| Abstract: | Live brewers' yeast slurry was incubated under carbon dioxide at 27°C and 39°C in 0·1% peptone solution and in bovine rumen fluid which had been clarified by removal of the population of bacteria and protozoa normally present. Numbers of viable yeast in both media remained constant for 12 h at 27°C; at 39°C loss in viability was 81 % in peptone and 94% in rumen fluid during the same period. When glucose was added to clarified or unclarified rumen fluid containing yeast slurry and incubated for 6 h at 39°C, ethanol was produced. Ethanol production was prevented if the slurry was treated with heat or chemical preservatives before addition to the rumen fluid. Unclarified rumen fluid from a steer fed a brome-alfalfa hay-grain ration contained 102–103 yeasts and moulds per ml. The results suggested that the feeding of live brewers' yeast slurry to ruminants could result in ethanol toxicity if fermentable carbohydrate were also present, though many of the yeast cells would succumb to heat inactivation at normal rumen temperatures. This risk could be eliminated by prior treatment of the slurry with heat or chemical preservatives. |
