What Causes Equine Cushing's Disease?

What causes Cushing's disease, and why does it seem like it's so prevalent in our horses?

This is a disorder that's better referred to as pituitary pars intermedia dysfunction (PPID). The word dysfunction is the best place to start, because this is a progressive disorder that begins with the dysfunction of the pituitary gland. This gland at the base of the brain sends out a number of hormones, and as the horse gets older and develops this condition, we see region of the pituitary gland--the pars intermedia--starts to send out more hormones. And it's really a collection of hormones that get sent out and affects the horse in many different ways.

We also call this Cushing's disease because there's an element of it that leads to an increase in cortisol and other stress hormones in the body. It’s not as straight forward as just elevated cortisol concentrations all the time, but it certainly has this underlying problem of an increase in stress hormones. So, it’s a dysfunction that develops overtime into a small tumor or multiple tumors in this particular region of the pituitary gland and the key part is that they are active tumors sending out too much hormone all the time, so that's what's causing the signs we’re seeing in the animals.

Why is it so common? Really because lots of this goes hand-in-hand with aging and this particular part of the pituitary gland is controlled by some nerves that basically degenerate over time. They degenerate in some horses faster than others, and those are the animals we see the disease in. As a horse gets older the risk of getting PPID increases, until we get to an age (in the 20s or 30s) where one out of three old horses will have Cushing's.

Sweet Feed Horse Cookies

Ingredients

• powdered sugar
• 4 cups sweet feed
• 1/4 cup brown sugar
• 3 cups molasses
• 2 grated carrots
• 2 grated apples
• 1/2 cup flour

Directions

1. preheat oven to 400 degrees
2. mix together all ingredients, except powdered sugar
3. form into large balls and press flat onto greased cookie sheet
4. bake for 20 minutes
5. cool, then sprinkle with powdered sugar

New Information on Heaves in Horses

Heaves, also called recurrent airway obstruction, is somewhat similar to human asthma. Horses with heaves are sensitive to the dust and mold spores found in bedding and hay. Exposure to these airborne particles causes irritation and inflammation in the airway. The result is exercise intolerance and a forced exhalation.

A study conducted at Virginia Tech University and funded by the Morris Animal Foundation found that horses with heaves have decreased levels of some important components of surfactant, a substance that helps to lubricate the small airways in the lung.

Further study could uncover therapies aimed at restoring normal surfactant composition. Also, keeping track of the composition of surfactant could be a way to measuring a horse’s response to treatment.

Flexion Tests in Horses: How Much is Enough?

A common part of a lameness exam is a flexion test in which a horse’s leg is held in a tightly flexed position for a short period of time, after which the leg is straightened and the handler is asked to trot the horse immediately. Subtle lameness is often made increasingly obvious after flexion, with the horse showing a more irregular gait that is an aid in diagnosis.

The period of time for which the leg is to be held in a flexed position has varied among practitioners. Short periods might not significantly increase the appearance of lameness, but longer periods often led to fidgeting horses and possible danger of injury to handlers.

A study conducted at Kansas State University used 34 horses in a study to analyze the importance of flexion time in evaluating lameness. The horses ranged from completely sound to extremely lame. All horses were jogged without having been flexed and then were jogged after a five-second and a sixty-second flexion. The same veterinarian performed all flexion tests, and all jogs were recorded on videotape. A panel of 15 veterinarians watched the tapes of the unflexed jogs and post-flexion tapes that had been edited so that the duration of flexion could not be determined. There was strong correlation in the lameness assessments regardless of how long the flexion was held, suggesting that a short period of flexion is as effective as a longer period for showing lameness.

Researchers commented that, regardless of results of a flexion test, this procedure is only one tool in determining the location, severity, and cause of a horse’s lameness. Diagnosis will be more exact when several types of examination procedures are carried out.