THE BLOWFLY

Press, Volume LXXIV, Issue 22491, 27 August 1938, Page 9

THE BLOWFLY

PREVENTION AND TREATMENT

AUSTRALIAN PRACTICES

Canterbury sheepowners have no occasion to be reminded of the losses and work entailed in their flocks by the blowfly last season. The trouble was the worst for ewes, probably due to the abnormally wet season. The attacks took an insidious form, developing on parts of the victim not visible without a close inspection, and by the time the trouble was .discovered in many cases there was little chance of the victim's recovery. The trouble is incidental, of course to all countries where wool growing is an industry of importance, and, strangely enough, is more rife in Australia than in New Zealand, in spite of the much smaller rainfall there. As offsetting any advantage that may lie in this is the greater heat and the encouragement to flies that such a condition bring* about. The prevalence of the disease in Australia naturally hf>diverted the best veterinary attention to a preventive or a cure, and a recent article in an Australian farm paper may be republished, with a suggestion to readers that it should be put aside for reference should there be a recurrence of the trouble next autumn: Normally blowflies are regarded as species of flies which "blow" or lay their eggs on dead and decaying animal matter, thus acting as scavengers and helping bo get rid of offensive materials in a fairly rapid and efficient manner. Unfortunately some of the species developed the habit of utilising live flesh as a host on which to lay their eggs. With short-haired animals such as cattle and horses this "blowing" occurs only when the flesh is broken, as in a wound. With sheep, however, soiling or moistening of the wool ha£ proved sufficient to attract the flies and induce "blowing." Wounds, too, play their part in inducing "strikes," wounds caused through fighting and by the marking of the lamb frequently beins infested.

Experience over many years has shown that, before "blowing" will occur, the wool must have a certain degree of moistness to attract the flies. Blowfly attack is most general at the crutch and pizzle wool which are made attractive to the flies by soiling with excreta and urine. In addition, however, wool moistened by dew or rain or even from the saliva of sheep which has been biting at its wool to allay irritation, is frequently struck. Closewoolled. wrinkly sheep whose wool retains moisture for comparatively long periods are more susceptible to attack than are the longer-woolled breeds, whose fleeces are more open and consequently dry out more quickly. According to veterinary officers of the Victorian department of Agriculture, the common species attack a fresh carcase in a definite order. First attack is by the Green Lucilia blowfly, which commences laying its eggs immediately. On the second day the brown blowfly deposits its eggs on the carcase. The maggots of these flies are smooth, and their action tends to liquify the carcase. On the third day the blue metallic fly deposits its eggs, from which emerge active, hairy maggots which commence to devour the smooth maggots of the other species of fly. This species of fly will not attack the carcase unless the maggots of the other species have already produced the necessary state of liquefaction. "Primary" Flies

The first species are classed as primary blowflies, and the metallic blue species as a secondary blowfly. In the "blowing" of sheep the two groups of flies act in much the same way as with carrion. Usually strike Is initiated only by one of the primary blowflies and previous infestation with the maggots of ihese flies appears to be necessary before the secondary flies will strike. In the absence of the primary flies, therefore, little "blowing" of sheep would occur.

It appears then, that the secondary species might be regarded as a useful variety, and that it should not be trapped indiscriminately with other species. The aim should be to reduce the number of primary blowflies without killing off a proportionate number of the secondary species. This may be accomplished by baiting traps with a material that attracts only the primary blowflies. Such a bait is keratin, which is made by treating raw wool with ether and alcohol to remove all the grease and then washing in warm water. The wool fibre obtained is mostly keratin, and this is treated with sodium sulphide. A small quantity of this'is placed in the trap on a pad of cottoo wool which is kept continually moist. The control of the sheep blowfly is best effected by trapping and carcase treatment. As previously mentioned if trapping is to give best results, the majority of the flies caught should be primary flies. Unfortunately the reverse is usually the case, since primary flies are attracted to the bait only as long as it remains comparatively fresh. From a sanitary standpoint, carcase treatment is necessary, but it will influence the number of flies only if the carcase is treated within three or four days of death. This would mean the death of the maggots of the primary flies breeding there, but, if treatment of the carcase is delayed, these maggots will no longer be present, and those destroyed will be the progeny of secondary flies. Such late treatment will do more harm than good, as far as the control of fly strike is concerned. Carcases are best treated by burning or, where this is impracticable, by the careful application of an arsenical dip powder to all portions of the carcase—particularly that part of the carcase in contact with the ground. Most Effective Methods

The most effective methods used are crutching, dipping, and either jetting or swabbing. Crutching consists of shearing the wool from about twjj inches above the tail to the point of the hocks, down either side of the crutch. Crutching is best done just before lambing. Dipping gives immunity to fly strike for some three or four weeks, as well as killing any maggots already on the wool. Jetting is done by means of a high-pressure pump, which forces a disinfectant through the wool to the skin. Dressings recommended for use in jetting are a 5 per cent, solution of monsol in water, or a 5 per cent, solution of lime sulphate. A 4 per cent, solution of carbolic acid in whale oil, with 5 per cent, of carbon tetrachloride added, is the best of the oily dressings. Jetting should be done in a race .and at least a quart of the solution should be applied to each sheep at a pressure of between 1001 b and 1601 b a square inch, according to the length of the wool. The solution should be applied to the crutch and over a slightly larger area than is shorn when crutching. In swabbing the disinfectant solution is applied by means of a small mop made by tying rags to the end of a f-tick. This should be dipped in the solution, and then thoroughly rubbed over the affected area.

Sheep should be examined regularly during the fly' season, and any that have been struck should receive immediate treatment with a suitable dressing, such as lysol or monsol. Struefc sheep shquld be placed in a separate paddock, where they canbe kept under observation and receive regular treatment until recovery is complete. Where the maggots have penetrated the flesh the dressing should be poured into the wound. A suitable dressing for this

purpose consists of 6 parts of creosote, 20 parts of turpentine, and 40 parts of olive oil or raw linseed oil.