The limits established for dairy cattle by the FDA for aflatoxin B1, vomitoxin, and fumonisin are 20 ppb, 5 ppm, and 30 ppm, respectively. The FDA has not published maximum concentrations for other mycotoxins with known deleterious effects on cattle such as T-2 (trichothecenes), ochratoxin, or zearalenone. Although the FDA does not suggest safety guidelines for zearalenone, the European Commission established 250 ppb as the maximum legal limit in complete feed for this mycotoxin.
Effect of ruminal pH
Because of mycotoxin degradation in the rumen, dairy cattle can resist better than other livestock the adverse health effects associated with their exposure. Therefore, the conditions in the rumen may affect the bioavailability of the mycotoxins and its rumen metabolites. A study conducted at the experimental animal facilities of INRA Auvergne-Rhône-Alpes (France) and published recently in the Journal of Dairy Science (Pantaya et al, 2016) investigated the effects of low ruminal pH on the bioavailability of mycotoxins in non-lactating dairy cows. Cows were fed a low- (15% starch dry matter basis) or a high-starch diet (30.8%) and received a single dose of mycotoxin contaminated cereal mixture containing 0.05, 0.2, 0.24, and 0.56 mg of aflatoxin B1, ochratoxin A, vomitoxin, and fumonisin B1 per kg of feed, respectively, through a ruminal cannula.
As expected, cows fed the high-starch diet had lower pH values, and they spent more time under the threshold pH value of 5.6 (0.5 vs. 2.6 hours/day). The authors found high-starch diet increased the bioavailability, estimated as an increase in the urinary excretion of the mycotoxin or its metabolite, of ochratoxin A and aflatoxin B1; however, the bioavailability of vomitoxin and fumonisin B1 remained unchanged.
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