Is It Safe to Feed Moist Hay to Horses?

A reader’s first-cutting hay brought in right from the field feels a bit damp. Our nutritionist explains why she should be cautious and how to tell if the forage is safe to feed her horses.
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is it safe to feed moist hay to horses
Hay put up with 12% or less moisture won't go through much fermentation, if any, and is safe to feed right after harvest. | Photo: iStock
Q.I was recently surprised to learn that my barn already has some first-cutting hay, and they’ve started to feed it. It’s very green and feels slightly damp to me. Is it safe to feed hay off the field? Does it need to be stored for some period of time before it should be fed?

—Via e-mail

A.First of all, I’m amazed that we are barely in March and you already have a cutting of hay. Don’t tell those still buried under feet of snow and inches of rain!

You are right to be cautious if the hay feels damp. This could indicate it might still go through a fermentation process, during which time it should not be fed. Growing up in England where the conditions were often damp, it was generally understood that the current year’s hay put up in late spring should not be fed until the autumn. In hindsight this was based on anecdotal wisdom, but there was some truth to it due to the fermentation issue. However, the waiting period between cutting and feeding might only need to be a few weeks

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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

2 Responses

  1. When storing hay with any noticeable or expected moisture level at all, we always spread salt on top of the bales as we stack them. It draws out the moisture from the center of the bales: eliminating the risk of mold, fermenting, and spontaneous combustion.

  2. I always enjoy Clair’s articles as she does an excellent job, although occasionally I feel obligated to add my opinion. What is really important here is whether we are talking about internal or external moisture. Internal moisture or stem moisture is from the plants not being dried out completely and external moisture is from outside the plants typically dew or rain moisture. External moisture normally does not create heat, spontaneous combustion, or fermentation. Internal moisture does cause these issues. Therefore 15% or even 20% external moisture is likely safe but 12% stem (internal) moisture may not be. As hay dries internal moisture will likely produce fermentation although at lower levels it is likely tolerable for most horses. This fermentation process is commonly referred to as a sweat and can last 3-4 weeks. Moisture testers are less reliable at measuring stem moisture because it is internal. On top of that more moisture is tolerable in small bales than in big bales and meters will measure different in different hays. Most horse owners do not have the knowledge or experience to differentiate these fine points therefore I always recommend that hay be baled for a minimum of 30 days prior to feeding to horses. If a person is out of hay and needs to feed early, bust bales open a week or so ahead to encourage drying which stops the fermentation process if the environment is dry enough. Rodney Ferry, DVM.

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