Sick sheep

While most of us enjoy the longer warmer days of summer, for our livestock, it can be a time of misery with the dreaded fly.

Sheep, of course, are particularly susceptible and since the nasty Aussie green fly invaded our land, even those animals that don’t typically attract flies can be under attack. The issue with the green fly is it will lay eggs on almost anything. Once, I left a pair of working socks on the line. It hadn’t rained, and it was hot and dry. When I went to take them off, they were full of little maggots. The tenacity of the green fly makes it even harder to keep stock safe from fly strike - but there are ways we can try to prevent it.


The signs that an animal has fly strike

The classic sign is twitching. This and stamping of the feet. The animal often tries to bite itself. It will run along with its head down and then abruptly lie down. Often animals will isolate themselves from the rest of the flock. The wool will become discolored and often a greenish or dark patch will appear over the tail and rump area. In bad cases, the wool will start to hang off the animal like a curtain. At this point, it can be hard to save the animal. 





There are several chemicals on the market for the control and prevention of fly strike - many of these also kill lice. The chemicals used nowadays are usually growth inhibitors, unlike in the past, when sheep were dipped in organophosphates. The growth inhibitor prevents either the egg from hatching or if they do hatch, prevents the maggot from growing and completing its life cycle. The dips come in various forms. These include spray-on dips or ones that are mixed and used to dip the sheep physically. Methods for dipping include shower dips, jetting races, or plunge dips. (The plunge dip is probably rarely used now ). 


How well the chemicals will work can depend mainly on the length of wool and breed type. Those with coarser, more open types of wool can usually get away with up to six months of growth, but merinos often need to be treated off-shear (just after shearing) if a spray type is used. If using the spray (pour-on) it’s important to check withholding times for meat and wool - some can have very long withholding times - up to two months, while others may only be a week.  




Keeping sheep clean around the back end is vital to keep sheep from being attracted to flies. If the summer is warm and wet, it is far better to have the sheep shorn. Warm, wet wool is an invitation for our green fly friends to lay eggs anywhere on the animal. If the summer is dry, keeping the crutch and inside of the back legs free from wool helps. Shearing in the summer also affords the animals some relief from carrying around a woolly coat in the heat. Lambs that are shorn mid to late summer also seem to grow better.

Camping grounds

No, we don’t mean the human camping grounds! Sheep love to camp in certain spots. Gateways seem to be a favorite. Underhedges and trees are also prime real estate. Of course, these areas get a build-up of faeces which just attracts flies. 


Here we have a bit of a moral dilemma! We want shade for our animals - they don’t like being in the scorching sun more than we do! But, we also don’t want those areas to become fly cities. There are management strategies we can use to help with this problem. One is to buy fly traps and hang them in the trees where the sheep like to camp. It is amazing how many flies will go into these. The other is to have the stock spread out far enough so there is room for everyone to camp, without being on top of each other. Long shelter belts are ideal as the animals will tend to space themselves out. 


Flies don’t like wind either, so if it's going to be windy try to have stock in paddocks that are subject to the prevailing wind. While animals don’t necessarily like being in the wind either, it beats being harassed by flies!


If possible, try shifting stock to new paddocks more often, to prevent the build-up of faeces.



It is important to keep up with drenching, especially for young lambs, to help prevent flystrike. A wormy bum will be an invitation for those flies to put down eggs. Wormy faeces are more attractive as they usually give off a certain smell. Animals that are suffering from a worm burden also have lower immunity and can be more susceptible to being struck. 


Good worm control can help lessen the risk of being fly-blown. Having said that, some animals seem to have a wool type that will have an odor that flies like and so may get struck even though they are clean. 



Just like selecting sheep that seem to have a better tolerance for worm burdens, selecting animals that don’t attract flies can also be a way to lessen the impact of fly strikes. Self-shedding sheep generally don’t seem to attract flies like their woolly counterparts and for many farmers, they are becoming a more viable option, especially with the low prices for stronger wool types.


Protection at tailing

Many farmers will give their lambs a squirt of fly protection spray at tailing when using rubber rings. This is because when the tail falls off, there is a raw stump that can attract flies. That combined with the lamb’s digestive system adapting to a higher grass intake and worm burdens can culminate in a fly strike storm. 



Regarding climate, once again, NZ’s climate can play a major part in the prevalence of fly strike problems. Hot, dry areas will generally have less of a problem, while muggy humid areas will need constant vigilance to stay on top of fly strike. Even in winter, those areas that don’t get freezing temperatures can still be at risk for flying, especially once autumn growth takes off. Fly eggs can survive for months or even years in cold temperatures, as soon as they warm up enough, they are activated and ready to wreak havoc.   



In summary, fly strike is a significant animal welfare issue in New Zealand sheep flocks, causing suffering and skin degradation. Having a plan ready for the fly season can help mitigate their harmful effects.