The Miniature Horse: More Than Just a Smaller Horse
Although the care of Miniature Horses is nearly the same as that of larger breeds, Minis are more susceptible to certain health problems.
Reprinted from The Horse Report with permission from the Center for Equine Health, School of Veterinary Medicine, University of California, Davis (UC Davis).
Gary Magdesian, DVM, of the UC Davis William F. Pritchard Veterinary Medical Teaching Hospital, and Mark Rick, DVM, of Alamo Pintado Equine Medical Center in Los Olivos, Calif., contributed to this article.
What comes in a small package, has all the characteristics people love about horses, and is easy to manage and a delight to have around? A Miniature Horse.
Miniature Horses are no taller than 38 inches and come in a rainbow of coat colors and patterns. They are easily trained, have a gentle nature, and can pull four times their own weight. These horses are descended from Shetland ponies and were selectively inbred for their size. In earlier times, small horse breeds were likely the products of surviving harsh natural climates and limited feed sources. As human knowledge of genetics grew, it became possible to breed specifically for size.
Miniature Horses have been bred for superb conformation and outstanding dispositions. The result is a proportionate little horse that is suitable to a variety of uses: as pets, show animals, and a form of therapy for disabled people and guides for the blind.
In the show ring, "Minis" compete in halter/conformation and in performance events such as obstacle driving. An organization devoted to small equines--the American Shetland Pony Club (ASPC)--includes the American Miniature Horse Registry (AMHR) among other registries. Founded in 1888, the ASPC began registering Miniature Horses in 1971. The AMHR includes an A division, which registers horses standing 34 inches or under at the last hair of the mane, and a B division for horses standing up to 38 inches. Regular Shetlands stand up to 46 inches.
Minis require similar care to their full-sized counterparts but, based on their size, they require much less space, making them accessible to more people, including those who have had no experience with horses. It is important that owners of Miniature Horses educate themselves thoroughly in good basic horse care as well as in the breed's unique needs. While some Miniature Horses are kept primarily as pets, they still need to be treated like horses, with appropriate nutrition, housing, room to run, regular hoof care, dental care, grooming, vaccinations, and parasite control.
As has frequently arisen with breeding a species for specific characteristics, desired traits can be accompanied by undesirable ones. In Miniature Horses, dwarfism is an unfortunate complication of breeding, even when both of the parents appear to be normal. In Minis, a dwarf is not only smaller than normal, it also has varying degrees and combinations of undesirable conformational faults.
These can include limb, spine and jaw deformities. A dwarf Mini can have just one or a combination of such traits. Mildly affected horses can lead normal lives, while the most severely affected ones can suffer from chronic pain or the inability to stand or move. In some instances, the deformities are not noticeable at birth but become obvious as the horse ages.
Although the care of Miniature Horses is nearly the same as that of larger breeds (but on a much smaller scale with regard to feed, deworming doses, medication, etc.), Minis are more susceptible to certain health problems, as discussed below. And, there are times when it can be dangerous to treat Miniature Horses the same as you would treat a full-sized horse. Many potential problems can be avoided altogether by providing the proper care and feeding these animals require.
Unique Health Issues of Miniature Horses
Obesity--Miniature Horses are prone to obesity. Most owners of large breed horses tend to overfeed the Minis. In addition, pasture restriction and daily exercise are less likely to occur. Many of the medical challenges Miniature Horses face can be avoided by maintaining an ideal body condition (a 5 out of 9 on the Henneke Body Condition Scale).
Ideally, Minis should consume approximately 1.5% of their body weight in hay daily. The average Mini weighs 250 pounds, and this translates to 3.5 pounds of hay per day. The backyard Mini in the United States does not expend a large amount of calories in exercise. Those used as cart animals, show horses and lactating mares will have higher nutritional demands and can require up to 3% of their body weight in forage. Small amounts of concentrates or alfalfa should be given only during the breeding season or for exercising and showing horses.
Vitamin and mineral supplements might be required for adults or foals, depending on the diet fed. Vitamin and mineral requirements are similar to large breed horses on a per weight basis. Protein requirements mimic those of large breed horses (per weight basis) and lower nonstructural carbohydrate content hays, such as certain grass hays, are recommended for Miniature Horses given their propensity for obesity.
