Favourable rains also bring unpleasant pests

Estimated reading time: 4 minutes

• The outlook for rain is still good but unfortunately, rain also brings with it diseases and pests, among them the scourge of blowflies.
• Some blowfly species prefer to attack living livestock instead. This problem developed in tandem with the wool industry.
• It is the smell of decomposition that attracts blowflies and provides a suitable environment for young larvae.
• The biggest setback is when the constant irritation keeps the sheep from feeding, leading to a loss in condition.
• Dipping the animals during the rainy season, between September and March, using a registered agent that is also registered for tick control. It is pointless to treat only the infected animals – the entire flock must be treated.

The outlook for rain is still good and producers are looking forward to another excellent season. Unfortunately, rain also brings with it diseases and pests, among them the scourge of blowflies.

We were blessed with ample rain this past season, but with the good also comes the bad – often in the form of an exponential rise in flystrike among sheep, with mostly wool sheep having to bear the brunt. Dr Donald Anderson, a veterinarian from De Aar, says that wet weather is to blame – the wetness causes the fleece to rot which, in turn, attracts blowflies. “Wool producers are struggling to keep this pest out of their flocks.

“Nature is wonderfully interwoven, and each species has its task. Even flies and blowflies have a job to do – they serve as nature’s cleaners. Most blowfly species lay their eggs on carcasses and the maggots, which hatch within days, feed on whatever flesh is left on the carcass. This cleaning action is the good deed that flies and blowflies perform. The problem is that they don’t know when to stop.”

Learn more about how to treat foot rot here.

Attacks on livestock

Some blowfly species prefer to attack living livestock instead. This problem developed in tandem with the wool industry. Sheep with a wet fleece are particularly prone to flystrike. This results in bacterial decomposition of the wool and superficial skin layers, more commonly known as fleece rot.

Dr Anderson says it is the smell of decomposition that attracts blowflies and provides a suitable environment for young larvae. The blowfly larvae that launch the initial attack create favourable conditions for secondary blowflies that, in turn, enlarge the wounds and tunnel even deeper into the tissue underneath the skin.

“This has a snowball effect, because the strong smell emanating from the wound attracts other flies and even more larvae end up in the wound. Flystrike in sheep mainly occurs in the breech and tail area, as it is most affected by manure and urine contamination. Deep skin folds, in which sweat accumulates, as well as infected wounds on the sheep’s skin also attract blowflies.”

Read more about to combat orf amongst your flocks here.

Signs and symptoms

According to Dr Anderson, blowflies can transmit bacterial diseases, but this is not the biggest problem when it comes to this pest. The biggest setback is when the constant irritation keeps the sheep from feeding, leading to a loss in condition. The animal appears lethargic and abortions often occur in ewes.

Poor internal parasite control often causes diarrhoea in the animals, increasing the chances of severe flystrike. The problem must therefore be treated well in advance.

Prevention and treatment options

Fortunately, it is quite easy to keep blowflies at bay and in this regard, prevention is the best treatment. Good hygiene and shearing practices should also form part of the preventive treatment.

Dr Anderson advises dipping the animals during the rainy season, between September and March, using a registered agent that is also registered for tick control. It is pointless to treat only the infected animals – the entire flock must be treated.

There are some parts of the country where blowflies have built up resistance to the active ingredients in dips. The best advice is to enlist the help of a veterinarian who will devise a plan that will protect your sheep from flystrike.

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Wool sheep can be treated preventively, but making use of excellent farming practices, such as selecting for sheep with fewer excessive skin folds, will go a long way in mitigating the problem. Another tip is to dock ewes’ tails so that it still covers the vulva, but she can swing it to keep blowflies away and lift it when she urinates.

“That way, the ewe’s breeches stay cleaner and drier, and the length of the tail won’t be a problem during mating either. There are several farming methods that can help prevent or at least alleviate blowfly attacks.” – Koos du Pisanie, Stockfarm

For more information, phone Dr Donald Anderson on 072 135 2190.