Mode of action of yeast culture (YEA-SACC 1026) for stimulation of rumen fermentation in buffalo calves

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The effect of daily supplementation of 5 g Saccharomyces cerevisiae yeast culture (YC, YEA-SACC 1026), 30 g NaHCO3, supernatant from 5 g YC (YCS), 5 g autoclaved YC (YCH) or 5 g γ-irradiated YC (YCR) to the diet of buffalo calves on rumen microbial populations and fermentation pattern was examined. Addition of 30 g NaHCO3 increased the rumen pH to the level observed with YC group. The pH and the concentrations of total, total viable and cellulolytic bacteria and total volatile fatty acids (VFA) were significantly higher while that of lactic acid, hexose-unit oligosaccharides and NH3-N were significantly lower in the rumen fluid of YC compared with the control group. The effect of NaHCO3 was 39·5 and 59·5% in decreasing the concentrations of lactic acid and hexose-unit oligosaccharides, 48·1, 47·2 and 45·5% in increasing the numbers of total, total viable and cellulolytic bacteria, 50·0 and 58·1% in increasing the concentrations of total VFA and protein and 51·3% in decreasing the concentration of NH3-N of YC. The corresponding values for YCR addition in the diet were 38·6, 45·7, 48·5, 44·4, 51·5, 39·1, 48·1 and 46·5%. The effect of YCS and YCH was only marginal, but conspicuous up to 2 h after feeding, in changing the above rumen variables when compared with the YC group. The results indicated that contribution of increase in pH in changing the rumen variables was approximately 50% of YC and almost all the stimulatory activity was associated with live yeast cells. Autoclaving of YC destroyed almost all and γ-irradiation of YC retained about 50% of stimulatory activity of YC. The effect of YC on rumen fermentation, which was maximum up to 2 to 4 h after feeding, decreased with time. © 1998 SCI.