How To Stop Hay From Going Mouldy

Some of the moulds that grow in hay include Aspergillus, Mucor and Penicillium and while it may be impossible to have completely mould-free hay, this article discusses the preventative measures you can take to help stop hay from going mouldy.

Why does mould grow on hay?

Hay with high moisture content has a high mould growth risk.

Hay that has been damaged by water or has high moisture content is susceptible to mould growth, especially when combined with conditions conducive to mould growing i.e. warm or humid weather.

Mould growth on hay occurs for 3 main reasons:

  1. The hay was baled with a high moisture content.
  2. The hay was rained on before baling, or after baling and before storage
  3. The hay was incorrectly or inadequately stored.
  4. Hay storage that isn’t up to scratch provides ample opportunity for mould to grow – no matter how much attention you have paid to moisture percentage and baling technique and timing

While we have looked at the 3 main reasons why mould growth occurs on hay, it is worth noting that “the potential for mould growth starts … in the standing crop.”

Fungi will always be present in the windrow; it is how this is managed that affects the future quality of your hay – informed decisions during growing and baling are essential.

Why should you prevent mould growth?

Mould growth generates heat, carbon dioxide and water, spoiling the hay – “excessive heating and moulding can cause the loss of as much as 1/3 of the feeding value of the hay bale.”

Aside from the inconvenience and the financial loss of spoilt hay there are other negatives associated with mouldy hay.

  • Mould growth causes nutrient loss and produces dust and spores – and in some cases mycotoxins.

Spores can cause respiratory issues for both livestock and humans and mycotoxins can affect the horse’s instestinal walls, or enter the blood stream and cause more issues. 

While horses are especially sensitive to mould, ruminant animals can still be affected if care is not taken. For example, some moulds can cause mycotic abortions or aspergillosis in cattle.

  • Taste, dust and loss of feed quality and nutritive content affects the palatability of hay causing livestock to turn off the feed.
  • A further concern is that mouldy hay is often heat-damaged ‘brown’ hay.

This browning reaction is known as the ‘Maillard reaction’ and “makes the nutrients unavailable to the animal, dramatically reducing the feed value of the forage.”

When brown hay is accompanied with a tobacco-like smell it is a sign of overheating caused by the high moisture levels heat generated by mould growth, increasing the risk of spontaneous combustion.

What preventative measures can you take?

  • To avoid mould on your hay bales, the hay needs to be made correctly in the first place. If hay has been poorly made it is likely to be affected whatever preventative measures you take afterwards.

Making sure your hay is cut at the right stage and baled at the correct moisture percentage is key to creating safe, nutritious and palatable hay. “The moisture of dry hay at baling is critical to hay quality during storage and can be the difference between high-quality hay and trash.”

  • If you are buying your hay in, request feed test results and inspect it well on delivery. Avoid hay that has been rained on in the bale, before storage.
  • Net wrapping your round bales helps avoid unwanted moisture entering the bale – as well as maintaining the integrity of the bale during handling and transport.
  • Keeping hay out of the elements with proper hay storage is key to preventing mould growth.

If hay is stored properly in a dry, well-ventilated, dedicated hay shed, the risk of mould is reduced dramatically.

“Outside storage combined with loss of feed value due to poor digestibility can result in a loss of total feed during storage of around 25%. That results in a 25% loss of the initial investments like land, fertiliser, time and fuel.”

  • Allow for airflow around your bales.
  • If you are worried about the bottom layer of hay drawing moisture from the ground during the wetter months, placing the bales on pallets or a protective layer of plastic/tarp can help. A hay shed with a well-prepared site and a good drainage system is not likely to have this problem though.
  • Regularly check your hay for mould growth and remove any affected bales from the stack.

A few points to keep in mind

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