Some owners underestimate the weight of a Mini by 20%, which equates to 50 lbs. Weight tapes tend to be inaccurate and scales are not a common resource. However, dewormers and other medications should be administered with caution and there are formulas to calculate body weight based on body length and girth width, as follows:
Estimated Body Weight (pounds) = (9.36 x girth inches) + (5 x body length in inches) - 348.5
Dental Issues--Healthy teeth are important to the general health of all horses. The most common cause of death in aged wild horses is the inability to chew food; these horses either die of intestinal obstruction or weakness or are taken down by predators. In addition to the ability of the horse to process its feed, the health of the teeth also affects the health of the sinuses and the condition of the nasal passageway (Frankeny, 2003).
Miniature Horses tend to have more problems with their teeth than do larger breeds of horses. This is likely due to the small size of their heads combined with the same number and size of teeth as found in a full-size horse, leading to overcrowding of the teeth. Overbites (brachygnathism) and underbites (prognathism) are common and can set a Mini up for years of abnormal dental wear if left untreated.
Veterinarians at UC Davis recommend that newborn foals have their first oral exam shortly after birth to identify any bite abnormalities. For foals with abnormalities, periodic reduction of dental overgrowths should be done from several months of age on to improve the range of motion of the jaw. Otherwise, annual dental exams, starting at one to two years of age, should be performed.
The young Mini is prone to sinus infections because of overcrowding of the dental roots in the smaller sinus space. This affects normal sinus drainage, and these horses will often display tearing of the eye on the affected side, swelling of the facial area below the eye, and a unilateral nasal discharge.
Minis tend to retain their deciduous teeth (baby teeth), which are also called caps. They will drool and display difficulty chewing. Specialized equipment is usually required to examine and correct these abnormalities in their much smaller oral space.
If owners of Miniature Horses do not invest in regular dentistry--perhaps because their horse does not wear a bit and has a voluptuous body condition--years of abnormal alignment and wear can lead to severe dental malocclusions that will predispose the horse to colic and choke and possibly shorten its lifespan.
Yearly dental examinations are highly recommended. In addition to routine dental care, teeth should be evaluated any time a horse shows signs of possible dental disease (difficulty chewing, dropping partially chewed food ["quidding"], excessive salivation, swelling of the face, nasal discharge, or a foul odor from the mouth or nose). Many problems can be successfully treated if addressed immediately.
Colic--Minis have robust appetites, but their predisposition for dental problems can impair their chewing capacity.
The reduced ability to grind feed combined with the robust food-seeking nature of the Mini creates a unique subset of common colic. Minis are prone to three distinct types of colic: fecaliths, enteroliths, and sand colic. The root "lith" means "stone".
Fecaliths are accumulations of long-stem feed, twine or hair, and manure that create a hard, rock-like obstruction in the small colon. These obstructions cause gas to build up and cause moderate pain. Similarly, trichophytobezoars, which is an accumulation of feed and hair, are sometimes seen in Minis that spend a lot of time standing around and grooming each other. It is much less commonly seen in horses that are pastured.
Enteroliths are mineral stones that form in the colon of horses fed a diet involving alfalfa hay. Alfalfa hay is rich in magnesium, protein, and phosphorus, and these components combine as magnesium, ammonium and phosphate around a central nidus such as a piece of wire or foreign material to form a stone. Arabian horses are the most common enterolith formers, and Minis are also at increased risk. Although horses can pass small enteroliths, surgery is often required to remove larger stones that cause obstruction. Abdominal radiographs have a 90% detection rate for enteroliths in a fasted horse. The small abdominal diameter of the Mini makes radiographic diagnosis a valuable tool and radiographs are recommended for any Mini experiencing multiple colic episodes or unrelenting abdominal pain.
Sand colic is also common in Minis because they tend to be scavengers and vacuum their surroundings. Sand settles in the colon, weighs the organ down, and abrades the lining of the colon to produce inflammation and diarrhea. Sand is readily visible on radiographs (X rays) and a fecal float for sand should be a regular part of the colic exam for a Miniature Horse. A fecal float consists of placing a large handful of feces into a plastic bag filled with water. The bag is hung, and the bottom is inspected for sand that will have settled after a few minutes. Sand can be treated with oral laxatives and psyllium, but occasionally it will cause the colon to displace or function poorly. Sand colics can require surgery when medical treatment does not resolve the problem. Feeding Minis on rubber mats, adding psyllium to the monthly routine, and avoiding sandy environments can help prevent this problem.
Hyperlipemia--The most significant metabolic difference between large breed horses and Minis that puts them at risk is their propensity for hyperlipemia. Miniature Horses, donkeys, and small ponies have a tendency to mobilize fat when their body senses an "energy crisis" and they are not able to meet their metabolic demands. Late-term pregnancy, lactation, stress, illness, or any factor that impairs appetite for more than 24 hours can initiate a crisis.
