Hay may look like the simplest part of a horse’s diet, but as University of Guelph professor Dr. Anna Kate Shoveller explains, it’s the foundation of equine health and far more complex than it appears.
Horses are designed to graze for 14-18 hours a day, relying on a steady flow of forage to protect the stomach, fuel the hindgut and support overall wellbeing. Whether we feed hay dry, soaked or steamed, those decisions matter. Each method shifts something, from dust levels to nutrients and even taste, and knowing the differences helps us choose what’s best for our horses. In a University of Guelph study, Shoveller and her team examined how these treatments change the hay, how horses respond and why the “right” choice depends entirely on the individual horse.
The Horse’s Vote
The University of Guelph study found horses appeared to prefer steamed hay equally to their normal dry hay, while soaked hay was a less‑favoured choice. In this research, horses were offered different hay types side by side, and their behaviour was monitored to see how long they spent investigating and eating from each option. Horses consistently ate less of the soaked hay and spent less time interacting with it, whereas dry and steamed hay were eaten more readily.
In addition to observing how the horses behaved, the research team also measured changes in the hay itself. Soaking was shown to wash out some nutrients, such as certain proteins and sugars, while steaming proved better at conserving them, which may help explain why horses gravitated toward the dry and steamed options. Researchers hypothesize that the horses may prefer hay that is more nutrient dense, since soaking results in losses of water-soluble carbohydrates and protein. Although texture differences were speculated as a possible factor, the study’s conclusions were based on the horses’ clear choices shown through interest in and time spent eating each hay type.
Your Hay Baseline
“Whether you're going to do secondary processing of your hay [steaming or soaking], it's the original hay that you select that is the most important decision that you're going to make,” said Shoveller. “The best way to understand the quality of your forage is to do a forage analysis, and that should be the foundation of your nutritional approach.”
When working with an equine nutritionist, Shoveller describes the starting point is factoring how much hay your horse consumes voluntarily, and then calculate their nutrient requirements. The next calculation is if their voluntary consumption of hay meets all their nutrient requirements before figuring out what they will need in the way of concentrates and supplements. First and foremost is predicting your hay and or pasture intake, then finding out the nutrient composition of that forage. For horses prone to obesity, selecting hay with a low nutrient profile is usually advisable, whereas nutrient dense hay is more optimal for the highest performing horses.
Nutritional Profile Changes
Soaking hay causes losses of soluble protein, potassium and non‑structural carbohydrates (NSCs), which would be sub-optimal for horses with high nutrient demands.
Soluble protein (SP) is the portion most readily digested and used; performance horses rely on it to build and maintain muscle for training and recovery. In the Ontario study, soaking hay for 30 minutes reduced potassium by 41 per cent, a key consideration for athletic horses that lose electrolytes in sweat.
Non-structural carbohydrates are the easily digestible simple sugars and starches in hay that supply fast-energy in contrast to the energy produced from fermenting structural carbohydrates, such as the components of total dietary and crude fiber, or structural carbohydrates. Non-structural carbohydrates are not part of the plant’s fibrous cell wall structure and contain mainly water-soluble carbohydrates (WSCs), are part of the NSC content, and are susceptible to being washed out during the process of soaking hay.
To make the concept relatable, Shoveller compares soaking versus steaming hay to boiling versus steaming carrots: boiling colours the water as nutrients leach out, while steaming keeps more nutrients in the food.
"When we steam carrots, the water below the steamer remains clear but when we immerse them in boiling water, that water will turn an orangey-brown from carotenoids. This signals the removal of carotenoids in the carrots and along with that, other soluble components of the carrots.
"In steaming, far more of the nutrients that are within carrots stay within the carrots. When we think about this concept and apply it to soaking or steaming hay, this is where soaking hay leads to a reduction in NSCs and specifically those are the carbohydrates that increase the horse's glycemic response. If I had an overweight horse that I'm trying to control weight on, that generally means I also want to control the glycemic index. So, I don't want to see big increases in blood glucose when they choose to eat larger portions. Soaked hay might be really practical for horses with metabolic syndrome and for horses that are easy keepers.
"If I have performance horses, young horses or old horses for this matter, who have a harder time getting the same amount of nutrients from the same feed, this is where steaming hay is an obvious go-to. We don't want to limit intake and we certainly don't want to limit nutrient intake with our horses that have really high nutrient requirements."
Nutrients Soaked Away Beyond Sugar
While soaking hay is often used to reduce sugar for metabolic or overweight horses, Shoveller emphasizes that sugars are not all that is washed away in the process. Along with the water‑soluble carbohydrates that many owners are intentionally trying to lower, soaking also removes a wide range of other nutrients, including minerals and micronutrients that would otherwise remain available in dry or steamed hay. Steaming does not cause these same nutrient losses, and dry hay, of course, maintains its original nutrient profile.
Shoveller explains that soaking hay creates a balancing act for owners. It is a useful strategy for horses where sugar reduction is desired, such as managing metabolic syndrome, insulin resistance or obesity. However, owners need to understand that they’re also reducing many nutrients the horse requires. When soaked hay makes up a large portion (or all) of the forage ration, she advises adding a ration balancer or appropriate supplement to replace the vitamins and minerals removed during soaking. This becomes especially important when the horse isn’t receiving anything in addition to forage.
