Increase wormer efficiency with correct usage

Patrick Bolger

| General

| Jun 15, 2018

cow calves in field

Use wormers correctly

To ensure the effectiveness of your wormer, and to avoid anthelmintic resistance on your farm, it is crucial to dose accurately.


In order to dose accurately, there are two key points:

– The particular live weight of an animal

– A perfectly calibrated dosing equipment to deliver the correct volume of liquid


The best way to accurately measure live weight is to use a weight scale or a weight band. Visual estimates should be avoided, as they usually deviate considerably from the real weight.


Under- and over-dosing can have serious, long term consequences, so every farmer should make efforts to ensure accurate wormer dosing.


You should always use the full dose, even when administering two different products at the same time.


Delivery Methods


Treatment should be avoided if the animal is wet, or if you anticipate rain within the next couple of hours, unless it is a waterproof product.

Never treat damaged skin and avoid areas which are covered in manure or mud.

Apply the wormer along the back, from the withers to the head of the tail.



Some products might need to be shaken before use.

Use clean, sterile syringes and needles. For multi-injection guns, disinfect the needles in between injections.

Restrain the animal

Clean the injection site with alcohol

Raise some skin and inject the dose carefully. If a large dose is to be administered, split it between two injection sites.

Dispose off needles and syringes in appropriate containers.



Always use the correct applicator, and ensure that you don’t cause choking or damage to the throat.

Insert the applicator from the front over the back of the tongue with gentle pressure. Once in the throat, release the bolus. Gently remove the applicator and make sure that the bolus has been swallowed.


Oral drenches

Oral drenching guns deliver over the back of the tongue into the rumen. Errors in dosing technique may allow cause the dose to bypass the rumen, which will reduce potency.

Ensure that the equipment is calibrated and in good working order. Run a test with product and deliver a few doses into a measuring cylinder. Never use water, as it will give false results.


The risk of resistance

Wormer resistance can develop if you under-dose, or if you use faulty dosing equipment. Worms with some resistance to a product could survive a lower dose, where a full dose would have killed them.



Read more on the topic:

Getting your worming strategy right

Understanding the different cattle wormers & how to reduce anthelmintic resistance on your farm



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