1. Assessing ovulation cycling and vaccine reversibility in American bison (Bison bison) treated with porcine zona pellucida (PZP)
Calvin L. Duncan1,2, Julie L. King1 and Paul Stapp2
1Catalina Island Conservancy, Avalon, CA
2Department of Biological Science,
California State University Fullerton, CA

2. Acknowledgments
Tyler Dvorak, Amy Catalano, Ben Coleman, and Laura Roll (field)
Dr. Barbara Durrant and Alan Fetter, Institute for Conservation Research (ICR), San Diego Zoo
Drs. Winston Vickers, Scott Weldy, and Kristi Krause (vets)
Drs. Kristy Forsgren and Bill Hoese (CSUF)
Dr. Jay Kirkpatrick (The Science and Conservation Center)
Funding:
Catalina Island Conservancy Eppley Foundation for Research Offield Family Foundation Bernice Barbour Foundation Harold McAlister Charitable Foundation

3. Santa Catalina Island
Coastal southern California with a Mediterranean climate and grassland, scrub and woodland vegetation
194km2
Resident population of 4,000 with 800,000 visitors annually
Most feral herbivores (wild pigs, goats, cattle, sheep) removed, but introduced mule deer and bison remain
194 km2

4. Bison on Catalina Island
Bison introduced to Catalina in 1924, with the herd growing as large as 524 individuals (1987)
Since 1969 culling via costly periodic shipments off-island have been used to reduce numbers
In late 2009 the Catalina Island Conservancy initiated a program to treat all cows in the herd with PZP

5. Table 1. Annual treatment schedule and delivery method of porcine zona pellucida (PZP) to free
ranging bison on Catalina Island, CA during
Year
Month(s)
Activity
Delivery method
Primer / Booster
Adjuvant
Cows
2009
Sept-Nov
Roundup
Syringe
Primer
FMA 35
2010
Feb-May
Field darting
Dart
12 of 13a
Apr-July
Booster
FIA
45 of 47b
2011
Apr-June
48c
Dec
FMA/FIA
13/4
2012
Jan 2
Apr-May
61d
2013
Feb-Apr
51e
2014
Mar-Apr
45f 45
a Additional unmarked adult cow was present but not detected in 2010
b One geriatric cow died early in the year
c One additional adult bison cow was discovered in the population
d Two geriatric cows died
e PZP vaccine withheld from 10 adult bison cows
f PZP vaccine withheld from 5 additional adult bison cows

6. Catalina bison populationa Calving age cows (> 2yrs)
Table 2. Annual calving and mortality rates calculated for a free ranging bison herd on Catalina Island,
California pre-porcine zona pellucida (PZP) vaccination (2010) and post-PZP vaccination
Year
Catalina bison populationa
Calving age cows (> 2yrs)
Calves produced
Calving rate (%)
Mortalities
Mortality rate (%)
2010
120 43
29 (15F : 14M)
67.4
5 (1F:4M)
4.2
2011
144
48b
5 (5F : 0M)
10.4
7 (2F:5M)
4.9
2012
142
61c
2 (0F : 2M)
3.3
6 (5F:1M)
2013
138 61
1 (0F : 1M)
1.6
3 (1F:2M)
2.2
2014
136 60
0 (0F : 0M)
0.0
a Island bison population estimate at the beginning of each calendar year
b Four juvenile cows from 2010 reached calving age, 1 unmarked adult cow was discovered
c Two geriatric cows died and 15 female calves from 2010 reached calving age

7. Success Reproduction reduced/halted
Documented efficacy of PZP in bison
Documented safety of PZP applied during pregnancy
- Confirmed fertility in calves born from cows that had received PZP while pregnant
Initiated tracking of efforts & costs associated with implementing a contraceptive program

8. Remaining questions:
Is PZP reversible in bison, especially after repeated treatments?
Does prolonged contraception alter breeding behavior, specifically the length or timing of the breeding season?
- Extended breeding season may be taxing on bulls
- Asynchronous (out-of-season) births may occur
Is contraception more cost effective than periodic removals?

