A drench is the common name used for anthelmintic and is a substance that kills targeted worms when given to an animal.

Drenches can be divided into several ‘chemical family’ groups – that is they each have a specific mode of action on the worm.

There are a few drench families on the market with an array of brand names.

Drench administration

For a drench to be effective it has to be administered correctly

  • Read the drench labels carefully
  • Follow label instructions
  • Do not under-dose. Weigh stock to check
  • Select dose based on bodyweight of the largest animals in the group
  • Ensure your drench gun is working well

Types of Drenches

Narrow spectrum

These are used to kill specific worms eg liver fluke, tape worms

Combination drenches

These contain a mixture of different mode of action active ingredients.

Combination drenches were developed in response to the increased prevalence of drench resistance.

Combinations usually contain two or three broad spectrum action groups.

For more information refer Wormwise Handbook page 27.

Using Drenches


For a drench to be effective it must be administered correctly.

Read labels:

  • Check active ingredient
  • Dose rate
  • Withhold period
  • Method of application
  • Safety precautions for operators eg personal protective equipment
  • Safety precautions for animals being drenched
  • Handling e.g shake before use
  • Expiry date
  • Storage conditions
  • Disposal instructions

Preparing stock

  • Weigh stock before drenching. Simply estimating weight can lead to under-dosing, resulting in not all worms present being killed and an increased chance of developing resistance. Over-dosing can be fatal.
  • Weigh a random sample of animals (40 suggested) and if there is a narrow variation then drench to the heaviest weight – not the average. If there is wide variation, draft the group into light and heavy animals and dose to the weight of the heaviest in each group.


  • Ensure all equipment is in good condition.
  • Check the drenching gun by placing your finger over the end and pressurising the trigger. This way you will find out if there are leakages or back flow.
  • Replace washers and valves if necessary.
  • Calibrate the drench gun by squirting ten x 10 ml squirts of the drench into a calibrated measuring cylinder. The volume should read exactly 100 m
  • If not, adjust the dose setting and check again.
  • Use the actual drench you will be administering rather than water in this test.
  • Check the drench gun nozzles for damage and ensure there are no rough edges that could damage mouths.
  • Keep new valves and washers on hand as spares.
  • Keep more than one drenching gun – clean and in working order – on hand.

Filling the backpack

  • Shake well to ensure suspensions are evenly mixed.
  • Check the setting of your gun to ensure that you have calculated and selected the correct volume to administer for the required weight.

Drench Administration

  • Do not rush. This is a skilled job and rushing or cutting corners will reduce the effectiveness of the treatment.

Oral Drenches

  • Hold the animal firmly with the head horizontal.
  • Carefully introduce the nozzle of the drenching gun into the side of the mouth and over the back of the tongue.
  • Administer the drench and withdraw the gun.
  • Release the animal when it has swallowed.
  • Check accuracy of gun again after drenching 200 animals.
  • Drench gun injuries to the throat, or drench that enters the lungs, can be fatal.
  • If using ‘hook’ in larger cattle, take care to avoid damage to mouths, and ensure each animal swallows the full dose.

Injectable drenches

  • Before starting, check the gun is delivering the correct dose by squirting a set number of doses into a measuring cylinder or calibrated medicine cup.
  • Animals must be dry and clean before being injected.
  • Use new sharp needles and change to a new sterile needle after every 50 animals.
  • Inject under the skin in anterior neck, so the injection is not going into muscle.
  • Careless injection can cause infections, residues or carcase damage resulting in downgrading at slaughter.

Pour-on drenches

  • Do not use pour-on preparations if the animals are wet or if heavy rain is forecast (even if the product claims to be rain-fast).
  • Apply along the midline of the back from the withers to the base of the tail, unless label instructions direct otherwise.

Controlled release capsules

  • Use the appropriate capsule applicator and the correct size of capsule for the weight of the animals.
  • Ensure the animal is appropriately restrained. Incorrect angle or unnecessary force can damage the animal’s throat, with potentially serious consequences.
  • It may be advisable to use a “priming” dose of a broad spectrum drench at the same time as capsule administration. Discuss this with your veterinarian.

After Drenching

  • Clean all equipment. Replace any damaged items.
  • At regular intervals, dismantle and thoroughly clean drenching guns.
  • Record all drench use in an appropriate documentation system.
  • Monitor the effectiveness of your drenching programme.