Feed the Breed: Consider Breed, Type when Designing Equine Diets

Whether donkey or draft, pony or horse, equid class dictates proper diet

Donkeys aren’t ponies. Ponies aren’t short horses. And drafts aren’t oversized lightbreeds. We know not all equids are created alike, but we’re not just talking about their height and shape. Certain breeds and types of horses are prone to metabolize their food slower or faster than others or develop diet-related disorders. In a recent study, for instance, researchers from the University of Melbourne, in Australia, discovered that different equine breeds have different insulin responses to oral glucose (insulin helps transport this crucial energy source throughout the body). Insulin levels can contribute to a variety of conditions, such as equine metabolic syndrome (EMS), insulin dysregulation, and laminitis.

In short, we must consider the breeds of our horses and ponies when planning their diets. Let’s take a look at what we currently know about feeding major equid categories and where we’re heading.

Mules and Donkeys

The domestic donkey’s ancestors evolved as browsers and grazers, surviving on low-energy fibrous plants. “Donkeys would travel for many miles to obtain food, spending 14 to 18 hours per day foraging over distances of 20 to 30 kilometers (about 12 to 18 miles),” says Faith Burden, PhD, director of research and operational support at The Donkey Sanctuary, in the U.K. Modern-day donkeys rarely have the opportunity to perform this combination of natural behaviors.

Like all equids, donkeys are hindgut fermenters and have evolved to handle a steady trickle of fibrous plant material moving through the gut at all times. But, “unlike horses, donkeys are highly efficient at digesting poor-quality fiber sources, and the donkey’s maintenance energy requirements are considerably lower,” says Burden. On average, a donkey’s daily digestible energy requirements range from 50% to 75% of that of a similar-sized horse.

Burden says researchers have shown that a donkey’s daily appetite at maintenance is 1.3% to 1.8% of body weight in dry matter per day. An overabundance of energy or calories in these animals can lead to a variety of health problems.

“An excess storage of energy as metabolically active adipose (fat) tissue can lead to inappropriate mobilization of lipids (into circulation), insulin resistance (reduced sensitivity to insulin that causes overproduction of this hormone), and enzyme dysregulation,” says Burden. While research to establish donkeys’ protein, vitamin, and mineral requirements is scarce, their protein metabolism and use does appear to differ from horses’.

“Experience would indicate that donkeys can survive on low-quality protein-containing diets, as evidenced by their ability to survive, breed, work, and grow on low-quality forages,” says Burden. The vitamin and mineral levels recommended for horses appear to be sufficient for donkeys, as well.

Donkeys
So what diet should a donkey consume? Burden suggests feeding fit, healthy donkeys a mixed forage-based diet, with cereal (barley or wheat) straw or coarse, low-energy hay to provide “bulk,” and adding higher-calorie fiber sources such as grass, hay, haylage, alfalfa, and beet pulp, depending on body condition, life stage, and workload.

“Donkeys rarely require energy-rich cereal grains, sweet feeds, or highly molassed products,” she says. “The feeding of such products is poorly tolerated, often wasteful, and frequently associated with the development of health issues such as laminitis, gastric ulceration, hyperlipemia (high fat levels in the blood that can cause liver and kidney damage), and colic,” not to mention obesity.

If you have a hard-working donkey, he does require cereal grains or concentrates, but Burden says his combined starch and sugar levels (nonstructural carbohydrates, or NSCs) should not exceed 15%. Ideally, they should be about 10%.

Also, donkeys are renowned for their thirst tolerance, but don’t confuse this with their water requirements, says Burden. Donkeys’ water needs are similar to those of horses, varying considerably depending on workload, ambient temperatures, and pregnancy and lactation status.

Make sure your donkey gets regular dental exams and maintenance so he can get the most out of his high-fiber diet. Offer logs and branches to satisfy his natural browsing behaviors and prevent him from chewing on fences and barns. Safe types include hazel, ash, hawthorn, apple, birch, alder, lime, poplar, and gorse.

Draft Horses

The most common and significant condition veterinarians can treat or prevent with diet in draft horses is a muscular disorder known as equine polysaccharide storage myopathy (PSSM/EPSM), says Beth Valentine, DVM, PhD, Dipl. ACVP, professor of anatomic pathology at Oregon State University’s College of Veterinary Medicine, in Corvallis. Historically called Monday morning sickness in working draft horses after a day of rest, PSSM/EPSM can lead to a variety of issues, from subtle hind-limb gait abnormalities to massive muscle damage from exertional rhabdomyolysis, or tying-up. It is a dominantly inherited trait, meaning just one parent can pass it on. Belgians commonly experience the neuromuscular disease shivers along with PSSM, although the two conditions appear to be unrelated.

Several clinical studies have confirmed that diet, particularly NSC levels, plays a significant role in PSSM/EPSM episode frequency and severity. Because the disease alters the simple sugar glucose’s storage method as glycogen in muscle, reducing sugar and starch intake could benefit these horses. Valentine’s research shows that replacing a significant amount of sugar and starch with fat can reduce PSSM/EPSM episode frequency and severity.

So what dietary changes should you consider for draft horses? “When draft horses show signs related to PSSM/EPSM, I recommend reducing dietary starch and sugar as much as possible and gradually increasing fat intake until the horse is eating 1 pound of fat (2 cups of vegetable-based oil) per 1,000 pounds of body weight per day,” says Valentine.

