Effects of Mycotoxins on Ruminal Bacteria and Animal Performance

Dairy producers have a difficult task when attempting to assess the possible exposure of their animals to mycotoxins. Information gleaned from the scientific literature suggests signs and symptoms for toxins which may actually not be likely to appear in a herd. Also, that same literature suggests concentrations at which the toxin exerts its effects. Those concentrations may have little meaning in a production setting in which multiple mycotoxins, as well as other production stresses, are at work. We do know, however, that mycotoxins do pass through the dairy cow’s rumen intact, although clearly some microbial metabolism can and does take place. At the same time, the mycotoxins may produce adverse affects on key rumen bacteria. Therefore, we cannot count on rumen microbiology to protect the dairy animal. Predicting signs which might occur in the herd exposed to mycotoxins is also futile. Such signs are generally not unique to particular mycotoxins if to toxic compounds at all. Changes in productivity, in reproductive capacity, in general health, behavior, etc. may all signal the presence of mycotoxins, although other causes may be equally to blame. The present report discusses some of these factors and suggests the approach dairy farmers may find most productive in dealing with the issue of mycotoxin contamination on their farms. Introduction Case study reports and research trials can provide both valuable and misleading clues about the effects of mycotoxins in ruminants. A herd experienced a decrease in breeding efficiency over an extended period (~ five months), with reduced birth weights, unhealthy calves, increased mastitis, prolapsed rectum, decreased feed consumption, and other signs. Corn contaminated with aflatoxin at up to120 ppb had been included in the ration. Once the contaminated material was found and removed, milk production rose by 28% (Guthrie, 1979). Choudary et al. (1998) reported that as little as 10 ppb of aflatoxin B1 (AFB) resulted in a significant reduction in feed consumption. Also responding in a dose-dependent fashion, rumen motility declined in dairy cows receiving 200 to 800 ppb AFB (Cook et al., 1986). Of course, many producers throughout the U.S. and other regulated production areas understand the loss that can occur when violative levels of aflatoxin M1 are discovered in milk. Calves consuming the cyto-necrotic T-2 toxin (at 10 ppm and above) developed ulcers of the abomasum and sloughing of rumen papillae (Cheeke, 1998). Goats fed 95 ppm fumonisin showed no overt signs of toxicosis although sphingolipid tests revealed toxinrelated pathology (Gurung, et al. 1998), but dairy cows fed that toxin did not present either circulating fumonisin or alterations in 1Contact at: 0107 Symons Hall, University of Maryland, College Park, MD 20742-5551, (301) 405-7761, FAX (301) 4058570, Email: [email protected]