Physitis in Horses

The term "physitis" refers to inflammation of a growth plate (physis) in young horses, with heat, pain, and swelling detectable around the growth plates of certain long bones. Possible causes include malnutrition, conformational defects, excessive exercise, obesity, and toxicosis.

Physitis occurs frequently in well-muscled, fast-growing foals during the summer, when the ground is dry and hard, and on stud farms where the calcium:phosphorus ratio in the diet is unbalanced. Therefore, it probably results from overload of the physeal area due to excessive loading or weakened bone and/or cartilage, or a combination of these factors.

Physitis in horses most commonly involves the distal extremities of the radius, tibia, third metacarpal or metatarsal bone, and proximal aspect of the first phalanx. It is sometimes associated with mild lameness and visible flaring at the level of the growth plate, giving the affected joints a typical boxy appearance. Radiography aids clinical assessment.

Treatment of physitis consists of decreasing food intake to decrease body weight or at least growth rate; restricting exercise to a yard or a large, well-ventilated, loose box with a soft surface (eg, peat moss, deep straw, shavings, or sand); ensuring that the feet are carefully and frequently trimmed; and correcting the diet, if necessary. The calcium:phosphorus ratio should be adjusted to 1.6:1.0, and protein content should limited to < 10% of dry matter.

As a preventive measure, older foals or yearlings that are fat or heavily muscled should be watched carefully for clinical signs of physitis, especially when the ground is hard and dry. When these conditions prevail, feed rations and exercise should be restricted.