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Lice in Cattle

Introduction

Cattle lice are insect parasites which live permanently on their host. They can be one of two types; chewing lice, which feed on skin, hair and debris, or sucking lice which feed on blood in a similar way to biting flies. Low levels of infestation on healthy animals lice do not generally cause any problems. However, heavy infestations can occur in some instances, particularly winter housing where thick winter coats and increased stocking densities create favourable conditions for lice to spread and multiply. High levels of louse infestations may indicate underlying issues with management, nutrition and health. Heavy infestation can cause intense itching and irritation, with rubbing causing animals to develop characteristic patchy areas of hair loss. Where large numbers of sucking lice are present animals may also become weak and anaemic. 

Economics and Welfare and Economics

At low levels these lice can be considered normal inhabitants of the skin with little to no economic or welfare cost. High levels likely indicate an underlying problem with husbandry or chronic disease which in itself may have a profound impact on welfare and economics. This should warrant further investigation. The irritation and itching behaviour caused by heavy infestations compromises welfare and can also reduce feed intakes and growth rates directly, with skin damage and secondary infection having further production costs. Sucking lice may also cause anaemia in heavy infestations.

Clinical signs and diagnosis 

Heavy louse infestations typically indicate an underlying issue with current animal husbandry practices and or health. The main signs associated with louse infestations are itching, rubbing and hair loss, usually late in the housing period when coats are at their thickest. They can also be a problem in thick, wet coats of out-wintered cattle. Constant itching can cause skin damage which allows secondary bacterial infections. Sucking lice can also be associated with mechanical spread of other diseases such as ringworm. Lice are not usually associated with crusting or oozing skin lesions. These signs should be investigated by a vet to determine the cause. 

 

Figure 1: Clinical signs of a significant louse infestation with hair loss on the head, neck and shoulders.

Figure 2. Louse infestation extending down the back and shoulders of a yearling in winter.

Lice are visible to the naked eye at 1-5mm in length depending on the species present. The most common louse in the UK is the chewing louse Bovicola bovis which is usually found on the head and neck, progressing down the back and shoulders to the rump in severe infestations. 

Figure 3. Lice in the hair of the face visible to the naked eye

There are several species of sucking lice affecting UK cattle. These are found most commonly around the head, neck and shoulders, but can be found in other locations such as the brisket and dewlap depending on the species present, extending to a more generalised distribution along the flanks with heavy infestation. 

Biting and sucking lice are easy to tell apart by the shape of the head under a hand lens or microscope. Chewing lice have wide heads with mouthparts designed for chewing of skin and hair debris, whilst sucking lice have narrow piercing mouthparts designed to draw blood meals. It is important to determine what type of mite is present, as this can affect treatment choice. 

Prevention and control

Clinical effects of louse infestations are less frequent in well fed, healthy cattle in clean housing with good ventilation and adequate space. They are often indicators of other underlying problems which should be investigated and addressed. Lice live exclusively on cattle, with transmission almost exclusively directly from animal to animal. Insecticides should not be used routinely to control lice in housed cattle, although some winter treatments for roundworm infections, specifically group 3-ML products used to treat type-2 ostertagiosis, may have the added effect of reducing louse infestations too.

Treatment

Treatment is generally only necessary when lice are causing clinical signs and skin disease. There are two classes of products which can treat lice. A number of synthetic pyrethroid products (e.g. permethrin and deltamethrin) carry a licence of efficacy against both sucking and chewing lice in spot-on or pour-on preparations. A number of group 3-ML products (e.g. ivermectin and moxidectin) are also licenced, with spot-on preparations effective against both chewing and sucking lice. Some injectable formulations also carry a licence, but are generally more effective against sucking lice than chewing lice. Many licenced products do not have any residual activity, and do not kill louse eggs. It is therefore important to check the data sheet for efficacy and duration against specific parasites and life stages. Consequently, a second application of treatment may be required two weeks later once any remaining eggs have hatched.

Use of any of group 3-MLs for lice should only be considered if the cattle also need to receive a roundworm treatment at the same time. If treatment for lice only is required, then the synthetic pyrethroids should be used instead to prevent selection for worm resistance, although there are also reports of resistance of lice to treatment with synthetic pyrethroids. Veterinary advice should be sought if this is suspected.