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Physitis in Young Horses: Diet Change Often NecessaryBy Kentucky Equine Research Staff · August 24, 2015

Considered a scourge among horse breeders everywhere, physitis is bound to pop up in any horse-breeding population sooner or later, regardless of how conscientious a breeder might be. Loosely defined, physitis is an inflammation of cartilaginous growth plates near the ends of long bones in growing horses.

Physitis generally develops between the ages of three and six months at three primary points: distal radius (above the knee), distal cannon (above the fetlock), and distal tibia (above the hock). Apart from lameness, the primary indication of physitis is the telltale joint inflammation caused by enlargement of the growth plate. The swelling will likely be firm to the touch and slightly warm.

“Physitis is more common on farms that use aggressive feeding practices for maximal growth,” said Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research (KER). “An overconsumption of energy is typically the root cause of physitis, assuming there’s been no physical trauma such as running on dry, hard ground.”

Foals and weanlings that are allowed to graze lush pasture and consume large concentrate meals are more prone to the problem than young horses that are kept in more moderate body condition and fed for slow, even growth.

“Every young horse should be treated as an individual, of course, but the sweeping commonality among those diagnosed with physitis is overfeeding of energy,” said Crandell. “Reworking the diet of young horses, usually in combination with stall rest if lameness exists, can make a world of difference. I’ve seen young horses do much better once some energy has been removed from the diet.”

The key to resetting a young horse’s nutritional program, according to Crandell, is ensuring the youngster is receiving the energy he requires for steady growth as well as all of the protein, vitamins, and minerals needed for sound growth.

After a complete nutritional evaluation, Crandell will usually suggest one or more ways to reduce energy intake, including (1) weaning the foal from the mare if it is old enough; (2) swapping energy-rich legume hay, such as alfalfa (lucerne), for a good-quality grass-based hay; (3) replacing high-energy concentrates with a ration balancer that provides adequate protein, vitamins, and minerals.

Some breeders are hesitant to change the ration because a revised diet might slow growth rate to a more modest speed, which conflicts with show or sale targets. “In the end,” said Crandell, “it’s most important to do what’s best for the health of the horse, and sometimes this means fine-tuning growth goals. Breeders shouldn’t be concerned that a slowdown in growth will affect mature size, as generally this will not happen. It might take a little longer to achieve physical maturity, but the advantages of sound growth far outweigh any benefits to a hurry-up-and-get-there approach.”

On the other hand, offering a young horse with physitis middling hay and no other source of nutrients is not the answer either, said Crandell. “Years and years ago, breeders would try to put the brakes on growth by pulling all concentrates and offering junky or low-quality hay. Predictably, growth decelerated and health sometimes suffered,” she commented.

“The understanding of nutritional requirements and developmental disorders has come a long way since that advice was commonplace, and we know now that young horses still require protein, especially lysine, and essential minerals, like calcium, phosphorus, zinc, copper, and others, even when faced with growth issues,” Crandell continued.

Do you have a young horse with a growth problem? Let KER help. Start the conversation now.

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