Nutritional value of anaerobically fermented beef cattle wastes as a feed ingredient for livestock. Chemical composition and in vitro and in vivo digestibility of fermentor biomass

Abstract

Studies were undertaken to determine the changes in chemical composition that occur when livestock wastes undergo thermophilic, anaerobic fermentation and whether the resulting microbial products would be suitable as a supplement for livestock feeds. A 48·6% decrease in dry matter (DM) occurred in the fermentation process. Total N and ash content did not change between the fermentor influent (FI) and effluent (FE). However, the percentage of the N in the form ammonia increased from 24·9% to 46·3% and the total Volatile Acids decreased markedly during the fermentation process. Centrifugation of the FE resulted in only a 42% recovery of N which decreased to 30% after drying. The amino acid composition of the centrifuged biomass was similar to alfalfa hay when expressed as g/16 g organic N, except for a higher methionine content. The FE contained a higher percentage of acid detergent fiber (20·0 versus 15·3) and lignin (6·4 versus 3·1) than FI. The presence of different fractions of the FE in an in vitro incubation did not alter the rates of digestion of starch or cellulose. Potassium, phosphorus, calcium and sodium were all present at greater than 1% of the effluent DM. Silica accounted for over 60% of the total ash in the dried centrifuged biomass. The utilization by sheep and cattle of biomass produced by fermentation of livestock waste was determined. In two experiments, dried centrifuged biomass (DCB) was fed to sheep and cattle at 0,5,10 or 20% of diet DM. Fecal N increased 0·3% and 0·43% for each 1% increment in DCB in sheep and cattle, respectively. Digestibility of the ash in the diet decreased from 59·5% in sheep fed the control diet to 28·4% in sheep fed the 20% biomass ration. In another experiment, the total FE was mixed directly with cracked corn and hay to provide about 6·5% of the diet DM. Significant reductions in digestibilities of diet DM, ash, organic matter, N and gross energy were observed in sheep fed the diet containing FE. Addition of bentonite to the control diet and the diet containing FE increased N retention. In a fourth experiment, FE was added to a basal diet containing 10% crude protein. Addition of FE to the basal diet increased retained N. In steers, no effect of FE was observed on apparent digestibilities of DM or N. No marked changes in ruminal VFA concentrations were observed due to feeding FE. Rumen fluid turnover, measured by polyethylene glycol dilution, and DM disappearance from the rumen, were not altered by feeding FE to steers compared with steers fed a control diet. There were no effects of diet on the in vitro rate and extent of digestion of starch or cellulose. The use of FE as a feed ingredient for livestock appears to have merit, although technical problems related to water removal and nutrient recovery remain to be solved.