Propionic Acid-Treated Hay: Is it Safe?

By Lynda M. Vanden Elzen

IMG_1463As horse owners, we always want to find the highest quality hay available for our horses.  Opinions vary regarding which type of hay is ideal, and a hay that is ideal for one horse may be detrimental to another.  One consistent requirement, however, is that hay is free of detectable mould and dust.  What horse owners may not be aware of is how narrow the window is for farmers to bale hay successfully, not only at the optimal plant maturity level, but also at safe moisture levels, while contending with unpredictable weather at the same time.  Losses due to rain and insufficient drying time can cost a farmer a lot of money, and cause heating, loss of nutritional value, and even spontaneous combustion.

Ideally, farmers tend to want to bale when the plants have dried to moisture levels from 13-17%, so that the hay is dry enough to avoid heating and significant loss of nutritional value and bale weight, but not so dry that it shatters.  Ideally, this hay will then cure to contain 10-12% moisture or less while maintaining nutritional value and palatability.  Mike Rankin of the University of Wisconsin Hay Extension points out:

“Moist hay that is put into storage can suffer extensive dry matter loss because of increased plant respiration and microbial activity. There is typically a 1% loss of dry matter for each percent moisture loss during storage to reach a stable equilibrium. These losses are from the non-fiber components of the plants.”

As a result of all of these factors, the risk of significant losses is high for hay farmers, and if wet hay moulds in storage, it will not be suitable horse feed.  In an effort to increase the window of acceptable moisture levels at baling, some farmers are now using drying agents, the most widely-used of which is called buffered propionic acid.

What is Priopionic Acid and Why Use It?

The Ontario Ministry of Agriculture, Food, and Rural Affairs defines propionic acid as follows:

“Propionic acid is an organic acid that acts as a fungicide, inhibiting the growth of aerobic micro-organisms that can cause heating and moulding. Other organic acids, such as acetic and citric acids are sometimes also included, but propionic acid is the most effective as a mould inhibitor.”

Propionic acid is a short chain fatty acid produced by microbial fermentation in the hindgut.  It is touted as safe because it is a natural acid that is already present in the horse’s digestive system.

In practical terms, treating hay with propionic acid during baling increases the baling window substantially, from the usual 13-17% moisture to up to 25-30% moisture.  Propionic acid application decreases the drying time needed significantly, once the hay has been cut, and also decreases the chance of heating and decreases nutrient losses once the hay is baled.  If a storm is coming when a farmer’s hay crop is drying before baling, the use of propionic acid can mean the difference between that farmer losing his entire crop and being able to bale and sell his hay.

According to Agriculture Victoria, the benefits of propionic acid use are as follows:

  • allow the safe baling of hay from slightly above target moisture levels up to 25% (or 30%) moisture depending on preservative type
  • allow baling after a shorter curing period which reduces risk of rain damage and sun bleaching. It may also allow baling earlier in a season in certain areas, when fodder is less mature and nutritive value higher reduce dry matter and nutrient loss caused by leaf loss and shatter, microbial activity and moulds enable baling over a longer period each day, resulting in more effective machinery and efficiency of labour usage
  • maintain hay colour (due to increased leaf retention) and often smells better
  • prevent dry matter and quality loss in storage due to bacterial, yeast and mould activity
  • reduce risk of spontaneous combustion
  • may increase animal intake
  • Animal and human health not affected due to lack of mould spores.

Many horse owners wish to avoid feeding hay that has been treated with propionic acid, but we also want pretty green hay that smells good, that hasn’t been bleached by the sun, is free of detectable mould and dust, and has optimal nutrient levels.  Perhaps propionic acid treated hay is something we should consider?

Disadvantages of Propionic Acid

Many sources suggest that propionic acid-treated hay is 100% safe to feed to livestock.  We have not found this to be true, necessarily, but due to a lack of scientific study, we can only hypothesize about potential harmful effects at this time, based on our anecdotal observations and those of equine nutritionists.

Handling Safety: In the early days when propionic acid was first introduced, it was found to be corrosive to baling equipment, so ammonium propionate (buffered propionic acid) was introduced instead, and is now recommended as an alternative.  Buffered propionic acid is much less corrosive and is safer to handle, but it is still corrosive and caustic.

Costs & Rate of Application:  As well, the amount of propionic acid applied to forage as it is being baled depends upon the moisture levels of that forage.  It is not as simple as moisture testing a few areas of the field and then calculating an average required.  Unfortunately, hay fields are not uniform, and so moisture testing must be done in various places and then the highest moisture reading must be used.  This means that the hay from an entire field is most likely to be sprayed with more acid than is required in order to compensate for a few wet areas.  Specialized equipment has been developed that tests moisture levels during baling and adjusts the quantity of propionic acid as it goes, but this is more costly.  Either way, propionic acid adds to the production cost, though if the farmer is in a situation where they may lose some or all of their crop due to rain after cutting and propionic acid treatment would save that hay, it may be cost-effective to treat the hay.

