Treatment methods
Most insecticides registered for use on cattle are not very active against louse eggs. This means that after treatment, eggs can still hatch and continue the infestation. With some insecticides, a follow-up treatment 2–3 weeks later is necessary. This time interval is critical to achieve control, as it allows time for the eggs to hatch but not to mature into adults which will lay eggs themselves.
The timing and frequency of treatments depend very much on individual circumstances. In many cases treatment in late autumn or early winter will give adequate control of cattle lice.
There are four methods of treatment available, but not all products control both biting and sucking lice, so check the label carefully and/or have the lice on your cattle identified. Spray-on and pour-on insecticides are probably the most widely used form of control, but insecticidal ear tags are also available. The injectable formulations of macrocyclic lactone (ML) worm drenches also control sucking lice.
Spray treatment
Hand spraying is practical for small numbers of cattle. Knapsack sprays, or any pump/spray unit with 0.7–0.8 mm spray nozzles capable of producing a ‘cone’ or ‘flat fan’ spray pattern, are suitable.
Commercial power spray units are also available. These are generally walk-through systems with one to three spray ‘hoops’. Cattle must be walked slowly through them to ensure adequate wetting.
With all spraying methods, thorough wetting of the cattle with the insecticide is essential.
Pour-on treatment
With pour-on treatments a small amount of insecticide is applied to the animal’s back. Depending on the product chosen, some insecticide will be absorbed across the skin and be moved throughout the body. Sucking lice that feed on blood are poisoned as they feed. Insecticide that remains on the skin and in the hair coat is distributed by cattle grooming. This residue aims to kill biting and sucking lice that come in contact with it. Always follow the ‘Directions for use’ on the product label to ensure proper application.
Ear tags
At the time of writing (January 2007) there were two ear tags registered to control lice:
• Warrior®, which contains two organophosphates, and controls both biting and sucking lice;
• PYthon®, which contains a pyrethroid insecticide, and is only registered for the control of biting lice.
For producers who choose to use ear tags only, it is recommended that these two products be used in rotation in order to delay the onset of resistance (provided that only biting lice are present). (Note: Both products also control buffalo fly.)
It is vital to remove (or replace) both types of ear tag after 3 months. Failure to do so will expose any new lice to sublethal doses of the product, which will allow selection for resistant lice.
Treatment by injection
As mentioned previously, some broad-spectrum injectable anthelmintics will control sucking lice but not biting lice. Read the product labels to identify a suitable product. It is important when using broad-spectrum pesticides to consider the impact of the treatment on non-target species such as dung beetles.
Macrocyclic lactone (ML) products offer the added benefit of activity against lice when used to drench cattle for nematode infection. Conversely, if MLs are used to treat a louse infestation, the treatment will also affect any worms present. Make sure the treatment strategy used is compatible with your drench-resistance management program.
Is lice treatment necessary?
Many experiments have shown that the treatment of cattle that have light to moderate infestations is not economically justified in terms of improved growth rate and body condition. However, in recent years there has been increasing emphasis on hide quality, and there is evidence that the majority of hide damage occurs when cattle are scratching due to the presence of lice.
If cattle are scratching because of lice, treatment is recommended. Besides improving hide quality, this will decrease the likelihood of damage to fencing and other fixtures that cattle tend to use as rubbing posts. Treatment is more likely to be necessary in winter, especially if nutrition is poor, and cattle are losing condition.
Cattlecare, the beef industry’s quality assurance program, requires that all reasonable steps be taken to improve hide quality, so producers who wish to become Cattlecare-accredited will need to control lice. An eradication program should be seriously considered.
Eradication
Another consideration is that if you are concerned only with control (i.e. you treat the cattle only until they stop scratching) and do not check that you are removing all lice, then you may be selecting for resistance.
In the case of sheep lice, there is already widespread resistance to some of the treatments used, and there is no reason to assume that this will not also occur in cattle lice. The best way to delay the onset of resistance is to:
• follow the manufacturer’s instructions;
• ensure that you do not underdose;
• check that treatments have been fully effective.
Assuming no resistance to the chemical used has developed, eradication of lice should be quite feasible if you comply with the following steps.
1. Treat all cattle with one of the treatments listed above, and ensure that you repeat the treatment according to the manufacturer’s instructions.
2. Ensure that the dose rate is accurate. Preferably weigh all cattle, or a representative sample.
3. Treat all cattle on the property at the same time, prior to calving. Choose a time when they are not stressed or in poor condition.
OR
If groups are treated separately, ensure that there is no contact possible between treated and untreated groups.
4. Immediately after treatment, move treated groups to a paddock that has not had cattle in it for at least a week.
5. Ensure that no contact with any neighbours’ cattle is possible, either through straying or through contact across fences.
6. Check that treatment has been effective. No adult live lice should be found on the animals when they are brought in again for their second treatment, and there should be no live lice at all a few days after the second treatment.
7. Consider treating in autumn, before louse numbers build up. This will allow a longer ‘test period’ of cold weather to follow, so that you are better able to gauge whether eradication has been successful.
