Franklin Vets Blog

Flystrike in Sheep

November 15, 2017

Anyone who has had animals with flystrike will know how awful this disease is. Flystrike is a serious disease that affects approximately 2 million sheep and 250,000 lambs in NZ on an annual basis.sheep

It is, therefore, a concern both from an economic and animal welfare perspective. Flystrike is particularly common in the warm and wet months of Summer and Autumn between December and April. In NZ, four different blowfly species contribute to this disease.

Sheep that have long unshorn fleece, especially prior to summer, are most at risk. Blowflies are attracted to the foul odour that is emitted from urine stained and daggy areas of the fleece, laying eggs directly on these damp warm areas. Once the eggs hatch, maggots are released, which bury into the sheep’s tissues so that they can eat flesh as a food source. During the feeding process, maggots cause extensive tissue damage and also release toxic ammonia secretions. Once flystrike has been initiated, further flies are attracted to the damaged area, and the sheep can die from ammonia poisoning as quickly as 2-6 days.

Early signs of flystrike can be very difficult to observe. Sheep may appear restless, nibble at areas of the body, exhibit shade-seeking behaviour or stamp their feet. Sometimes affected sheep will not show any signs until a significant amount of maggots are present and have caused the animal to feel uncomfortable. Only at this stage will the wool fall out, the fleece become blackened or sores become visible.

Treating Affected Sheep:

Immediate treatment with Cyrex is required for any sheep with active flystrike. Cyrex is a liquid containing both cyromazine and spinosad and is highly effective in killing flies and maggots. To treat active flystrike, a flystrike dressing solution needs to be made. Remove the wool from around the area to be treated using clippers or shears. To make the dressing solution, mix 10mL of Cyrex with 5L of water and use a watering can to apply the solution to all affected areas so that areas are soaked as much as possible. Prepare a fresh dilution of flystrike dressing daily and repeat for a total of 5 days.

The extensive tissue damage involved can also cause substantial pain, distress and infection, leading to toxaemia. A vet should be consulted so that the animal can be adequately treated with pain relief medication, anti-inflammatories and antibiotics. Any affected animals will need to be checked daily to ensure they do not become flystruck again. Any flystrike sores need to be treated as early as possible. Wounds that are extensive or deep can be incredibly difficult to treat and in severe cases, euthanasia is often the only humane option remaining.

Flystrike Prevention:

Shearing sheep and lambs is key in preventing this disease. Shearing should be done twice a year, in November, before the weather gets wet and warm, and again in June. Shearing sheep regularly helps to remove dags and prevents the wool from getting wet and dirty. Sheep should never be wearing more than a year’s wool growth and they must be shorn if they are.

Unfortunately, despite shearing, there is one type of blowfly (Australian green blowfly) that can strike even relatively clean and well-shorn areas on sheep. Checking areas of the skin along the back or around the poll and ears regularly is recommended in summer.

Less than 20 sheep

For the lifestyle farmer, it is often more practical to use long-acting pour-on or spray-on Elanco Cyrextreatments. For lifestyle clients with sheep numbers less than 20, Cyrex is the flystrike prevention product of choice. The first Cyrex application should occur on December the 1st, at the latest, with the second application occurring 12 weeks later on the 1st of March. At the prevention dose rate, Cyrex lasts for 12 weeks (3 months). Simply mix 4mL of Cyrex with 2L of water and then apply half the solution to the back and half the solution to the front (tummy) of the sheep using a watering can. The wool should be completely soaked with the solution. Repeat this process for each sheep. For best results, Cyrex should be applied to dry wool. If it is raining then the application of this product should be delayed, unless the application is for active flystrike treatment purposes.

More than 20 sheep

For clients with sheep numbers over 20, a product called CLiKZiN should be applied as a flystrike preventative. CLiKZiN is a spray-on containing an active ingredient called dicyclanil that should last 16-18 weeks if applied correctly. To ensure long-term residual CLiKZiNprotection, CLiKZiN should be applied 4 weeks after sheep have been shorn. If the fleece is too long, wet, soiled or the product has been applied incorrectly, then a shorter period of protection may occur.

To achieve the best results, it is very important that CLiKZiN is applied onto all areas to be protected. Since this product needs to be applied a month after shearing for best results, shearing should be carried out early November so that CLiKZiN can be applied to sheep early December. CLiKZiN application should then be repeated again in early March to protect animals through to the end of May.

Any cuts or injuries on sheep should be monitored carefully until wounds have healed. If your sheep currently have or have had diarrhoea then they could be parasitised and are therefore more at risk of developing flystrike.

If your sheep are not on a solid drenching programme that is specific to their age group, or you are unsure what product they should be receiving, then please contact Franklin Vets to discuss this further. If your sheep require shearing and have not had any flystrike prevention applied by November/December, please contact Franklin Vets so that we can help you help your sheep.

Read the label carefully and follow manufacturer’s instructions because each treatment has different specifications. It is important to be aware that following treatment with Cyrex and CLiKZiN there is a withholding time on the meat before it can be eaten and also on the wool before it can be sold. There are many control treatments on the market and it is important to select one suitable for your situation. Please don’t hesitate to consult your Franklin Vets veterinarian for advice.