Storage Safety: Hay that has been treated with propionic acid, thus hay with a higher moisture content, should not be stored next to untreated hay, as the moisture from the treated hay can migrate to the dryer hay and cause it to mould.  As well, there is research that shows that over time, the propionic acid will dissipate from treated hay.  If at that time (4-12 months post baling) the moisture content in the hay is still too high, the bales can mould at that time.

Metabolic Effects:  Propionic acid is one of three volatile fatty acids (VFA) that are produced in the hindgut by the hindgut microbiome during forage fermentation.  Dr. Juliet Getty hypothesizes that due to propionic acid’s rule in glucose production, feeding hay treated with propionic acid to sugar-sensitive horses can be potentially harmful:

“Propionate is a major precursor toward glucose production through a process known as gluconeogenesis. And that’s a problem for the IR horse. Once propionate is absorbed and metabolized, it is converted to glucose! So when you feed alfalfa that has been treated with propionic acid, you are essentially increasing your horse’s blood glucose level, just as you would if you had fed a hay with a large amount of sugar and starch. Increased glucose leads to increased insulin. And the rest is… well, you get the picture.”

After reviewing some further studies on the effects of short-chain fatty acid fermentation, it seems that recent evidence suggests that there may be a link between the gut bacteria associated with propionic acid and a host of effects on the digestive system, brain, and behaviour.  Dr. Derrick F. MacFabe, MD, states:

“Propionic acid (PPA) and its related short-chain fatty acids (SCFAs) are fermentation products of ASD [Autism Spectrum Disorder]-associated bacteria (Clostridia, Bacteriodetes, Desulfovibrio). SCFAs represent a group of compounds derived from the host microbiome that are plausibly linked to ASDs and can induce widespread effects on gut, brain, and behavior. Intraventricular administration of PPA and SCFAs in rats induces abnormal motor movements, repetitive interests, electrographic changes, cognitive deficits, perseveration, and impaired social interactions.”

In Conclusion:

At this time, given what we know about the use of propionic acid as a hay preservative, it seems that there may not yet be enough conclusive information available for us to make the call about whether or not to feed treated hay to our horses.  There is certainly reason to be cautious, especially when feeding propionic-treated hay to sugar-sensitive horses.  In contrast, given the growing volatility of our global weather patterns, it may be necessary at times for some farmers to treat their hay in order to ensure that we will have the supply of hay we need to feed our livestock; treated hay is better than no hay at all!  As with most things horse-related, this is not a simple “yes” or “no” answer, and so it seems the most responsible course of action would be to watch for further study, and evaluate the suitability of propionic-treated hay on a horse by horse basis.



“Acid Treated Hay for Horses” – Harvest Tec (

“Preventing Mouldy Hay Using Propionic Acid” – Ontario Ministry of Agriculture, Food, and Rural Affairs (

“Selecting and storing horse hay” – Krishona Martinson, PhD and Paul Peterson, PhD, University of Minnesota Extension (

“Preserving Baled Hay with Organic Acids” – Mike Rankin, University of Wisconsin Extension (

“Hay Preservatives” – Agriculture Victoria (

“Hay Desiccants and Preservatives” – Dan Undersander, University of WIsconsin Extension (

“Role of short-chain fatty acids in the hind gut” – W. von Engelhardt , J. Bartels , S. Kirschberger , H.D. Meyer zu Düttingdorf & R. Busche (

“Alfalfa and the Insulin Resistant Horse – The True Story” – Dr. Juliet Getty, Ph.D. (

“Short-chain fatty acid fermentation products of the gut microbiome: implications in autism spectrum disorders” – Derrick F. MacFabe, MD (

Hay Storage Safety


By Lynda M. Vanden Elzen
(Published originally in the Langley Times, June 29 2016, page 27)

Pages-from-i20160629054201873Did you know that hay can spontaneously combust, causing barn fires and loss of life, equipment, and structures? Hay is cut in the field, and then baled and stored. If the plants do not dry sufficiently before baling, the hay bales will go through a curing process in storage, sometimes called a “sweat.” This curing process produces heat, which can build up to over 200°F and ignite! When hay is baled before it is dried sufficiently, heat can build as a result of live plant tissue respiration coupled with bacteria and mold growth. Ambient moisture in the air surrounding stored hay can also be a factor.

In the Lower Mainland of BC, our wet climate can produce a perfect storm leading to hay combustion due to the high ambient moisture in our air, and the difficulty our local farmers can experience when trying to dry their hay sufficiently before baling. Hay should test at 10-12% moisture or less in order to avoid risk of heating. In dryer climates, hay can be baled and stored safely with higher moisture levels of up to 15%. Unfortunately, in the lower mainland and other areas with excessive ambient moisture in the air, hay baled and/or stored at higher moisture levels cannot cure properly, because the air is already saturated, leaving nowhere for excess moisture in the hay to go. Very high ambient moisture in the air can even increase moisture inside the bales!

