That white patch in your haylage is Yeast, not a toxic mould!

Anyone who has fed haylage to their horses will have, at some stage, noticed patches of white film, usually just below a small hole in the bag. The first assumption is that this is mould, and you would be kind-of right but, the second assumption that it is unsafe to feed to your horses would be wrong. How can a white mould be safe for my horse? Well, let’s first find out what it is.

White mould found on haylage is likely to be yeast! Yes, yeast. The following is an extract from Dennis Hancock PhD, Associate Professor and Extension Officer at The University of Georgia, USA. Assoc Prof Hancock stated in an industry information leaflet:

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White mould is usually associated with baleage bales that were baled too dry to ferment well, but it can occur even if they were baled at the proper moisture level. It often grows on the flat sides of the bale or just under small holes in the plastic. White mould is a harmless yeast, usually in the Mucor or Monila genus. The mould spores for these species are too large to cause respiratory issues, and they produce no known mycotoxins. Livestock often will push this mouldy material out of the way or consume it.

Moulds that are green, blue, yellow, or red are indicative of a problem.

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We have now established that the white patches are, in fact, yeast, and not a harmful mould. Being yeast, could they even be beneficial to the horse? Maybe.

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Plant yeasts and moulds are both derived from fungi (fungus). The variety derived from the Mucor species is a result of the fungi being deprived of oxygen, like a haylage bag, causing them to grow as a spherical, multipolar yeast. Yeasts derived from Mucor species have been found to enhance the fermentation process of various fruits, perhaps even ensiled products like haylage, and improve the production of key microbial metabolites. Such metabolites are increasingly being found to have significant benefits in both the physical and mental health of mammals, including horses.

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Monila is a non-aflatoxigenic variety of fungi which means they don’t produce any dangerous mycotoxins. Monila has been shown to have the capability of preventing the formation and spread of specific mycotoxins in various fruits and vegetables. Currently, Monila genus fungi is used as an antimicrobial agent for the biological control of the aflatoxigenic (toxic), Aspergillus. In theory, it may be possible that Monila may be able help prevent the ingestion of mycotoxins in horses, not
cause them.

So, the next time you open a bag of Manuka Haylage and notice some white spots on your lovely fresh haylage, remember, it is yeast, not mould and that it may even be helping to improve your horse’s health, not make it worse!

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Dr Mark Barnett PhD
Equine Nutritional Consultant
MTB Equine Products