Horses of any size have a fabulous appeal for animal lovers, and none more so than the Miniature breeds, fondly referred to as “Minis.” Because of their cuteness, it is easy for an owner to treat them with a bit too much tender care, especially when it comes to feeding. Minis are smart and endearing, and they have a way of looking soulfully through the fence, just egging you on to give them a little something extra to munch. Therein lies the problem: Minis are small in size and, in general, their primary job is to be loved on. The result is a fat Miniature Horse or Donkey because they like to eat, we like to feed them, and they don’t get much exercise to utilize their groceries.

A Mini Pasture Pet?

Philip Johnson, BVSc, MS, MRCVS, Dipl. ACVIM, professor of equine medicine at the University of Missouri-Columbia veterinary school, has been a longtime proponent of dietary management of obesity and hormonal problems in horses. He shares some thoughts on how the lifestyle of Miniature Horses and Donkeys contributes to obesity: “Miniature Horses and ponies are genetically distinct groups that are characterized by being relatively insulin insensitive–in other words they have been bred and evolved to be ‘thrifty.’ They are very prone to develop obesity when fed rations that contain energy-dense, high-calorie components combined with forage sources that are based on improved grassland species intended for food animal species. Moreover, Miniature Horses are ‘small’ and too easily overfed; their owners often do not adjust rations appropriately for their size, especially in light of low levels of physical activity.”

Bob Wright, DVM, works at the Ontario Ministry of Agriculture, Food, and Rural Affairs, focusing on nutrition of all livestock species, and especially on the value of forage. Wright agrees that many Minis spend a lot of time standing around: “They don’t have a daily or weekly activity that burns off a lot of calories, and the majority of Minis have inherited a metabolism that makes them ‘easy keepers.’ ”

In addition to this sedentary lifestyle, he adds, “Many live pampered lives with good shelter and/or winter blankets, which shield them from the weather and, thereby, further reduce caloric needs.”

Wright recommends a Mini’s diet should be formulated for maintenance requirements based on an ideal body weight. Then the feed amount is adjusted for added requirements such as pregnancy, colder ambient temperatures, and wind chill or other environmental and physical stressors. He urges owners to carefully watch for changes in weight and body condition from month to month, and season to season, and to modify the diet accordingly.

Joe Pagan, PhD, president of Kentucky Equine Research (KER), has devoted his professional career to managing dietary requirements of horses. He comments, “Because very little research has been done on the specific requirements of Miniature Horses, feeding recommendations must be based on standards for other equines, tempered by experience with Minis and careful observation of individual animals.”

How Much Does He Weigh?

One of the biggest issues in determining how much feed a Mini should receive is the estimation of its body weight. Pagan reports on a study at KER that weighed 49 Miniature Horses, ages ranging from 1 to 12 years. On average, those horses weighed 213 pounds, and he notes that less than 15% weighed as much as 250 pounds, which is a commonly assumed weight for Minis. A telling feature of this study is that when Mini owners were asked to estimate their horse’s weights, they were incorrect by 20% in both directions, i.e., over and under the actual weights. So, in general, Pagan reports that it is difficult for an owner to accurately configure a feeding program for a Mini just by looking at an individual and making a “guesstimation” of weight. Weight tapes are notoriously inaccurate, he says, and even more so for Mini weight estimations.

With that in mind, the folks at KER formulated an equation to help solve this problem. Specific measurements (in inches) of girth, height, and length of an individual Mini are plugged into equations to determine body weight (in pounds). Pagan explains, “To measure girth, place the tape just behind the front legs and over the withers. Pull the tape snug, but not tight enough to depress the flesh. For height, stand the horse squarely on level ground or pavement and measure the vertical distance from the ground to the top of the withers. If there is a question as to the exact location of the withers, allow the horse to lower its head and neck as if to graze and measure to the highest point in front of the saddle area. The tape should be kept perpendicular to the ground, not laid against the horse. Length is measured from the middle of the horse’s chest, along the side, and around to a point under the center of the tail.” You should arrive at a fairly reasonable estimation of body weight of a Mini by using the formulas below.

