- Email: [email protected]
Sheep blowfly strike reduction using a synthetic lure system
Preventive Veterinary Medicine 59 (2003) 21–26
Sheep blowfly strike reduction using a synthetic lure system Michael P. Ward a,∗ , Rebecca Farrell b a b
Department of Primary Industries, Animal Research Institute, Locked Mail Bag 4, Moorooka 4105, Qld, Australia Department of Primary Industries, Queensland Department of Primary Industries, PO Box 20, Cunnamulla 4490, Qld, Australia Received 16 July 2002; accepted 10 February 2003
Abstract The effectiveness of a synthetic lure system to reduce the incidence of blowfly strike in sheep flocks was assessed, using randomised field trials. Four field trials used eight total groups of sheep randomised to treatment (flytrap) or control on two properties in southern Queensland between 1999 and 2001. Treatment consisted of the operation of flytraps in paddocks as per manufacturer’s recommendations. All sheep were inspected physically each month for flystrikes. Flytraps were associated with a reduction in flystrike incidence of 38–55%, compared to control sheep. Results confirm that traps are a useful component of a flystrike-control program. The use of fly traps by a substantial proportion of woolgrowers could assist the Australian wool industry to meet targets of reduced pesticides on shorn wool. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Blowfly strike; Lucilia cuprina; Trap; Sheep; Australia
1. Introduction Blowfly strike is endemic in the Australian sheep industry, causing substantial economic loss and welfare concerns. Flystrike can be prevented through the use of organophosphorous and insect growth-regulator pesticides. However, the Australian wool industry is attempting to reduce pesticide use because of concerns over pesticide residues on wool and environmental and occupational health-and-safety consequences of using pesticides in agriculture (Williams and Brightling, 1999). ∗ Corresponding author. Present address: Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, 725 Harrison Street, West Lafayette, IN 47907-2027, USA. Tel.: +1-765-494-5796; fax: +1-765-494-9830. E-mail addresses: [email protected], [email protected] (M.P. Ward).
0167-5877/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-5877(03)00059-X
22
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
One method of reducing either the amount of pesticide used in sheep and wool production and/or the number of pesticide applications required during the wool-growing season is to suppress blowfly populations by trapping. Blowfly traps are based on liver/sodium sulphide combinations, and have been used in Australia at least since the 1930s. More recently, a synthetic lure consisting of kairomones has been developed (Urech et al., 1993). A trap using this lure was released commercially in 1994 as Lucitrap® (Bioglobal Pty Ltd., Level 1, 417 Collins Street, Melbourne 3000, Vic., Australia). This trap system is effective in suppressing blowfly populations (Urech et al., 1993). However, these initial trials conducted during the early 1990s were unable to demonstrate a parallel flystrike reduction in sheep flocks grazed in paddocks in which traps were operated (Urech, unpublished data). To investigate the effectiveness of traps in reducing blowfly strike, further trials were commenced in 1999 (Ward, 2001a). Preliminary observations from 1999 to 2000 trials suggested that Lucitrap® might reduce flystrike incidence by 46%, but results were inconsistent and appeared to depend on the class of sheep enrolled and on seasonal conditions (Ward, 2001a). Trials have been repeated during the period 2000–2001. This report presents results of these trials and an overall assessment estimate of the effectiveness of Lucitrap® in reducing flystrike in sheep flocks.
