes the potential for disease transmission compared with mesophilic (ambient temperature) systems. In addition, fermentation systems have the potential of improving the nutritive value of the nitrogen present in the waste.
Data in this paper describe the chemical composition of the cattle wastes and different fractions of effluent obtained from the anaerobic fermentor and the in vitro digestibility of these fractions. In vivo experiments in cattle were also used to evaluate the potential feed value of the fermentor biomass using short-term (21 to 35 day) digestion and metabolism studies.