BLOWFLY STRIKE

Wairarapa Times-Age, 20 February 1939, Page 8

BLOWFLY STRIKE

SYMPTOMS AND TREATMENT. STATEMENT BY MR G. K. L. KNOTT. “Blowfly strike periodically becomes an acute problem to the farmer, particularly on the higher country,” said Mr G. K. L. Knott, M.R.C.V.S., a veterinary officer of the Livestock Division of the Department of Agriculture, in a statement to he Press. “Outbreaks of strike have been known for more than 30 years, among Merino and halfbred lamb and hogget flocks, but it is during the last 10 years only that such serious notice has been taken of the fly,” he said. “Formerly it was considered that both back and crutch strike could be explained as being the result of soiling with droppings. It is now clear, however, that crutch strike from faecal matter, that is, grass scour or dags, but seldom intestinal worm scour, accounts for less than 10 per cent of the total strike. Urine staining, which results from breech wrinkles or a twisted or damaged vulva in ewe lambs, is at the root of the remaining 90 per cent of crutch strikes. For a crutch to be properly susceptible to strike the skin most be scalded by urine, either caught in the wrinkles or misdirected on to the leg. It is the breakdown products of the skin that attract the flies to lay eggs. Urine on the wool alone is seldom susceptible. This form of strike has been occurring during the present dry spell.” Strike on the back or tail was less easily accounted for. In less than half of the cases of back strike there was a growth of bacteria in the wool and on the skin during periods of wet autumn and summer weather. This fleece rot or dry yolk helped to attract fly to the fine-woolled sheep, but in many instances the wet tip wool itself could cause the fly to lay eggs without the inducement of dip scald or fleece rot. The muggy weather that accompanied back strike not only kept the fleece wet but also allowed the flies to remain active and encouraged the development of maggots. It was apparent that strike took place either as a result of the structure of the breech, independently of the weather, or because of the action of warm continuous rain on fine wools. “FEMALE FLIES RESPONSIBLE." The female flies responsible for this loss of thousands of pounds worth of sheep and wool annually were those of. the yellow-brown hairy species, and, less commonly, the bronze green species. Blue bottles and the striped-field flies did not blow living sheep. To prevent strike on the breech, an early crutching of lambs in late December or early January, followed by two monthly recrutchings, was necessary. In Australia, useful results had followed jetting with calcium arsenite or boric acid and glycerine, but in this country crutchings was the more suitable procedure. To reduce scald resulting from faulty valvae, every care should be taken to cut ewe lambs’ tails short, to prevent cutting off the tip of the vulva, and to remove scabs from the vulva. No satisfactory prevention of back strike was known, but spraying with calcium arsenite was giving promising results. Spraying with whale oil emulsion and shifting the sheep from the paddock where strike occurred would alleviate the intensity of strike. A mixture of boric acid and glycerine formed a good but expensive dressing for fly wounds. Boric acid dusted on alone was useful. A one in 50 solution of liquid carbolic sheep dip or similar disinfectant material was effective in driving out maggots and in sterilising the wounds, but it was wise to follow up with an application of lubricating or whale oil. Oil might also be emulsified in with the antiseptic. Carbon tetrachloride or dichlorobenzene and lanolene were sound dressings.

It was not recommended that astringent, drying or harsh material such as kerosene or bluestone should be employed, since the skin cracked and healed badly after such treatment.