Mould is the dust like coloured fuzzy structure that a lot of fungi form when growing conditions are correct. Some fungi form mushrooms and others are single cells that we can’t see with the naked eye but can see changes in the feeds they’re growing on.

There are thousands of species of mould-forming fungi and these moulds can produce hundreds of different toxins (mycotoxins) that can affect the body in many different ways. Moulds may affect the body directly causing pneumonia, mastitis or abortions, or via toxins causing a myriad of symptoms.

Storing winter feed in good condition can be difficult especially during a wet summer like we had this year, and we have had a lot of reports of mouldy feeds.

Mould decreases the ME and palatability of feed, as well as limits vitamins and thiamine. The end result is a feed that tastes bad, won’t make them gain weight and has limited vitamin support.

There is a certain amount of each type of mould cows and sheep can tolerate, the exact amount is unknown so therefore we don’t have a ‘safe’ amount of spoiled feed that you can feed.

The rumen is an excellent ‘decontaminator’ of mycotoxins and moulds, therefore sheep and cattle are more resistant to disease than monogastrics like us, pigs or horses, however dairy cows, high producing sheep and beef cattle around calving may be more susceptible to mycotoxins due to altered rumen transition times and a suppressed immune system. Young calves and sheep with undeveloped rumens are also susceptible.

Clinical signs vary from poor doers and weight loss to pneumonias and abortions. I once saw cows with blistered swollen vulvas from mouldy feed and no other signs, likely due to estrogenic effects of certain mycotoxins, vaginal and rectal prolapses can happen too. Occasionally we see sporadic abortions in sheep and cattle from mycotic placentitis-fungal infection of the placenta (photo below).

Feed analysis is hard because mould growth is inconsistent, the affected feed may be gone before signs are apparent and mycotoxins aren’t uniformly distributed within a feed. Lab analysis is expensive and limited to only a few mycotoxins out of the over 400 known. Diagnosis is usually from the history.

Remember that bacteria like Listeria can also overgrow in spoiled or improperly stored feeds like silage.

The general consensus is white mould is probably okayto some degree, others probably aren’t. If you have to feed mouldy feeds, the main solution is dilution –that is feeding good feed with the mouldy stuff and preferably feeding the worst of it to adult non-pregnant cattle and sheep.