Forage as the Main Staple

To begin configuring a diet for a Mini, Wright likes to start with a hay-only diet, with no grain or supplements, noting, “The greatest problem is keeping weight off this type of horse. I recommend feeding hay on a dry matter basis at 2% of ideal body weight for the adult horse, or 2 pounds of dry matter per 100 pounds of body weight. Since dry baled hay is roughly 90% dry matter and 10% moisture, it may be necessary to increase this to 2.2% of ideal body weight to determine the weight of hay fed on an as-fed basis.”

Pagan is also conservative in his approach, agreeing on the wisdom of feeding primarily a forage diet. He suggests that by scaling down what a full-sized horse generally eats in hay or grass for the smaller size of a Mini, it works out to offer 4-4.5 pounds of hay per day, or even less. To feed accurately, hay must be weighed on a scale and not fed by volume or guesswork.

That said, each horse is an individual, regardless of whether it’s a Mini or larger horse, and each needs to be fed for its unique metabolism and specific needs. Wright urges, “The trick is to observe the horse and adjust the feeding program based on gain or loss of body condition or relative to changes in weather conditions.”

Wright suggests that once the forage needs are met for basic maintenance, then other dietary requirements can be addressed, such as micronutrients. He suggests, “Typically the forage fed to Minis will contain a high proportion of grass species and preferably few, if any, legumes. Grass hays typically meet desirable calcium-to-phosphorus ratios, but the hay may need to be tested to ensure that it is not deficient in either mineral. The difficulty comes when trying to supplement micronutrients, such as copper and zinc, without adding calories.”

Pagan recommends offering small amounts of alternative supplements that provide micronutrients, yet do not pose a threat from grain overload.

Johnson, Pagan, and Wright all stress that a Mini should not be given unlimited access to grass pasture, as this enhances the tendency for obesity and presents the Mini’s digestive tract with an excess of sugars and carbohydrates and highly fermentable feed material. A grazing muzzle is a helpful tool to minimize ingestion of pasture grasses.

Obesity and Hyperlipemia

Obesity is a huge problem in Minis, not only for its increasing a horse’s risk of developing laminitis, but because of another health hazard common to ponies and Miniature Horses and Donkeys. These individuals are predisposed to developing a syndrome known as hyperlipemia or hypertriglyceremia, which can have life-threatening consequences. Johnson describes it in these terms: “Specifically, hypertriglyceremia means that the measured concentration of triglyceride in plasma is elevated above a normal reference range, while with hyperlipemia, the measured concentration of lipid (fat) in plasma is elevated above the reference range. Triglycerides are a main component of the disease process in Minis, but other lipids also can add to hyperlipemia, such as free fatty acids and cholesterol.”

Johnson stresses, “Obesity is a prerequisite for this syndrome, and it is common that owners allow Miniature Horses to become obese. Added to that is the fact that Miniature Horses are relatively insulin insensitive, and insulin resistance is critical for this disease.”

Johnson explains that one function of insulin is to “stabilize” the body’s fat stores and to regulate the extent to which fat is mobilized. He continues, “With insulin resistance, many other hormones that signal fat mobilization then act in an unopposed fashion. There is a genetic predisposition to insulin resistance, and obesity adds to that. In addition, extra fat adds as a source of the problem when it is mobilized.”

Rather than differentiating these two syndromes, Johnson prefers to use the term “hyperlipemia/hepatic lipidosis syndrome” to describe the accrual of lipid in the organs, especially the liver. Johnson notes, “Hyperlipemia occurs when the body mobilizes fat and the plasma becomes ‘clogged’ with fatty oil. It gets into the organs (especially the liver and kidneys) and causes organ dysfunction on many levels.”

When the kidneys are infiltrated with fat, they are unable to filter lipid from the plasma, adding to the degree of sickness. In general, he states, “Hyperlipemia is a multiorgan disease.”

Johnson says studies show ponies are predisposed to a massive release of lipids (fats) from storage sites in the body, especially when they are stressed and catecholamines such as adrenaline are released.

