What is the best worming schedule for horses?

Well let’s be clear right from the start it’s not the best “worming” schedule for horses, it’s the best deworming schedule for horses.

You will not be giving your horse worms but rather treating him in case he does have worms.

Below we will explain the different types, symptoms you might see in your horse if he has worms and how to treat your horse and when.

What types of worms do horses get?

While there are over 20 different types of internal parasites which can and do infect horses in Australia there are 5 basic groups of worm types.

Strongyles – both Large & Small
Found in the large intestine adult Large Strongyles (may also be called bloodworms) can either attached to the walls, live in the intestinal contents or may migrate through blood vessels, hence the common name Bloodworms.Horse ingest larvae while grazing, which in turn develop into adults with the female laying eggs inside the horse which of course the horse excretes and the cycle starts again. The Large Strongyles take approx. 6 – 11 months to mature once your horse has ingested them.These nasties really affect the tissues they come in contact with, whether that be inflammation and swelling in the intestine & gut lining or swelling and potentially blockage and death to tissue ends as they travel through blood vessels.The Small Strongyles do not migrate to other organs but instead reside in the intestinal wall, and take approx 6 – 10 weeks to grow to maturity after the horse has ingested them.These guys actually “bite” the lining of the intestine, causing large pieces of gut lining to be destroyed; as well as feeding on your horses blood at the same time.

All horses can be affected by strongyles but young horses are most vulnerable.

  • Large Roundworms (Ascarid)
    These worms end up residing in the small intestine of the horse, but once again start out by the horse picking up the eggs whilst grazing. The complete life cycle takes approx. 3 months and proceeds as follows: the female lays large amounts of eggs which are passed out in manure, the horse picks up the eggs (which can remain infective for years in the environment). These eggs then hatch in the stomach and intestines, the larvae then migrate into the blood circulation system and are carried to the lungs and liver. Some large roundworms will sit in the gut and compete with the horse for nutrition.
  • Pinworms
    Or as I like to call them “bottom dwellers”, these worms do not migrate but live their life in the large intestine and rectum of your horse. Probably the least harmful of all the horse worms as these guys don’t travel into blood vessels and organs, they are nonetheless very irritating to your horse.Apologies in advance for the visual graphic you will now have but the female crawls out of the horses rectum and lays her eggs in a sticky substance around your horses bottom and then returns inside. These eggs can then be ingested orally and develop in the colon before moving their way towards the light if you will.These worms are incredibly irritating to your horse and so they naturally itch and will rub their tails/bottoms on fence posts, bedding, stall walls, feed buckets, just about anything they can reach thus depositing the eggs and contaminating other areas. This itching can be so severe that some horses will rub out all their tails and make the dock bleed.
  • Bots – Now it’s not just worms but flies also, specifically the Bot Fly which lay yellow eggs on the hair of the horse and this is how it begins.The clever fly usually lays the eggs on the horses front legs, near the throat and under their tummy. The horse either ingests the eggs or once the eggs hatch the larva then migrate to the mouth of the horse and burrow in, usually on either the lips, tongue or gums of the horse.During the next two stages the larva will migrate down the throat and attach to the stomach lining before fully developing and being passed in manure, where the hatch as the fully grown fly and the cycle begins again. This is a Spring to Autumn cycle, and you won’t see Bot Flies or eggs during other times of the year.
  • Tapeworms – And now for something completely different we have worms which are hosted in mites! Tapeworms are introduced to your horse via a “host” which is the Forage Mite. The mite picks up the eggs of the tapeworm in the manure of infected horses, the tapeworm begins developing in the mote and then your horse picks up the mite through grazing.Once the horse has ingested the mite the tapeworm is released and will attach to the horses intestine at the ileo-caecal junction; which is where the small intestine enters the large intestine. The Tapeworms attach via 4 suckers and proceed to not only damage the gut lining but rob the horse of nutrition.