Warning signs can include steam rising from your hay which may condense on the roof and barn eves. Molds can begin to grow on those surfaces, and there may be a tobacco-like odour around the hay bales. If these signs occur, it is advisable to remove livestock and equipment from the vicinity and call the fire department for assistance. Use extreme caution when moving hay from a stack that is heating, as this could introduce oxygen into the stack and cause the bales to ignite! In addition to the risk of combustion, hay that is baled with too much moisture will lose nutritional value during the curing process. Agriculture Victoria (AUS) provides the following guideline for protein loss during curing of round bales, as an example:

Yield loss of round bale hay is that 1% of original yield will be lost for each 1% moisture that is lost as stored hay reaches its equilibrium storage moisture. For example, when hay is baled at 22% moisture which then dries to 14% moisture, dry matter loss will be approximately 8%.”

In order to avoid possible heating and combustion of stored hay, it is advisable to purchase tested hay with moisture levels of less than 10-12% and to avoid stacking hay in your barn that was baled less than 3 weeks prior.



“Haystack fires (spontaneous combustion) – Agriculture Victoria (AUS) (

“Causes and Prevention of Spontaneous Combustion of Hay” – Lester R. Vough, Forage Crops Extension Specialist, University of Maryland (

“Spontaneous Combustion and Hay Fires” – Ontario Ministry of Agriculture, Food and Rural Affairs (

“Spontaneous Combustion of Hay” – Steve Fransen and Ned Zaugg, Washington State University Extension (

A Missing Link for the Metabolic Horse

By: Lynda M. Vanden Elzen

We spend a lot of time here talking to customers about how to feed their sugar-sensitive horses.  People call looking for low sugar hay, and inevitably we end up talking about their horses with them.  We like to get a wholistic picture of the horses we are helping to feed so that we can make the best recommendations to their owners.  More often than not, the horse is a mature, sedentary animal, and the owner admits with great guilt that they don’t ride him as often as they should.  More and more, horses are living sedentary lives in stalls and small paddocks, many with the best of everything….except what is one of the most crucial aspects of their welfare – exercise.

The reality is that we can feed a metabolic horse a diet that is low in sugars, but there is a great deal more to it in terms of creating a wholistic plan to help that horse to maintain a healthy weight.  In terms of feeding the sugar-sensitive horse, usually the ideal forage is low in carbohydrates, moderate in protein, and higher in fibre, while still being palatable enough that the horse will eat it.  But I think, just like we tend to do with ourselves, we get very focused on diet, at the expense of considering the importance of exercise.  It is not as simple as “calories in / calories out”; exercise increases muscle mass which burns more calories, decreases leptin resistance, and leads to psychological well-being, which translates to lower cortisol levels and a happier horse.  Horses evolved to move almost constantly and many of their body systems depend on freedom of movement, from their hooves to their skeletal systems, to their lymphatic and cardiovascular systems.

Dr. Juliet Getty, PhD, circulated an article in recent years, “Empty Fields Everywhere – Why Movement is So Important” in which she expressed dismay at driving through Kentucky with its gorgeous, empty fields and ornate barns full of horses kept in stalls.  In that article, she outlined the relationship between exercise and the reduction of insulin resistance:

“Sedentary horses lose muscle mass and can become insulin resistant. Muscle uses a large amount of glucose for energy; the more muscle mass your horse has, the more glucose transporters are produced, leading to increased insulin sensitivity. Therefore, exercise not only burns calories, but reduces insulin resistance. Exercise also helps reduce leptin resistance.”

In another article of Dr. Getty’s, about slowing the progression of PPID (Equine Cushings), she states:

“Don’t neglect exercise. It not only burns calories, but exercise makes cells more receptive to insulin, allowing the horse’s body to burn fat. The blood insulin level declines, thereby reducing inflammation and the risk of laminitis. Exercise also helps protect muscle mass (which the cushingoid horse is losing). Finally, it makes your horse more sensitive (less resistant) to leptin, a hormone that is supposed to tell your horse to stop eating.”

In an article on insulin resistance by Dr. Eleanor Kellon, VMD, she points out:

“The most successful therapy for IR in both humans and horses is exercise and diet control. Exercise primes the muscle to take up glucose by pathways that are independent of insulin, resulting in less work for insulin to do and improved IR. The effect lasts for about 24 hours…There are no magic bullets and no short cuts with IR. Exercise is often the missing element with domestic horses and matching the ancestral exercise level is difficult if not impossible for most people. This necessitates tighter control of sugar and starch in the diet of horses prone to IR.”

