Horse worming medication usually comes in a plastic tube which you put in your horse' mouth and squeeze, which pushes the medication into his mouth. Hopefully he then swallows it and the worming task is complete. Some steps to keep in mind:

  • Set Quantity of Medication. Worming medication tubes usually have enough medication for a large horse, so for smaller horses or ponies you should use only part of a tube. To ensure that you give the correct amount, the tubes normally have a screw on the plunger which you adjust appropriately for the weight of the horse. 
  • Remove Cap. The tube of worming medication may have a small cap that covers the outlet. Don't forget to remove the cap, as otherwise you may shoot the cap into the horse's mouth along with the medication.
  • Administer Medication. Place the tube in the horse's mouth and squeeze the medication out. A steady squeeze which puts the medication into the mouth is appropriate; do not squeeze so rapidly that it squirts the medication down the horse's throat as it may actually go down the trachea and lead to choking (as well as being ineffective in this case). To minimize potential issues with the horse spitting the medication out, put the tube in the side of the mouth (rather than the front), with the outlet a few centimeters further in than the corner of the mouth.
  • Ensure Medication is Swallowed. Many horses will resist being wormed (disliking the smell and taste of the paste) and some will spit the paste out. See below for tips on how to avoid this. If the medication is spit out, one need to make a judgement of how much the horse swallowed and how much was spit out, then try again to medicate the horse with the quantity which was spit out.
  • Dispose of Medication. Once the horse has been given the worming medication, dispose of the tube and remaining medication. However, you have two small horses, a single tube may be enough for both horses, in which case you can use the quantity screw to adjust the amount of medication so that you worm both horses with a single tube (cheaper than buying two tubes and throwing both of them away still half-full). Ensure that animals do not have access to used tubes or remaining medication. Dogs can be attracted to the smell and taste of the worming paste, with a number of dogs becoming very ill (some died) upon eating it due to overdosing. 
  • Worm Other Horses. If your horse is pastured with other horses, it is best to worm all the horses at the same time (e.g. the same day) to reduce the amount of cross-infection from one horse to another. For more details on factors that affect worm infection rates and associated worming frequency requirements, see worming alternatives.

Horses Refusing Worming Medication

Unfortunately many horses dislike the taste and smell of worming medication, so they may refuse to let you put the medication in their mouth or they may spit it out. Below are a number of techniques you can use to minimize such problems:

  • Empty Mouth. As the medication is a sticky paste, it is difficult for the horse to spit out once the paste is in its mouth. However, if the horse already has food in its mouth (e.g. hay, grass) then it can much more easily spit out the medication with the food. To avoid this, one could try to first remove any food from its mouth (taking care to avoid being bit). Somewhat easier is to simply tie the horse away from food for a few minutes until it swallows any food in its mouth. Note that one should avoid letting the horse feed for the first few minutes after being medicated, as they may use this opportunity to mix the medication with their food (e.g. hay) and then spit the food out with the medication stuck to it. For this reason, using treats shortly before or shortly after worming a horse is often counter-productive.
  • Halter and Rope. Many horses will move their head away when you try to squirt the medication into their mouth. If a horse jerks its head just as you are squeezing the medication in, you can end up with half the medication on the floor or on the horse's head. Use of a halter and rope, firmly held to hold the horse's head in place, sometimes helps. However, not always, as a horse is stronger than a person and if they really object to the medication they may still jerk their mouth away.
  • Hold Head Up. After putting the wormer into the horses mouth, holding the head in an elevated position for a moment or two reduces the risk of the horse spitting the medication out.
  • Tickle Tongue. Some experienced handlers will put a finger into the side of the horse's mouth and tickle the tongue, which stimulates the horse's swallow reflex. However, due to the risk of being bitten if done incorrectly, this should be left to people experienced in such things.
  • Two People. With difficult horses, it sometimes helps to have one person hold the horse while the other administers the medication. 
  • Respected Master. Horses have more respect (or obedience) for certain people (e.g. owner, trainer). If a horse is difficult to worm, consider asking the person most respected by the horse to administer the medication.
  • Mix with Food. If there is a particular food (e.g. grain) which the horse is very fond of, one can try mixing the paste with the food. Some horses will react by eating both, others by eating neither. Buying a liquid wormer and mixing it with the food tends to work better than trying to persuade a horse to eat a paste mixed with food.
  • Tasty Wormers. Some brands are flavored (e.g. mint flavor) to make them more attractive to horses. Although this works for some horses, others refuse the flavored versions as well.

The Carrot Method

In addition to the above, another approach is what I call the 'carrot method':

  • Approach the horse with a number of carrots and with the medication hidden behind you (e.g. in back pocket). 
  • Move to the side of the horse.
  • Push the end of a carrot into the side of its mouth (as if it was the worming tube) and let it eat the carrot.
  • Cover the eye on your side of the horse with your hand so that he cannot see what you are about to do (do this after the first carrot so that he does not startle at the touch of the carrot). Then give another carrot, the same as before.
  • Repeat with a couple more carrots, so that it gets used to having something pushed into its mouth.
  • Once the horse is relaxed, wait a moment until it has finished eating and swallowing the carrots. Then, while keeping its eye covered with one hand, use the other to put the end of the tube into the horse's mouth in the same way as you did with the carrots. Quickly squeeze the tube to administer the medication before the horse realizes that it is not another carrot.

The above approach assumes that your horse is used to eating carrots and likes them. If this is not the case, one can use another vegetable which is more to your horses's taste.

Training Your Horse

The above are short-term solutions for horses which object to being wormed. For the longer term, if you have difficulties worming your horse, you may want to train it to be more accepting.

One approach is to fill a syringe (just the plastic tube, without the metal needle) with apple sauce and administer it to the horse in the same way as you would administer wormer. Doing this from time to time will allow the horse to get used to having a tube placed in its mouth and teach it that this can be a pleasurable experience which should not be resisted.

With some horses (especially young horses which are not used to being touched in this way), the objection is not only to the paste but also to having a hard object placed in their mouth. The above technique can be used to reduce or eliminate this objection. With young and inexperienced horses, it is helpful to get them used to being touched around the mouth by periodically touching and massaging them in this area. Such touching and massaging should be only for short periods, as doing so for long periods can be unpleasant to the horse and have the opposite effect (increasing resistance rather than reducing it).

Alternatives to Paste

The most common form of worming medication is paste in a tube, as discussed above. Other forms include liquid (which can be squirted into the mouth or mixed with food), granules (normally mixed with food) and tablets (usually flavored and given to the horse like a treat).

Correct Dosing

Try to judge your horse's weight reasonably accurately and give the horse the corresponding amount of wormer medication: If you don't know your horse's exact weight, it is easy to give the horse slightly too much or slightly too little; but minor inaccuracies are normally not an issue. However, giving your horse substantially too little is not only ineffective but also contributes to the development of medication resistant worms (a growing problem). The opposite extreme, giving your horse too much, will have little benefit in terms of effectiveness and it may affect your horse's health (depending on various factors, including the level of overdose).

Related Articles and References

For related articles, click on Horse Worms, Worming and Wormers.