2. Materials and methods Two properties (A and B) were used as study sites. The location of these properties has been described (Ward, 2001a). During 2000–2001, treatment paddocks comprised paddocks in which traps (Lucitrap® ) were operated and that adjoined other paddocks on all boundaries (either the same property or a neighbouring property) in which traps were also operated. Control paddocks were comprised of paddocks in which traps were not operated and adjoined a neighbouring paddock (either the same property or a neighbouring property) in which traps were also not operated. These paddocks previously had been used for Lucitrap® trials during 1999–2000 (Ward, 2001a). Treatment and control paddocks— ranging in area from 80 to 140 ha—were stocked with Merino-cross sheep at a stocking rate of 2.5–4.5 ha−1 . In July 2000, sheep were randomly allocated (coin-toss) to paddocks from the same group of sheep (weaner ewes and wethers aged approximately 10 months on Property A, and wethers aged 2–3 years on Property B). Traps were operated following manufacturer’s recommendations at a rate of at least one per 100 sheep. Because sheep numbers per paddock were not multiples of 100, trap coverage ranged from one per 71 to 91 sheep. Traps were recharged with lure for every 3 months during the trial. The lure used (Lucilure® ) consists of chemical attractants designed to mimic the odours of the primary food sources of the sheep blowfly (Lucilia cuprina)—fleece rot, animal carcasses, urine and faeces. These synthetic lures are specific for L. cuprina (Urech et al., 1996), which is responsible for 80–90% of flystrike in Australian sheep flocks (McLeod, 1995). Between August 2000 and June 2001, sheep on both Property A and B were inspected at monthly intervals by the same technical assistant, and managers were requested to observe sheep more closely than usual during the study period. Flystrike was diagnosed by observing each sheep individually for evidence of myiasis and physically examining each sheep for signs indicative of strike (strike odour, moisture, fleece discolouration). These strikes were
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
23
regarded as overt or covert, respectively. By having flock managers operate traps and gather sheep for each inspection, an attempt was made to blind the technical assistant to the status of the sheep inspected. Strikes that occurred were treated as previously described (Ward, 2001a). The risk of flystrike within each treatment and control group was calculated using the number of flystrike cases as the numerator, and the number of sheep-days at-risk as the denominator. If a sheep was struck, it was assumed to be no longer at-risk of flystrike during the study period—because resistance to flystrike may occur following exposure to L. cuprina larvae (Watts, 1979). Incidence of flystrike in treatment and control groups on each property was compared by estimating relative risk and 95% confidence intervals (Win Episcope, Version 2, Epidecon, Zaragoza, 1998). The number and species of blowflies caught in traps was not recorded, because predation by ants prevents accurate counts being made (Denwood et al., 1999). An overall assessment of the effectiveness of Lucitrap® use in reducing the risk of blowfly strike in trial groups, based on the current report and a previous report (Ward, 2001a) was derived by calculating etiologic fractions from estimates of relative risk from the four trials conducted (Property A, 1999–2000 and 2000–2001; Property B, 1999–2000 and 2000–2001) and 95% confidence intervals. Estimated relative risks were tested for homogeneity with a χ 2 -test based on a one-way weighted analysis of variance (weights based on the inverses of the within-study variances; Epimeta, Version 1.2, Centres for Disease Control, Atlanta, 1996).
3. Results In July 2000, a total of 1199 sheep were enrolled (765 on Property A and 434 on Property B) and randomised to control and treatment paddocks. On Property A, treatment and control groups consisted of 363 and 402 sheep, respectively, and on Property B treatment and control Table 1 Summary of trials conducted between 1999 and 2001 on two properties located in southern Queensland, Australia to determine the effectiveness (treatment) of Lucitrap® (Bioglobal Pty Ltd., Melbourne) in reducing the risk of blowfly strike in sheep flocks Property
Year
Group
Flystrikes
Sheep-days at-risk
Relative risk
95% confidence interval
S.E.(RR)
A
1999–2000
Control Treatment Control Treatment
37 40 2 0
18613 37368 110112 122208
1.9 – 2.2a –
1.2, 2.9 – 0.2, 24 –
0.4 – 2.7 –
Control Treatment Control Treatment
2 0 3 2
56816 57200 64057 67186
2.0a – 1.6 –
0.2, 22 – 0.3, 9.4 –
2.5 – 1.4 –
86
533560
–
–
–
2000–2001 B
1999–2000 2000–2001
Total a
–
–
Relative risk estimated assuming one case of flystrike occurred in each treatment group.
24
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
groups consisted of 222 and 212 sheep, respectively. Between August 2000 and June 2001, a total of 379 and 413 mm of rainfall was recorded on Properties A and B, respectively. Pasture was dry between August and October, and during January and June. During other periods, green pasture was present. In the study groups on Property A, two cases (0.3%) of flystrike were observed in the control group during the study period. Both were overt strikes (that is, detectable without physical examination and parting of the fleece) in the inguinal region, occurring in January 2001. No deaths occurred attributable to flystrike. Strike wounds were treated with diazinon. Trial sheep were drenched (using a macrocyclic lactone anthelminthic, Ivomec® ) for internal parasite infestation in August, December and February. All sheep were shorn in September. No flock pesticide applications were made. A total of 110,112 and 122,208 sheep-days at-risk were accumulated in control and treatment groups, respectively. During the period August 2000 and June 2001, five cases (1.2%) of flystrike were detected in the study groups on Property B. Strikes occurred on the body (2), shoulder, tail and head of sheep. All strikes were overt, except for the head strike. Strikes occurred between November and January, and all strike wounds were treated with diazinon. Trial sheep were drenched
Fig. 1. Effectiveness of Lucitrap® (Bioglobal Pty Ltd., Melbourne) to reduce the risk of flystrike in sheep flocks: relative risks and 95% confidence intervals of blowfly strike associated with not using Lucitrap® in four trials conducted between 1999 and 2001 on two properties located in southern Queensland, Australia.
