Lice Treatment in Cattle

Lice are external parasites of cattle which can cause intense irritation and affect the appearance of stock due to the self-trauma associated with rubbing and scratching. There are a number of lice species that affect cattle and the main ones are classified as either biting or sucking lice. Biting lice (Bovicola bovis) (Fig. 1) feed on skin debris. Sucking lice (Fig. 2) include thelong-nosed louse (Linognathus vituli), the short-nosed louse (Haematopinus eurysternus) and Solenopotes capillatus. Sucking lice suck blood and can cause anaemia if infestations are heavy enough.

Coming into the autumn and winter months of the year lice become more of a problem in cattle. This is because cooler conditions and denser hair coats allow lice numbers to build up on cattle especially if they are under nutritional stress or have other chronic diseases at the same time. Lice prefer lower temperatures and less intense sunlight so their numbers decrease in summer and build up in winter however lice eggs or nits (Fig. 3) can survive over summer. Their life cycle is relatively short, as little as 3-4 weeks, so if cool conditions persist, lice numbers can pick up quickly. Lice spread very readily between cattle and the main route of transmission is by direct contact.

As lice spread via direct contact, prevention depends on keeping clean stock away from infested or potentially infested cattle. This entails maintaining good fences, quarantining and/or treating stock with unknown status brought onto the property, complete musters and appropriately timed treatments with effective products. Timing of treatment is important in the control of cattle lice. At the first signs of cooler weather, any lice eggs that have survived summer will start to hatch. No treatments available kill the eggs so it is important to start treatment early in the season before nymph and adult stages build up. Treatment should be timed for the first few weeks of the cold weather season. A complete muster is important and reinfestation needs to be prevented by maintaining good fences and quarantining newly introduced cattle. A treatment each winter can prevent new infestations from eggs that have survived over summer. Also, if there is an unexpected warm period during winter this can cause lice to become dormant and stock should be inspected again once the weather cools again. Ivermectin-based products such as Baymec or Bomectin are effective for the control of the lice species listed above. Both injectable and pour on formulations are highly effective against sucking lice however injectable products tend to have lower efficacy against biting lice. If lice are the primary parasite target then a product such as Baymec pour-on has the advantage of controlling both sucking and biting lice as well as providing up to 56 days extended activity against the biting louse,
Bovicola bovis and the sucking louse, Linognathus vituli.

Using a product like Baymec in autumn as part of a total internal parasite control strategy may have they additional benefit in removing gastro-intestinal worm burdens at this time which may affect productivity especially if pasture quality is declining.