A postal survey of blowfly strike occurrence in two Queensland shires

OBJECTIVE: To describe the occurrence of blowfly strike in sheep flocks in two shires located in south-eastern Queensland. DESIGN: Postal survey of woolgrowers within Stanthorpe and Inglewood shires. PROCEDURE: Questionnaire posted to woolgrowers in June 1999 seeking information on the monthly occurrence of flystrike and number of sheep at risk. RESULTS: Incidence of body strike and breech strike between August 1998 and May 1999 was 1.1 and 0.5%, respectively. The highest incidence of body strike and breech strike was reported in lambs (6.1%) and weaner sheep (1.5%), respectively. The seasonality of the incidence of body strike was bimodal (November and February), whereas the seasonality of the incidence of breech strike was unimodal (April). Occurrence of body strike within a 3-month period in flocks located within 40 to 50 km of each other was significantly (P < 0.05) clustered. CONCLUSION: Body strike appears to be more common than breech strike in the study area, mainly affects lambs and weaners and high-risk periods occur during late spring and autumn. Study results provide valuable information for planning blowfly strike control programs in the area such as timing of management procedures, use of fly traps), and enable the economic impact of flystrike on the industry in this area to be assessed.     

Techniques for analysis of disease clustering in space and in time in veterinary epidemiology

Techniques to describe and investigate clustering of disease in space — the nearest-neighbour test, autocorrelation, Cuzick-and-Edwards’ test and the spatial scan statistic — and in time — the Ederer–Myers–Mantel test and the temporal scan statistic — are reviewed. The application of these techniques in veterinary epidemiology is demonstrated by the analysis of a data set describing the occurrence of blowfly strike — both body strike and breech strike — between August 1998 and May 1999 in 33 commercial sheep flocks located within two local government areas of southeastern Queensland, Australia. By applying a combination of these methods, the occurrence of blowfly strike in the study area is well-characterised in both space and time. Guidelines for investigating disease clusters in veterinary epidemiology are discussed.     

Time-space clustering of reported blowfly strike in Queensland sheep flocks

The reported occurrence of blowfly strike in 57 sheep flocks in Queensland, Australia, was investigated for time-space clustering in an exploratory study using Knox's method. Flystrike occurrence peaked in late spring and early summer, with an additional late-autumn peak in southern-Queensland flocks. A total of 1596 case-pairs was examined. Significant clustering (P = 0.07) was only detected for case-pairs occurring within 3 months and 150 km of each other; 164 case-pairs were declared close compared to an expectation of 151. We suggest that factors common to a district (such as rainfall and temperature) are responsible for clustering of flystrike in Queensland.     

Efficacy of ivermectin in a controlled-release capsule for the control of breech strike in sheep

Objective To investigate the efficacy of ivermectin in an intraruminal controlled-release capsule (CRC) against blowfly strike.
Design Pen and field trials with controls.
Animals Pen studies: Two breech strike trials involving 60 Romney and 60 Merino sheep. One body strike trial using 100 Merino sheep.
Field trials: Eight trials in New Zealand used 1000 Romney and Romney-cross sheep. Fifty Merino lambs in one trial in Australia.
Procedure Pen studies: Sheep were allocated to two equal groups. One was not treated, the other sheep received a CRC that delivered ivermectin at 20 μg/kg/day for 100 days. In the breech strike trials, each animal was given an oral laxative 2 days before exposure to adult Lucilia cuprina . In the body-strike trial, the sheep sheep were kept wet to increase susceptibility prior to the release of blowflies.
Field trials: Fifty or 200 sheep allocated to equal groups of nontreated or treated with the CRC and grazed at pasture exposed to natural blowfly challenge.
Results Pen studies: Breech strikes developed in 24 of 60 controls but in none of 60 CRC-treated sheep. There was a 35% reduction in the number of CRC-treated sheep struck on the body.
Field trials: The average number of breech strikes in CRC-treated sheep was reduced by 86% (P < 0.001). The number of body strikes in the treated groups was a reduced by 27% (P < 0.05).
Conclusion The ivermectin CRC is a useful aid in controlling breech strike, but provides only moderate reduction in the incidence of body strike.     