Signs of worms and potential damage

The best advice I can give you is to treat for worms regularly and not to wait until you see signs of a worm burden/infestation. And yes we will discuss with what and how often soon.

But signs/symptoms you may see in your horse which can be caused by worms are as follows:

  • The Beginning: Early warning signs include a dull coat, generalWormy Coat poor condition, inability to put on weight either with reduced appetite or not, weight loss which may be rapid or just gradual, mild colic or colic like symptoms, generally anxious and itching tail/backside.
  • The Middle: Lower tolerance to exercise (puffing easy, refusing to go forward), loose manure or diarrhea, more susceptible to infections signs may include coughing or nasal discharge, anemia (gums look white not a nice pink colour), recurrent colic or severe bout of colic
  • The End: Pneumonia, stomach rupture, physical blockage of the small intestine, emaciation, severe and continuous diarrhea and gut emergencies including acute colic, torsion of the gut (when a piece of the intestine is twisted on itself), intussusception (when a portion of the intestinal tract telescopes into an adjacent portion) or volvulus (when a segment of intestine knots or twists on itself, similar to torsion), perforation (when the intestine tears or has a hole). These gut emergencies are life threatening, require immediate veterinary attention and often result in death.

Why should I have a regular schedule to deworm my horse?

The best worming schedule for horses will have your horse covered 12 months of the year and will also include pasture management including removing manure regularly, rotating horses, reducing stocking rates, supplementary feeding if required; this will reduce the risk of many/most of the above conditions in your horse.

So what do I use?

You will read much about rotational wormers, and some companies seem to want to make this more complicated than it needs to be. Put very simply there are two types of active ingredients in horse wormers – Mectin and Azole. The majority of horse wormers are either Avermectin (mectin-based) or Benzimidazole (azole-based).

BimectinWhilst we use to rotate the active ingredient every time we wormed our horses the more current thinking is that this was resulting in worm resistance (ingredient not being as effective at killing the worms) so the best practice worming advice is now Slow Rotation.

Slow Rotation means you change the class of active ingredient in your wormer every 12 months.
Personally I like to worm every 12 weeks and exchange the active ingredient every fourth time so my schedule looks like this:

Autumn – 1st March – Mectin-base

Winter – 1st June: Mectin-base

Spring – 1st September: Mectin + Praziquantel

Summer – 1st December: Azole-base

Autumn – 1st March – Azol-base

Winter – 1st June: Azole-base

Spring – 1st September: Mectin + Praziquantel

Summer – 1st December: Mectin-base

Virbac have a great little chart on their website, if you’d like more information about what product to use when.

You said there was only two active ingredients!

So what is Praziquantel I hear you ask? This is the only other ingredient you need to think about, as it is the only ingredient which will kill Tapeworm. So if you are using the Mectin based wormers in 2018, choose one with Praziquantel included as well. I usually make this my Spring wormer (see above).

So what do you really need to know about the best worming schedule for horses?

There are a multitude of different wormers out there, they come in paste or granule, either 6 weekly or 12 weekly doses and all sorts of pretty coloured boxes.

All of this is irrelevant, it doesn’t matter what you choose as long as the ingredients in the wormer are mectin-based one year and azole-based the next year (approximately) with a dose of Praziquantel thrown in there each year.

Worming Your HorseAnd finally you need to actually give your horse the wormer on a regular schedule. I personally like the every 12 week wormers and I like to use the change of seasons as people are usually talking about this eg. Oh it’s the first day of summer this weekend, and it reminds me to worm the horses.

If you’d like to follow my lead and add worming to your Horse Health Calendar you are welcome to use the dates above.

As always if you have any questions or require clarification on any of the topics we have covered here, add your question below and we will be happy to help you out.

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Horses are my passion. And while not everything in horses is black and white, and there are many choices you will need to make for your horse, I hope to explain things in a way that helps you make informed decisions, so you can provide the very best life to your horse.