Chip, summer 2015

Chip, summer 2015

My own horse, Chip – a morgan/appaloosa cross – is prone to overweight, and I have pictures of his sire, a purebred morgan, who had a huge cresty neck.  Chip is built like a bulldog quarter horse and is metabolically thrifty, and I know he is in a high risk category for developing insulin resistance,   As well, morgan horses are prone genetically to develop insulin resistance and Equine Cushings, so special care must be taken for these horses to keep them in optimal health, especially as they age.  Chip lives out on grass in the dry season here, and normally has to wear a grazing muzzle during daylight hours, to simulate grazing on sparse pasture, and to limit both his overall intake as well as the volume of carbohydrates he is able to consume.   Two summers ago (2014), I wasn’t riding him, and he had to wear his grazing muzzle during daylight hours for the whole season.  Last summer (2015), when I was riding him 7-10 hours a week, or even more some weeks, he was able to live for most of the season without his muzzle while maintaining a healthy body condition score.  He carried less weight than he had the year before, while eating more!  Also worth noting is the fact that 2015 was a drought year, so the grasses were much more stressed (therefore likely higher in sugars) than they had been in 2014, yet he was still able to go muzzle-free! The difference?  Exercise, and lots of it.  I think we grossly underestimate the importance of exercise for these horses, and it doesn’t do them any favours.

We can and should control the diets of our sugar-sensitive horses.  Higher fibre, low sugar, moderate protein hay, mineral balancing, and an adequate amino acid profile are all important for the metabolic horse, but exercise is often overlooked, to the detriment of our equine partners.



“Empty Fields Everywhere – Why Exercise is So Important” – Dr. Juliet Getty, Ph.D. (

“PPID Progression Can Be Slowed Down” – Dr. Juliet Getty, Ph.D. (

“Commentary: Considerations for the IR Horse” – Eleanor Kellon, VMD (

What is “Quality Hay”?

Written by Lynda M. Vanden Elzen

IMG_9370Nearly every day, someone asks us, “What is quality hay?”  Is 2nd cut better than 1st cut?  Is timothy better than orchard grass?  Are alfalfa mixes better than grass hay?  Is soft hay better than coarse hay?  Is low sugar hay better than “regular” hay?  These are all good questions.  The answer is that it depends on the horse you’re feeding.

Many horse owners who come here to look at hay want pretty, dark green, soft second cut, and then when we ask them about their horse, they tell us they have an overweight, sedentary quarter horse.  The hay analysis notwithstanding, soft hay is usually lower in fibre, which means the horse can eat more of it more quickly.  This is great for a hard keeping thoroughbred, but not so great for a fat pony.  A hay that is dark green in colour can be high in protein and nutrients, but it can also be high in nitrates, especially when you’re talking about our local hay here in the Fraser Valley.  High nitrates can tend to cause diarrhea in many horses.  So, from this short introduction, I think you can see that an appraisal of hay quality is relative to the horse who will be eating it.

A short checklist for evaluating the quality of hay relative to the horse who will be eating it:

Cut, Texture & Stage of Maturity

First cuts tend to grow for a longer period of time, so the plants are more mature – thus more stalky – at the time they are cut and baled.  Second cuts contain less mature plants, so tend to be softer.  As well, alfalfa tends to come up stronger in second and subsequent cuts, as it prefers dry soils and hot weather.

From Ashley Griffin, M.Sc, at the University of Kentucky:

“Nutrient value largely depends on the age at which the hay was harvested. Early maturity hay is very leafy and has a high nutrient density and palatability. Late maturity hay contains coarse, thick stems and fewer leaves than early maturity hay. Hay type should be matched to the horse type. Early maturity hay would be perfect for growing horses and lactating mares, but it may not be the best choice for horses with low nutrient requirements. Mid- to late-maturity hays are best for horses with low nutrient requirements, because the horses can eat more to satisfy their appetites without overeating and becoming fat.”

Species of Grass and/or Legume

Timothy and other grass hays tend to be lower in energy and protein and higher in sugars than alfalfa and other legumes, but the only way to know the nutrient value of hay is to test it.  Please check out our detailed articles on “Alfalfa and Protein” and “Timothy and Sugars“.

How Does it Test?

Hay testing can provide a great deal information about exactly what your horse is eating.  Gone are the days when we had to rely on how hay looked or what was in it – now we can tell, within about a 2% variance, how much protein, fibre, and energy it has, the carbohydrate and moisture levels, and with certain kinds of testing we can know mineral content as well.  Test results are often surprising, so we have learned above all that we just cannot assume how any hay will test.  Grass hays tend to test higher in sugars and lower in protein than legume hays like alfalfa, and alfalfa tends to have a much higher mineral content due to the fact that the roots of the alfalfa plant extend much deeper into the soil than those of grass species.  Alfalfa hays also tend to contain more energy per bite than grass hays (visible on the test as Digestible Energy or Relative Feed Value). The amount of fiber (ADF, NDF, Lingin) is important to consider as well, as it affects the amount of total feed the horse is able to consume in a given period.