Rainfall and breed effects on the efficacy of ivermectin jetting fluid for the prevention of fly strike and treatment of infestations of lice in long-wooled sheep

SUMMARY An ivermectin-based jetting fluid was assessed for its efficacy in the prevention of blowfly strike and treatment of lice in long-wooled sheep. The ivermectin concentrate was diluted to 0.03 mg/mL and applied via a standard hand jetting technique. In insectary studies, using laboratory-reared Lucilia cuprina, sheep jetted with ivermectin were protected from induced breech and body strikes for 18 weeks after treatment. Merino and Corriedale sheep were equally protected, as were sheep subjected to 25 mm simulated rainfall at 1, 3 or 6 hours after jetting. Naturally occurring infestations of lice, Bovicola (Damalinia) ovis, were successfully treated with ivermectin jetting fluid in Merino and Corriedale sheep using a standard hand jetting technique. In addition, the efficacy of treatment was not affected by simulated rainfall at 1, 3 or 6 hours after treatment.     

The prevalence and dynamics of Salmonella enterica IIIb 61:k:1,5,(7) in sheep flocks in Norway

Fifty randomly selected sheep flocks from a region in central Norway were sampled in December 1999 to determine the flock prevalence of Salmonella enterica subspecies diarizonae serovar 61:k:1,5,(7) (S. IIIb 61:k:1,5,(7)). From each flock, 15–41 rectal swabs were collected from individual sheep of different age groups and examined for S. IIIb 61:k:1,5,(7). Positive flocks were visited again in January–April and each time, rectal swabs from the same animals were collected and examined for this specific serovar. Seven flocks (14%; 95% CI 6.3–27%) were positive for S. IIIb 61:k:1,5,(7) in December; in all, 10 sheep out of the 1233 (0.8%) were positive at the first sampling. From the seven positive flocks, six, five, six, and nine animals were positive in January, February, March, and April, respectively. Of the total 21 individual sheep tested positive from January to April, 15 were >2 years old (OR_ex=3.26; 1.1–10.2). Six out of the seven positive flocks were large flocks (>117 ewes). Sharing of rams between flocks did not seem to be a risk factor for the presence of S. IIIb 61:k:1,5,(7) in a flock.     

Prevalence of breech-strike in mulesed, clipped and unmulesed Merino hoggets in south-eastern Australia

Objective To compare the prevalence of breech flystrike (‘breech‐strike’) on 12–20‐month‐old Merino hoggets that were mulesed, had breech and tail clips applied (‘clipped’) or were left unmulesed but treated strategically with long‐acting insecticide. Design A cohort study on three farms in southern Victoria. Methods Three treatment groups were established at lamb marking on each farm. The unmulesed group was treated with dicyclanil when 12 months old in September or October (‘early‐season treatment’). The prevalence of breech‐strike and key risk factors, including soiling of the breech with faeces (‘dag’) and urine (‘stain’), and breech wrinkle, were compared between the groups. Results Over all the farms, breech‐strike occurred on 1.1% of mulesed sheep and 7.7% of clipped sheep. Clipped sheep had a relative risk of breech‐strike of 18.2‐, 16.8‐ and 3.0‐fold that of mulesed sheep on the three farms. Unmulesed sheep treated with dicyclanil had a similar prevalence of breech‐strike to that of mulesed sheep (overall 0.9%, range 0–2.5%), but had significantly more dag, stain and wrinkle. Conclusion Early‐season treatment of unmulesed sheep prevented most breech‐strikes during the spring and early summer, and offers a short‐ to medium‐term option for the control of breech‐strike in south‐eastern Australia. There were some benefits associated with using clips, namely less dag and stain, and a shorter time spent crutching. However, to control breech‐strike the clipped sheep should be treated the same as unmulesed sheep. Reducing the prevalence and severity of dag will be a major component of strategies to control breech‐strike of Merinos in this region.     

