In many cases, nitrogen retention increases as a result of decreased urinary excretion. If the ratio of soluble to insoluble tannins is high, then protein digestibility is affected more than fiber digestibility. If the same ratio is low, fiber digestibility is the most affected. Toxicity to microorganisms Tannin toxicity to rumen microorganisms has been described for several bacteria species such as Streptococcus bovis, Butyvibrio fibrosolvens, Fibrobacter succinogenes, Prevotella ruminicola, and Ruminobacter amylophilis . Three mechanisms of toxicity have been identified enzyme inhibition and substrate deprivation, action on membranes, metal ion deprivation.
Tannins induce changes in morphology of several species of ruminal bacteria.
Toxicity to ruminants Hydrolizable tannins Hydrolizable tannins are toxic to ruminants. Microbial metabolism and gastric digestion convert HTs into absorbable low molecular weight metabolites . Some of these compounds are toxic. Protanthocyanidins Toxicity from PA is difficult to separate from their effects on the digestion of proteins and carbohydrates. PAs are not absorbed by the digestive tract, PAs may damage the mucosa of the gastrointestinal tract, decreasing the absorption of nutrients, PAs may reduce the absorption of essential aminoacids.