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The Endocrine System (Cushings/PPID)

Principal Body System: Endocrine
Definition: All glands that produce hormones.
Function: Regulates body activities through hormones transported by the cardiovascular system.

Living longer can bring about health issues that than we didn’t need to consider in the past, and although age isn't always a factor with Cushings/PPID, the endocrine system, and specifically the pituitary gland, can be adversely affected.

Our own experience with Cushings came out of the blue. Many years ago on his daily walk, our then young daughter’s elderly second pony, Dinky, suddenly presented seriously lame with his breathing worryingly laboured – all the signs of laminitis. This literally happened overnight - the previous day he'd been fine; the next, he wasn't.

Although we instantly addressed his symptoms, there were other signs that had niggled us - we hadn't had him long and were still getting to know him, but we were approaching summer and his winter coat wasn't shifting. He was also noticeably drinking and urinating more. We suspected Cushings and got him tested. It came back positive.

Then in 2014, our daughter's third pony, Cookie, who is still with us albeit now retired, also started showing the classic signs of non-shedding curly coat which seemed to appear from nowhere, alongside noticeable lethargy and sadness. She was 15 at the time.

Cushing's Disease, aka PPID (Pituitary Pars Intermedia Dysfunction), is all about hormones going wonky. It's a name given to a specific dysfunction of the pituitary gland which causes hormonal disturbances. The Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary, the region which controls the functioning of the secretory cells. It relies on dopamine as its neurotransmitter - a chemical messenger that helps transmit brain signals - to regulate secretions.

As horses age, as with us humans, the decrease in dopamine occurs naturally. As the older horse becomes susceptible to the loss of dopamine, the Pars intermedia produces an excess of hormones, including the hormone ACTH (Adrenocorticotropic) which stimulates the production of cortisol, a stress hormone produced by the adrenal gland.

And so begins the metabolic effect.

As if managing the other symptoms of PPID isn't a juggling act enough, cortisol increases sugars in the bloodstream and enhances the brain’s use of glucose.

When the horse is anxious, the system sends signals to the adrenal glands to release adrenaline and cortisol. While the fight-or-flight reaction in the body stays active, cortisol continues to release sugars into the bloodstream.

Here come the side effects of high cortisol levels - we're looking at weight gain, typically cresty necks and rear/belly fat pads, insulin resistance (IR) and abnormal glucose metabolism, all the precursors to metabolic laminitis. It’s a vicious circle - as cortisol levels increase, insulin levels must then increase to try and keep glucose within what the body thinks are ‘normal’ levels. In humans, we call chronic, unregulated levels of insulin ‘diabetes’.

ACTH levels are also renowned for increasing around autumn when the days become shorter and the body’s natural hormone levels change in response to the natural Circadium Rhythm, the 24-hr cycle in the physiological process of all living beings, determining sleeping/feeding patterns, brainwave activity, hormone production, cell regeneration and other biological activities.

Getting the PPID/IR/EMS controlled and managed is essential in order to minimise the associated laminitis risk. Controlling the cortisol levels restores the insulin response in the hooves. There is no cure for PPID, but the good news is that once it's been diagnosed, management is fairly straightforward and can help the horse to return to a comfortable lifestyle.

Top Tips

  • Lower cortisol and increase dopamine levels naturally. Stress and certain health conditions can raise cortisol, lower dopamine levels and cause weight gain. Keep levels balanced by maintaining a happy equilibrium; exercising and allowing quality rest, alongside feeding a natural, species-appropriate diet and adding a vitamin/mineral supplement that support healthy cortisol and dopamine levels.
  • Exercise is really important, not just to rid the body of fat cells, but it's also increases dopamine levels. Regular exercise also helps to burn the extra blood sugar made available through elevated cortisol levels.
  • In addition to the countless physical benefits, exercise can also have psychological benefits. Studies show that exercise can increase the amounts of both dopamine and serotonin neurotransmitters in the brain, as well as helping your horse feel more energised overall. In a May 2007 article in the Journal of Neuroscience, it was noted that exercise could cause the brain cells that use dopamine to work more efficiently, and an August 2007 article in the journal Neuroscience Letters noted that continuous exercise also reduced damage to brain cells that release dopamine.
  • Quality rest time helps lower cortisol levels because otherwise the body’s nervous system stays in a state of alertness that requires cortisol. Getting proper rest also increases serotonin and dopamine, which help control feed cravings.
  • Feed omega-3 fats as they help trigger the production of serotonin, as well as being a good food source of the trace mineral selenium. A low intake of this mineral has been linked with depression.
  • Brewers Yeast is extremely beneficial for the metabolic horse, as it provides the full compliment of the B-Complex vitamins which can help lower cortisol levels.

Steps you can take to lower cortisol and stimulate dopamine levels naturally

  • Follow a daily regime of 20-30 minutes exercise, even if it’s just a brisk walk. The body's reaction to exercise creates brain activity that regulates hormone and brain chemicals.
  • Add a vitamin/mineral supplement that supports good overall health and balances your forage/grazing. Avoid sugar, grains, bad fats (PUFAs) and processed feeds which can cause dopamine levels to drop.
  • In addition to supporting overall health, Vitamin C is helpful in supporting dopamine - rosehips are jam-packed full of Vitamin C.
  • A calm, happy horse with horse buddies creates positive brain activity, increasing the amount of feel-good substances such as dopamine and seratonin.