David ramsey daniel o brien rick smith melinda cosgrove james averill stephen schmitt brent rudolph
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Management of on-farm risk to livestock from bovine TB in white-tailed deer within Deer Management Unit 452: Predictions from a spatially-explicit model. David Ramsey, Daniel O’Brien, Rick Smith , Melinda Cosgrove, James Averill , Stephen Schmitt, Brent Rudolph.

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Spatial model of bTB in WTD in DMU452

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David ramsey daniel o brien rick smith melinda cosgrove james averill stephen schmitt brent rudolph

Management of on-farm risk to livestock from bovine TB in white-tailed deer within Deer Management Unit 452:Predictions from a spatially-explicit model

David Ramsey, Daniel O’Brien, Rick Smith, Melinda Cosgrove, James Averill, Stephen Schmitt, Brent Rudolph


Spatial model of btb in wtd in dmu452

Spatial model of bTB in WTD in DMU452

  • Recent development of a spatial model of TB in WTD has examined the efficacy of management options for DMU452 [Ramsey et al. 2014. J. Wildl. Manage 78(2):240-254.]

  • Modelled scenarios included

    • Increase in harvest

    • Vaccination

    • Increase in harvest + vaccination

    • The effect of baiting

  • All scenarios were examined as to their efficacy to eradication of TB from WTD within 30 years


  • Findings from the deer tb model

    Findings from the deer TB model

    • Current MDNR management is unlikely to eradicate TB over the next three decades

    • Eradication is possible within three decades, but is likely to require substantial increases in current harvest and/or vaccination

    • TB establishment in a previously TB-free region is ~8 times more likely if baiting occurs during the hunting season

    • In the meantime, cattle on farms within DMU 452 continue to be at-risk of TB infection from WTD


    The way forward

    The way forward?

    • If complete eradication of TB from WTD is too difficult, should focus change to risk mitigation for livestock?

    • Acceptable management options may exist that will minimize risk of on-farm transmission from WTD to livestock

    • Extend current spatial model to include transmission of TB from WTD to livestock


    Modelling livestock transmission

    Modelling livestock transmission

    • A spatial “livestock” layer was created for the existing model using records from the Michigan Department of Agriculture & Rural Development

      • Farm location

      • Area of cleared pasture

      • Stocking rate

    • Data on the TB cattle herd infection (aka breakdown) rate 2003 – 2012 was also collated and used to calibrate transmission

    • TB transmission dependent on stocking rate and contact rate with infected WTD


    Dmu 452 farm locations their relative areas

    DMU 452, farm locations & their relative areas


    Mean cattle herd infection rate year vs predicted

    Mean cattle herd infection rate/year vs predicted


    On farm risk by location no mitigation

    On-farm risk by location (no mitigation)

    High risk

    Mod risk

    Low risk


    Effect of management on transmission to livestock

    Effect of management on transmission to livestock

    • Evaluate effects of various management options on the risk of transmission to livestock (herd infections/breakdowns)

    • Management of WTD within DMU452

      • Increasing harvest rate

      • Vaccination

      • Increase harvest + vaccination

    • On-farm management practices

      • Restricting contact between WTD and cattle on farms

      • Local WTD control in the vicinity of farms

    • Scenarios examined with and without baiting


    Spatial model of btb in wtd in dmu452

    Effect of management of WTD in DMU452 on cattle herd infection rates on farms


    Increasing harvest rates

    100

    80

    60

    40

    20

    0

    Antlered

    Antlerless

    Increasing harvest rates

    2x

    2x

    Multiple of current harvest

    Harvest rate

    1.5x

    1.25x

    3x

    current

    2x

    1.5x

    1.25x

    current

    3

    1

    2

    4

    1

    2

    3

    4

    Scenarios


    Effects of increasing harvest on hb with baiting

    Effects of increasing harvest on HB (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x


    Effects of increasing harvest on hb no baiting

    Effects of increasing harvest on HB (no baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x


    Harvest 90 vaccinated annually with baiting

    Harvest + 90% vaccinated annually (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x


    Harvest 90 vaccinated annually no baiting

    Harvest + 90% vaccinated annually (no baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x


    Vaccination only with baiting

    Vaccination only (with baiting)


    Vaccination only no baiting

    Vaccination only (no baiting)


    Spatial model of btb in wtd in dmu452

    Effect of on-farm management


    Restriction of contact between wtd and cattle

    Restriction of contact between WTD and cattle

    • Baseline model assumes unrestricted contact between WTD and cattle on farms

    • Examined the effect of restricting contact on cattle herd infections

    • Practically this can be achieved (for example) by

      • Improved fencing

      • Restricting access to food sources


    On farm contact reduction

    On-farm contact reduction (%)

    No reduction

    High risk

    Mod risk

    Low risk


    On farm contact reduction1

    On-farm contact reduction (%)

    20% reduction

    High risk

    Mod risk

    Low risk


    On farm contact reduction2

    On-farm contact reduction (%)

    50% reduction

    High risk

    Mod risk

    Low risk


    On farm contact reduction3

    On-farm contact reduction (%)

    80% reduction

    High risk

    Mod risk

    Low risk


    On farm contact reduction4

    On-farm contact reduction (%)

    90% reduction

    High risk

    Mod risk

    Low risk


    Local control of wtd

    Local control of WTD

    • Manage WTD in the vicinity of farms only

    • Less expensive option than management of deer across the entire DMU

    • What size buffer would be adequate to achieve significant reduction in herd infections?