For hyperlipemia to occur to the extent that it is responsible for clinical disease, Johnson explains that the following criteria are generally present:

• The individual must be obese at the outset;
  
• The individual is usually also insulin-resistant, such as with fat Miniatures, Miniature Donkeys, and ponies with underlying Cushing’s disease or metabolic syndrome;
  
• The individual develops a “negative energy balance,” i.e., goes off feed for any reason, suffers a systemic illness, or is a mare that is lactating;
  
• The individual is subjected to stress from transport, bad weather, disease, overcrowding, or poor nutrition, as examples; and
  
• An individual experiences a combination of these contributing risk factors.

Johnson reports that there are important events that predispose an animal to hepatic lipidosis, particularly in a fat Mini, noting, “Any event that suppresses appetite is a predisposition.” This includes illness or disease of any kind: gastrointestinal disturbances, kidney failure, infection, cancer, internal parasites, Cushing’s disease. It can even occur during a natural condition like pregnancy. Signs of hyperlipemia include marked lethargy, weakness, and anorexia (loss of appetite), which further adds to the pathogenesis of the problem. More advanced cases also display signs of liver failure, such as jaundice, yawning, head-pressing, staggering, weakness, leaning, falling, colicky behavior, and recumbency.

Prevention is Key

Johnson suggests ways to prevent obesity and hepatic lipidosis in Minis, noting that the first step in prevention is to avoid obesity by not overfeeding and by encouraging exercise. He reminds owners, “Insulin-resistant individuals should not be fed rations that contain excessive carbohydrates or products that are dense with calories or characterized with a high glycemic (sugar) index.”

Johnson stresses, “Remember that Miniature Horses need much less food than regular-sized horses. Even free-choice access to pasture and hay is potentially dangerous.”

He also suggests that obesity-prone, chronically laminitic Miniature Horse mares should probably not be used for breeding for fear of promoting what is likely a genetic trend. Insulin resistance worsens as a part of normal pregnancy, and it is common that medical consequences of insulin resistance develop during pregnancy, including laminitis and hyperlipemia.

It is better to start a Mini out on a correct diet rather than having to make dietary modifications later to manage obesity. Wright encourages owners to find a balance in what is fed: “To prevent Mini weight problems, there is a tendency of owners to limit feed or to pasture them on fields with little or no feed. This causes a Mini to continually look for something to eat, with a tendency to eat boards on the barn or fence or any green plant or tree which they would not touch otherwise. To satisfy an urge to chew and eat, they may consume poisonous plants, such as horsetail, red maple leaves, or black walnut hulls.”

Small colon impactions are common intestinal maladies in Mini Horses, so eating inappropriate materials adds to this risk.

Exercise, Exercise, Exercise

In all cases, the value of physical activity cannot be understated. Johnson promotes exercise, urging, “These horses should be actively exercised to the maximal extent possible barring the occurrence of any musculoskeletal problem that precludes exercise.” A Miniature Horse should be given a job and exercise regimen to keep him slim. Wright recommends an activity demand such as driving or pulling to burn any excess calories. He also recommends housing a Mini outdoors with a run-in shed and ample room to move around, noting, “A Mini should be fed as far away from the run-in shed as possible to encourage walking. Keeping a Mini with compatible pasturemates also encourages exercise from play.”

Take Home Message

When it comes to feeding, Wright urges Mini owners to treat their Minis like livestock rather than pets. A Mini owner should resist the urge to be a “barn chef,” giving a Mini a scoop of this and a pinch of that. He stresses that it is best to rely on first principles of dietary management: Address the cause of the obesity problem by reducing calories and increasing physical activity. Johnson stresses that prevention of obesity-related metabolic illness in Minis is best accomplished by not overfeeding, by avoiding obesity, and encouraging physical activity. Pagan sums up a basic philosophy in feeding a Mini, or any horse for that matter: “Feed each horse as an individual, taking into account size, weight, state of growth, metabolism, and work.”