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How do parasites affect my horse?

Article ID: 486
Last updated: 15 Jul, 2011
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The main parasites that horses can be afflicted by are ticks, lice, worms and bots.

The three main ticks that can affect horses in Australia are cattle ticks, New Zealand cattle ticks (bush) and paralysis ticks. Cattle ticks are found in Queensland, N.E. NSW, the Northern Territory and Western Australia. The New Zealand cattle tick (also called the bush tick) occurs in Australia and New Zealand. In Australia it is found in the coastal region of south east Queensland, the NSW coastline and north eastern Victoria.

Paralysis ticks are usually found in coastal areas of eastern Australia in late winter, spring and summer. These ticks cause paralysis and can sometimes kill a young foal but adult horses have some resistance.

Some affected horses will rub the area that the ticks attach themselves excessively. Horses in tick areas must be checked regularly and if any ticks are found they can be sprayed with a pyrethrum based insect repellent (or roll on). Wait about an hour and then apply the solution again. The tick should drop off soon after or if not you can then remove it with tweezers as it should be dead. Do not pull them off alive as this may result in the head of the tick being left under the horse’s skin. If the horse shows any adverse effects then a veterinarian should be consulted. If you live in a tick free area you must report the tick finding to your local agriculture department (DPI or similar).

Lice can affect any horse but horses that are low in condition and unhealthy are more susceptible. Lice can be seen around the mane and tail area and the affected horse may rub itself. Treatment involves powders or washes etc. that can be obtained from produce or saddlery stores and it is usually necessary to treat all of the horses on the property even if only some show signs. Rugs and saddle blankets will also need treatment.

The major parasitic worms that affect horses are the large and small strongyles, tapeworms, roundworms and pinworms. Stomach bots are another type of parasite being the larvae of a type of fly. Bots are not as harmful as worms however they still require regular control.

The common signs of worm infestation are tail rubbing, pale gums, ill thrift, colic and poor coat. If a horse is showing any of these signs, they may be attributable to a significant worm burden. Worms can also cause diarrhoea or sudden death in some extreme cases.

Parasitic worms rely on a specific host animal to complete their life cycle. The cycle of most equine worms involves eggs being passed out in the dung which then hatch out as larvae, the larvae attach themselves to grass which in turn is eaten by a horse. Once in the horse the larvae migrate through the organs of the body (different worms have different behaviours) causing damage as they go. Eventually the larvae, after becoming adults, end up in the digestive system of the horse and deposit eggs which pass out with the dung. Thus the cycle goes on.

Controlling parasitic worms is best done using a number of methods. Some of the things that you can do to minimise the worm burden of your horse are: -

• Use an effective anthelmintic (worming) paste when necessary. It is better to use a broad spectrum (and usually more expensive) product less often than a cheaper narrow spectrum product more frequently. Speak to your vet about an effective program for worming your horse as over use of worming pastes is leading to resistance in worms which means that in the future they are not going to work properly.

• Collect droppings daily or every two days at the most in small paddocks.

• Avoid feeding on the ground if there is manure present.

• Harrow larger paddocks in the hot dry months and/or when the temperature is very low/frosty to break up droppings and kill worm larvae.

• Rotate horses to fresh pastures or to pastures grazed by cattle or sheep. Different animal species help to reduce worms in each other as the worms cannot survive in the ‘wrong’ animal.

• Do not overstock horse paddocks which will lead to high levels of manure and more worms.

• De worm any new horses before they are released into a paddock, keep them in a yard and collect the manure for at least three days afterwards. Bag this manure up and take it to the tip rather than add it to your compost heap.

Bots are often thought of as worms when in fact they are the larval stage of the bot fly. The flies are active in summer, laying eggs on the lower body of the horse, particularly on the legs, shoulders and belly. The eggs are the size of a pin head and yellow coloured. They can be seen clearly on an affected horse. When the horse bites itself (to scratch an itch) or mutual grooms with another horse that has them, the eggs are taken into the mouth. After burrowing in the gums for some weeks, the larvae are swallowed and attach themselves to the stomach wall for several months before being passed out in the dung to develop into adult flies. The egg-laying activities of the adult flies cause considerable annoyance to horses in summer although they do not sting the horse. Although bots cause mild ulceration at their attachment sites in the stomach and on very rare occasions these ulcers may perforate, infestations generally present no problem to most horses.

Although a tedious task, it is possible to remove bot eggs from the horse by scraping or clipping, but this should be done in a yard, and not where horses graze. Horses should be given a ‘boticide’ in early winter when fly activity has ceased and the larvae are in the stomach. Boticides are included in certain worming products. Check the product that you are planning to use to see if it includes one.

For more information see the Equiculture/Horse care/more information page


This website provides general information which must not be relied upon or regarded as a substitute for specific professional advice, including veterinary advice. We make no warranties that the website is accurate or suitable for a person’s unique circumstances and provide the website on the basis that all persons accessing the website responsibly assess the relevance and accuracy of its content.
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