The Basics of Hay Preservatives

By Dr. Emma Matcham (Extension State Specialist in Forage Agronomy)

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This blog post is presented as a follow-up article to a presentation by Dr. Emma Matcham at the NE Ohio Hay Day, which was hosted by Norden and Trumbull County Extension on August 2nd, 2025.

Hay producers largely understand the value of mowing and baling in a timely manner, since delayed harvest can dramatically reduce protein and digestibility of hay. But, just because we understand the importance of timely harvest doesn’t mean that the weather always cooperates. Hay preservatives are one tool producers can use to reduce the time needed between mowing and baling, which can help us take advantage of smaller windows of fit weather. 

What are hay preservatives?

Hay preservatives are products that intend to reduce microbial growth in hay. They are sprayed onto hay during or after mowing, but before baling. The most common types of preservatives are acids (propionic, lactic, acetic, or mixtures) or ammonia.  

Preservatives differ from other types of products marketed to spray on hay during cutting, such as desiccants or inoculants. Desiccants aim to improve the dry down speed, but don’t reduce microbial growth. Microbial inoculants aim to change the species of microbes that grow on wet hay, but don’t reduce microbial growth overall. 

What are the Benefits of hay preservatives?

The main benefit of hay preservatives is that they allow hay to be safely baled at moisture levels up to 25%. Some preservatives can reduce hay spoilage at moisture levels of 25-30%, but the effects of preservatives at moistures above 25% are a lot less consistent. Recent meta-analyses of the effects of hay preservatives indicate that hay treated with acid-based products (like propionic acid) generally has slightly higher protein than untreated hay, due to a combination of reduced leaf losses from faster harvesting and lower temperatures during storage. In some cases, acid-based preservatives can also reduce visual mold ratings, increase sugar content, reduce dry matter losses, and increase digestibility. (Metanalysis by Killerby et al. (2022): 10.1093/jas/skac023). 

Tips for applying Hay preservatives

  • Have a good estimate of your yield and moisture levels before you start applying. Preservatives are applied at rates based on your tonnage, so having a close estimate ensures you can apply accurately.
  • Ensure preservatives are applied evenly.
  • Check your nozzle tips to make sure they are in good condition. This helps with even coverage.
  • Dilute your acid with water (50/50 mix) to improve coverage.
  • When storing hay treated with preservatives, make sure it does not come in contact with dry bales that weren’t baled with preservatives

Want even more information on application rates and tips? Check out the slide set from Dr. Matcham’s presentation at the NE Ohio Hay Day

👉 View and Download Slide Set Here