The Horse

MAR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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20 March 2019 The Horse | Proportional dwarfism has brought us the true "miniature" breeds of animals of different species—Miniature Schnau- zers, Miniature Goats, and, of course, Miniature Horses, among others. These animals are usually healthy and carry normal genes for proportionally dwarfed individuals. Disproportional dwarfism creates animals that can face sometimes-severe health issues, due mostly to their dispro- portionate body. Worse, because dwarf- ism is hereditary, a breeder could end up with an entire herd of unhealthy animals. "The goal is to remove these dispro- portionate dwarf genes from breeding programs entirely," Eberth says. Squeezing Everything in There Genetic mutations cause dispropor- tional equine dwarfs to have short, stocky, skeletons (see for the details on dwarf DNA). But those mutations have no effect on organ development. Practically speaking, this means things don't fit. "You've got this tiny, misshapen hard tissue structure, and you're trying to pack all these normal-sized soft tissues in- to it," Eberth says. "It just doesn't work." The situation is not only painful—and increasingly so as the Mini gets older— but also disruptive to proper organ func- tion. Plus, those organs still demand "nor- mal" nutrition, says Liz J. Barrett, DVM, MS, Dipl. ACVS, associate veterinarian at Hagyard Equine Medical Institute, in Lexington, Kentucky. She treats the dwarfs at The Peeps Foundation, which specializing in the rescue, rehabilitation, and care of dwarf Minis in Lexington and in Wellington, Florida. "The dwarf is a smaller size, but his internal organs still require the same amount of nutrients as a bigger animal," she says. Unfortunately, though, those organs don't always get what they need—either because the owners misunderstand nutritional needs or because the organs "outgrow" their frame. "The disease itself doesn't kill the dwarf as he ages; it's the complications that kill him," says Eberth. "Dwarfism can kill by starvation or colic, due to the internal organs being restricted in size and those smaller skeletal structures just compact- ing the internal organs that are the same size as if the horse were (a) full-grown (nondwarf Miniature Horse)." Locked Jaws, Roach Backs, and Other Secondary Effects When bone growth gets stunted, the entire skeletal system becomes bulky, twists, and deforms. You commonly see this affect dwarfs' jaws, says Eberth. The teeth start out normal, but as the jaw grows abnormally, they become poorly aligned. "They often get an underbite, and the front teeth don't wear anymore and just keep growing," he says. "Then the molars get out of alignment, and they develop hooks. They literally can't grind or chew." Meanwhile, the joints become re- stricted to the point that the jaw locks up. "They need a lot of dental maintenance, up to four times a year or more," Eberth adds. The horses' vertebrae become mis- shapen during the ossification (bone de- velopment) process. This is complicated by the fact that the spine is supporting a disproportionate body, resulting in poor spinal alignment. "The only way they can deal with these abnormalities is by form- ing a roach back (up-curving spine)," says Eberth. The roach back sets off a domino effect of musculoskeletal issues, including hip dysplasia, hip rotation, goose rump, and sickle hocks. The humped back, plus the nature of the disease itself, leads to a host of other problems, says Barrett. "We see orthope- dic issues, a lot of angular limb defor- mities, flexural limb deformities, and arthritis," she says. Arthritis can occur in dwarfs as young as a year old due to uneven weight-bearing on the joints. While she's performed surgery on some of the dwarfs at The Peeps Foundation to correct orthopedic issues, she says she's found that conservative treatment with corrective shoeing or braces is better— mainly because these little guys don't handle anesthesia well. "They don't seem to have a normal metabolic status for some reason and can run into liver issues with all the drugs," she says. "Plus, they're just very small—much smaller than most humans—so dosing is critical." Their size and proportions might also make them more likely to pick up respira- tory diseases, she adds. "The dwarfs seem to be the ones that are more likely to have a snotty nose," she says. "I don't know if it's something to do with their immune system or if it's just that everything is smaller and it's harder to clear things." Dwarf Minis also tend to have cardiac issues, says Josh Dolan, co-founder of The Peeps Foundation. "I have 25 dwarfs DWARFISM: NOT A SMALL PROBLEM Though many dwarfs appear to be "fat," their big bellies come from bulging organs, not obesity.

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