Cushing's: Pasture Management, Seasonal Awareness Key

How owners manage pastures and seasonal consumption of grass carbohydrates can significantly affect horses with Cushing's disease, according to researchers from the University of Tennessee's College of Veterinary Medicine. And, while the researchers' study did not focus directly on laminitis, owners could avoid laminitis by heeding its findings.

Horses with Cushing's disease, a relatively common hormonal disturbance in older animals, tend to be susceptible to other ailments, but the most life-threatening is laminitis, according to Nicholas Frank, DVM, PhD, Dipl. ACVIM, lead author of the study on the effects of seasonal grazing on Cushing's horses. Laminitis is inflammation of the laminae, which connect the hoof wall to the coffin bone inside the hoof.

"Laminitis is the worst complication and the most common reason a horse with Cushing's would be euthanized," said Frank. He noted there are several theories on why horses with Cushing's could be predisposed to laminitis. Cushing’s could weaken the hoof structure, and it could affect delivery of blood and nutrients to the foot, possibly making hooves more susceptible. Researchers also theorize that insulin resistance (IR) is more likely to occur among Cushing's horses, making them more likely to develop laminitis, Frank said.

The researchers examined the glucose and insulin levels of eight horses with a Cushing's diagnosis and nine control group horses when turned out to pasture and again after they were confined to stalls over the course of a year. Investigators also examined carbohydrate levels of the pasture grasses to determine if there was a seasonal correlation with insulin and glucose levels in the study population.

Frank noted that grass with the highest carbohydrate levels affected glucose and insulin levels in the Cushing’s horses. Grass carbohydrate levels were highest in April, May, and September.

The researchers recommended that veterinarians submit blood tests to determine whether horses diagnosed with Cushing's also suffer from IR. If tests confirm IR, owners should be wary of turnout, especially during the months that carbohydrate levels in grass peak. "Owners may need to limit grazing time or use a grazing muzzle for insulin-resistant horses," he said.

Although not addressed in this study, other research has shown that weather conditions and even time of day can also affect the carbohydrate content of grass.

Also, when moving affected horses to a new pasture, horse owners should take care. "This should be done with use of a transition period since changing the grass could also change the way glucose and insulin are being handled (by the horse's body)," he said.

"Owners need to manage the animal and know that there is an interaction with what it is eating," added Frank. "When they get in trouble with laminitis, it could be that a horse with insulin resistance has been grazing on a pasture that has exacerbated this problem."

The study, "Association of Season And Pasture Grazing With Blood Hormone And Metabolite Concentrations In Horses With Presumed Pituitary Pars Intermedia Dysfunction," is scheduled to be published in the upcoming issue of the Journal of Veterinary Internal Medicine.

The abstract is available on PubMed.

About the Author

Arlene J. Newman

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