This disorder of lipid metabolism causes fat to be released from lipid stores and transported to the liver where it is converted to glucose. Obesity increases the risk of hyperlipemia. When the horses are off feed or stressed the lack of insulin stimulates a cascade of events, which triggers fat breakdown.
This breakdown of fat leads to fatty acids that are taken up by the liver. These are reformulated into triglycerides that are released into the bloodstream, and the horses develop "fatty" blood. The fat influx often overwhelms the liver and causes hepatic lipidosis, which is an excessive amount of fat inside the liver cells as well as infiltrating organs. The fat infiltration interferes with normal liver function, leading to failure or rupture of the liver. Rapid intervention with intravenous glucose and nutritional support, coupled with insulin therapy, is necessary to prevent this.
Affected Minis will often show a decline in appetite, lethargy, and weakness before signs progress to incoordination (ataxia), abdominal pain, tremors, diarrhea, jaundiced coloration, seizure, head pressing, and, if left untreated, death. Even aggressive treatment can be ineffective once the liver is overwhelmed; there is a 70% mortality rate associated with delayed treatment, whereas early medical treatment can be associated with a good outcome.
Hyperlipemia should be suspected in any Miniature Horse that has been off feed for more than 24 hours. Prompt veterinary attention is the key to successful reversal of this condition. The physical appearance of fat or alterations in markers of fat and liver metabolism in a blood sample will confirm the suspicion of hyperlipemia.
Prevention of hyperlipemia is very important because this condition is difficult to treat. Miniature Horses should be on a diet that provides adequate nutrition but does not induce obesity. Extreme stress should be avoided as much as possible, and horses that are in a stressful situation should be closely monitored for loss of appetite. Any sickness or loss of appetite should be addressed immediately to determine whether supportive therapy should be initiated.
Reproduction--The incidence of dystocia, or difficult births, in Miniature Horses is much higher than in full-sized breeds. This is probably due to the fetopelvic disparity (small size of the mare's pelvis relative to the large fetus) and to fetal malpresentations (abnormal presentation, posture, or position of the fetus) in the Mini. In addition, the umbilical cord can become twisted and entangled around the foal.
Regardless of the cause of the dystocia, once a foaling problem arises, it is more difficult to correct because manual manipulation of the fetus is more complicated in the smaller uterus. Therefore, UC Davis veterinarians highly recommend that owners of Miniature Horses seek the attendance of a veterinarian for any foaling mares so that if complications arise, immediate assistance can be given.
The increased rate of congenital abnormalities also makes loss of pregnancy more likely in this breed. The abortion rate in Minis can approach 30%. It is very important to monitor Minis used for breeding in their last trimester. Gestational length has been observed to be shorter in the Mini, with an average of 320 days and wide individual variation. The impending signs of parturition are similar to those in large breeds, with vulvar relaxation, softening of the tail head, mammary development, and lactation occurring within the last six weeks of gestation.
Eclampsia--Clinical eclampsia is not commonly seen in large breed horses but can be a life-threatening complication associated with pregnancy and lactation in Miniature Horses. Eclampsia is a dramatic drop in systemic calcium concentrations that can occur in late gestation or early lactation. The body requires calcium for normal muscular and electrical activity, and signs of low calcium include muscle tremors, sweating, anxiety, bloat, colic, and pupil dilation. Left untreated, it will progress to recumbency, seizures, and death. To the uninformed eye, this set of symptoms mimics a severe colic.
Foals--The average weight of a miniature horse foal is approximately 20 pounds. These small patients require extra attention to drug dosages and equipment size. They are prone to angular and flexural limb deformities and careful assessment of their conformation is necessary at birth.
Common abnormalities include valgus (toed out) or varus (toed in) conformations. Tendon contracture, and the opposite called tendon laxity, are both problems that can occur in Mini foals. Other congenital defects include heart defects (e.g., ventricular septal defect), brachygnathia or prognathia (discussed earlier), patellar abnormalities, and dwarfism (discussed earlier). Patellar abnormalities include lateral deviation or luxation of the patella. When trying to stand, the affected foal fails to extend its stifles and adopts a crouching position or does "the splits".
There are aspects of Miniature Horse care that are very similar to the large breed horse. Obesity is one of the largest obstacles in this breed, and regular exercise and feed restriction that is relative to size are necessary to sustain health. Routine maintenance of their teeth, their feet and their vaccination and deworming schedules should be similar to those of their larger counterparts. Their size can work for them and against them, and a knowledge of their unique health considerations is valuable to anyone considering adding one to their herd.
POLL: Equine Lameness Concerns