Surveys to assess the amount of pesticide in wool and the use of pesticides by woolgrowers in Queensland.

OBJECTIVE: To measure the amounts of pesticide residue in wool grown in Queensland between 1997 and 1999, and to describe the use of pesticides for the control of lice infestations and blowfly strike in Queensland sheep flocks. DESIGN: Pesticide residues were measured in a random sample of wool from Queensland clips offered for sale during 1998 and 1999. Information on pesticide use was obtained from a trace-back postal survey. PROCEDURE: Samples taken from wool lots were tested for the presence and amount of organophosphorus (OP), synthetic pyrethroid (SP) and insect growth regulator pesticides. A questionnaire seeking information on flock characteristics and pesticide use was sent to the manager of each flock from which a wool sample was tested. RESULTS: The mean amount of OP and SP residue was 2.0 and 0.8 mg/kg, respectively. Ninety-five and 98% of wool samples contained < 9 mg/kg and 7 mg/kg of OP and SP residues, respectively. The mean amount of cyromazine, diflubenzuron and triflumuron was 12.7, 5.8 and 13.0 mg/kg, respectively. The amounts of OP, cyromazine and triflumuron residues were greater in wool from flocks located in southern Queensland. CONCLUSION: Most (95%; 95% CI, 92-97%) Queensland wool clips grown between 1997 and 1999 meet the suggested Australian maximum acceptable residue amounts for OP and SP pesticides.     

Strategic use of crutching and dicyclanil to protect unmulesed sheep against breech strike

Objective   To test strategies for the application of dicyclanil and mid-season crutching to maximise protection of unmulesed sheep against breech strike.
Procedure   Three hundred and eighty unmulesed Merino weaners were randomly allocated to four groups either left untreated or treated by different strategies with 50 g/L dicyclanil. Treatments included breech treatment alone and breech plus body treatment, with two application times, immediately after shearing and 6 weeks after crutching or shearing. To assess protection, larval implants with newly hatched Lucilia cuprina larvae were applied to 10 different sheep from each group at 3, 4, 5 and 6 months after crutching and shearing and assessed for the development of strike at 48 hours. The concentration of dicyclanil was measured in wool samples clipped from the breeches of the test sheep.
Results   All dicyclanil treatments gave significant reduction in strike in comparison to controls up until 4 months after crutching but protection in the sheep treated immediately after shearing had waned at 5 months. Treating at 6 weeks after crutching provided significant reduction ( P < 0.05) in strike for 6 months. Results for strike incidence immediately after shearing and concentration of dicyclanil in the breech wool also suggested improvements in protection by delaying treatment for 6 weeks.
Conclusion   In most environments it should be possible to protect unmulesed sheep against breech strike with a carefully planned integrated control program incorporating strategically timed crutching, shearing and dicyclanil application. Delaying treatment with dicyclanil to at least 6 weeks after shearing or crutching increased the protection provided in comparison to treatment immediately after shearing.     

Prevalence and on-farm risk factors for diarrhoea in meat lamb flocks in Western Australia

Diarrhoea is a widespread problem for sheep enterprises worldwide. A cross-sectional epidemiological study was conducted using a questionnaire to determine the prevalence of diarrhoea and associated risk factors where there was evidence of recent diarrhoea (active diarrhoea or fresh faecal soiling of breech fleece) for meat lambs on farms in southern Western Australia during 2010. The response rate was 41.4% (139/336). Evidence of recent diarrhoea was reported on 64.8% of farms, with a mean of 6.9% lambs affected per farm. Location of a farm and a higher annual rainfall were associated with an increased diarrhoea prevalence. Binary logistic regression analysis suggested that the drinking water source was associated with the incidence of diarrhoea, since lamb flocks supplied with dam water were 117 times (95% CI: 18.2, 754.8) more likely to have observed diarrhoea or fresh breech fleece faecal soiling than lamb flocks supplied with other sources of water. Faecal worm egg counts were used by 65% of respondents to determine whether an anthelmintic treatment was warranted and 74% of respondents administered a treatment to their meat lambs. In response to a range of diarrhoea scenarios presented to respondents (5%, 25% and 50% of the flock with evidence of recent diarrhoea), 15.1% would have elected to administer an anthelmintic treatment regardless of differences in prevalence.     

Epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep in a semi-arid region of eastern Ethiopia

A study on the epidemiology and seasonal dynamics of gastrointestinal nematode infections of sheep was carried out in a semi-arid region of eastern Ethiopia for 2.5 years (May 2003 to September 2005). The experimental flock comprised a total of 60 Black Head Ogaden sheep, consisting of four equal groups of young male and female and old male and female sheep. These grazed on communal pastures together with a larger university flock, as well as with animals owned by neighbouring small-holder farmers. A new experimental flock was established each year of the study. Parasitological data (EPG, faecal culture L3, PCV and FAMACHA estimates) and animal performance (weight change) were recorded each month on all experimental animals. In addition, four tracer lambs were assigned each month to the flock to determine the seasonal patterns of infective larvae acquired from pasture. Results showed distinct seasonal patterns associated with the bi-modal annual rainfall. High levels of infection occurred during the short and long rain seasons with peaks occurring in May and September of each year. Haemonchus contortus was the most prevalent parasite, followed by Trichostrongylus spp., with a number of other nematode species being occasionally recorded. H. contortus showed and increased propensity to undergo arrested development during the dry seasons. Correlations between EPG and PCV, EPG and FAMACHA eye scores, and PCV and FAMACHA eye scores were all highly significant (P<0.001). However, there was no significant association between the EPG and LW of the study animals during each study year. This information will provide a basis for developing epidemiologically based control strategies for gastrointestinal nematode parasites that are appropriate for flocks owned by small-holder farmers of semi-arid areas of eastern Ethiopia.     

Longitudinal study of the spread of ovine Johne's disease in a sheep flock in southeastern New South Wales

OBJECTIVE: The aim of this study was to apply whole flock testing over time to determine the prevalence, distribution and spread of infection in a recently infected flock, with a view to planning intervention strategies for disease control. PROCEDURE: Serology, pooled faecal culture (PFC) and histology were used to determine the distribution and persistence of infection in a sheep flock in south east New South Wales between 1997 and 2002. Partial flock testing was done up to June 2000, after which annual whole flock testing, using PFC was performed. RESULTS: Faecal shedding of M a paratuberculosis was not detected in home-bred sheep until 7 years after the introduction of infected sheep in 1993. For at least 7 years there was clustering of infection and shedding within two age groups only. The infected groups appeared to have been exposed to infection (mycobacterial contamination) at an early age (<12 months) and commenced shedding at 5 years of age or older. Groups that were exposed to contamination as adults did not shed detectable amounts of M a paratuberculosis during the study period. CONCLUSION: Clustering of detectable infection in age groups of sheep that were exposed as lambs was a feature on this farm, providing indirect evidence of finite duration of survival of M a paratuberculosis on pasture and the influence of age on the susceptibility of sheep to develop detectable M a paratuberculosis infection. Spread of infection occurred very slowly and was probably related to the long incubation period (exposure to shedding interval) of 5 years observed on this farm. The findings suggest that partial flock culling, selective grazing management and vaccination could lead to a reduction in mycobacterial contamination on farm to a level at which patent infection no longer occurs. Better understanding of disease spread within flocks over time through flock profiling using PFC will help in devising surveillance strategies (including testing protocols for market assurance testing) to detect infected flocks where there has been clustering and slow spread of infection.     

