THE ENDOGENOUS POLYSACCHARIDE UTILIZATION RATE OF MIXED RUMINAL BACTERIAL AND THE EFFECT OF ENERGY STARVATION ON RUMINAL FERMENTATION RATES

Authors: VAN KESSEL, JO ANN - CORNELL UNIVERSITY; Russell, James

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: In ruminant farm animals (cattle, sheep, goats), microbial protein is the major source of amino acids reaching the small intestine. Other workers indicated that ruminal bacteria were very prone to even short periods of nutrient starvation, and it appeared that a large percentage of the ruminal microorganisms might be dying in vivo. These results suggested that frequent feeding might improve feed use efficiency. Our in vitro studies indicated that ruminal bacteria do not lose their ability to ferment until the starvation time is 8 to 12 hours and in vivo experiments corroborated these results. Bacteria from cows fed once per day were always metabolically active. Based on these results, frequent feeding cycles may not be necessary.

Technical Abstract: When mixed ruminal bacteria were starved in vitro for 24 h, cellular ATP decreased, but there was little decline in cell protein. Starved ruminal bacteria utilized nucleic acids (primarily RNA), but the decline in ATP was more closely correlated with decreases in polysaccharide. Because polysaccharide declined at a first order rate of 23% per h, it was possible eto estimate the endogenous metabolic rate at various stages of starvation. The bacteria were initially able to ferment soluble carbohydrates at a rate of 700 ug of hexose equivalent per mg of protein per h. Starvation had little impact on the rate of soluble carbohydrate fermentation until 8 to 12 h, and the endogenous metabolic rate was less than 10 ug of hexose per mg of protein per h. The bacteria digested ball-milled cellulose at a rate of 25 ug of hexose per mg of protein per h for 8 to 12 h. Even bacteria that had been starved for 24 h digested cellulose at a rate of 16 ug of hexose per mg of protein per h. The bacteria produced methane from hydroge and carbon dioxide at a rate of 70 nmol of methane per mg of protein per min. Short periods of starvation (<12 h) had little impact on methane production, but longer times caused an almost complete inhibition of methanogenesis. The bacteria deaminated amino acids at a rate of 30 nmol per mg of protein per min, and the critical phase of starvation was again 8 to 12 h. Ruminal bacteria that were harvested 24 h after feeding had 10- fold less polysaccharide than bacteria 2 h after feeding, but this polysaccharide supported high rates of soluble carbohydrate fermentation, cellulose degradation, deamination and methane production.