Rain-affected hay

Can I ensile rain-affected hay?

Plastic wrap is not a ‘silver bullet’ for hay that was rain affected before baling or for hay that is too wet. Wet weather during the hay season often leaves farmers and contractors with quandaries such as 'It’s about half to one day off being OK to bale, but now rain is threatening' and 'The hay was cured enough and being baled when it started to drizzle'. A response by many seems to be, 'Wrap it in stretch wrap plastic and turn it into silage' or at least 'The plastic will stop it from going mouldy'.

There is no cut and dried right answer here. Sometimes you may get away with avoiding mouldy hay by wrapping it but more often than not, you won’t.

Lower quality pasture

In mid to late November/early December, most pastures will have a lot of stem with seed heads prominent. This means the quality of the forage on the ground will be well down. See below for approximate values.

Metabolisable energy (MJME/kgDM)Crude Protein (%CP)Neutral Detergent Fibre (% NDF)Dry Matter (%DM)
<9.59–11>5070–80

At this moisture content (20–30 per cent) the forage will be too wet for hay but generally too dry for silage.

Option 1: Ensiling

If ensiled, the result is often unpalatable, mouldy and/or foul-smelling fodder. There is not enough moisture to allow a satisfactory lactic acid type fermentation to convert plant sugars to acids producing silage. However, there is enough moisture and trapped air to allow some plant respiration and microbial activity resulting in heating and mould growth.

A compounding issue is that soil is often splashed onto the forage or inadvertently picked up during tedding or raking. This soil contains undesirable soil organisms which can contribute substantially toward a poor fermentation. To increase your chances of a successful fermentation you will need to individually or continuously in-line wrap the rounds or squares, i.e., not stacked in pits under plastic.

At a cost of approximately $14 to $28/bale to wrap small rounds to large square bales including the cost of plastic, it is costly for low palatability and low-quality silage.

Option 2: Baling

If the moisture content is only 3 to 6 per cent above the ideal baling moisture content, the best outcome might be to bale it as hay and apply a reliable hay preservative.

  • Always use hay preservatives at the correct rate.
  • Remember wet hay is much heavier than cured hay.
  • Ensure the preservative covers as much of the forage as possible.

Higher quality pasture

If the crop is pasture or lucerne and is medium to high quality (more leaf and less stem or thinner stems for lucerne) the same series of events still apply. However, there will be less air trapped in these more tightly packed bales. Beginning with a higher quality base where plants contain more sugars for the fermenting bacteria to digest.

The closer this forage is to silage dry matter per cent (although there will still be a reduction in quality), the better the chances of a positive outcome. With this scenario, still individually wrap and/or use a preservative.

There is no magic answer to the question ‘Is it worth wrapping material too dry for silage or too wet for hay?’. Ultimately the quality of the original pasture will give you an indication of the options you have.

Square bale of hay with mould as a result of baling when too wetHand opening section of hay bale to show mould as result of baling when too wet

Page last updated: 28 May 2022