THE EFFECT OF CATTLE DIET ON THE METABOLISM OF 3-NITROPROPANOL BY RUMINAL MICROORGANISMS

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Abstract
Rumen fluid was obtained over a 2-yr period (1980–1981) from cattle on various diets, to determine the effect of diet on microbial metabolism of 3-nitropropanol (NPOH), the toxic metabolite that occurs in certain species of the legume family. In both years, NPOH was degraded most rapidly (P < 0.05) when range diets contained Kentucky bluegrass (Poa pratensis). Pinegrass (Calamagrostis rubescens) range was associated with high rates of NPOH degradation (< 200 μmol∙L−1∙h−1) in 1980 but not in 1981. Feedlot (alfalfa hay and grain, alfalfa hay, and corn silage), pasture (orchardgrass and alfalfa) and bluebunch wheatgrass range (Agropyron spicatum) diets showed lower rates of NPOH metabolism, but a new stand of orchardgrass (pasture) yielded high rates of NPOH metabolism in 1981. Rapid rates of nitrite reduction were correlated with the degradation of NPOH, suggesting rumen bacteria that detoxify nitrite and NPOH may be similar. The induction of NPOH metabolism by dietary components is considered and ruminal rates of NPOH metabolism are discussed in relation to forage quality. Preliminary results indicate that nitrate may serve as a substrate for inducing ruminal detoxification of nitrite and NPOH in cattle. Key words: Detoxification, rumen microorganisms, 3-nitropropanol, miserotoxin, cattle nitrite