Best practice treatment of sheep parasites

This page explains how to treat sheep parasites safely and effectively. It also outlines the main types of wormers, how to use them and the best practice steps to follow for each method of administration.

Anthelmintics (wormers) are used to treat and prevent parasite infections – roundworm, tapeworm, lungworm and liver fluke.

These products fall into the following groups:

• Group 1: (White, BZ) Benzimidazoles
• Group 2: (Yellow, LV) Levamisole (Imidazothiazoles)
• Group 3: (Clear, ML) Macrocyclic lactones, including avermectins and milbemycins
• Group 4: (Orange, AD) Amino acetonitrile derivatives (Monepantel)
• Group 5: (Purple, SI) Spiroindoles (Derquantel available as a multi-active)

The parasite control guide also covers combination products, flukicides and synthetic pyrethroids for cattle, as well as combination products, narrow spectrum, injectables for sheep scab, plunge dips and pour-ons for sheep.

Subcutaneous injections must be given carefully to make sure the product is placed under the skin, not in the fleece or muscle.

The sheep must be well restrained and the skin ‘tented’ away from the underlying muscle.

The preferred injection site is 10–15 cm (4–6 inches) below the ear on the side of the neck (see Figure 1).

Usually, a 1.6 cm (5/8 inch) needle is ideal.

After administration, the site should be gently massaged.

Figure 1. Subcutaneous injections

Intramuscular injections are made into muscle (Figure 2, needle on the right).

Again, care is needed to make sure the product is deposited in muscle and not just under the skin. This requires sheep to be well restrained.

The correct site is on the side of the neck 10–15 cm (4–6 inches) in front of the shoulder in the mid-neck area, well above the large jugular vein.

Insert a 2.5–4 cm (1–1.5 inches) needle at a 60-degree angle to the neck, aiming inwards and upwards towards the head.

Again, massage in after administration.

Using the neck site for intramuscular injections ensures no valuable cut of meat is damaged, and constant neck movement helps distribute the product.

Figure 2. Intramuscular injections

Pour-ons and spot-ons need to be applied accurately and each manufacturer may recommend subtle differences.

Incorrect application could impact the effectiveness of the products.

Use appropriate and calibrated guns. Always clean with warm soapy water and then rinse after use. Store in a safe, dry place.

When treating sheep with these products, make sure they are applied along the back line. If placed on one side, the product will not spread evenly around the body.

No pour-on or spot-on is effective against sheep scab.

Underestimating the weight of sheep is a common cause of underdosing.

Select and weigh the biggest sheep in the group to determine the correct dose.

If there is a wide range of weights, consider splitting the group, then weigh the heaviest in each section.

Check that the weigh crate is accurate and correctly calibrated before starting.

Always check that the gun is delivering the right amount before you drench.

Remove the plunger from a 10 ml syringe, put a thumb over the end and squirt the dose into it, making sure there are no air bubbles left.

Adjust the gun until the dose delivered is correct.

Drenching guns should also be well maintained and replaced regularly.

Clean equipment with warm soapy water after use and check springs and tubes to make sure there are no kinks that will form air bubbles.

Wormers should be stored securely, away from direct sunlight at 4–25°C.

Check the use-by date and, once open, use within the time shown on the packaging.

Shake white (BZ) products well before use.

The drenching technique is a vital part of ensuring that the wormer does its job effectively.

Make sure the sheep are properly restrained and cannot leap around when they are being drenched so they swallow the whole amount.

Sheep can also suffer serious injury, or even death, if they are unrestrained and the gun penetrates the tissues at the back of the mouth.

Place a hand under the head and tilt slightly to the side (Figure 3). Slot the nozzle in the gap between the molar and incisor teeth and then over the back of the tongue.

If the wormer is just put into the mouth, it will bypass the rumen via the oesophageal groove and will be less effective. This is particularly important for Group 1 – white (BZ) drenches.

Figure 3. The drenching technique

There are no medicinal products licensed for use in showers and/or jetters.

Any blowfly, lice or scab treatments administered in this way are done so illegally.

For plunge dipping, it's essential to know the capacity of the bath. Use only the two closed systems to check the bath and to top up.

Always top up as per instructions; if not, the dip wash will strip out and later sheep will not carry enough product for it to be effective.

Do not dip tired, thirsty or heat-stressed sheep. Allow dipped sheep to drain in designated draining pens, and do not return to pasture until excess dip has been shed.

When dipping, use protective clothing, handle equipment carefully and stick to the manufacturer’s instructions.

Sheep dipping must be carried out professionally and must comply with all relevant legislation to safeguard animal welfare, human health and the environment.

It's also vital to minimise the risk of resistance developing in sheep scab mites to organophosphates (OP).

Organophosphate (OP) dips

OP dips can only be purchased and used under the supervision of someone with a Certificate of Competence (NPTC Level 2 Award in the Safe Use of Sheep Dip).

This can either be the farmer or a contract mobile dipper.

For plunge dipping to control sheep scab:

• Sheep must be in the dip for at least one minute
• The head needs to be immersed under water twice

Used sheep dip must be discarded according to regulations because it can be harmful if disposed of incorrectly.

Sheep must not be drenched with a levamisole (Group 2 – yellow) anthelmintic for at least 14 days before and 14 days after dipping.

• Using medicines responsibly
• Worm control in sheep
• Liver fluke control in grazing livestock