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Windsor P.,University of Sydney | Eppleston J.,Tablelands Livestock Health and Pest Authority | Dhand N.,University of Sydney | Whittington R.,University of Sydney
Australian Veterinary Journal | Year: 2014

Objective: Examine the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (Mptb) at least 5 years after starting vaccination with Gudair™ in flocks of varying initial prevalence of ovine Johne's disease (OJD) and identify risk factors for variation in vaccine efficacy. Methods: Pooled faecal culture (PFC) was conducted for 41 flocks from southern NSW and Victoria to determine estimates of current OJD prevalence. The data were compared to estimates of prevalence at or prior to commencement of vaccination at least 5 years earlier, based on available serological or PFC tests when vaccination commenced. A cross-sectional study was conducted to identify risk factors for differing prevalence levels in 36 of the flocks. Results: Historical data enabled classification of 37 flocks as high (13; 35.1%), medium (10; 27.0%) or low (14; 37.8%) estimated initial OJD prevalence. Results of PFC in 2008-09 identified that 81.1% (30/37) of flocks had detectable shedders, with 48.6% (18/37) flocks still classified as medium or high OJD prevalence, including 50% (7/14) of flocks initially classified as low prevalence. Shedding was not detected in 18.9% (7/37) flocks. Flocks with OJD prevalence exceeding 1% at 5 years or more following the commencement of vaccination were associated with reports of sheep straying and introduction of new sheep. Conclusion: Despite significant declines in estimated OJD prevalence following vaccination for ≥5 years, 81.1% of flocks were shedding Mptb and considered at risk of spreading the disease or suffering recrudescence of losses if vaccination were to cease. Flock managers are advised to persist with vaccination. © 2014 Australian Veterinary Association.

Dhand N.K.,University of Sydney | Johnson W.O.,University of California at Irvine | Eppleston J.,Tablelands Livestock Health and Pest Authority | Whittington R.J.,University of Sydney | Windsor P.A.,University of Sydney
Preventive Veterinary Medicine | Year: 2013

This study was conducted to evaluate the effectiveness of Gudair™ vaccine in decreasing the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in flocks of varying initial prevalence. Thirty-seven self-replacing Merino flocks from New South Wales and Victoria (Australia) that had been vaccinating lambs with Gudair™ for at least five years were enrolled in the study. These flocks had been tested prior to or at commencement of vaccination using pooled faecal culture, agar gel immunodiffusion or both tests. These pre-vaccination test results were used to estimate pre-vaccination prevalence. Post-vaccination prevalence was estimated from culture of usually 7 pools of 50 sheep collected from the enrolled flocks in 2008-2009, approximately five or more years after commencement of vaccination.A Bayesian model was developed to estimate and compare the pre- and post-vaccination prevalences for the enrolled flocks. Apparent pre- and post-vaccination prevalences for flocks were modelled as functions of the true pre- and post-vaccination prevalences, respectively, and the sensitivities and specificities of the respective diagnostic tests. Logit-normal models were specified on pre- and post-vaccination true prevalences and were then used to make inferences about the median and 90th percentile of the prevalence distributions and their differences. Priors were mostly specified based on published literature or analysis of abattoir surveillance data for this population of flocks.The analysis found a significant decline in ovine Johne's disease prevalence from a pre-vaccination median prevalence of 2.72% [95% probability interval (PI): 1.40; 6.86%] to a post-vaccination median prevalence of 0.72% (0.39; 1.27%). However 30 of the 37 flocks still contained sheep that were shedding MAP in their faeces. The results suggest that vaccination with Gudair™ is usually effective in reducing the prevalence of faecal shedding but the response to vaccination is variable among flocks. The Bayesian approach reported here could be implemented in similar situations to compare prevalences where information from multiple diagnostic tests with varied sensitivities and specificities is available. © 2013 Elsevier B.V.

