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Bot Flies

With reports of increased horse bot flies activity in some areas of the district, it is timely to remind horse owners of what the bot fly is and how it can be controlled

By Department of Primary Industries - 23rd December 2003 - Back to News

There are three species of bot flies (Gasterophilus sp.) affecting horses in Australia. The most common one being Gasterophilus intestinalis (or equi). Their importance as horse parasites is often underestimated and thought to be of little impact.

Bot flies are active mostly in summer and early autumn, but in warmer weather this may be extended.

The adult flies do not live longer than a few days. Although they do not bite, their presence is very annoying to the horse who can become restless and difficult to manage. Horses can be seen resting their jaws on the neck or withers, tossing their heads or running in an attempt to resist the flies trying to deposit the eggs. The most common spots where clusters of eggs could be seen are the forelegs, but also chest, mane, shoulder and flank. They are yellowish-brown in colour (darker brownish eggs of G. nasalis can often be found under the jaw).

Once eggs are deposited, they hatch when animals lick or nuzzle the coat. Larvae attach to the tongue and then burrow into the cheeks and tongue for about a month (larvae of G. nasalis often deposit in the gum pockets between the molar teeth) before moving down to the stomach. Once there they attach to its wall and grow for up to 10-12 months before passing out in the faeces in the spring or early summer. The larvae pupate in the soil and adult flies emerge in about three to five weeks to begin another cycle of egg lying.

The migrating larvae damage cheeks, tongue and gums, making eating painful. Affected spots, in particular between molars, can become infected with bacteria with pus sometimes seen. Severely affected horses lose condition and do not thrive. Concurrent worm infestations further exacerbate the condition.

The larvae attached inside the stomach cause deep indentations in its wall and although they often heal, there is evidence that complications develop in some horses. These are secondary infections entering the abdominal cavity through the damaged stomach wall, resulting in infection and inflammation of the spleen, peritonitis, gastric ulcers, pleurisy etc. which in odd cases could be fatal.

Control of the infestation is not difficult if applied at the right time. Affected horses can be successfully treated with Ivermectin, which kills migrating Gasterophilus larvae and other gastrointestinal parasites. The timing of the treatment is crucial, aimed at killing as many larvae as possible during late autumn and winter. Treatment should not be delayed until spring, as the larvae are leaving the body at that time and it is not effective.

As the bot flies tend to stay in a small area, every horse should be treated there.

LUMPY JAW

Lumpy jaw is an infectious condition seen mainly in cattle and is characterised by bony swellings of both upper and lower jaws. Other species are susceptible including man. These swellings are hard and immovable, obviously bone, which is the distinguishing feature from soft tissue abscesses. Occasionally the swellings will burst and discharge a thick, yellow, gritty pus. The bacteria that cause lumpy jaw can survive in ground or water troughs for considerable periods.

Transmission is usually via wounds in the mouth, especially at the gum tooth margin, allowing entry of the bacteria Actinomyces bovis. Affected animals should be isolated and treated or sold for slaughter.

Lumpy jaw is treated with intra venous injections of sodium iodide and this is best achieved by employing your private veterinary practitioner. Lumpy jaw used to be on the list of compensatable diseases but was withdrawn some years ago. The decision to either sell for slaughter or treat is best made early and sale via saleyards is permitted providing the condition of the animal does not become an animal welfare concern

Source: http://gippsland.com/

Published by: news@gippsland.com

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