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Chemical groups and actives

Cattle parasite treatments

Cattle parasite control requires the use of treatment products for both internal (endo-) and external (ecto-) parasites as part of an integrated parasite management (IPM) program. Products used to control internal parasites (gastro-intestinal nematodes, tapeworms and flukes) may also have a crossover effect on external parasites (ticks, flies, lice and mites). The best parasite control is achieved when a treatment is chosen for best effect against the primary targeted pest. However, it is important to consider the effects this treatment will have on other parasites (as noted on the label) to reduce the build-up of chemical resistance.

Chemical activity

Each parasiticide has a particular chemical structure or ‘active’ component. The active operates to disrupt an essential life process in the parasite. Actives within the same chemical group generally have a similar mode of action and target the same life processes. Therefore, if resistance develops to one chemical active in a group this usually confers cross resistance to other chemicals in the same group. Chemical mixtures and combinations incorporate two or more active ingredients; mixtures use multiple actives to target different parasites and chemical combinations use multiple actives to target the same parasite.

Chemical groups for treating cattle against ticks

  1. Synthetic pyrethroids (SPs): treat ticks, flies and lice
  2. Organophosphates (OPs): treat ticks, flies and lice
  3. Macrocyclic lactones (MLs): treat ticks, roundworms, lice, flies and mites
  4. Insect growth regulators (IGRs): cattle tick and lice
  5. Amitraz: treat ticks
  6. Chemical mixtures and combinations

Choosing and using products

Choosing a Product

The product you choose to treat ticks on cattle depends on the following factors:

1. Tick species

Treatment for 1-host ticks (cattle tick) are very different from those used for multi-host ticks (paralysis tick, bush tick), so it is important to understand which species is the target for control. Product labels should be checked to ensure that the product is effective at killing the target species.

2. Impact on other parasites

The spectrum of activity of chemical products varies widely. For instance, amitraz has a narrow spectrum, killing ticks while having no impact even on other external parasites, whereas synthetic pyrethroids (SP) have a medium spectrum, providing control of a range of external parasites, and macrocyclic lactones (ML) have a broad spectrum, killing internal parasites such as roundworms as well as external parasites. Consider other parasites when choosing products. Where possible, choose a product to address only the parasites of concern at the time of treatment to reduce the risk of resistance developing from unnecessary overtreatment of non-target species.

3. Chemical resistance

Acaricide resistance is common and widespread in Australia. Resistance has been reported to all chemical classes used to control ticks. Where resistance is suspected, a sample of ticks should be tested to determine the resistance profile of the tick population. A chemical should not be used where resistance to that chemical class has been detected.

4. Speed of activity

Some chemical acaricides (e.g. amitraz) are contact poisons that act immediately whereas others (e.g. macrocyclic lactones) act systemically and require the ticks to take blood meals to acquire a lethal dose, meaning it may take up to a week for all of the ticks to be killed. Other products (e.g. fluazuron) are development inhibitors that provide control by preventing the ticks from moulting and ticks may survive several weeks after treatment. The required speed of activity must be taken into account when choosing a product. For instance, if clearing cattle of ticks immediately prior to sending them to a saleyard or when needing to knock paralysis ticks off calves, a fast acting product must be used.

5. Short vs long acting products

While some products (e.g. amitraz) provide no persistent activity, other products (e.g. fluazuron, long-acting macrocyclic lactones and chemical eartags) can provide ongoing control for many weeks. In general it is best to use long-acting products where there is ongoing high tick pressure or in high risk situations (e.g. young calves exposed to paralysis ticks). Indiscriminate use of long-acting products can increase the risk of developing resistance through unnecessary exposure of tick populations to a particular class of chemical.

6. Withholding periods (WHP), export slaughter interval (ESI) and retreatment intervals

It is essential to choose a product with appropriate withholding periods (WHP) and export slaughter interval (ESI) according to the time left before the animals go to slaughter or their milk is used for human consumption. Retreatment intervals may be important where frequent application of a product is required to ensure ongoing protection in high risk situations (e.g. calves exposed to paralysis ticks). Consult the APVMA website.

Using products

  • Avoid unnecessary treatments, see ‘Deciding when to treat cattle tick’.
  • Follow the label instructions to ensure correct dose and use of treatments, and be aware of contra-indications (situations where a chemical might be harmful if used).
  • Pour-ons and injectables—Calibrate applicators to ensure the correct dose is delivered. Calculate the dose based on the heaviest animals in the mob. It is difficult to estimate the body weight of cattle accurately without regular reference to a set of scales. Where possible, weigh the animals and treat according to individual weights. This will ensure that heavy animals are not under-dosed, and light animals are not overdosed.
  • Sprays—Ensure spray races are operating at the correct pressure and that all nozzles are working. When using a spray pack, ensure the animal is completely wet. Avoid hand sprays. Preferably use liquid products in sprays, but if using powder products, ensure they are dissolved thoroughly.
  • Dips—Ensure dips are charged and mixed appropriately, and all animals are thoroughly submerged. Stabilise dips if contents are to be used subsequently.

For help in selecting a product to treat ticks see the TickBoss cattle products search guide.

Application methods

There are a variety of application methods for administering chemical products to cattle. Each product is formulated to ensure that the application method will transfer the chemical to a location that will affect the target parasite, e.g. direct contact via the skin or uptake as the parasite ingests host blood, plasma or tissue. More options are available for treating external parasites (flies, ticks, lice and mites) than internal parasites (roundworms, tapeworms and flukes). The different application methods are listed below.

Methods to treat cattle against ticks

  1. Pour-on
  2. Subcutaneous injection
  3. Dip
  4. Spray
  5. Ear tags (aids in control of paralysis tick only)

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