Fly-strike hits sheep hard Keep an eye on discoloured wool

1. Flystrike identified 2. Exposing the area 3. Infection cleared 4. Prevention spraying

Have you ever had that itch so annoying that you had to scratch?

Sheep don't possess this same ability and many people who run sheep as lawn mowers or just keep a few intended for the deep freeze don't understand the impact that fly-strike has on their animals.

This is really advice intended more for the small holder, because they often don't know how to identify it, and by the time they do, it's too late.

All they'll see is a bit of discoloration in the wool, with no inkling about what is going on underneath.

It pays to observe your sheep regularly for this, and for any odd behaviour that could indicate a health problem of some kind.

There are several types of blowfly that can lay eggs on the body of a sheep, the worst being the Australian Green blowfly. Flies are attracted to damp areas where they lay their eggs and target the tail, crutch, and pizzle which are damp due to urine, faeces and other body excretions such as foot rot. A buildup of dags can attract flies, as can humid weather conditions.

Once the fly has laid its eggs, the maggots hatch after 12 to 24 hours incubation period. They then start feeding on the underlying skin tissue.

Within a short period of time maggots have burrowed under the skin of the sheep. Once the infection has reached this stage the sheep is very distressed and will lie down in the shade, biting and scratching at itself.

A further symptom of fly-strike is a changing of wool colour where the maggots are located, becoming a dark grey to black colour. If the symptoms go untreated much longer the wool will start to fall out.

Treatment will require the wool to be shorn from the infected area to expose the maggots to the sunlight and cause the skin to dry out but remember to treat the uninfected shorn margins for sunburn. On severe cases it may pay to protect the raw skin with a cover.

I use an electric shearing handpiece which is portable and safe.

Following this, the stage of infection will determine the scale of treatment needed. The area will probably need to be disinfected to kill the maggots and prevent more eggs from being laid.

There are various preparations available from your local veterinarian services (where you pay for only the amount used on each sheep) or if the number of sheep involved warrants larger volumes you can get these from your local stock firm. If the infection is severe enough, antibiotics should be used to prevent further infection.

Prevention methods vary depending on the length of time the protection is needed. Sheep can be dipped or sprayed or a product applied that can also kill lice. Always read and follow the instructions and adhere to the withholding times for meat consumption and shearing. It is also necessary to wear protective clothing and apply in an open area as fumes from some organophosphates can make you quite nauseous.

To keep the incidence of fly- strike low ensure sheep are free from dags and bury dead animals such as possums and keep offal pits covered. Also eliminate all possible fly breeding grounds and note that flies do not like windy or draughty areas.

Neville Wallace farms a small holding near Hawera.

Editor's note: Readers may have their ways of preventing or treating flystrike. If so, let's hear about them.

- © Fairfax NZ News