Pathogenic fungi are opportunistic organisms that grow on plants and seeds. They generally contaminate stressed or damaged feed, when the conditions for their growth (eg ambient temperature, humidity) are correct. The three main fungal genera that pose challenges to livestock production are Aspergillus, Fusarium, and Penicillium.

As part of their metabolism, these fungi produce mycotoxins that can affect animal metabolic pathways differently and ultimately can lead to the death of more susceptible species and / or individuals. The genus Fusarium is generally very frequent in feed and forages, with a well-known toxin from this group such as Deoxynivalenol (DON; Vomitoxin).

Affected animals show different symptoms after consuming contaminated food, such as gastrointestinal problems, diarrhea, immunity depression, and poor general performance. Effects on the gastrointestinal tract include increased permeability of the epithelium that allows toxins to enter the circulation and fluid to return to the lumen.

Circulating Fumonisins are toxic to cells, particularly liver and kidney, and are also known to affect immune function in metabolic pathways not yet well described. A recently proposed mechanism has been the impairment of the inflammatory response necessary to recognize the mycotoxin itself. DON has been suggested to downregulate Myeloid Differentiation Factor 88 (MyD88), an essential adapter molecule for most Toll-like receptors (TLRs), which mediate the induction of inflammatory cytokines.

At present, very little is known about the effects of these mycotoxins on circulating white blood cells. Ruminants, of course, have an advantage compared to non-ruminants due to the characteristics of their digestive system. Fermentation in the rumen acts as a detoxifying chamber to varying degrees for anti-nutritional factors in plants, as well as mycotoxins in fungi.

An example is DON which is transformed within 24 hours to the less toxic epoxy metabolite DON (DOM-1) when incubated in ruminal fluid. Other mycotoxins can escape into the rumen reticulum unaffected or become metabolites that retain their biological activity. An example is aflatoxin B1 which can be partially degraded in the rumen to aflatoxicol (toxic) and then absorbed and transformed in the liver to aflatoxin M1 (toxic), which can later appear in milk.

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