Most people want dark green hay.  Many of the sources we consulted to prepare this article state that higher quality hay tends to be dark green.  This is true, but it is only part of the whole truth.  A dark green colour can indicate higher protein and nutrient levels, but it can also indicate high nitrate levels.  From the Kansas State University Research Extension:

“The potential for high nitrate concentrations occurs when crops such as corn, sorghum, cereal grains and some grasses are exposed to drought, hail, frost, cloudy weather, or soil fertility imbalance. Nitrates accumulate in the lower portion of the plant when stresses reduce the crop yield to less than that expected based on the supplied nitrogen fertility level. When fed to livestock, nitrates interfere with the ability of the blood to carry oxygen…Nitrate toxicity is a misnomer because nitrite (NO2 ), not nitrate (NO3 ), is poisonous to animals. After a plant is eaten, rumen bacteria rapidly reduce nitrates in the forage to nitrites. Normally, the nitrites are converted to ammonia and used by rumen microorganisms as a nitrogen source. However, if nitrite intake is faster than its breakdown to ammonia, nitrites will begin to accumulate in the rumen. Nitrite is rapidly absorbed into the blood system where it converts hemoglobin to methemoglobin. Red blood cells containing methemoglobin cannot transport oxygen and the animal dies from asphyxiation.”

Nitrates accumulate in a plant when the plant continues to take them up from the soil, but is unable to use them.  Factors influencing nitrate accumulation include anything that may stress the plant and stop it from converting the nitrates it has absorbed into amino acids (protein), or over-fertilization.  Some examples of plant stressors are drought, lack of sunlight, inclement weather, and cold temperatures.  Plants store their nitrates in their lower portions, so the height of the cutter blade when cutting hay can impact nitrate levels as well.  Higher nitrates can tend to cause diarrhea in horses, and we see this often in our local Fraser Valley hay especially.

Was the Hay Treated with a Drying Agent?

Another factor that can influence hay colour is moisture content at bailing.  Higher moisture hays will tend to be darker green, where lower moisture hays were usually left out in the sun longer to dry so will be more bleached.  This is why hays which were treated with propionic acid, a drying agent, will tend to be darker green and also tend to be less prone to dust or mold – because propionic acid application allows hays to be baled at 18-20% moisture as opposed to 10% or less in non-treated hay.  However, propionic acid has its own set of risks and drawbacks.  Dr. Juliet Getty hypothesizes:

“Not considered to be harmful, propionate is one of three volatile fatty acids (VFA) naturally produced by the hindgut bacteria during hay fermentation. The other two VFAs are acetate and butyrate. These VFAs are a significant energy source for your horse. Acetate is utilized by many tissues including the heart, muscles, and the brain. Butyrate provides energy for the cells that line the hindgut epithelium. Propionate is a major precursor toward glucose production through a process known as gluconeogenesis. And that’s a problem for the IR horse. Once propionate is absorbed and metabolized, it is converted to glucose! So when you feed alfalfa that has been treated with propionic acid, you are essentially increasing your horse’s blood glucose level, just as you would if you had fed a hay with a large amount of sugar and starch. Increased glucose leads to increased insulin. And the rest is… well, you get the picture.”

In our anecdotal experience here, we have also noted that some customers who have been feeding treated hay from other suppliers have had trouble with hard manure and loss of appetite in their horses.  This may or may not be due to having consumed treated hay, however it is worth noting.

Are Dust, Mold or Foreign Material Present?

Consuming excessively dusty and moldy hay can inflame the respiratory tract and cause heaves.  Molds in hay can also cause colic and produce mycotoxins.  That said, all hay contains some dust and mold.  Hay is grown outdoors in hay fields and there is just no way to ensure that any hay is free of dust or mold. Mold spore levels can be judged as follows, according to Pennsylvania State University:

 Feeding Risksa at Various Mold Spore Counts
a Risks refer primarily to effect of mold per se without regard to possible mycotoxin content. Dust may also reduce feed consumption.

Data from Richard S. Adams, Kenneth B. Kephart, Virginia A. Ishler, Lawrence J. Hutchinson, and Gregory W. Roth. 1993. Mold and mycotoxin problems in livestock feeding. The Pennsylvania State University.

Mold Spore count per gram Feeding Risk and Cautions
Under 500,000 Relatively low Risk
½ to 1 million Relatively Safe
1 to 2 million Feed with Caution
2 to 3 million Closely observe animals and performance
3 to 5 million Dilute with other feeds
Over 5 million Discontinue feeding

All hay should be inspected prior to feeding to check for mold, dust, and foreign materials such as weeds and anything else that may have been captured inadvertently at bailing.  We have seen some pretty interesting things show up in hay bales – from sticks and mud, to a dead coyote!  Farmers hay hundreds of acres at once in many cases so these things happen!  That said, most of the time, if a horse is being fed enough, he won’t try to eat moldy hay, weeds, or foreign materials.

