Characteristics of live and killed brewer's yeast slurries and intoxication by intraruminal administration to cattle.

The physical and nutritional characteristics of live and killed brewer's yeast slurries and the possible toxicity of intraruminal administration of loading doses of these by-products were evaluated. Dry-matter (DM) percentages of live brewer's yeast slurry ranged from 10.5 to 29.0, and DM percentages of killed brewer's yeast slurry ranged from 14.6 to 18.5. Total crude protein (N X 6.25) percentages of live and killed yeast slurries (DM basis) were 44.1 and 43.1; ethanol percentages (wet basis) were 6.96 and 1.84, respectively. Phase contrast photomicrographs showed distinct differences in morphology between live and killed yeast cells. Intraruminal administration of loading doses (0, 2.3, 4.5 and 6.8 kg) of live and killed brewer's yeast slurries to bull calves induced clinical intoxication at the 4.5-kg and 6.9-kg dosages of live brewer's yeast slurry. No toxicity was induced either with the killed brewer's yeast or with the 0-kg or 2.3-kg dose levels of live brewer's yeast slurry. The clinical signs and plasma ethanol concentrations suggested ethanol intoxication. Ruminal NH3 concentrations increased to over 70 mg/dl with the 4.5-kg and 6.9-kg dosages of live brewer's yeast slurry, but they did not exceed 35 mg/dl with an equivalent dosage of killed brewer's yeast slurry.