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
25
for internal parasite infestation in June, November, February and May. All sheep were shorn in February. No flock pesticide applications were made. In control and treatment groups, 3 and 2 strikes were detected and a total of 64,057 and 67,186 sheep-days at-risk were accumulated, respectively. The incidence of flystrike in these groups was not significantly different (relative risk 1.57, 95% confidence interval, 0.26–9.42). Overall, a total of 2149 sheep were included in trials and they had 86 flystrikes (Table 1). To allow estimation of relative risks, if flystrike was not detected in a trial group it was assumed that a maximum of one strike could have occurred in the group. Conservatively estimated relative risks of flystrike for sheep without Lucitrap® protection on Properties A and B during 1999–2000 and 2000–2001 were 1.9, 2.2, 2.0 and 1.6. These relative risk estimates were homogenous (χ 2 = 0.061, P = 0.996). Based on the four trials conducted between 1999 and 2001 on the two properties (Fig. 1), the use of Lucitrap® was associated between 38 and 55% reduction in flystrike in these randomised trials.
4. Discussion Flystrike in many wool-growing regions of Australia is variable. For example, in a study of flystrike occurring in Queensland sheep flocks between 1993 and 1999, monthly flock incidence of flystrike ranged from 0 to 17% and annual flock incidence ranged from 19 to 71% (Ward, 2000). Annual flock incidences of 60–90% have been estimated for New South Wales flocks (Wardhaugh and Morton, 1990). Between August 1998 and May 1999, the mean within-flock incidence of flystrike in 32 flocks located in southern Queensland to be 1.6% for body strike and 0.4% for breech strike, based on woolgrower responses to a postal questionnaire (Ward, 2001b). These are likely to be underestimates, since the ratio of overt to covert strikes may be as high as 1:5 (Wardhaugh and Dallwitz, 1983) and not all covert strikes will progress to overt strikes and be detected. In an observational study conducted during 1972–1973 and 1973–1974 in New South Wales, the incidence of breech strike and body strike reported by woolgrowers ranged from 3.5 to 4.3 and 0.4 to 3.2%, respectively (Watts et al., 1979). Therefore, the occurrence of flystrike in three out of the four trials (control groups) reported in the current study may be considered low (<2%). However, the incidence of strike was 19% in the trial on Property A during 1999–2000, forcing suspension of the trial on preset animal welfare criteria (Ward, 2001a). Generally low-to-moderate within-flock incidence of flystrike (<5–10%), but high between-flock incidence (>50%), poses control problems for woolgrowers. New South Wales woolgrowers were concerned about flystrike because of its unpredictability, sudden onset and the size of outbreaks that could potentially occur (Watts et al., 1979). Attempts have been made through modelling to increase the predictability of flystrike (Wall et al., 2000; Ward, 2000, 2001c), but these models have not been applied widely on a real-time basis. Lack of flystrike predictability means that most woolgrowers rely on pesticides to protect sheep from flystrike. The solution that is used is pesticide applications to prevent flystrike. Between 1995 and 1997, and 1997 and 1998, it was estimated that 81 and 52% of Queensland woolgrowers applied pesticides to sheep to control flystrike, respectively (Ward and Armstrong, 1998, 2001). If trial results suggesting that the use of Lucitrap® is associated with 38–55% reduction in flystrike can be extrapolated to Australian sheep flocks managed under a similar
26
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
grazing system to those of the trial flocks, this approach to flystrike-control might play a role in reducing the amount of pesticide that is used in the wool industry. Further research on the integration of Lucitrap® use with the application of pesticides, management practices, breeding and predictive models to control blowfly strike in Australian sheep flocks is required.
