Courtesy of AAEP
By Nicole Jones, DVM
The American Miniature Horse is a curious, intelligent and delightful breed that has been selectively bred down in size from larger breeds while maintaining as near-perfect conformation as possible. Despite their small size, these horses are not dwarves or runts, but well-proportioned mini horses. Care of the Miniature Horse is nearly the same as that of the larger breeds but on a much smaller scale with regard to feed, deworming doses, medication, etc. Although these tiny equines appear as smaller replicas of the larger breeds and share many similarities, minis seem to be more susceptible to certain health problems than their full-sized cousins. This article is intended to point out the most commonly noted conditions that afflict the Miniature Horse preferentially as compared to larger breeds of equines.
Many new Miniature Horse owners join the “mini world” with lots of experience in a larger breed of equidae. Although most are aware of the smaller portions of feed that a smaller horse would require, some owners find it very difficult to feed such a small amount of grain and hay or limit the amount of grazing on pasture to their lovable companions. Miniature Horses are very easy to overfeed due to their small size and metabolism, and as a result, many minis tend to be obese. Obesity in horses, whether large or small, can predispose to laminitis (founder), poor performance, and decreased reproductive efficiency. Strict feeding recommendations based on your Miniature Horse lifestyle should be accurately assessed, planned and followed to avoid excess body condition; this can be accomplished by contacting your veterinarian or a representative from one of the feed manufacturers.
Hyperlipidemia is a condition that Miniature Horses are well-known for although it also affects ponies and donkeys. In short, hyperlipidemia (or hyperlipemia) is a disorder of lipid metabolism that may lead to fatty infiltration of the liver, clinical signs of liver disease, loss of appetite and, ultimately, death. The disease often occurs in obese individuals that are stressed, anorectic (off-feed), pregnant or lactating. It frequently develops following a primary illness of several days duration such as diarrhea, endotoxemia, parasitism, pituitary tumor or neonatal septicemia, but can occur any time a horse is unable to satisfy its own metabolic energy needs (late gestation, early lactation, hormonal imbalance, etc). Affected horses usually will begin with anorexia and lethargy, progressing to incoordination, abdominal pain, head pressing, circling, diarrhea, convulsions and death. It is important for owners and veterinarians alike to always suspect hyperlipidemia in any obese mini with severe depression, anorexia, neurological signs, and icterus (jaundice). Owners may prevent this condition by providing appropriate nutrition while avoiding obesity, stress and engaging in good routine health care.
Miniature horses seem to be more susceptible to colic than full-sized horses, which is possibly the result of incorrect grinding of feed due to poor teeth, consumption of poor-quality coarse hay or inadequate water consumption (an average adult mini should consume 2 to 4 gallons of water per day depending on their size and the ambient temperature). The small colon is the most common site of disease in Miniature Horses, and impaction is the most common cause of colic either due to fecalith (hardened fecal ball), enterolith (mineralized intestinal content) or undigested feed. Another problem is that colic in these small equines can be a major diagnostic challenge. One reason for this is that rectal palpation is limited to the most caudal portion of the abdomen due to the small size of the pelvis in comparison to full-sized horses. Another challenge is that the clinical signs seen in Miniature Horses are frequently not the classic colic symptoms seen in full-sized horses in that some may only show depression and anorexia. Nevertheless, most of the medical treatment protocols for colic are the same in Miniature Horses (flunixin meglumine, mineral oil and feed withdrawal); however, it is important to remember that they are particularly susceptible to hyperlipidemia and should therefore not be held off feed any longer than is necessary.
Many Miniature Horse owners are involved in breeding since there is less of a focus on using them for riding or performance purposes. Unfortunately, the incidence of dystocia (difficult births) in the Miniature breed is much higher (15 to 20 percent) than full-sized breeds (2 to 4 percent). This may be due to fetopelvic disparity (the small size of the mare’s pelvis and a disproportionately large fetus) or fetal malpresentations (abnormal presentation, posture or position of the fetus) caused by the small amount of space within the uterus for the fetus to move during parturition. Regardless of the cause of the dystocia, once difficulties arise, it is even more difficult to correct the problem due to the difficulty with manual manipulations of the fetus because of the small size. Dystocia is a serious and potentially life-threatening condition.
Miniature Horses often have more problems with their teeth than do larger breeds of horses. Most likely, this is due to the small size of their heads along with the presence of the same number of teeth as found in a full-sized horse which leads to overcrowding of the teeth. As a result, tooth wear may be uneven and predispose Miniature Horses to colic. Additionally, retained deciduous teeth (retained caps) and chronic sinus infections are commonly associated with dental overcrowding. Thus, routine dental examinations and care one to twice a year are strongly recommended.
Among other medical issues that preferentially afflict the Miniature breed are dwarfism, upward fixation of the patella (“locked stifle”), increased or decreased sensitivity to drugs and vaginal adhesions.