9. Methods Continued annual PZP vaccination by darting
PZP withheld from 10 cows in 2013 and 5 cows in 2014 to test reversibility for cows treated for 3-4 consecutive years
Field observations of breeding behavior and collection of fecal samples from all 60 resident cows between 1 June 2014 to 30 June 2015

10. Bulls capable of detecting estrous in cows
- Sniff or lick anogenital region & perform Flehmen response
- Vomeronasal organ – detect pheromones
Recorded 3 behaviors indicative of estrous cycling
Heavy tending by bull
Copulation
Tail-up high (cow)

11. Presence/absence of mounting sores
- Fresh mounting sores (FMS)
- Healing mounting sore (HMS)

12. Collected fecal samples to test for progesterone levels in all 60 cows (13 mths) - Analyzed at ICR, San Diego Zoo

13. Bison Breeding Season Mainland herds Catalina Island
Breeding season - June through September
Majority of breeding behavior mid-July through mid-August
Calving season – April through early June
Majority of calves arriving in late April through mid-May
Catalina Island
Breeding season – Late May through mid-August
Calving Season – Early March through mid-May

14. Bison Estrous Cycle Estrous cycle Estrus – lasts 12-24hrs
- 21 days (range 17-24)
Estrus – lasts 12-24hrs
Ovulation - 12hrs after estrus
Ovulatory follicle becomes the corpus luteum (CL)
- Produces progesterone
The CL matures after 16 days and then regresses
Progesterone drops
Estrous cycle of a domestic cow

15. Locating Bison in the Field
Fitted 5 cows with GPS collars
G2110E Iridium collar (Advanced Telemetry Solutions)
- Used prior monitoring data to select individuals not commonly found together

16. Results
Aided by 5 GPS-collared animals, cows were sampled on 152 days over 13 months, resulting in observations and 1098 fecal samples
As of current (July 2017), no calves have been born on Catalina since 2013, despite Reversal cows being off PZP treatment for 4-5 years

17. Results
Fecal progesterone values varied greatly among individuals, but not between PZP and Reversal cows
- baselines calculated for 52 cows following Brown et al. (2001)

18. Results – Individual Profiles
Treatment cow 9011
Standardized approach (Brown et al. 2001)
4 cycles detected – behavior
7 cycles detected – FP values
2 occasions of overlap
4 + 7 – 2 = 9 cycles
Subjective approach
9 cycles detected

19. Results – Individual Profiles
Reversal cow 9020
Standardized approach (Brown et al. 2001)
2 cycles detected – behavior
11 cycles detected – FP values
2 occasions of overlap
– 2 = 11 cycles
Subjective approach
9 cycles detected

20. Results
Except for April-May 2015, a large fraction (30-70%) of cows showed behavioral or hormonal signs of estrous cycling each month
mating
calving
PZP: cycles, SD = 2.0, N = 41
Reversal: 7.3 cycles, SD = 2.2, N = 11

21. Summary and conclusions
PZP contraception is effective, but was prolonged for at least 4-5 years after treatments ceased for cows treated for 3-4 years
- Severe 5-year drought may have been a factor
Number of years of PZP treatment should be reduced if a rapid return to fertility is desired
Catalina Island Conservancy did not administer PZP in 2016 or 2017 and will wait until calves are born to re-assess program

22. Summary and conclusions
With conception blocked, bison cows showed evidence of estrus nearly year-round, with bulls responding with typical breeding behavior
Effects of an extended rut and out-of-season births were not apparent on Catalina, but might be a concern in the bison's native range, where the climate is severe and large predators are present

23. Addressing Potential Concerns
Health and survival of bison bulls in response to an extended/continuous breeding season
- 7-13yr old bulls >750kg – dominant age group
- Make up <13% of the overall population
- Dominance ranking change year to year
- Dominance often only maintained for 2-3 weeks
Prolonged/continuous ovulation cycling in females may speed up the rotation of bulls through periods of dominance but may not necessarily have significant effects on bull health or survival

24. Addressing Potential Concerns
In the absence of a non-breeding season dominance appeared to be maintained through non-contact behaviors
- Frequency of battles not equally intense all year round
- Did not observe an increase in injuries to bulls

25. Addressing Concerns Out-of-season births
- Not yet confirmed – no calves
Conceivable considering prolonged/continuous ovulation
- Not uncommon in many herds
- Birth synchrony and season also influenced by:
Forage availability
Population size

26. Addressing Potential Concerns
Among other studies (horses)
- Out-of-season births not found to significantly affect survival of offspring
- Improved condition of females permitted to forgo pregnancy and nursing
Increased ability to care for offspring even in adverse conditions
- Birth season/synchrony presumed to return in response to environmental triggers (photoperiod, resource availability)

27. Management Considerations Catalina Island
Bison population has been maintained <150 individuals for 7 consecutive years
- Several management challenges persist
Ecological impacts
Poor health/nutrition of remaining animals
Direct human/bison incidences or conflicts
Complaints of low visibility - tours
Continued maintenance costs
Time to reassess overall management approach if ecological integrity of the island and the welfare of the bison are a priority

28. Questions?