Acknowledgements The authors gratefully acknowledge the assistance of woolgrowers who provided sheep and facilities to conduct this study, and the technical assistance of Mr. Dan Roche who regularly inspected all sheep enrolled in this study. Support for this study was provided by Australian woolgrowers and the Australian Government through the Australian Wool Research and Promotion Organisation. Trial design and conduct was approved by the Department of Primary Industries South Region Local Animal Ethics Committee (SLAEC-DPI-016).
References Denwood, T.C., Lang, M., Barr, W., Champion, S.C., Horton, B.J., Horton, J.D., 1999. The effect of flytrap site on catches in Lucitrap® flytraps in a cool temperate climate. Wool Tech. Sheep Breed. 47, 230–240. McLeod, R.S., 1995. Costs of major parasites to the Australian livestock industries. Int. J. Parasitol. 25, 1363–1367. Urech, R., Green, P.E., Rice, M.J., Brown, G.W., Duncalfe, E., Webb, P.D., Pritchard, D.A., 1993. Field performance of synthetic lures for the Australian sheep blowfly Lucilia cuprina (Diptera: Calliphoridae). In: Corey, S.A., Dall, D.J., Milne, W.M. (Eds.), Pest Control and Sustainable Agriculture. Commonwealth Scientific and Industrial Research Organisation, Melbourne, pp. 277–279. Urech, R., Green, P.E., Brown, G.W., et al., 1996. Field evaluation of a novel sheep blowfly trap. In: Poppi, D.P., Farrell, D.J., Love, K.F. (Eds.), Proceedings of the Australian Society of Animal Production, Brisbane, p. 357. Wall, R., French, N.P., Fenton, A., 2000. Sheep blowfly strike: a model approach. Res. Vet. Sci. 69, 1–9. Ward, M.P., 2000. Forecasting blowfly strike in Queensland sheep flocks. Vet. Parasitol. 92, 309–317. Ward, M.P., 2001a. Effectiveness of a synthetic lure to reduce blowfly strike incidence: preliminary observations. Vet. Parasitol. 97, 77–82. Ward, M.P., 2001b. Blowfly strike in sheep flocks as an example of the use of a time-space scan statistic to control confounding. Prev. Vet. Med. 49, 61–69. Ward, M.P., 2001c. Use of interpolated climatic parameters to predict risk of blowfly strike in Queensland sheep flocks. Prev. Vet. Med. 49, 115–124. Ward, M.P., Armstrong, R.T.F., 1998. Pesticide use and residues on Queensland wool. Aust. Vet. J. 76, 739–742. Ward, M.P., Armstrong, R.T.F., 2001. Surveys to assess the amount of pesticide in wool and the use of pesticides by woolgrowers in Queensland. Aust. Vet. J. 79, 358–362. Wardhaugh, K.G., Dallwitz, R., 1983. Covert flystrike. In: Proceedings of the Second National Symposium on Sheep Blowfly and Flystrike in Sheep, University of New South Wales, Sydney, pp. 84–91. Wardhaugh, K.G., Morton, R., 1990. The incidence of flystrike in sheep in relation to weather conditions, sheep husbandry, and the abundance of the Australian sheep blowfly, Lucilia cuprina (Wiedemann) (Diptera: Calliphoridae). Aust. J. Agric. Res. 41, 1155–1167. Watts, J.E., 1979. Body strike of sheep. In: Proceedings of the National Symposium on Sheep Blowfly and Flystrike in Sheep, New South Wales Department of Agriculture, Sydney, pp. 23–32. Watts, J.E., Murray, M.D., Graham, N.P.H., 1979. The blowfly strike problem of sheep in New South Wales. Aust. Vet. J. 55, 325–334. Williams, S.H., Brightling, A., 1999. The Australian wool industry’s response to the issue of pesticides residues. In: Besier, B. (Ed.), Proceedings of the Australian Sheep Veterinarian Society Conference, Australian Veterinary Association, Hobart, pp. 77–84.
