Equine Matters - Winter 2018

03 As the colder months approach us, we no longer have the worry of the flies and midges of summer; in the winter months however, there are other external parasites that can cause clinical problems in the horse. The most common of these are lice and mites. There are important differences between lice and mites that all horse owners should be aware of. Equine Matters Winter 2018 External Parasites Equine Lice and Mites All you need to know about these irritating external parasites The winter months present the risk of external parasites that can cause problems in the horse. Caroline Blake BVSc Cert ES (Soft Tissue) MRCVS Torch Equine Vets Lice There are two different lice types that commonly affect horses in the UK: the sucking louse- Haematopinus Asini , and the biting or chewing louse - Damalinia Equis . The sucking louse tends to be larger (4-5 mm long) and feeds by sucking the blood at the root of the long mane and tail hairs. The smaller biting louse (1.5-2 mm) (Figure 1) feeds on dead skin cells causing intense irritation and tends to move around the body more especially in the flank and neck areas. Lice thrive in the horse’s denser winter coat and numbers reduce after coat shedding in the spring. Lice tend to affect horses with a less robust immune system and so more commonly the younger or older animals are affected. Horses with underlying disease such as PPID (see page 7) or malnourished animals also tend to be more severely affected. Lice live their entire life-cycle on the horse. The eggs are laid and stick to the base of the hair where they hatch into larvae and grow into adults. The eggs take 2-3 weeks to hatch, which is important to remember when treating these horses. The whole life cycle from egg to egg laying adult can take 30 - 40 days. Figure 1: Damalinia Equis Clinical Signs Horses with lice are primarily itchy. They will constantly rub their mane or tails and may chew at themselves (Figure 2). The horse may appear restless. The hair-coat is often dull, with flaky dandruff visible. There may be patchy hair-loss and bare areas. In more severe cases horses will rub areas of skin until they become raw and bleeding. Scabbed areas may be apparent, as well as thickened skin patches. Very severe infestations may lead to anaemia due to the lice sucking blood, and such horses fail to thrive and may be in poor body condition. Figure 2: Horse chewing flanks