Extensive rearing hinders Maedi-Visna Virus (MVV) infection in sheep

Maedi-Visna Virus (MVV) seroprevalence and its relationship with housing and mode of rearing of replacement ewe-lambs was investigated in 38 non-randomly selected sheep-flocks in Spain. They included extensive lamb-producing Manchega cross-bred flocks raised almost permanently at pasture, semi-intensive Latxa dairy flocks housed 2-8 months/year and intensively raised Assaf dairy flocks housed most time and at higher stocking density in less ventilated buildings than other flocks. Most flocks raised replacement lambs naturally with their dams until weaning and as a separate flock thereafter until lambing at one year of age. Seroprevalence (95% confidence intervals) was 77%, 25% and 5% (4-6) in intensive, semi-intensive and extensive flocks, respectively and the median (interquartile range) flock-seroprevalence was 82% (66-94) in intensive flocks, 31% (14-31) in semi-intensive flocks and 4% (0-7) in extensive flocks. Seroprevalence was lowest in one year-old sheep and increased to flock levels during the year after introduction into the adult flock in most intensive flocks and more gradually in other flocks. Adult flock seroprevalence was associated with housing time but this relationship was not evident within a particular rearing system, indicating that other unknown factors are critical in horizontal MVV-transmission. Low seroprevalence in extensive flocks further supports previous indications that lactogenic MVV-infection is relatively inefficient and horizontal transmission is necessary to ensure long-term maintenance of MVV and this could explain that MVV has not been reported from countries with mainly extensively reared sheep such as Australia and New Zealand. Moreover, it indicates that MVV-control in extensive and semi-intensive flocks can be simple and inexpensive.     

The efficacy of ivermectin jetting fluid for control of blowfly strike on sheep under field conditions

SUMMARY Seventeen trials involving 5737 sheep were conducted to test the efficacy of ivermectin jetting fluid (30 ppm in water) for the control of blowfly strike when applied to sheep either by standard hand jetting or through an automatic jetting race. Sheep were observed for up to 14 weeks after treatment and all strikes recorded. The level of fly challenge varied between trials, resulting in strike rates in untreated sheep ranging between 0 and 94%. At 12 weeks after treatment there were 93% fewer strikes in hand jetted sheep and 84% fewer strikes in machine jetted sheep when compared with untreated sheep. At this time point there was a 90%, 86% and 93% reduction in poll, body and breech strikes, respectively, when hand jetting was used, whereas machine jetting reduced poll, body, breech and pizzle strikes by 84%, 81%, 79% and 100%, respectively.     

Pesticide use and residues on Queensland wool

Objective To determine practices for control of louse infestation and blowfly strike in Queensland sheep flocks that are associated with organophosphorous and synthetic pyrethroid residues on wool.
Design Information on residues was obtained from a survey of Queensland wool clips. Information on pesticide use was obtained from a trace-back postal survey. The association between pesticide use and residues was assessed using generalised linear models, controlling for potential confounding by flock location.
Procedure Between 1995 and 1997 Queensland wool clips were randomly sampled. Samples were tested for the presence and amount (mg per kg of greasy wool) of organophosphorous and synthetic pyrethroid pesticides. A questionnaire seeking information on flock characteristics and pesticide use was sent to the manager of each flock from which a wool sample was tested.
Results The median amount of OP and SP residue was 0.8 and 0.25 mg/kg, respectively, and 91 and 95% of wool samples contained < 8 mg/kg of OP and SP residues, respectively. The frequency of OP pesticide use for louse control was significantly (P = 0.005) associated with mean OP residue amount, and the timing of SP use for louse control, in relation to shearing, was significantly (P < 0.001) associated with mean SP residue amount.
Conclusion Most Queensland wool clips have acceptable amounts of residues after the use of OP and SP pesticides, but wool growers can further reduce residues by effectively controlling louse infestation with pesticide applications early after shearing and the use of non-chemical methods of ectoparasite control.     