In Conclusion

The definition of “quality hay” depends on the horse who will be eating it.  There are some absolutes that are true across the board, as above, such as mold and nitrate content, but in terms of protein, texture and fibre, trace mineral content, carbohydrates/sugars, and energy content, there is no answer that is true across the board, because every horse is an individual.

Many of our horses these days are overweight and sedentary, and many of those are metabolically thrifty as it is, thus many of them can benefit from a higher fibre, lower sugar, moderate to lower protein, lower digestability hay.  It keeps them eating longer between feedings and reduces the total amount of calories they can consume in a given time period.  In contrast, a harder keeping, harder working horse like a racing thoroughbred or an event horse requires as many calories per bite as we can get into them, so a softer, higher protein, higher energy, lower fibre hay is better for them.  Your horse is an individual, so the definition of what is a quality feed for your horse is as unique as he is.



“What You Need To Know About Horse Hay”  – Dr. Dennis Cash Ph.D, Montana State University, Ashley Griffin M.Sc, University of Kentucky, Jennifer Nadeau Ph.D, University of Connecticut, Dr. Christine Skelly Ph.D, Michigan State University (

“Selecting Horse Hay” – Ashley Griffin M.Sc, University of Kentucky (

“Forage Facts Publication Series – Nitrate Toxicity” – Kansas State University Research and Extension (

“Quality Hay Production” – Cooperative Extension Service, University of Kentucky College of Agriculture (

“Hay Judging” – Oklahoma Cooperative Extension Service PSS-2588 (

“Do not feed moldy hay to horses” – University of Minnesota Extension (

Timothy & Sugars

Written by Lynda M. Vanden Elzen, edited by Tamara Wrayton

Timothy Grass, Langley BC

Recently, we posted here about some of the many misconceptions and some general information about Alfalfa & Protein, and the article got a big response.  Alfalfa is not the only type of hay that is misunderstood – we receive calls from customers all the time who have been told that timothy hay is always low in sugar, or that it is “too rich” for their horses.  We have even heard of vets and equine nutritionists, supplement companies, forum threads and websites etc, telling horse owners to feed timothy hay to their laminitic ponies because it’s always low sugar or always low in calories.  Well, we’re here to tell you it is just not anywhere near that simple.  Feeding any kind of untested hay to sugar-sensitive horses is very risky.  We have done tests ourselves on timothy we didn’t end up buying because the NSC (Non Structural Carbohydrate) values were up to 24%, when sugar-sensitive horses should not consume an NSC of more than 10-12% depending on whose research you’re following.  Even regular hardworking horses with healthy sugar metabolisms should not consume hays with NSC values over 18%.  Please check out our Testing & Nutrition page for further testing guidelines provided by Shelagh Niblock, BSc.Ag., PAS.

No type of hay is always low sugar, or always high in protein, or always anything.  The only way to know the nutritional content of your hay is to test it.  Period.  You cannot tell by looking at it, smelling it, tasting it, by what cut it is, where it was grown, how that same hay tested last year, what time of day it was cut, whether your horses do or don’t like it, what colour it is, how coarse it is – the list goes on – and you still can’t tell.  Sorry.

On hay tests, sugar values show up as WSC (Water Soluble Carbohydrates), ESC (Ethanol Soluble Carbohydrates), Starch, NSC (Non Structural Carbohydrates, which can be calculated as WSC + Starch), and Fructans (WSC-ESC).  Here are some definitions of these terms from Dr. Juliet Getty, PhD:

Non-Structural Carbohydrates (NSC) —  the total amount of sugar, starch, and fructan. To obtain %NSC, add together %WSC (water soluble carbohydrates) + %Starch. If your horse needs to have a low sugar/low starch diet, the %NSC should be <12%.

Water-soluble carbohydrates (WSC) —  measures simple sugars and fructan levels. Simple sugars are digested in the foregut and raise insulin levels. Too much can lead to laminitis because of elevated blood insulin. Fructan, on the other hand, is digested in the hind gut. Too much can result in laminitis caused by endotoxins in the bloodstream.

Ethanol-soluble carbohydrates (ESC) —  a subset of WSC and gives you a better idea of the simple sugar level. WSC minus ESC provides a fair measurement of fructan levels.

Starch —  normally digested in the foregut down to individual glucose (blood sugar) molecules; therefore, it has a strong elevating effect on blood insulin levels.