Sheep blowfly strike reduction using a synthetic lure system Michael P. Ward a,∗ , Rebecca Farrell b a b
Department of Primary Industries, Animal Research Institute, Locked Mail Bag 4, Moorooka 4105, Qld, Australia Department of Primary Industries, Queensland Department of Primary Industries, PO Box 20, Cunnamulla 4490, Qld, Australia Received 16 July 2002; accepted 10 February 2003
Abstract The effectiveness of a synthetic lure system to reduce the incidence of blowfly strike in sheep flocks was assessed, using randomised field trials. Four field trials used eight total groups of sheep randomised to treatment (flytrap) or control on two properties in southern Queensland between 1999 and 2001. Treatment consisted of the operation of flytraps in paddocks as per manufacturer’s recommendations. All sheep were inspected physically each month for flystrikes. Flytraps were associated with a reduction in flystrike incidence of 38–55%, compared to control sheep. Results confirm that traps are a useful component of a flystrike-control program. The use of fly traps by a substantial proportion of woolgrowers could assist the Australian wool industry to meet targets of reduced pesticides on shorn wool. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Blowfly strike; Lucilia cuprina; Trap; Sheep; Australia
1. Introduction Blowfly strike is endemic in the Australian sheep industry, causing substantial economic loss and welfare concerns. Flystrike can be prevented through the use of organophosphorous and insect growth-regulator pesticides. However, the Australian wool industry is attempting to reduce pesticide use because of concerns over pesticide residues on wool and environmental and occupational health-and-safety consequences of using pesticides in agriculture (Williams and Brightling, 1999). ∗ Corresponding author. Present address: Department of Veterinary Pathobiology, School of Veterinary Medicine, Purdue University, 725 Harrison Street, West Lafayette, IN 47907-2027, USA. Tel.: +1-765-494-5796; fax: +1-765-494-9830. E-mail addresses: [email protected], [email protected] (M.P. Ward).
0167-5877/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0167-5877(03)00059-X
22
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
One method of reducing either the amount of pesticide used in sheep and wool production and/or the number of pesticide applications required during the wool-growing season is to suppress blowfly populations by trapping. Blowfly traps are based on liver/sodium sulphide combinations, and have been used in Australia at least since the 1930s. More recently, a synthetic lure consisting of kairomones has been developed (Urech et al., 1993). A trap using this lure was released commercially in 1994 as Lucitrap® (Bioglobal Pty Ltd., Level 1, 417 Collins Street, Melbourne 3000, Vic., Australia). This trap system is effective in suppressing blowfly populations (Urech et al., 1993). However, these initial trials conducted during the early 1990s were unable to demonstrate a parallel flystrike reduction in sheep flocks grazed in paddocks in which traps were operated (Urech, unpublished data). To investigate the effectiveness of traps in reducing blowfly strike, further trials were commenced in 1999 (Ward, 2001a). Preliminary observations from 1999 to 2000 trials suggested that Lucitrap® might reduce flystrike incidence by 46%, but results were inconsistent and appeared to depend on the class of sheep enrolled and on seasonal conditions (Ward, 2001a). Trials have been repeated during the period 2000–2001. This report presents results of these trials and an overall assessment estimate of the effectiveness of Lucitrap® in reducing flystrike in sheep flocks.
2. Materials and methods Two properties (A and B) were used as study sites. The location of these properties has been described (Ward, 2001a). During 2000–2001, treatment paddocks comprised paddocks in which traps (Lucitrap® ) were operated and that adjoined other paddocks on all boundaries (either the same property or a neighbouring property) in which traps were also operated. Control paddocks were comprised of paddocks in which traps were not operated and adjoined a neighbouring paddock (either the same property or a neighbouring property) in which traps were also not operated. These paddocks previously had been used for Lucitrap® trials during 1999–2000 (Ward, 2001a). Treatment and control paddocks— ranging in area from 80 to 140 ha—were stocked with Merino-cross sheep at a stocking rate of 2.5–4.5 ha−1 . In July 2000, sheep were randomly allocated (coin-toss) to paddocks from the same group of sheep (weaner ewes and wethers aged approximately 10 months on Property A, and wethers aged 2–3 years on Property B). Traps were operated following manufacturer’s recommendations at a rate of at least one per 100 sheep. Because sheep numbers per paddock were not multiples of 100, trap coverage ranged from one per 71 to 91 sheep. Traps were recharged with lure for every 3 months during the trial. The lure used (Lucilure® ) consists of chemical attractants designed to mimic the odours of the primary food sources of the sheep blowfly (Lucilia cuprina)—fleece rot, animal carcasses, urine and faeces. These synthetic lures are specific for L. cuprina (Urech et al., 1996), which is responsible for 80–90% of flystrike in Australian sheep flocks (McLeod, 1995). Between August 2000 and June 2001, sheep on both Property A and B were inspected at monthly intervals by the same technical assistant, and managers were requested to observe sheep more closely than usual during the study period. Flystrike was diagnosed by observing each sheep individually for evidence of myiasis and physically examining each sheep for signs indicative of strike (strike odour, moisture, fleece discolouration). These strikes were