A caveat for soaking hay concerns time. As we know, drenched hay quickly grows moldy. Once hay becomes wet, it creates ideal conditions for rapid microbial growth, especially in warm weather. For most situations, soaking should be kept to the minimum effective duration and fed promptly afterward. Many equine nutritionists recommend soaking hay for 15-30 minutes and no longer than one hour. Research supports this guidance: a University of Minnesota study notes that 30 minutes in warm water or 60 minutes in cold water is effective for reducing carbohydrates. Shorter soaks have also been shown to have an impact, with 15 minutes resulting in significant decrease of sugar levels in some types of hay. If you are thinking of soaking hay, talk with your equine nutritionist to discuss desired results and make sure it’s the right strategy for your horse and to ensure that any nutrients lost in the process are balanced appropriately.
Respiratory Concerns
Reducing particles the horse may inhale at meal time is one step toward improving respiratory health.
Shoveller said, “When we think about dust from hay, both soaking and steaming will reduce it, so long as the dust isn’t coming from mold that produce mycotoxins.”
That stipulation is key: if “dust” is actually moldy fines and spores, no amount of wetting the forage will solve the underlying problem. In fact, you may end up masking an issue that needs to be addressed at the source. Mold matters, even in small amounts.
“Mold and mycotoxins can be extremely deleterious to horses, and even small amounts can reduce performance,” cautioned Shoveller. “We can't fix poor hay, we can't fix heavily moulded or mycotoxin contaminated hay with either one of these techniques [steaming or soaking].”
For that reason, suspect hay that is dusty or musty, should be tested for mold and mycotoxins or discarded. Furthermore, good storage practices (dry, ventilated, off the ground), careful selection and minimizing indoor dust sources (bedding, traffic, wetting aisles before sweeping and sweeping when there are no horses in the barn) all support healthy air supporting both horses and those who work with them.
For horses that are especially reactive or when caretakers need the most controllable, low‑dust option, processed forage may be a practical next step.
“For horses that need the lowest dust possible, I would move to pelleted or extruded hay,” recommended Shoveller. “Those products are checked for mold and mycotoxins, and the pelleting or extrusion process reduces the ability for mold to grow.”
Pellets and cubes don’t replace the need for good ventilation and overall dust control measures, but they can cut down on inhaled particulates at feeding time while maintaining nutritional consistency.
Shoveller added, “Sources of dust inside tend to be far greater than the sources of dust outside.”
For horses with respiratory problems, outdoor pasture is usually the best option. And 24/7 group turn out helps to meet the behavioural needs of horses. Shoveller encourages considering all the environmental dust exposures and implementing every management technique possible.
Gut Health, Ulcers and the Case for Consistent Forage
We have already digested that horses are built to graze 14-18 hours a day, with a steady trickle of forage moving through the stomach and into the hindgut. That slow, continuous flow matters because the equine stomach secretes hydrochloric acid all the time, not just at mealtimes. When long gaps occur without available forage, the stomach environment becomes more acidic which significantly raises the risk of ulcers.
Frequent, fibre‑rich chewing supports the production of saliva, which is nature’s antacid for the horse’s stomach. The forage journey continues from the stomach to the hindgut for ongoing fermentation to generate energy to keep their systems running and fuelling daily work. Consistent access to forage protects the stomach up front and keeps the engine humming in the back.
Shoveller emphasized, “Constant forage helps to keep the stomach ulcer-free and healthy.”
Automated Hay, You Say?
Potentially reducing the risk of ulcers could be a side-perk from a new study on automated hay feeders which has received funding from Equine Guelph at the University of Guelph. The idea of automated hay feeders is to mimic natural grazing "feeding little and often" both during the day and overnight. This could help busy barns maintain healthy equine digestive systems, especially through the hours where staff are not on site. The project is scheduled to begin June 1, 2026 in the Okanagan region of British Columbia with Dr. Katrina Merkies, Professor in the department of Animal Biosciences at the Ontario Agricultural College, Dr. Megan Ross and master’s student Alayna Riddell.
“The main focus of the study is to look at social dynamics and voluntary physical activity in relation to providing hay from automated feeder,” said Merkies. “However, forage meals with long gaps are a known risk factor for ulcers. Feeding smaller, more frequent meals is considered optimal for the equine digestive system and may help lower ulcer risk.”
Automated feeders can be loaded with a hay bale and programmed to open multiple times, targeting a percentage body weight in total daily forage to be dispensed and adjusting the duration based on how quickly the allocation is consumed. By spreading access across many windows, the system supports the protective trickle feeding pattern without requiring staff to feed seven to 12 times a day — an ideal most barns can’t manage.
When asked how the equine welfare and behaviour focused study will be structured, Ross explained, “We’ll monitor eating and drinking frequency, social and agonistic interactions, and use a 24/7 halter‑mounted sensor to log distance travelled and activity patterns.”
When first introduced to the automated feeder, horses may learn to anticipate feeder opening times and an increase in social interactions may occur in response to the limited resource. However, once horses learn that forage will be available regularly and often throughout the day, displacements at the feeder should taper off. The automated feeders will be installed on fencelines in paddocks and the halters will allow tracking of movement, distance travelled and activity patterns. The team plans to compare findings from automated feeding to those recorded during unlimited hay access.
The researchers note that while ad-lib, unlimited access to hay meets the need for constant gut fill, some horses overeat and are therefore at risk for obesity and the complications that go along with it. An automated schedule may offer a middle path of frequent, predictable access that protects the stomach and supports hindgut fermentation, while avoiding unchecked intake. It may also ease management of metabolic horses (e.g., those pulled off pasture) by delivering more frequent, but controlled portions, including overnight, when human labour is hardest to supply.
Once the team has recruited barns and horses in varied group sizes, they will begin with feeders open continuously to establish baseline behaviours then transition to scheduled feeding windows.
In situations where time, turnout or staffing limit how often hay can be offered, automated feeders may help close the gap between what horses need and what is realistically possible in a busy barn.
(Equine Guelph)