There are some factors that can contribute to hay testing a certain way.  For example, because grasses accumulate sugars throughout the day in order to grow during the night without photosynthesis after the sun goes down, the sugars in the grass are lowest in the very early morning before the sun comes up.  If the grass hay is cut at this time, then the sugars will most likely be lower than they would have been if that same hay had been cut in the late afternoon, but you can only compare that one specific hay to itself.  You cannot generalize and say that all hay cut at 5am will be low sugar; likely that specific hay will be lower sugar than it would have been if it had been cut at 4pm.  But even that depends on other factors, including the overnight and daylight temperature, cloud cover, shady vs sunny areas of the field, and how stressed the grasses are due to things like weather, drought conditions – I think you see that it is not black and white.

From Kathryn A Watts, B.S. and N. Jerry Chatterton, PhD:

Sugars are the substrates for all plant growth, thus, they are critical to plant growth and development.  Sugars are produced by photosynthesis during daylight.  At night plants use energy from sugars formed by photosynthesis to grow.  Whenever the rates of photosynthesis exceed plant growth rates, carbohydrates accumulate.  At times, plant stresses decrease growth rates more than photosynthesis and carbohydrates accumulate.  Factors that contribute to plant stress include water and nutrient deficiencies, salty soils, as well as cool temperatures, especially those below 5°C.

There are some things you can tell by looking at hay: a coarser hay is probably higher fibre, for example.  You can look at a hay that is a mixture of grasses or grass and alfalfa and see the approximate percentage of each species that makes up the mixture.  Grasses that have been left to grow for a longer period of time will have more mature stalks and seed heads, where alfalfa hay that is post-bloom will contain purple flowers.  Usually, second cuts don’t grow for as long a period of time as first cuts, so they are softer (i.e. they contain less mature plants.) Plants that have gone to seed – so post-bloom alfalfa and grass hays with seed heads – will tend to be lower in protein than they would have been if they had been cut before the seed heads or flowers appeared, and grasses in the active heading stage will probably be higher in sugars.  Unfortunately, none of these observations can tell us anything about sugar levels or protein levels as compared to other hays.

Kathryn A. Watts, B.S., and N. Jerry Chatterton Ph.D support the idea that rules of thumb with regard to sugar levels in grass don’t always work:

In general, mature plants that are high in fiber are low in carbohydrates.  However, environmental conditions have a very large impact on carbohydrate content.  Under some circumstances, environmental factors may be more important than stage of plant growth.  Very young, rapidly growing grass under ideal conditions are often lower in carbohydrates than at later stages of vegetative growth.  Conditions in the spring and in the fall often favor carbohydrate accumulation, regardless of the stage of plant growth.  A frost, or a hot, dry wind, may cause rapid changes in carbohydrate concentrations within a very short time.  Climate and plant species are so important in determining carbohydrate levels of forages that it is difficult to generalize about carbohydrate concentrations, especially in forages from various parts of the country or world.  Simple statements such as “avoid grazing lush grass” do not guarantee low carbohydrate levels.  Certainly, there are times when ‘lush’ grass is high in carbohydrate.  Instances when grass plants are cool temperature stressed, or when in the heading stage, are often troublesome times and should be of concern to care takers of sugar intolerant equines.

We see many hays here that look like they’ll probably be lower sugar – they have more alfalfa than grass – and then the test comes back and we find we were wrong.  It happens all the time.  We had a 2nd cut orchard/alfalfa mix in 2014 that was probably 50% alfalfa, soft, green, and lovely, with few seed heads.  The NSC was almost 22%.  We also see significantly different tests from the same farmer’s field depending on the year.  The only way to know is to test.

Timothy hay in particular tends to be quite variable in protein and sugar content.  Why is that?  Well, first let’s define what timothy is, because we find many horse owners are unable to distinguish between timothy and orchard grass, or other grass hays.

From the United States Department of Agriculture Natural Resources Conservation Service Plants Guide:

Timothy is a relatively short-lived, cool-season, introduced perennial grass that grows in stools or clumps. It has a shallow, compact, and fibrous root system. It grows in erect culms 50 to 100 cm (20 to 40 in) tall. Leaves vary in length from a few inches to more than a foot and are about 0.6 cm (0.25 in) wide, narrowing gently toward the tip.

Cool season grasses like timothy, orchard grass, and brome are able to grow in more northern climates because they are better at storing sugars than warm season grasses like those that grow in the southern United States.  Great for the grass – not so great for overweight sedentary horses.  In contrast, grass hays tend to be lower in digestible energy than legume hays like alfalfa, so it becomes a balance between providing adequate protein and minerals while ensuring the sugar levels and caloric density are not too high.




Orchard Grass

grass-smooth brome

Smooth Brome Grass


Meadow Brome Grass

The best way to tell the difference between timothy, orchard grass, and brome grass is by its seed heads.  Here are some photos, from the Ontario Ministry of Agriculture, Food, and Rural Affairs, of the various types of seed heads for your reference (left).

