Hay for Horse Health

Horses with conditions such as muscle or metabolic disease might have special hay needs to stay healthy.

Hay. It’s an essential part of a horse’s diet, fueling the equine body and equipping it for optimal function with energy, protein, vitamins, and minerals. In fact, we know that for many horses, and especially during certain times of the year, hay becomes the most critical part of the forage diet, which is why we work so hard (and spend so much!) to find and secure quality hay for our horses. It’s also why we’re always scrutinizing, shaking, and smelling flakes of hay before feeding them to our horses.

But great hay can only go so far for horses with certain health conditions—it can even harm them if certain nutrient levels are too high or low. So, what and how much hay do we feed our horses with metabolic or other conditions that diet impacts?

The Healthy Horse’s Hay Needs

To get started, we need to review how we build the normal, healthy horse’s hay ration. The average horse should consume around 2% of his body weight per day in forage (including grass), but New Jersey equine practitioner and consultant for the Veterinary Information Network Kate Hepworth-Warren, DVM, Dipl. ACVIM, maintains that there is no one-size-fits-all hay ration for a healthy horse.

“You have some horses that are easy keepers that do fine with grass hay alone,” she says. “All horses need hay. What type and what you supplement with will depend on the type of horse.”

For example, “some Thoroughbreds may need to be fed 2% of their body weight,” she continues. “They may even need up to 3%. And they probably need grain and a diet balancer.”  

The hard-keeping Thoroughbred, says Hepworth-Warren, might need some alfalfa mixed with grass hay to get enough protein. “Whereas a similar-sized Quarter Horse, like my porky mare, may need only grass hay and never any grain.”

The authors of the textbook Equine Internal Medicine (by Reed, Bayly, and Sellon) note that plant leaves contain higher nonstructural carbohydrate (sugars and starches) and protein levels than stems, so hays with a high leaf-to-stem ratio generally have a higher nutritional value.

But, as you might suspect, higher nutritional value isn’t a good idea for every horse (Here’s looking at you, rotund little pony!). Different levels of hay nutrition might be more appropriate for the changing needs of horses with a few specific diseases.

Hyperkalemic Periodic Paralysis (HYPP)

Dietary management is critical to minimizing clinical signs in horses (primarily Quarter Horses) affected by the genetic muscle disorder HYPP.

These horses have a mutation of the skeletal muscle sodium channel gene, which causes the muscle cells to release potassium and also causes muscle hyperexcitability. Signs of clinical HYPP can range from muscle tremors to paralysis and even death.

Hepworth-Warren recommends avoiding high-potassium hays, such as alfalfa, and feeds containing molasses when feeding horses with the HYPP mutation. She stresses the importance of keeping these horses on a consistent diet with plenty of grass turnout. “Most HYPP horses are easy keepers anyway,” she says. “Any feed change has to be very, very gradual. Don’t run out of hay and change feeds overnight.”

Low-potassium hays, such as late-cut grass hay (e.g., timothy, Bermuda), are better choices for these horses.

Equine Metabolic Syndrome (EMS)

Horses with this disorder are prone to collecting fat in specific areas of the body (typically the crest, tailhead, shoulder, udder, or sheath) or just generally appearing obese. These horses typically also have abnormal blood insulin responses to carbohydrate or sugar intake (insulin resistance, meaning they have lost sensitivity to insulin that the pancreas releases, which makes it harder for the fat, muscle, and liver cells to transport glucose out of the bloodstream and store it as glycogen) and are predisposed to laminitis.

Hepworth-Warren points out that not all horses with EMS are obese. Knowing these animals’ insulin status is important, because it can indicate whether they will be highly sensitive to carbohydrates, even if they don’t look like classic EMS cases. She suggests that owners of EMS horses “feed hay that looks to be of poor quality but isn’t moldy. Those horses also should not have alfalfa and don’t need the lush green hay that we think looks the tastiest. These may only need to be fed 1.5% of their body weight in hay to maintain a good weight.”  

