What You Need to Know About New Hay

Hay season can be a stressful time for many, from the farmers harvesting it, to the horse owners purchasing it. With the variety of variables that influence the nutritional quality and safety, there are many considerations to be made. During this time of year, I receive tons of questions about new hay. Is it safe to feed right away? Does it need time in my barn to cure first? When is the ideal testing time? – You get the idea. Let’s dive into these burning questions and provide you with some knowledge to help you better navigate hay season.

Moisture Content

Producing hay is a science, an art and requires a good amount of luck as well. My partner is a farmer and harvests many acres of hay each year, sometimes unexpected rain occurs and there is nothing he can do to remedy the situation. It just is what it is. However, as a horse owner, is it important to understand the quality of the hay you are purchasing, particularly the moisture content is critical to be aware of in regard to safety.

When hay is cut, it must spend time drying in the field. Additionally, it will be raked to rotate the plants to ensure that it is uniformly dry prior to baling. Hay that is destined to be baled dry will be left in the field until it reaches about 15% moisture. This can take multiple days of air drying in the field. When hay is baled at over 15% moisture, there are a plethora of issues that can occur and as a horse owner, it is in your best interest to avoid this hay.

Preservatives & Mold

When purchasing hay, my first priority is that it is safe for my horse to consume. Moldy hay should never be fed to horses. During wet seasons, hay producers may consider treating their hay with preservatives if weather does not allow for adequate drying time. These products allow the forage to be baled at a higher moisture content.

There are two common types of preservatives used, mold inhibitors or those containing acid (e.g., propionic acid). The preservatives will be applied to the forage when it is baled, and this allows for the hay to be baled at 15-30% moisture which provides more flexibility to the producer during wet years. Organic acid (preservative) treated hay is safe for horses. Research has shown that during preference tests, the horses did prefer the non-treated hay, but when only given treated hay, their forage consumption did not decrease.

Feeding & Fire Safety

Hay that is too wet is a very serious safety issue. Every year we hear about barn fires that are traced back to the spontaneous combustion of hay. ‘Spontaneous’ is not truly the correct term in my opinion, as it is not random, but actually quite predictable. This combustion is driven by the moisture and biological activity within the hay bale.

If the plants are not dry enough when baled, they will respire and as the sugars continue to break down, they release moisture and heat. When the heat increases within the bale it can begin to smoke and eventually burst into flames. The safety range varies, but above 20% moisture is when you may begin to see these issues. This range does vary depending on bale type, for example, round bales tend to be a greater risk as they have the longest distance from the center of the bale to where moisture is able to be released into the air.

How soon after baling can you feed new hay safely?

There is a prevalent myth across the industry that all hay needs to be cured for weeks, or some horse owners even say months, before it is fed to horses. This is simply not true, as any hay that has been properly dried prior to baling can be fed to your horse as soon as it is required.

Hay that has excess moisture when baled will ‘sweat’ after it is put in the barn. This depends on a variety of factors such as the moisture level, the species of grass/legumes, and how dense the bale is. During this process heat is produced as fermentation is occurring within that bale. This is hay that should not be fed to horses.

If you open a bale and feel heat, then it should not be fed to horses. This is where the ‘curing’ myth comes into play as many owners believe that all hay must ‘sweat’ for multiple weeks prior to feeding or testing. Unfortunately, if the hay was not cured properly in the field prior to baling, it may not even be safe to feed after allowing it to cure further in the barn as too much moisture increases the risk of mold. Additionally, these bales are at a greater risk of spontaneous combustion causing barn fires.

One consideration that is frequently overlooked when discussing new hay safety, is the transition period. Almost every horse owner that I encounter understands that any change in concentrate feeds must be done slowly over the course of 7-14 days. However, the typical management of forage is to abruptly switch from one batch to another. This is a serious management issue, as hay is the majority of the horse’s diet. Therefore, when that fibre switches it shocks the microbes in the hindgut and can cause serious gastrointestinal upset.

So, when managing your hay, ensure that you have a minimum of 14 days of crossover between your hay batches. When I purchase hay for my horses, I ensure that I have about 6 weeks of crossover which allows ample time for testing and a transition period of a few weeks.

When can you test your hay?

It is impossible to talk about hay feeding safety without mentioning testing. As an owner of a very easy keeper and a horse that has PPID (Cushing’s disease), I never feed them any untested hay. If your hay has been cured properly and baled at an acceptable moisture content, then you can test it right away!

If the hay is too wet, you’ll want to wait until the ‘sweating’ has subsided. The length of time this takes varies greatly. For my clients, I normally recommend trying to wait about 2 weeks to test the hay as that provides some time for sweating if there is excess moisture, but still ensures that the hay can be tested prior to feeding.

When you purchase hay, talk to your producer and ask them about their process. An experienced hay producer will understand the importance of properly cured hay, and therefore, the hay will likely be safe to feed and test right away.

Take Home Message

Hay is the majority of what we feed our horses, so ensuring safety and nutritional quality is critical to optimal equine management. With hay season being here, taking the time to understand forage safety and when you should be testing your new hay batches is important. Producing hay is both a science, an art and just plain luck, so take the time to work with your hay producer in choosing a forage that works well for your herd, but also approach each situation with empathy as producing quality hay has numerous challenges outside of the control of the producer.

If you have any questions about your hay or want some assistance in getting it tested feel free to send an email to balancedbaynutrition@gmail.com. Hay testing is so immensely critical, that Balanced Bay provides free hay testing instructions via email to anyone who would like them!

By: Madeline Boast, MSc. Equine Nutrition


Battle, G. H., Jackson, S. G., & Baker, J. P. (1988). Acceptability and digestibility of preservative-treated hay by horses.

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