Gabb S.,Australian Department of Primary Industries and Fisheries | Hatcher S.,Australian Department of Primary Industries and Fisheries | Eppleston J.,Tablelands Livestock Health and Pest Authority | Watt B.,Tablelands Livestock Health and Pest Authority | Thornberry K.J.,Australian Department of Primary Industries and Fisheries
Animal Production Science | Year: 2012

The effectiveness of yard weaning to manage the weaning transition period for Merino sheep was investigated on three commercial properties in the New South Wales Central Tablelands. Three experiments were conducted, Experiment 1 investigated the duration of yard weaning, Experiment 2 compared two alternative rations provided to yard-weaned animals, while Experiment 3 compared yard weaning with paddock weaning. The 'Control' for each of the three experiments was each producers' normal paddock-weaning strategy with comparisons based on post-weaning growth rates and weaner survival. Liveweights were recorded at weaning and at 15, 50 and 180 days post-weaning. Growth rates were calculated from liveweight measurements. Survival was determined by the continuing presence of an individual animal at subsequent measurements. Compared with the paddock-weaned Control group, variable responses in liveweight, growth rates and weaner survival to 50 and 180 days post-weaning occurred in the three experiments. Yard weaning was not superior to any of the producers' normal paddock-weaning practices, however, favourable seasonal conditions in early 2010 prompted high growth rates in the paddock-weaned Control animals relative to those achieved by the yard-weaned animals. Further research is required to determine the optimum duration of confinement and ration (including composition and method of delivery). This work should include comparisons of the behaviour of paddock-and yard-weaned animals and model production benefits versus economic costs for a range of production systems and market scenarios. © 2012 CSIRO.

Eppleston J.,Tablelands Livestock Health and Pest Authority | Begg D.J.,University of Sydney | Dhand N.K.,University of Sydney | Watt B.,Tablelands Livestock Health and Pest Authority | Whittington R.J.,University of Sydney
Applied and Environmental Microbiology | Year: 2014

The duration of survival of both the S and C strains of Mycobacterium avium subsp. paratuberculosis in feces was quantified in contrasting climatic zones of New South Wales, Australia, and detailed environmental temperature data were collected. Known concentrations of S and C strains in feces placed on soil in polystyrene boxes were exposed to the environment with or without the provision of shade (70%) at Bathurst, Armidale, Condobolin, and Broken Hill, and subsamples taken every 2 weeks were cultured for the presence of M. avium subsp. paratuberculosis. The duration of survival ranged from a minimum of 1 week to a maximum of 16 weeks, and the provision of 70% shade was the most important factor in extending the survival time. The hazard of death for exposed compared to shaded samples was 20 and 9 times higher for the S and C strains, respectively. Site did not affect the survival of the C strain, but for the S strain, the hazard of death was 2.3 times higher at the two arid zone sites (Broken Hill and Condobolin) than at the two temperate zone sites (Bathurst and Armidale). Temperature measurements revealed maximum temperatures exceeding 60°C and large daily temperature ranges at the soil surface, particularly in exposed boxes. © 2014, American Society for Microbiology.

Celi P.,University of Sydney | Eppleston J.,Tablelands Livestock Health and Pest Authority | Armstrong A.,University of Sydney | Watt B.,Tablelands Livestock Health and Pest Authority
Animal Production Science | Year: 2010

This paper reports on the effects of selenium supplementation on liveweight (LW), greasy fleece weight (GFW), fibre diameter (FD), impact of parasite infection and plasma glutathione peroxidase (GSH-Px) activity in weaned Merino sheep reared in a selenium-deficient area (blood GSH-Px<40 U/g Hb). At weaning, 208 Merino wethers were assigned to two groups: control (CTRL) and treatment (SEL). The SEL group was injected with 0.5 mL of Deposel, a slow release selenium injection. LW, blood and faecal samples were taken at 6-week intervals over a 24-week period. At the end of the trial the animals were shorn and GFW and FD measurements were taken. The SEL group had significantly higher (P<0.01) LW compared with the CTRL group at Weeks 6, 12, 18 and 24. There was a significant difference (P<0.05) in GFW between the SEL and CTRL group, 2.93 and 2.75 kg, respectively. There was no difference in FD between the two groups. A trend (P<0.06) towards lower faecal egg counts in the SEL group was seen but the difference between the two groups was not significant. As expected, the SEL group had significantly (P<0.001) higher plasma GSH-Px activity compared with the CTRL group. In conclusion, selenium supplementation in weaned Merino sheep reared in a selenium-deficient area could increase the LW and GFW of the young sheep while perhaps reducing the level of parasitic infection. © 2010 CSIRO.

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