Divvy up theses horses’ hay in slow-feed or similar haynets to keep them foraging, essentially helping their reduced ration last longer. And because lower-quality hay might not meet all their nutritional needs, you might need to add a low-calorie ration balancer or a vitamin and mineral supplement to their diet.

Soak hay to reduce its carbohydrate content if your horse has EMS or PSSM.

While “weighing hay is something people don’t like to do,” says Hepworth-Warren, she does suggest owners purchase a small luggage scale to weigh each bale of hay. And clearly, she says, grain is a no-no for these horses.

Many people, including Hepworth-Warren, advocate soaking hay to reduce its carbohydrate (starch) content, but the 2010 American College of Veterinary Internal Medicine consensus statement on equine metabolic syndrome states that “a recent study demonstrated that results vary markedly among different hay samples, so this strategy cannot be relied upon to completely address the problem of high water-soluble carbohydrate concentrations in the hay that is being fed to a horse or pony with EMS.”

In other words, you can’t just soak the hay and call it done. It’s a good idea, then, to have a laboratory analyze your EMS horse’s hay for carbohydrate content.

Polysaccharide Storage Myopathy (PSSM)

Like horses with EMS, these horses, says Hepworth-Warren, “can’t process carbs as well. You want to feed them similar to an EMS horse.”

These horses have a defect in the breakdown and processing of carbohydrates and accumulate polysaccharides in the muscle, making them prone to rhabdomyolysis (tying-up) and exercise intolerance. In addition to regular turnout and exercise, these horses do best on a high-fat (13%), low-starch (less than 10%) diet.   

Hepworth-Warren suggests supplementing a diet of good-quality, low- to moderate-quality grass hay and low-starch grain with a fat source such as corn oil or commercial fat supplements (to make sure the horse is still getting enough calories). And, again, “Soaking hay can remove a lot of starches,”
she adds.  

Equine Gastric Ulcer Syndrome

All ages and breeds of horses can develop ulcers in their esophagus, stomach, and small intestine.

The authors of a 2009 study on the dietary management of equine gastric ulcer syndrome note multiple risk factors, including intense exercise, intermittent feeding, stall confinement, and high-concentrate (grain-heavy) diets.  

For horses affected with gastric ulcers, the key, says Hepworth-Warren, is “keeping hay in front of them all the time or, better yet, keeping them turned out on pasture. Some research has shown if there is a long period of fasting (as seen with once or twice daily meal feeding), these horses have more acid buildup (in the stomach).”  

These study authors (Andrews et al.) suggest alfalfa hay “may have a protective and antiulcer effect in horses.” Hepworth-Warren, however, says the jury is still out on this. “Some older research suggests alfalfa, which is higher in calcium and protein, can buffer the stomach acid,” she says. “There is always ongoing research into gastric ulcers, and the way feed affects them depends on the type of ulcers that the horse has.”

Other Conditions

Hepworth-Warren mentions a few other special-needs cases when it comes to feeding (or not feeding) hay. For horses with recurrent choke she suggests soaking hay to soften it before feeding. She also suggests soaking to minimize hay dust for horses with recurrent airway obstruction (RAO, heaves).

She notes that Miniature Horses “are the exception to the ‘all horses need hay’ rule because they like to develop small colon impactions.” However, she adds, 24/7 pasture grass is risky in Minis because “they are always on the edge of foundering.” For Minis prone to impaction, she recommends a low-starch pelleted feed. Some can tolerate hay very well, whereas others might need to be on a complete feed.

Take-Home Message

When purchasing hay, says Hepworth-Warren, “the main thing is thinking about your particular horse. I don’t know if the cutting necessarily makes a ton of difference. You want good-quality hay.”

While color is not always an indicator of quality, she says, it is important to make sure the hay is “palatable and not moldy and not overly stemmy.”

Above all, she says, “People need to know they can’t feed every single horse the same. Measure appropriately—a flake is not a flake is not a flake.”  

While many horses do well on an all-hay diet, the composition of that diet must meet each horse’s needs. When in doubt, work with your veterinarian or nutritionist and send your hay in for an analysis. And, when making any feed changes, do so gradually.