In this article, we have singled out timothy because it is the grass hay about which the most myths and misconceptions are circulated, but all cool season grasses are similar in that they store fructans and are very good at storing sugars in general.  This is what enables them to survive in colder climates.  It also means that when those grasses are stressed, they hay we make from them can vary widely in sugar levels.  That said, in our experience, having tested hundreds of stacks of hay, timothy seems to vary more in sugar levels than the other grass hays we test.  It turns out that timothy has a unique carbohydrate storage system.

According to the Washington State University Extension Drought Advisory:

Timothy is unique among grasses in that during the autumn it develops a corm, which is a bulb-like structure, from an elongated internode. Water soluble carbohydrates, mainly fructans (chains of fructose sugars with a terminal glucose sugar), fill the corm until after the flowering stage in the spring. Fructan concentration then declines in the seedhead stem as starch content increases in the seedheads. Very little fructan is stored in the seeds at crop maturity, since starch is the primary storage carbohydrate in the seed. Highest fructan concentrations are found in stem bases (the region from soil surface to approximately 3″ above the ground) and the corms. Fructans molecules are stored in the vacuole of cells and vary in length and size, depending on the grass species. Fructans are produced from sucrose (common table sugar) during photosynthesis and can be created any time of the day or night. Timothy fructan molecules are larger than those in other cool-season grasses and actually more resemble those of onions.

To illustrate how much timothy can vary, we created the following infographic to display at our trade show and horse show booths as a conversation starter with the horse people we meet. You can click on it to open a larger version if this one is too small:

Test Comparisons - 1st cut Timothy (11x17)You’ll find that the test on the left was an excellent batch of timothy, but the one on the right contained a sugar level that is unsafe for the majority of horses, and has woefully inadequate protein levels as well.  These two hays looked very similar and were grown in the same area during the same year and cut at approximately the same time.  Feeding the hay from the test on the right to a sugar-sensitive horse every day would be like feeding a diet of mars bars and caramel corn to a diabetic person.  Timothy is not always or even often low sugar.  Sometimes it is.  But the only way to know if the timothy you are feeding is low sugar is to test it.  If somebody tells you timothy is always low sugar hay, they are wrong.  

All of that said, we must remember that we cannot generalize that all horses should eat a low sugar/carbohydrate diet with an NSC under 10-12%.  Shelagh Niblock, BSc.Ag., PAS and Senior Nutritionist at Hi Pro Feeds points out that where horses in the past worked for a living and were rarely obese, and did not live into old age after their functional lives had ceased, our 21st century horses tend to be overfed, underworked, and as a result, are suffering from metabolic issues they would not have 100 years ago.  For these horses, and for those with other disease conditions that are exacerbated by excess sugar, low starch diets are crucial.  But, for horses who still do work hard for a living, carbohydrates are an important energy source.  According to Shelagh:

Both starch and sugar are important energy sources for the high performance equine athlete and, when fed appropriately, they are not dangerous or “bad” for your horse, assuming that he is otherwise healthy. Carbohydrates such as starch should be fed in small amounts per meal so that the starch is digested before it moves out of the foregut. Excessive starch fermentation in the hindgut can cause deleterious changes in hindgut bacterial populations, potentially resulting in health problems such as gas colic, chronic and/or acute laminitic episodes, and hindgut ulcers, to name a few. Small meals ensure that starch is more likely to be digested in the small intestine and that fluctuations in blood glucose as a result of starch digestion are smaller and more efficiently regulated by the insulin secreted by the pancreas.

In conclusion, the take home message here is that we simply cannot generalize that all timothy or other grass hay is low sugar, or that all horses will thrive on a low sugar diet.  We can’t generalize at all; every stack of hay and every horse is an individual, and must be treated as such.  The factors that influence both the sugar levels in grass hays and the carbohydrate requirements of horses are complex.  We would prefer to be able to lay out a list of cut and dry feeding guidelines for all horse owners to live by – it would make our jobs easier and our horses happier!  Unfortunately, it just isn’t that simple.



“United States Department of Agriculture Natural Resources Conservation Service Plants Guide” (

“Managing a Horse with Laminitis on Grass Pastures” – Ann Swinker, Penn State University Extension Equine Specialist (
“Factsheet: Pasture Grasses Identified” – Ontario Ministry of Agriculture, Food, and Rural Affairs (

“Drought Advisory” – Washington State University Extension (

“How to Interpret Your Hay Analysis Report: the Basics” – Dr. Juliet Getty, PhD (

“A Review of Factors Affecting Carbohydrate Levels in Forage” – Kathryn A. Watts, B.S., N. Jerry Chatterton, PhD (

“Low Starch Diets: Manage Carbohydrates to Your Horse’s Best Advantage” – Shelagh Niblock BSc.Ag., PAS (