Viva Las Vagus…wait, WHAT?!

Viva Las Vagus…wait,

WHAT?!

Part One of Three Part Series By Melanie Grubb-Miller

Now that I have your attention and you have an Elvis earworm, let’s talk about the Vagus nerve response in horses, and for that matter, in humans. It applies to both. We humans can “hack” the Vagal nerve response, to settle ourselves before competitions, or lessons. How? With the breath! More on that later.

It’s my understanding that the neurological system is divided into central and peripheral areas. The brain and spinal cord make up the Central Nervous System. There are 12 cranial nerves that originate in the brainstem to innervate the organs of sight, smell, and hearing, the muscles of swallowing and mastication, the tongue, sensation of the face, and use of the eye and facial muscles. Abnormalities of these nerves will produce changes in head carriage, balance, eye position, ear and eyelid tone and position, vision, smell, hearing, chewing, and swallowing food. The 10th cranial nerve, the Vagus nerve, also affects cardiac function, respiratory function, and GI motility.

See the image below, and follow the path of this nerve, that can create some of the mystery symptoms.

Dorsal vagal complex: The DVC is thought to be the most primitive branch of the parasympathetic nervous system and is responsible for immobilization. This response to potential dangers, shock, overwhelm, a stallion grasping the mare, upon mating, or even, ill-fitting tack.

The DVC is responsible for what is most commonly referred to as the freeze response (immobility), but also is involved in collapsed immobility, fainting, and feigning death. Fragmentation (dissociation) is also common when horses are dominated by the DVC, as in “if I can’t get my body to safety, then I’ll just leave my body.” Have you ever had a horse, whereupon, you tighten the girth, they nearly collapse? Or when you clean the hoof, they go down on that knee, as if they cannot hold them themselves upright? Perhaps, you just cannot get to the root of why your horse has begun to shut down. Could be that the DNS is being affected. This is common in OTTB horses. I have a theory it could be due to the way they are girthed up at the track, that clean and jerk motion, a pinching girth, along with all the nervous energy of the impending race. But, as I said, it is just a theory. I have firsthand experience with this, from an OTTB I once owned. Poor dear boy would nearly faint, upon tightening his girth.

When he was frightened, he would literally freeze, all the while, I could feel his heart pumping like a drum, in my calves. What can you do to relieve these symptoms?

For starters, talk to your vet about your suspicions, and get feedback from him or her, to rule out any other possible medical issues or abnormalities. Check your tack. Bridle fit is it affecting the fascial nerves by pressing on the fascial crest, or the zygomatic bone, at the intersection of the noseband. Is your browband too tight? That tension can affect the innervation in the temporal bone. Just to name a couple of possible points to check.

We can do many things to help these types of symptoms in our beloved partners, but first, we must educate ourselves, and be the strongest advocate for our horses. To say, “Well, that is just how he is, he hates the girth/saddle/bridle/being ridden!” NO. Horses talk to us with their bodies, PAY ATTENTION!

In part two, I will discuss the Sympathetic nervous system, to better understand the mysterious language of the horse.