Abstract:
Animal Production in Australia INCIDENCE OF BLOWFLY STRIKE IN WILTSHIRE HORN X MERINO SHEEP M.L. TIERNEY* The (Thatcher wool from observed and also Wiltshire Horn is a breed of sheep which sheds its fleece annually and Pascoe 1973). In crosses with Merinos, sheep are produced which shed the head, neck, belly and breech regions. The extent of the shedding increases as the percentage of Wiltshire Horn in the crosses increases with age (Tierney 1979). Data are presented for the incidence of crutch or tail strike in uncrutched, unmulesed, February-shorn ewes of various genotypes. From 1974-75 to 1976-77 an average of 5.4% of '/2M l/2WH ewes were struck on the crutch or tail each year. Over the same period an average of 34.7% of 14 ewes of similar ages were struck. Over these years, about 50% of ewes showed appreciable shedding from the belly and breech as lambs, and in excess of 90% showed shedding from both areas at later ages. None of the M ewes showed appreciable shedding from either region. It has been possible to compare 3/4M '/4WH, 5/8M 3/8WH and '/2M '/2WH ewes over the period 1978-79 to 1980-81. No M ewes of comparable age were available for comparison in these years. The results for these three years are presented in Table 1. TABLE 1 Incidence of blowfly strike in various types of WH X M cross ewes Over these years there was virtually no shedding from the belly and breech by 3/4M or 5/8M ewe lambs, while approximately 50% of the '/2M lambs showed shedding. At older ages the figures were approximately 20%, 50% and in excess of 90% for the three genotypes. The increase in degree of shedding from the belly and breech regions in WH X M ewes with increasing levels of WH in the cross has, then, been associated with a decrease in the level of blowfly strike on the crutch and tail areas. THATCHER, L.P., and PASCOE, M-J. (1973). J. Agric. (Vic.). Z 71:2. TIERNEY, M.L. (1979). Proc. First Conference on Wool Harvesting Research and Development, Melbourne. p. 485. 't Animal Research Institute, Queensland Department of Primary Industries, Yeerongpilly, Qld 4105. 631