horse struggling with death (artwork on the front of a house)
7. Colon infarction
An infarction is a blockage in a small artery. The tissue that is cut off from the supply of blood eventually dies. Examples in humans include a heart attack or cerebral infarction; but these do not occur in animals. An infarction that can occur in horses concerns the blockage of an artery to the intestines. A colon infarction causes severe stomach pain that is referred to as colic. The pain suffered often drives horses to lie down and roll back and forth.
Colon infarctions in horses are caused by the larvae of a certain worm (Strongylus vulgaris). The mature worms are present in the intestines of the horse, but the larvae penetrate the intestinal wall and crawl upward in the blood vessels until they reach the superior mesenteric artery. That runs along the back of the horse between the two kidneys. It is their home for a few months. A lump, called a worm aneurysm, then develops in the wall of the artery. Aneurysms of this kind often grow to the size of a man’s fist and have been known to grow to the size of a child’s head. The larvae separate from the artery wall after a few months and they are transported via the bloodstream back to the intestine. They again penetrate the intestinal wall; but this time, they move in the other direction, entering the intestines. There, they develop into mature worms. They mate and produce eggs that are deposited onto the grass via the animal’s manure. This marks the beginning of a new wave of contamination for grazing horses.
The disorder of the mesenteric artery is usually not obvious to the owner. But every once in a while, a clump of larvae breaks loose from the worm aneurysm. It gets stuck where the branches of the mesenteric artery become narrower; the blood flow is then obstructed. That infarction does not go unnoticed, as the horse experiences severe colic. It falls to the ground, rolls back and forth on its back, lashes out wildly with its legs and head and is soaked with sweat; it hits against walls and beams, groans and moans. It is a terrible thing to see. This behaviour can be so severe that the animal hurts itself. The colic attacks can occur so suddenly that you are no longer safe in the vicinity of the animal concerned. A horse can survive minor colon infarctions; but it will die if a larger part of the intestine dies off. This struggle with death takes hours, sometime up to a day. Painkillers do not help; not even in the highest dose. There is nothing you can do.
The major breakthrough in preventing colon infarctions in horses came with the discovery that the medication avermectin not only kills mature worms in the intestine, but also the larvae elsewhere in the body, in a worm aneurysm for example. That discovery proved to be even more important to horses than the discovery that penicillin can kill bacteria throughout the body. In the nineties, a paste containing an anti-worm agent derived from avermectin became the new medication of choice for treating worms in horses. A colon infarction has since become a rare occurrence.
The new worm medications are not yet available in 1984. I have the evening shift when I get a call concerning a horse with colic. The mare Olivia is acting lunatic and is soaking in sweat. The heart is pounding against my stethoscope, but the belly is silent: no rustling can be heard in the intestines. From behind, I feel my way around the bowels as I walk behind the horse. The walking is meant as a distraction and enables me to anticipate colic attacks so that I can retract my arm before the horse throws itself on the ground.
All of the bowels are where they should be: there is no dislocation or any signs of twisting of the intestines. But farther forwards, with my arm up to my armpit in the mare’s rectum, my fingertips feel a bulge in the abdominal aorta. Back then, it was not uncommon for a horse to have a worm aneurysm, even if it had been treated regularly with an anti-worm agent. I then have to remove my arm as quickly as I can, as the next colic attack presents itself. I inject a painkiller. The mare must then be walked, as this stimulates the bowel movement and the blood flow. My pager then sounds: I have been summoned to a second horse with colic.
I am back after about an hour. The condition of the mare is simply miserable: she is groggy and dehydrated due to the exertion and her sweating. The mucous membrane of her eye is dark purple; the belly is swollen but motionless: the intestines are no longer functioning. Internally, everything is still where it should be. Her heart is beating quickly and irregularly. “She can’t keep this up much longer. Her heart can’t take it anymore”. Another colic attack overtakes the animal. As an ultimate painkiller, I have morphine derivatives, but I doubt she will even survive the injection in the state she is in. What are the owner’s thoughts? “You must do what you think is best.” His voice is flat, but the emotion is tangible. The mare moans as she lies rolled up against the wall of the stable. I fill the syringe. Her blood is thick and dark. I slowly empty the syringe in the vein. The mare gasps; the heart gives a last sputter. The eye reflex is gone. The mare is dead.
A lovely vase with flowers is delivered to our home a few days later: ‘Thank you very much for the supporting care for Olivia’. That is not only kind, it is major: the end being what it was and yet still gratitude. Later, I heard that the owner had asked his wife and children to call on the veterinary surgeon to care for him in his final hours. That is the most precious compliment that I have ever received for my work.
© Leo Rogier Verberne