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
23
regarded as overt or covert, respectively. By having flock managers operate traps and gather sheep for each inspection, an attempt was made to blind the technical assistant to the status of the sheep inspected. Strikes that occurred were treated as previously described (Ward, 2001a). The risk of flystrike within each treatment and control group was calculated using the number of flystrike cases as the numerator, and the number of sheep-days at-risk as the denominator. If a sheep was struck, it was assumed to be no longer at-risk of flystrike during the study period—because resistance to flystrike may occur following exposure to L. cuprina larvae (Watts, 1979). Incidence of flystrike in treatment and control groups on each property was compared by estimating relative risk and 95% confidence intervals (Win Episcope, Version 2, Epidecon, Zaragoza, 1998). The number and species of blowflies caught in traps was not recorded, because predation by ants prevents accurate counts being made (Denwood et al., 1999). An overall assessment of the effectiveness of Lucitrap® use in reducing the risk of blowfly strike in trial groups, based on the current report and a previous report (Ward, 2001a) was derived by calculating etiologic fractions from estimates of relative risk from the four trials conducted (Property A, 1999–2000 and 2000–2001; Property B, 1999–2000 and 2000–2001) and 95% confidence intervals. Estimated relative risks were tested for homogeneity with a χ 2 -test based on a one-way weighted analysis of variance (weights based on the inverses of the within-study variances; Epimeta, Version 1.2, Centres for Disease Control, Atlanta, 1996).
3. Results In July 2000, a total of 1199 sheep were enrolled (765 on Property A and 434 on Property B) and randomised to control and treatment paddocks. On Property A, treatment and control groups consisted of 363 and 402 sheep, respectively, and on Property B treatment and control Table 1 Summary of trials conducted between 1999 and 2001 on two properties located in southern Queensland, Australia to determine the effectiveness (treatment) of Lucitrap® (Bioglobal Pty Ltd., Melbourne) in reducing the risk of blowfly strike in sheep flocks Property
Year
Group
Flystrikes
Sheep-days at-risk
Relative risk
95% confidence interval
S.E.(RR)
A
1999–2000
Control Treatment Control Treatment
37 40 2 0
18613 37368 110112 122208
1.9 – 2.2a –
1.2, 2.9 – 0.2, 24 –
0.4 – 2.7 –
Control Treatment Control Treatment
2 0 3 2
56816 57200 64057 67186
2.0a – 1.6 –
0.2, 22 – 0.3, 9.4 –
2.5 – 1.4 –
86
533560
–
–
–
2000–2001 B
1999–2000 2000–2001
Total a
–
–
Relative risk estimated assuming one case of flystrike occurred in each treatment group.
24
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
groups consisted of 222 and 212 sheep, respectively. Between August 2000 and June 2001, a total of 379 and 413 mm of rainfall was recorded on Properties A and B, respectively. Pasture was dry between August and October, and during January and June. During other periods, green pasture was present. In the study groups on Property A, two cases (0.3%) of flystrike were observed in the control group during the study period. Both were overt strikes (that is, detectable without physical examination and parting of the fleece) in the inguinal region, occurring in January 2001. No deaths occurred attributable to flystrike. Strike wounds were treated with diazinon. Trial sheep were drenched (using a macrocyclic lactone anthelminthic, Ivomec® ) for internal parasite infestation in August, December and February. All sheep were shorn in September. No flock pesticide applications were made. A total of 110,112 and 122,208 sheep-days at-risk were accumulated in control and treatment groups, respectively. During the period August 2000 and June 2001, five cases (1.2%) of flystrike were detected in the study groups on Property B. Strikes occurred on the body (2), shoulder, tail and head of sheep. All strikes were overt, except for the head strike. Strikes occurred between November and January, and all strike wounds were treated with diazinon. Trial sheep were drenched
Fig. 1. Effectiveness of Lucitrap® (Bioglobal Pty Ltd., Melbourne) to reduce the risk of flystrike in sheep flocks: relative risks and 95% confidence intervals of blowfly strike associated with not using Lucitrap® in four trials conducted between 1999 and 2001 on two properties located in southern Queensland, Australia.
