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Preparation for winter, and deworming...


PREPARING OUR HORSES FOR WINTER

Of the management steps we take to prepare Dobbin and his sisters for winter, few are as important as treating for internal parasites, also known as deworming.

If we categorize the worms by how they feed within the horse, there are three groups.
The round worms are the most obvious and probably do the least amount of damage.
The stomach (and small intestine) worms, which do the most damage and are the most common.
The bots are the result of the little bee pestering our horses right now, they can do a great deal of damage to our horses’ stomachs.
We will briefly discuss each group.

The round worms, or Ascarids, affect primarily the young.  They are less common in two year olds, because the horse’s immunity starts to develop against the worm and prevents their reproducing.  They create a great deal of excitement when found in the stool, as they are the size of earth worms (and big ones, at that!).   Most of the damage they do is due to their huge numbers within the intestine and their physical size.  They can cause blockage and rupture of the intestine when their numbers become so great they dam the flow of contents.  Almost as important is the damage they cause during migration.  After the foal ingests the eggs, the eggs hatch and release a small worm, or larva.  These penetrate through the intestine wall and use the blood supply to migrate, traveling through the liver and into the lungs.  In those unfortunate cases where we do postmortem exams, we often see scarred spots on the liver where the larva migrated.  Within the lung, each larva’s movement leaves a scarred track.  A large number of these will cause irritation resulting in a chronic cough.  Eventually the worms return to the intestine and start producing eggs.  These eggs are indestructible and once passed onto the ground, will stay there for years, waiting to be ingested by the next foal.

The parasites that actually attach to the lining of the stomach and intestine consist of the stomach worms, large and small strongyles, the Strongyloides, and the pin worms.  These attach themselves to the stomach lining and live off the blood supply of the host.  With large numbers, there can be enough blood loss to cause anemia.   In addition, there is some inflammation around each attached worm.  When you multiply this by millions, there can be enough inflammation to interfere with digestion.  The combination of anemia and decreased digestion of the food that is available can certainly lead to diarrhea, weight loss, or at least lack of gain and degenerating body condition.

Bots are the worms that attract our attention this time of the year.  Their life cycle includes the small bee that resembles the honey bee.  It is flying around the legs of our horses and sends them into orbit.  It is trying to lay the larva packet on the hair of the chest or legs.  It will do no direct harm to the horse in the process, but the horse sure thinks it will!   The small yellow spots contain a larva setting atop a spring.  When these are touched by the rough, warm, moist lips or tongue of the horse, the top springs open and the larva is launched.  Once on the tongue or gums, it will start its migration to the stomach.  There it will develop into a grub attached to the lining.  Here it will stay until spring, when it matures enough to detach.  Next spring it will be  passed in the stool, hatch into the bee, and the process starts all over again.

When enough of the bots are attached, there can be enough irritation to the stomach to cause the horse to go off feed, and it may interfere with digestion of what is eaten.  The more aggressive bots may burrow right through the lining of the stomach into the abdomen. Their presence and the escaping stomach fluids causes a sever infection called peritonitis.


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