This means removing all high-starch and -sugar concentrates from the diet. Offer forages, either grass or legume pasture or hay, at a minimum of 1.5% of body weight per day. In most cases, horses with PSSM/EPSM can graze lush pasture as long as they are consuming the recommended amount of fat and do not become obese. Regular exercise and turnout can also help prevent episodes.

For youngsters and horses that might have this abnormal type of metabolism but are not showing physical signs, Valentine suggests providing them with half the treatment “dose” of fat. “If PSSM/EPSM issues ever arise, the amount of fat in the diet can be increased,” she says.

As a general nutritional principle, Valentine always recommends draft horses get a vitamin E supplement, a powerful antioxidant that can be deficient in diets of horses not grazing green grass pasture most of the year. Also, depending on their area, you might add a selenium supplement.

Feed the Breed: Ponies

Ponies

When you picture a pony, more than likely he’s pleasantly plump. Pony breeds prominently exhibit the EMS ­phenotype—observable characteristics associated with the disorder, such as obesity and a cresty neck. In 2006 a group of researchers from Virginia Polytechnic Institute and State University (Virginia Tech) found a dominant mode of inheritance for prelaminitic metabolic syndrome in an inbred herd of Dartmoor and Welsh ponies, suggesting genetics play a role in a pony’s EMS development.

Hyperinsulinemia, an excessive insulin response to rising blood glucose levels, falls under the EMS umbrella and could lead to laminitis development. In most cases hyperinsulinemia occurs as a result of obesity; researchers from Charles Sturt University in Australia found sustained hyperinsulinemia in obese Shetlands and Welsh-cross ponies when they compared blood insulin values to nonobese horses eating the same free-glucose-containing meal. Could simply being a pony, regardless of obesity, be a factor? It appears so. The team found that nonobese mixed-breed ponies also had elevated hyperinsulinemic responses to an in-feed glucose dose (Bamford et al., 2013).

So, knowing all this, how should we feed ponies? One of the first recommendations is to prevent overweight ponies from becoming obese because of their weight loss resistance. Potter et al. (2013) found a restricted diet to be fairly ineffective at reducing obese mixed-breed ponies’ weight. After a four- to six-week diet restriction, Standardbred horses reached a body condition score (BCS) below 5, whereas ponies only decreased from around a 7 to a 6 after 12 weeks of diet restriction. Light to moderate daily exercise had no effect on weight loss in this study. In contrast, researchers on another study found that using a dynamic feeder that encouraged ponies to perform persistent low-intensity exercise, in addition to a restricted diet, did reduce BCS (de Laat et al., 2016).

Pasture could be a significant source of excess calories for ponies. For example, when grazing during a six-week study, ponies consumed an estimated average of 3.8% of their body weight in dry matter, slightly over 50% more than the normal intake of 2.5% of body weight (Longland et al., 2011). And when limiting pasture turnout to three hours per day, ponies increased their grass consumption from 0.49% to 0.91% of body weight in dry matter intake per day within six weeks (Ince et al., 2011). Wearing grazing muzzles for 10 hours a day did slow ponies’ weight gain compared to those allowed to graze freely (Longland et al., 2016). However, ponies adjusted their eating behavior after just one week of wearing a grazing muzzle, and by Weeks 2 and 3 the ponies actually gained weight.

Severe dietary restrictions can be more effective yet stressful on ponies, possibly leading to gastric ulcers or behavioral issues. When scientists put obese Shetland ponies on a 21-week weight loss plan involving a diet of low-energy hay and a ration balancer, the ponies experienced a significant drop in body condition score (Bruynsteen et al., 2015). Ponies are more prone to hyperinsulinemia than other breeds, so only implement severe restrictions under a nutritionist and veterinarian’s guidance. With this in mind consider the following recommendations:

  • Avoid high-NSC feeds, including starches, sugars, and fructans from pasture;
  • Feed a hay containing 10 to 12% NSC, at most. If this isn’t available, soak hay in water for 30 to 60 minutes to reduce the NSC fraction before disposing of the water and feeding;
  • Most ponies maintain their ideal weight on forage alone. Use a low-calorie ration balancer to provide a complement of vitamins, minerals, and amino acids; and
  • If ponies do need to gain weight, increase the calories in their ration by feeding more hay, introducing a highly digestible fiber source such as beet pulp, or supplementing with a fat source.

Horses

Feeding recommendations for horses currently focus on known diseases rather than genetic differences. However, evidence suggests breeds such as Morgans, Paso Finos, Quarter Horses, and Andalusians might be more prone to developing EMS. Whether a genetic component exists in these breeds remains to be discovered, but you might consider proactively feeding to reduce the risks of EMS. Read more on this topic at TheHorse.com/110374.

We do know that certain genetic lines of Quarter Horses related to the stallion Impressive might be affected by the muscle disorder hyperkalemic periodic paralysis, or HYPP. In these horses, a mutation in the sodium channel gene causes the channel to become leaky when blood potassium levels fluctuate. Therefore, the focus turns to managing diet to maintain steady blood potassium concentrations. Read more about feeding horses with HYPP at TheHorse.com/19839.

Wrapping It Up

Just as with height and coat color, genetics set the blueprint for how a horse or pony responds metabolically to their diet. Here’s what we do know:

  • Most donkeys do just fine on a low-quality forage source alone;
  • Drafts and Quarter Horses can suffer from a muscle disorder that’s easily managed with diet changes; and
  • Ponies tend to have a greater insulin response, regardless of their diet.

Regardless of breed, always feed your equids as individuals, and design their diets based on their unique nutritional needs.