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Worms & Drenching

Worms are one of the main threats to stock health and production, impacting the viability of their farming operations.

Two popular concepts of how worms affect livestock are they compete for nutrition with the animals they infect, and cause damage to the gut, leading to inefficient feed utilisation and scouring.

Low exposure to worms suppresses appetite and change grazing behavior. They also induce an immune response which requires energy and protein.

This then becomes a cost to the animal resulting in reducing production. This is often not noticeable and is basically subclinical.

The basis of a successful worm management strategy is to prevent their negative effects on animal health and production by:

  • Restricting the exposure of susceptible stock to infective larvae
  • Reducing the contamination of pasture with worm eggs shed by infected stock.

Pasture management, stock management and drenching are key tools for worm management.

See link for in depth information on worms and worm management.

Haemonchus (barber’s pole) suck blood and cause anemia directly from blood loss. Bunostomum (hookworm) also sucks blood, but is less common now as farming practices change.

Barber’s Pole Worm (Haemonchus contortus)

This usually appears from summer onwards, especially after rain. The increased moisture causes a large hatch of worm eggs on the ground, and the level of infective larvae rises rapidly. Haemonchus is a blood sucker, so the symptoms are of blood loss rather than scouring as seen with other worms. Specific long acting drenches are best for coping with this; a lot of what appears to be resistance is actually reinfection. As pasture burdens can be high, reinfection can occur in a matter of days after using a short acting drench.

If you wait to drench in response to an outbreak, you can still lose some lambs. It is therefore best to use a preventative drench containing Closantel such as Genesis Ultra.

Due to the longer action of these products, they have long withholding periods (Genesis Ultra is 56 days).

However, moxidectin-containing drenches such as Exodus and Trimox have shorter withholding periods (ten and 28 days) and can be used for lambs being picked for the works regularly.

When to start drenching

This depends on the individual farm, as calves grazing all together on a pasture will have a higher exposure than those housed or grazing with cows.

Calves rarely need drenching before they are weaned, they tend not to need their first drench until they’ve been weaned at 3-4 weeks. Ideally, take 6-10 faecal samples and do pooled faecal egg counts before you decide to drench the calves for the first time. An egg count over 250 (eggs per gram) means that they need drenching and it can be several months after weaning before levels get this high.

One very important point is not to mix drench with milk or drench at or near the cafeteria. This is because a suckling calf can cause the ‘oesophageal groove” to close, resulting in drench by passing the rumen, causing toxicity which can be fatal. This is especially applicable to drenches containing Abamectin and or Levamisole.

For the first 12-15 months of life calves should be drenched with a combination drench i.e, two or more active ingredients.

Combination drenches contain Levamisole for the control of “Cooperia” which levels peak in Autumn. Levamisole is often ineffective against Ostertagia so need combining with BZ (white drench) or ML (Endectocide).

Using an oral drench in young stock is preferred and research has shown combinations are better for slowing the onset of resistance.

Once animals reach a point where oral dosing is not practical or safe, then injectable or pour-on drench methods become options

Examples of oral combinations are: ‘Arrest C’ (Albendazole and Levamisole) ‘Switch’ (Abamectin and Levamisole) and ‘Matrix C’ (BZ, Levamisole and Abamectin).

Examples of pour-on combinations or injectable combinations are: ‘Eclipse Pour-on (abamectin and Levamisole) and Eclipse-E injectable (Eprinomectin and Levamisole).

The most cost effective strategy is to use ‘Arrest C’, ‘Switch C’ until the stock are too big to oral drench and then move onto ‘Eclipse’.

Drench intervals for Calves vary but typically work on 4-6 weeks for oral and 6-8 weeks for pour-on/injectable.

Once the calves are over 15 months old they can be treated with a single active ingredient, Genesis, Eprinex or Dectomax.

Young stock dosing (<120kg) guidelines

  • No matter what age they are, weigh them regularly and split into groups if necessary – poor weight gains are the first sign of many sub-clinical diseases as well as outright under feeding.
  • Drench guns calibrated (using a measuring cylinder to check).
  • Dose rates and product double check.
  • Never mix drench with milk or give near calfeteria.
  • Don’t drench dogs with abamectin as “mectins” can be very toxic to dogs.

Regardless of the method of application, taking the time to make sure drenching is done properly is important, as incorrect administration is a leading cause of drench problems.