1. Factors influencing population-level effectiveness of PZP immunocontraception in two western wild horse populations
Allen Rutberg, Kayla Grams, and John W. Turner, Jr.
Cummings School of Veterinary Medicine at Tufts University, The Humane Society of the United States, and University of Toledo
8th International Conference on Wildlife Fertility Control
Washington, DC
July 19, 2017

2. Where has PZP been used?

3. Porcine Zona Pellucida (PZP) immunocontraceptive vaccine
Protein extracted from pig ovaries
PZP-vaccinated females produce antibodies that block fertilization.
If eaten, PZP is destroyed in digestion.
Native PZP is EPA-registered for use on wild horses and burros as “ZonaStat-H.”

4. Assateague Island National Seashore, Maryland
35+ years of continuous data
Lineage of all horses known
No removals for population control
All native PZP, delivered by dart

5. Assateague Wild Horses: Foals Produced and Population Size, 1969-2013
There were no removals at Assateague. The population drop was caused by a combination of a really bad storm and a EEE outbreak (mosquito borne). In the initial research phase, not enough mares were treated to stop population growth; in , the NPS wrote an EA for management by PZP. Once that was implemented the population was stabilized, but because of the extended lifespans experienced by PZP-treated mares, it was about 10 years before the population decline began. No Foals being produced though?? Allowed to have 1 or 2 foals to represent the genetics of the population and then put back on PZP. Growth over the year has been 10% only??
1Beginning of PZP Research
2Beginning of PZP Management of Horse Population

6. Additional wild horse herds with PZP-associated population effects
Rachel Carson National Estuarine Research Reserve, NC
Cape Lookout National Seashore, NC
McCullough Peaks HMA, WY
Pryor Mountain Wild Horse Range, WY
Little Book Cliffs HMA, CO
Spring Creek HMA, CO

7. What about large HMA’s where field-darting wild horses is not feasible?

8. “PZP-22”: a long-acting vaccine?
“Native PZP” emulsion PLUS controlled- release PZP pellets with QA-21 adjuvant

9. Remind me again of how many years you studied this
Remind me again of how many years you studied this? And you gave primer and pellets, and re-treated? What time of year? I know, I can read your paper, just need the nitty gritty now to get this going.

10. The Annenberg Study Goals: Study sites:
Examine the population, health, and behavioral effects of PZP-22 application to diverse wild horse populations on western public lands
Study sites:
Sand Wash Basin HMA, CO
Cedar Mountains HMA, UT
Jarita Mesa WHT, NM

11. Sand Wash Basin HMA, Colorado
638 km2
Elevation: 1900–2660 m
AML:
Horses moderately approachable
Limited movement of horses off HMA

12. Cedar Mountains HMA, Utah
727 km2
58% candidate wilderness area
Elevation: m
Water seasonally scarce
AML:
Horses very wary
Extensive use of adjacent military property
K. Grams

13. PZP Treatments of Wild Horses at Sand Wash Basin and Cedar Mountains
2008: 62 hand-primed with PZP-22
2010: 34 booster-darted with PZP-22
16 booster-darted with native PZP
Cedar Mountains
- All hand-injection
2008: 70 primed with PZP-22
2012: 39 boosted with PZP-22
16 boosted with native PZP
85 newly primed with PZP-22

14. Sand Wash Basin & Cedar Mountains: Efficacy Summary
Initial PZP-22 treatments showed modest efficacy in years one and two
One booster of mares primed with PZP-22 delivered 3+ additional years of contraception
Booster could be delivered by hand or by dart
PZP-22 and native PZP boosters showed similar effectiveness
I thought we were going to say that currently PZP-22 isn’t available and that the best way to manage would be with native, or that if you can remotely dart to use native??
(Rutberg et al Wildlife Research 44: )
Population Effects?

15. Mortality Rates Sand Wash Basin HMA, CO
SWB Average Annual Mortality: Foals, 6.4%; Non-foals, 1.4%

16. Foaling Rates and PZP Treatment, Sand Wash Basin HMA, CO
Hand-
Primers
Dart-
Boosters

17. Population Growth at Sand Wash Basin HMA, CO

18. Sand Wash Basin Population Growth: Observed vs. Projected
Projection based on annual growth rates of 22%

19. Sand Wash Basin: Summary
77% of mares treated in 2008
Effectiveness of initial PZP-22 treatments lower than expected
October administration possibly a factor
Remote boosting effective for three years
No new mares treated after 2008
Proportion of mares treated declined throughout study
Population effects modest but highest after booster administration

20. Mortality Rates, Cedar Mountains HMA, UT
CM Average Annual Mortality: Foals, 3.1%; Non-foals, 2.6%

21. Foaling Rates and PZP Treatments, Cedar Mountain HMA, UT

22. Population Size and Growth Rate, Cedar Mountain HMA, UT
Removals
+ boosters
+ primers

23. Cedar Mountains Population Growth: Observed vs. Projected
Projection based on growth rate of 24.4%, with 2012 removals

24. Cedar Mountains: Summary
Only 52% of mares treated in 2008
Effectiveness of initial PZP-22 treatments lower than expected
Boosters hand-injected in 2012 gather effective for three to four years
New mares treated in 2012
Proportion of mares treated rose to 68%
Population effects initially modest but dramatic after 2012 priming and booster treatments

25. Conclusions
Keeping 70% or more of the mares treated will dramatically reduce population growth
Current best practice: prime with PZP-22, boost with native PZP.
Low fertility among young females buffers the population against rapid rebound of foaling
No evidence of a rebound effect after contraception
With current technology, 2-3 cycles of treatments should achieve population growth targets
If enough horses are gathered!

26. Acknowledgments The Annenberg Foundation
Science and Conservation Center, Billings, MT
Drs. Irwin Liu and D.R. Flanagan
Amanda Conner, Kira Donnelly, Kate Guntly, and Josh Irving
BLM Salt Lake and Little Snake field offices
U.S. Army Dugway Proving Ground
Great Escape Mustang Sanctuary
Heidi Hopkins, Stephanie Boyles Griffin, and The Humane Society of the United States