For a horse to be considered “miniature,” it must be no taller than 38 inches. While miniature horses can suffer from any health issue affecting regular-size horses, their small size does result in a reduced prevalence of certain conditions. For example, hip dysplasia -- a condition most commonly associated with large dogs -- can affect a miniature, but is more common in larger animals. The correlation between size and risk of hip dysplasia is generally true of all mammals.
Causes of Hip Dysplasia
Hip dysplasia occurs when the ball of the hip joint doesn’t fit snugly in the socket. This poor fit leads to an exacerbation of the general wear and tear that affects any joint, causing pain, stiffness and lameness. Well-bred miniatures are at low risk of hip dysplasia, but those who have been selectively bred for exaggerated physical characteristics have a generally higher risk of all joint and bone conditions than miniatures that have been bred only for small size.
Dislocation Isn’t Dysplasia
Miniature horses are at higher risk than regular-size horses of certain bone and joint problems. One such problem is joint dislocation. While some of the symptoms may be the same, dislocation is not the same as dysplasia and the treatments for these conditions differ. The former is typically caused by trauma such as a bad landing from a jump, rather than a congenital predisposition to an ill-fitting joint, and requires corrective, rather than preventative, measures.
As with dogs, for whom hip dysplasia is a much more common health problem, the symptoms of hip dysplasia in horses can be very subtle to start with. They include limping, discomfort when getting up from a lying position, the favoring of one limb over others and reluctance to exercise.
In most cases your veterinarian will recommend management rather than treatment. Only in the most severe instances is a vet likely to recommend surgery, as the risks and expense of operating often far outweigh the potential benefits. Management techniques for hip dysplasia include applying heat to the joint, feeding a weight-control diet to avoid excess strain on joints and keeping your horse from jumping or running, instead focusing on gentle exercise.
Because miniature horses are bred for their appearance, exaggerations of physical characteristics, such as short-leggedness, are often considered desirable. These exaggerations have a physical cost, however. The only way to prevent hip dysplasia is for horse breeders to check that a mating pair have good hip health. If horses display symptoms of hip problems of any kind, it is best that they not be used for breeding.