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
25
for internal parasite infestation in June, November, February and May. All sheep were shorn in February. No flock pesticide applications were made. In control and treatment groups, 3 and 2 strikes were detected and a total of 64,057 and 67,186 sheep-days at-risk were accumulated, respectively. The incidence of flystrike in these groups was not significantly different (relative risk 1.57, 95% confidence interval, 0.26–9.42). Overall, a total of 2149 sheep were included in trials and they had 86 flystrikes (Table 1). To allow estimation of relative risks, if flystrike was not detected in a trial group it was assumed that a maximum of one strike could have occurred in the group. Conservatively estimated relative risks of flystrike for sheep without Lucitrap® protection on Properties A and B during 1999–2000 and 2000–2001 were 1.9, 2.2, 2.0 and 1.6. These relative risk estimates were homogenous (χ 2 = 0.061, P = 0.996). Based on the four trials conducted between 1999 and 2001 on the two properties (Fig. 1), the use of Lucitrap® was associated between 38 and 55% reduction in flystrike in these randomised trials.
4. Discussion Flystrike in many wool-growing regions of Australia is variable. For example, in a study of flystrike occurring in Queensland sheep flocks between 1993 and 1999, monthly flock incidence of flystrike ranged from 0 to 17% and annual flock incidence ranged from 19 to 71% (Ward, 2000). Annual flock incidences of 60–90% have been estimated for New South Wales flocks (Wardhaugh and Morton, 1990). Between August 1998 and May 1999, the mean within-flock incidence of flystrike in 32 flocks located in southern Queensland to be 1.6% for body strike and 0.4% for breech strike, based on woolgrower responses to a postal questionnaire (Ward, 2001b). These are likely to be underestimates, since the ratio of overt to covert strikes may be as high as 1:5 (Wardhaugh and Dallwitz, 1983) and not all covert strikes will progress to overt strikes and be detected. In an observational study conducted during 1972–1973 and 1973–1974 in New South Wales, the incidence of breech strike and body strike reported by woolgrowers ranged from 3.5 to 4.3 and 0.4 to 3.2%, respectively (Watts et al., 1979). Therefore, the occurrence of flystrike in three out of the four trials (control groups) reported in the current study may be considered low (<2%). However, the incidence of strike was 19% in the trial on Property A during 1999–2000, forcing suspension of the trial on preset animal welfare criteria (Ward, 2001a). Generally low-to-moderate within-flock incidence of flystrike (<5–10%), but high between-flock incidence (>50%), poses control problems for woolgrowers. New South Wales woolgrowers were concerned about flystrike because of its unpredictability, sudden onset and the size of outbreaks that could potentially occur (Watts et al., 1979). Attempts have been made through modelling to increase the predictability of flystrike (Wall et al., 2000; Ward, 2000, 2001c), but these models have not been applied widely on a real-time basis. Lack of flystrike predictability means that most woolgrowers rely on pesticides to protect sheep from flystrike. The solution that is used is pesticide applications to prevent flystrike. Between 1995 and 1997, and 1997 and 1998, it was estimated that 81 and 52% of Queensland woolgrowers applied pesticides to sheep to control flystrike, respectively (Ward and Armstrong, 1998, 2001). If trial results suggesting that the use of Lucitrap® is associated with 38–55% reduction in flystrike can be extrapolated to Australian sheep flocks managed under a similar
26
M.P. Ward, R. Farrell / Preventive Veterinary Medicine 59 (2003) 21–26
grazing system to those of the trial flocks, this approach to flystrike-control might play a role in reducing the amount of pesticide that is used in the wool industry. Further research on the integration of Lucitrap® use with the application of pesticides, management practices, breeding and predictive models to control blowfly strike in Australian sheep flocks is required.
Acknowledgements The authors gratefully acknowledge the assistance of woolgrowers who provided sheep and facilities to conduct this study, and the technical assistance of Mr. Dan Roche who regularly inspected all sheep enrolled in this study. Support for this study was provided by Australian woolgrowers and the Australian Government through the Australian Wool Research and Promotion Organisation. Trial design and conduct was approved by the Department of Primary Industries South Region Local Animal Ethics Committee (SLAEC-DPI-016).
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