Ruminal Microflora, Mycotoxin Inactivation by Ruminal Microflora and Conditions Favouring Mycotoxicosis in Ruminants: A Review

Unlike poultry, pigs and other animals, ruminants are quite resistant to adverse effects of mycotoxins. This is because the ruminal microflora and microfauna act as first line of defence by detoxifying and degrading the mycotoxins originated from feed. Ruminal fluid has a diverse ecosystem containing 50 genera of bacteria, 25 genera of cilliate protozoae, 5 genera of anaerobic fungi and 108-109/ml of bacteriophages. This number might be much larger as many of them are non-culturable. Ruminal ecosystem converts ochratoxin, aflatoxin, diacetoxyscirpenol (DAS), T-2 toxins and deoxynivalenol (DON) to less toxic ochratoxin-α, aflatoxicol, de-epoxy DAS, HT-2 toxin and de-epoxy DON respectively. While fumonisins are tolerant to ruminal degradation and zearalenone is converted to more toxic α-zearalenone. However, their oral bioavailability is very low due to which they do not cause intoxication in ruminants. This detoxifying ability of ruminal microflora is saturable. Different factors like metabolic disorders (rumen acidosis, milk fever etc), abrupt change in diet, high protein diet, negative energy balance, antimicrobial activity of some mycotoxins etc can decrease the detoxifying ability of ruminal microflora. Under field conditions, animals are under the exposure of different mycotoxins present in concentrates and roughages as a result of which detoxifying ability of microflora becomes exhausted producing a high internal challenge in animals.