The effectiveness of mulesing in flystrike control in Corriedale and crossbred sheep in Tasmania.

Abstract

THE EFFECTIVENESS OF MULESING IN FLYSTRIKE CONTROL IN CORRIEDALE AND CROSSBRED SHEEP IN TASMANIA R.N.D. REID* and A.L. JONES** Summary Radical and modified Mules operations were performed on Corriedale and Crossbred (Border Leicester-Corriedale) ewe lambs in each of three years. In both breeds, Mulesing resulted in a significant reduction in breech-strike with the radical Mules being more effective than the modified. Mulesing did not significantly affect live-weight or total dag free wool production. These results illustrate the need, even in plain bodied sheep, to inhibit wool growth in the breech area. Despite developing interest in breeding an 'easy care' Merino, it appears thatselection could never avoid the need to inhibit breech wool growth by some artificial means. I. INTRODUCTION Blowfly strike constitutes a major economic and management problem on a high percentage of sheep properties throughout Australia (Bureau of Agricultural Economics 1972). Since the blowfly has developed a resistance to currently available insecticides (Shanahan and Roxburgh 1974), the importance of the Mules operation as .a method of breech strike control has increased. The value of mulesing in reducing the incidence of breech strike in the Merino has been indicated by Dun (1964) and Lightfoot (1964). With the increased emphasis on low labour requirement, easy care sheep, and high sheep numbers per man, the.effectiveness of the Mules operation in controlling blowfly strike in plain bodied Corriedale and Crossbred sheep was investigated in this experiment at Cressy Research Station in Northern Tasmania. II. MATERIALS AND METHODS (a) Sheep In each of the years 1971, 1972 and 1973, August drop Corriedale ewe lambs were randomised at lamb marking into three groups of 35 lambs '- radical and modified Mules operation as described by Jones (1968) and an unmulesed control group0 Three similar groups of Crossbred (Border Leicester-Corriedale) lambs were formed in each year.. The mulesing was performed.at marking. The twenty month experimental period.following mulesing for each of the three years of introduction are subsequently called years in this paper. The groups were run together on predominantly white clover (ptifoZ<wn repens) and perennial ryegrass.(l;oZiwn pererzne) pastures. The groups were drenched at shearing in November, and in March of each year, * Department of Agriculture, Box 192B, G.P.O., Hobart, Tasmania. 7001 ** Department of Agriculture, Box 407, P.O., Launceston, Tasmania. 7250 185 (b) Measurements Lambs were weighed at marking, 4 weeks after marking and at weaning, Liveweights were also recorded at the 8 and 20 month crutchings, but no significant differences were observed (P < 0.05). For the twenty month period following treatment all sheep were observed regularly for flystrike, increasing to daily checks when flies were active. Struck sheep had a minimum quantity of wool removed 'from the affected area, and this area was then treated with Diazinon(R)o Breech strikes in the crutch and tail area were recorded against the treatment. Body strikes were noted. Individual fleece weights were recorded at lamb and'hogget shearing, At each shearing and crutching all soiled (dags) and urine stained wool was separated, weighed and recorded for each sheep. *As much wool as possible was removed from all dags. III. RESULTS (a) Flystrikes The-percentage of sheep struck in the breech was the highest in the control' groups for both breeds in all years (Table 1). TABLE 1 Percentage of introduced sheep with breech strike over 20 month periods The 1971 and 1972 Corriedale radical groups had significantly fewer sheep struck than their corresponding modified groups (P < 0.05). There was no significant difference between the Corriedale radical and modified treatment groups strikes in 1973. The radical and modified Crossbred groups had similar protection from flystrike in all years. In all treatments there were fewer strikes in the Crossbred group than in ' the Corriedale group. (b) Dags and Stains In all years in both breeds the radical groups hadthe lowest weight of dags and stains removed over the 20 month experimental period (Table 2), It was only the 1971 Corriedale radical Mules group that was significantly cleaner than the modified treatment (P < 0.05). (R) Registered trade mark. 186 TABLE 2 Mean weight of dags and stains per sheep (gm) (Includes two shearings and two crutchings) (c) Wool Weight There (Table 3). treatments total wool was a variable response to treatments in wool production However, any apparent differences in wool production between were removed when the weight of dags was deducted from the produced per head. TABLE 3 IV. DISCUSSION . The lack of any significant reduction in liveweight or wool production due to mulesing supports the findings of Lightfoot (1964) and Dun and Donnelly (1965). Fear of a growth check is a frequent 187 barrier-to the industry acceptance of mulesing in Tasmania. The low acceptance of mulesing is reflected in the 7% of the Tasmanian sheep population being mulesed, compared with 31% of the national sheep population being mulesed in 1970 (Bureau of Agricultural Economics 1972). The marked reduction in flystrike in both breeds due to mulesing reported here, demonstrates the value of the operation in Corriedale and Crossbred sheep. The majority of the breech strikes occurred in the period December to May, which is commonly the time of greatest blowfly activity in Tasmania. In the control groups in both breeds, some sheep were struck more than once over the twenty month period. The radical Mules provided the best protection in the Corriedale flocks, while both types of Mules operations gave good flystrike control in the Crossbred flocks. These results support the finding of reduced flystrike in mulesed Merino sheep reported by Lightfoot (1964)) in which flystrike was reduced from 46% to 5% in lamb groups, by mulesing. The Corriedale and Crossbred are plainer bodied breeds than most strains of the Merino, b.ut the results reported here indicate the need for mulesing in even plain bodied breeds. Work at Trangie has shown that selection over six generations against skin fold, in a Merino flock, has significantly reduced the skin fold character (B.J. McGuirk, Personal communication 1975). Despite this mulesing is still practised in this flock. Therefore selection against skin fold is unlikely to be successful in achieving easy care characteristics in the absence of artificial wool inhibition in the breech. The reduction in the prevalence of dags and stains reported here is in agreement with the results of Douglas (1965). Whilst this is undoubtedly a factor in the reduced incidence of breech strike (Watts 1975), it is also significant in directly facilitating shearing and skirting. The latter is of importance in an era of increasing interest in cost saving in clip preparation, and illustrates that flystrike control is only one of the-management advantages in mulesed sheep. v. ACKNOWLEDGEMENTS The assistance of the staff of the Cressy Research Station during this trial was greatly appreciated. We would also like to thank Messrs. P.R. Gillis for guidance and T.D. Semmens for assistance in the analysis of the data. VI. REFERENCES BUREAU OF AGRICULTURAL ECONOMICS ,(1972). Wool Economics Research Report No. 22 DOUGLAS, D.S. (1965). Agricultural Gazette of New South Wales 76 : 720 Agricultural Gazette of New South Wales z : 1058 DUN, R.B. (1964). DUN, R.B. and F.B. DONNELLY (1965). Australian Journal of Expesental Agriculture and Animal Husbandry 5 .: 6 Tasmanian Journal of Agriculture 79 :, 196. JONES, A.L. (1968)'. LIGHTFOOT, R.J. (1964) .Western Australian Journal of Agrzulture 5 : 412 SHANAHAN, G.J. and N.A. ROXBURGH (1974). The Journal of the AustFalian Institute of Agricultural Science _40 : 249 Australian Veterinary Journal (in press), WATTS, J.E. (1975). 188