    5 km buffer around farms 32 of total dmu area

    5 km buffer around farms (32% of total DMU area)


    Local vaccination within 5km buffer no baiting

    Local vaccination within 5km buffer (no baiting)


    Local control within 5km buffer no baiting

    Local control within 5km buffer (no baiting)


    An aside if prevalence in deer has gone down why are cattle herds still getting infected

    An aside: If prevalence in deer has gone down, why are cattle herds still getting infected?

    • Speculation that because cattle herds are still becoming infected, there must be some wild species (other than deer) infecting cattle

    • At least two existing lines of evidence argue against such speculation

      • Modelling

      • Spatial variations in deer prevalence


    Effects of increasing harvest on hb with baiting1

    Effects of increasing harvest on HB (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x

    Deer prevalence:

    ~0.7%

    ~4 years

    ~4 years

    Figure 3A, Ramsey et al., 2014, J. Wildl. Mgt. 78(2):245.


    Effects of increasing harvest on hb with baiting2

    Effects of increasing harvest on HB (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x

    Deer prevalence:

    ~0.6%

    ~8 years

    ~8 years

    Figure 3A, Ramsey et al., 2014, J. Wildl. Mgt. 78(2):245.


    Effects of increasing harvest on hb with baiting3

    Effects of increasing harvest on HB (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x

    Deer prevalence:

    ~1.1%

    30 years

    Figure 3A, Ramsey et al., 2014, J. Wildl. Mgt. 78(2):245.


    Effects of increasing harvest on hb with baiting4

    Effects of increasing harvest on HB (with baiting)

    Antler

    Antlerless

    1.25x 1.25x

    1.5x 1.5x

    2.0x 2.0x

    2.0x 3.0x

    Deer prevalence:

    ~0.05%

    ~18 years

    ~18 years

    Figure 3A, Ramsey et al., 2014, J. Wildl. Mgt. 78(2):245.


    Tb prevalence in deer varies locally

    TB prevalence in deer varies locally

    2003

    29N 6E: 3.0%

    DMU452: 1.7%


    Tb prevalence in deer varies locally1

    TB prevalence in deer varies locally

    2003

    29N 6E: 3.0%

    DMU452: 1.7%

    2006

    31N 5E: 3.1%

    DMU452: 2.3%

    2006

    30N 5E: 4.9%

    DMU452: 2.3%


    Tb prevalence in deer varies locally2

    TB prevalence in deer varies locally

    2003

    29N 6E: 3.0%

    DMU452: 1.7%

    2006

    31N 5E: 3.1%

    DMU452: 2.3%

    2006

    30N 5E: 4.9%

    DMU452: 2.3%

    2012

    27N 5E: 5.6%

    DMU452: 1.7%


    The future predicting local variations in tb prevalence

    The future: predicting local variations in TB prevalence


    Conclusions dmu wide control

    Conclusions (DMU wide control)

    • Compared with TB control in WTD directly, management aimed at reduction of cattle herd infections requires much less effort ($)

    • But… management needs to continue in perpetuity as TB remains in the wider deer population

      • Gains will be rapidly lost once management ceases (e.g. lifting of baiting bans)

    • A 25% increase in harvest and no baiting would halve the rate of cattle herd infections within 3-5 years and reduce it by 95% within 15 years

    • Vaccination each year achieving 50% coverage would also achieve the same result


    Conclusions farm level control

    Conclusions (farm level control)

    • Substantial reduction in the risk of herd infections is achieved if contact between WTD and cattle on farms is reduced by at least 80%

    • Local control measures can also be effective

      • Vaccinating at least 50% of WTD within 5 km of farms will reduce the cattle herd infection rate by 95% within 13 years

      • Culling 50% of deer in addition to harvest within the 5 km buffer would reduce the herd infection rate by 95% within 10 years


    Conclusions

    Conclusions

    • That cattle herd infections continue to occur annually despite reductions in TB in deer is expected, and consistent both with modeled predictions and what we already know about TB in deer

    • Results suggest that without effective wildlife risk mitigation, TB prevalence in deer at the DMU452 scale will need to be maintained well below 1% before cattle herd infections do not consistently occur every year, and well below 0.1% before there is a high probability of having no annual cattle herd infections


    Thank you

    Thank you


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