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Hay Preservatives: 5 Ingredients You Need To Know About

As Featured in Natural Horse Magazine, V 19 Issue 4

Hay is a whole food, right? It is if naturally cured prior to baling - otherwise it contains preservatives, which may have adverse effects on you and your horse’s health.

The moisture content of hay is monitored prior to baling. With too little moisture, hay becomes brittle, loses nutritional value, and can potentially become unpalatable. Too much moisture can cause hay to mold and experience thermal expansion in storage severe enough to cause combustion creating a severe fire hazard.
Tractor spraying a hay crop with preservatives
This article was Featured in Natural Horse Magazine Oct/Nov/Dec 2017
Optimum moisture content prior to baling is approximately 12-18% depending on the size of the bale. Spray on hay preservatives are used to enable a farmer to begin baling sooner, at moisture levels up to 30%. This inhibits mold growth while the hay continues to cure (moisture content decreasing) after baling. Various adverse health conditions can occur after long or short term exposure including inhalation and ingestion of “safe” levels depending on the concentrations applied and sensitivity of the livestock. 

5 Common Ingredients Used in Hay Preservatives

Some common ingredients used in hay preservatives are:

1 & 2 - Ammonium Propionate (buffered propionic acid) & Propionic Acid (more corrosive) are organic acids and the most common main ingredients in hay preservatives. Propionic acid was 1st registered as a pesticide in the early 1970’s. In a chronic feeding study using propionic acid, the high dose rats had hyperplasia, ulcers and other effects in the forestomach.  Both can cause skin irritation, serious eye irritation and respiratory irritation. Classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) but is not authorized as a food additive in Europe. 

3 - Propylene Glycol is able to lower the freezing point of water and used as aircraft de-icing fluid but is classified by the U. S. Food and Drug Administration as "generally recognized as safe" (GRAS) for use as a direct food additive. It is prohibited for use in food for cats due to links to Heinz body anemia. Possible adverse reactions are: skin and digestive tract irritation, allergic reactions, potentially toxic to the kidneys and liver, neurological symptoms, cardiovascular problems, respiratory issues, potentially bio accumulative.

4 - Ammonium Hydroxide  is a colorless liquid chemical solution. It forms when ammonia dissolves in water and is found in many industrial products and cleaners. Some of these are flooring strippers, brick cleaners, and cements. Ammonium hydroxide is poisonous. FDA regulations classify ammonium hydroxide as safe (“generally recognized as safe” or GRAS) at certain levels. Potential adverse reactions are skin irritation, serious eye irritation and respiratory irritation.

5 - Food Dyes: Green No. 3, Yellow No. 5 and Blue No. 1 are commonly added to hay preservatives to present a fresh green appearance and improve marketability. These are carcinogenic.

Some if not all of these may also cause GI tract irritation, being most noticeable to individuals who may have ulcers or a poor gut flora population.

What Hays are More Likely to Contain Preservatives?

Cool season grasses such as Timothy, Orchard and Rye because of the wet, cool climates where they are grown, cut, cured and baled and alfalfa. Larger bales require lower baling moisture percentages; the risk of preservatives present in large square and round bales increases dramatically. Grass hays grown in arid climates (mostly warm season grasses) rarely if ever are sprayed with preservatives; the expense is not necessary. The moisture content reduces at a rapid rate naturally. Feeding a combination of warm and cool season grasses is beneficial due to the diverse amino acid profiles and reducing the risk of preservatives in 100% of the hay fed.

Unfortunately hay preservatives are necessary for farmers otherwise too many crops would be destroyed and the price of hay could skyrocket. To be as proactive as possible, ask your grower if they use preservatives. If so, what cuttings/loads/fields received the lowest concentrations and purchase that hay. Inhalation is as much if not more of a health risk as ingestion. Slow feeders may minimize inhalation of acid/chemical dust because they can't bury their nose in the hay. Feeding from ground level allows the nasal passages to drain effectively. If you experience skin or respiratory irritation handling hay, preservatives could be the cause. Whether these additives and preservatives are safe is debatable. If given the choice, I'd rather not handle or feed hay treated with chemicals. Being well informed about the forage you are feeding is prudent and enables you to make educated choices on behalf of your beloved companions. See also: Nitrates in Hay Exposed - What You Need to Know.
The Standard and Mini Hay Pillows promote a natural grazing position enabling nasal passages to drain effectively.

More Helpful How-to Slow Feeding Resources


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Monique Warren, Hay Pillow Founder with the Hay Pillow Slow Feeder product line - standard ground hay pillow, mini hay pillow, hanging hay pillow & horse trailer manger hay pillow

About the Author

Monique Warren invented the Hay Pillow® slow feeder and is the owner of Hay Pillow Inc. ​Warren has been an equine guardian for over forty years and slow-feed advocate for over 10 years. She contributes equine nutrition, digestive and hoof health articles to publications such as Equine Wellness, The Journal, The Naturally Healthy Horse, Natural Horse Magazine, Nicker News, The Horse's Hoof and Miniature Horse World Magazine. Equine nutrition and horses feet are her passions. She resides in Southern California.

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