Are mycotoxins really dangerous for dairy cows?

In comparison to monogastrics, ruminant animals are generally considered to be less susceptible to mycotoxicoses. This is based on the assumption that rumen flora degrade and inactivate in-feed mycotoxins. However, a number of mycotoxins resist rumen breakdown and ruminants often have to deal with a myriad of different challenges because their diet is complex. What’s more, transition cows are particularly sensitive to moulds, fungal spores and mycotoxins.

The complex diet challenge

Ruminant diets typically contain both concentrates and forages. This increases the risk of exposure to multiple mycotoxins. Forages (grazed and conserved), fermented feeds and by-products all represent a significant risk to cattle depending on soil contamination, forage harvesting date, silage management, purchased feed origins and on-farm feed storage conditions.

Mycotoxin sources

Forages : Mycotoxins in forages (grass, hays, silages) present the greatest threat to cattle. Even fresh grass for grazing can be contaminated with several mycotoxins. These typically include fungal endophytes that produce mycotoxins, which protect the plant in some way, such as ergovalineand lolitrem B, as well as Fusarium mycotoxins, such as zearalenone or deoxynivalenol (DON).

Identifying moulds in silage (Mahanna, 2009):

Fungus	Mould colour	Associated toxin(s)
Penicillium	Green-blue	Ochratoxin, citrinin, patulin
Aspergillus	Yellow-green	Aflatoxin, ochratoxin
Fusarium	Pink-white	Zeralenone, DON, T-2, Fumonisin

Mycotoxin sources: bedding

Straw bedding can be contaminated with mycotoxins. This also presents a risk to cattle, particularly for dry cows that often consume large quantities.

Mycotoxins compromise animal health and performance.

It’s important to note that many of the symptoms associated with mycotoxicosis are non-specific often meaning that a mycotoxin issue is ‘last in the queue’ when diagnosing. The main effect of many mycotoxins is impairment of the immune system. Animals that are immune-compromised will be a greater risk of pathology from other infectious and metabolic diseases simply as a result of their ‘weakened’ state. Other effects include gastrointestinal disturbances, feed intake depression and reproductive abnormalities. ZEA is often responsible for the latter. Cystic ovaries, irregular cycles and embryonic abnormalities all fall under the remit of ZEA. Probably one of the most important but underestimated effects is the antibiotic action of Penicillium mycotoxins. Patulin, PR toxin and Roquefortine C are all produced by Penicillium moulds and have the same action in the rumen as Penicillin does in the human body – antibiotic.

Contamination avoidance is virtually impossible but following good silage management practices can go a long way to minimising the risk to livestock. One of the key points is the recognition and understanding of the mycotoxin problem. Part of this is recognition of the fact that the majority of exposure is to chronic, low concentrations of multiple mycotoxins and, as such, any interventions, including use of a mycotoxin binder, must be able to deal with a wide suite of mycotoxins at any one time.