Risk factors for lamb mortality on UK sheep farms

Data on neonatal-lamb mortality and flock history were recorded by veterinary students working on 108 sheep farms in the UK in Spring 1997. The mean reported mortality incidence risk was 10.0% (median 9%; inter-quartile range 5.9–12.3%). The outcomes were incidence risks of stillbirth, perinatal (within 24 h of birth) mortality and postnatal (>24 h after birth) mortality. Exposures were screened for univariable associations with mortality risk. Logistic binomial multiple regressions adjusted for confounding, with farm as a random effect. This study has raised hypotheses for management factors associated with lamb mortality that warrant further study. Intensive rearing systems appear to be associated with increased perinatal and postnatal mortality, although housing ewes at lambing was associated with a decreased risk of stillbirth. High perinatal mortality also was associated with poor mothering-pen hygiene, flocks that foster more lambs, and failure to provide appropriate nursing for sick lambs. Larger flocks, poor ewe condition at breeding, and flocks with higher ewe-replacement rates were associated with higher postnatal mortality.     

Use of interpolated climatic parameters to predict risk of blowfly-strike in Queensland sheep flocks

The risk of blowfly-strike was investigated in 160 sheep flocks in Queensland, Australia. The association between blowfly-strike--measured by the use of pesticides in response to flystrike reported by flock managers during the period 1994-1997--and interpolated rainfall and temperature data was examined using survival analysis and stepwise regression. The statistical model explaining the most variation in risk of blowfly-strike included average maximum temperature and its second-order polynomial 4 months preceding flystrike. The model was validated using reports of blowfly-strike from 87 flocks during the period 1997-1999 (collected using the same method as for model construction) and interpolated maximum temperature data. Although there was overlap of 95% confidence intervals derived for model coefficients estimated using both construction and validation data sets, false-negative and false-positive misclassification percentages were 33.3 and 53.3%, respectively. False-negative misclassification was greater for flocks located in southern Queensland, and false-positive misclassification was greater for northern Queensland flocks.     

Serological survey and epidemiological investigation of maedi-visna in sheep in Finland

A survey for antibodies to maedi-visna virus (MV) in the Finnish sheep surveillance flocks was conducted in 1994. Examination of a total of 12931 serum samples from animals over 1 year of age from 545 flocks (81% of all flocks) revealed eight seropositive flocks and the subsequent epidemiological investigation yielded one additional seropositive flock, indicating a low prevalence of 1.6%. The infection was very probably imported from Sweden in 1981, but it was not detected until the survey was conducted 13 years later. The entire primary infection flock was slaughtered in 1995. 77% of the sheep were seropositive but the animals were clinically healthy and only one (5%) of the contact flocks of the primary infection flock had contracted the infection. This secondary infection flock, 77% of which was seropositive, was slaughtered in 1994; however, animals in this flock had respiratory problems and the lungs of three sheep showed typical MV lesions. Seven (24%) of its contact flocks had contracted the infection and these each had one or two seropositive animals except for one flock which had seven (18%) seropositive animals. The results show that the initial spread of MV can be insidious and wide before infection is revealed in surveys or any clinical cases are encountered.     

Bluetongue virus seropositivity in sheep flocks in North West Frontier Province, Pakistan

The objectives of this study were to describe the prevalence and distribution of serum antibodies to Bluetongue virus (BTV) in a sample of 38 sheep flocks in northern areas of the North West Frontier Province of Pakistan and to identify demographic and productivity variables that are associated with BTV seropositivity. Blood samples were taken from a random sample of ewes in each flock in April 1995. The owners of the flocks were interviewed regarding some demographic, husbandry and productivity variables of the flocks on the day of blood sampling. A competitive enzyme-linked immunosorbent assay was conducted to test the serum samples for BTV group-specific antibodies. BTV seropositive reactions were obtained in 184 (48.4%) out of 380 tested sera, and in 89.5% (34/38) of the flocks. In the 34 seropositive flocks, the prevalences ranged from 12.5 to 100% (median = 47). A multivariable logistic analysis was carried out to study the influence of demographic and productivity variables on the BTV serological status of the sheep flocks. Abortion risk in the previous lambing season was mildly associated with the serological status of the flock (adjusted odds ratio = 1.16, P = 0.07). For the seropositive flocks, a linear multiple regression showed that distance travelled by the flock during transhumant movement was significantly associated with percent seropositivity (partial regression coefficient (± SE) = − 0.091 ± 0.045).