An Australian research project has identified compounds in Merino sheep wool that are attractive to blowflies.
Timing of treatment(s) and correct application of products play an important part in preventing or reducing the damage flystrike causes and the stress to flock owners.
The new generation of flies that emerge after overwintering in the soil appear in the warmer temperatures. After mating, the females are attracted to sheep by the odour of wool grease, green dags or urine odour on the breech wool.
Initial strikes mainly occur in these areas, e.g. shoulder strike from the wool grease odour and bacterial action at the skin level or dag strike/urine strike around the base of the tail.
Unchecked, these strikes occur with up to 200 eggs deposited by one female fly. The eggs hatch in less than a day and then larvae develop by moulting, with each larvae stage aggressively damaging the skin layer and penetrating the tissues. All this damage is compounded by the attraction of more flies and sheep not previously treated with a flystrike preventative die a painful death. In the summer the complete life cycle of Lucilla spp flies can be as short as four weeks.
Shearing, crutching and/or dagging lambs, two-tooths and ewes in early summer alleviate the risk of flystrike. The tell-tale signs of a flystrike sheep are biting, twisting and irritation caused by the early larvae attack; this will indicate the need to check the whole mob and use a flystrike dressing treatment on affected sheep after clearing up the struck areas with a shearing handpiece.
The best way to prevent flystrike is by saturation methods, jetting or the use of pour-ons with a T-bar applicator along the backline and around the breech – preferably with a dual action (fly and lice) combination product.
Timing of application for flystrike is important (generally within 4-6 weeks of shearing) when the wool length will retain the flystrike chemical for the claimed protection period on the dip label. Note that the length of protection claimed on the label of flystrike dip products will be stated as “up to” a number of weeks.
At certain times of moist and warm weather, particularly in sheltered paddocks or locations where flystrike can be severe, shorter periods may necessitate shorter treatment intervals.
One often-used procedure with lambs is to run them through a jetting unit as they leave the race (after drenching with an anthelmintic in the race at 28 day intervals).
Another way to efficiently cover the backline and breech with chemical is by using a conveyer to space the sheep as they are jetted or the pour-on is applied.
The application of a pour-on for flystrike also needs care.
Coverage as indicated on the product label needs to be meticulous and done carefully, with the farmer wearing recommended chemical-proof over-trousers -- not shorts. Pushing large numbers through the application procedure often leads to failures in the sheep receiving the correct placement of the chemical.
Reading the application rate or the dip mixing rate is important, as is use on the same day of mixed dip wash, because overnight settling out of the active chemical will markedly reduce the protection benefit.