Reimmunization Increases Contraceptive

Effectiveness of GonaCon-Equine Vaccine in

Free-Ranging Horses (Equus caballus):

Limitations and Side Effects

Investigators:

D. Baker1, J. Powers2, J. Ransom2, B. McCann2, M. Oehler2,

J.Bruemmer1, N. Galloway2 , D. Eckery3, and T. Nett1

1Colorado State University, 2National Park Service, 3United States Department

of Agriculture/ Animal and Plant Health Inspection Service

Study Area

• Southwestern North Dakota

• 46,000 acres – fenced

• 130 horses – 15 bands

• Historical demonstration herd

Theodore Roosevelt National Park

• Diverse Badlands typography

• Multiple wild ungulate species

• Abundant year-round forage

• Few predators

• Alter native plant communities

• Compete for limited forage resources

• Limited methods of population control

United States Geological Survey

Management Problems:

Overabundant Feral Horses

• Vaccine

• GnRH antibodies

• Inhibits ovulation and spermatogenesis

• Tested in many wildungulate species

• Single treatment –multiple years

• Safe

• EPA approved for feral horses, burros, and white-tailed deer

GnRH Vaccine (GonaCon-Equine)

Ovary

Ovum

Testis

spermatogenesis

Hypothalamus

GnRH

Anterior Pituitary

FSH LH

testosterone

estrogen/progesterone

Reproductive Pathway

Gonads

Brain

ovulation

BLOCK

BLOCK

Objective

• To determine the effective duration and safety of a single

vaccination and subsequent reimmunization with

GonaCon-Equine in free-ranging horses

Methods: Animal Capturing and Handling

Experimental Horses

2009 (October): Primary Vaccination

• 29 GonaCon-Equine; 28 saline

• Similar in age, pregnancy status,

stage of gestation, body condition,

general health

2013 (September): Reimmunization

• 4 years post-primary

• Same mares recaptured and processed

• 25 GonaCon-Equine; 26 saline control

• Similar in pregnancy status, stage of gestation, body condition, and general

health

Methods: Reproduction

Foaling Proportions:

• Weekly observations of each study mare for presence or absence of a foal during March 1- August 1 each year

Vaccine Effectiveness:

• Vaccine effectiveness as the proportionate reduction in foaling between control and treated mares.

• Scan sampling – time

budgets

• All-occurrence – social

behaviors

Ransom et al. 2014

Methods: Behavior

Methods: Injection Site

Reactions

Results: Reproduction

• No difference in maintenance

behaviors (feeding, resting,

travelling)

• No difference in social

behaviors (herding, agonism,

reproductive)

Results: Behavior

Results: Injection Site Reactions

• ~70% swelling or abscess following a single vaccination

• ~50% similar reactions following reimmunization

• No evidence of lameness, or depression, was observed for

any treated mare following either vaccination

Conclusions:

GonaCon-Equine was demonstrated to be safe but

minimally effective (30%) and short duration (2 yrs.) when

administered as a single inoculation to free-ranging horses.

However, when the primary vaccination was followed by a

booster immunization, four years later, it was shown to be

highly effective (90%) and long-term (4 yrs.) without

significant adverse side effects.

Management implications?

Future Research:

1. Continue to monitor duration of effectiveness, return to

fertility, and effects on the phenology of parturition

2. Continue to monitor the long-term side-effects of

reimmunization on treated females

3. Develop and test remote dart delivery of vaccine

4. Determine the most effective reimmunization schedule

5. Conduct population level studies

Reimmunization Schedule ?

Objective: Determine the optimum interval between the primary and

booster immunization.

Hypothesis: Decreasing the interval between the primary and booster

immunization will decrease effective duration of GonaCon-Equine.

Experimental design:

Years after 1st vaccination: 4 2 1 0.5

Sample size: 25 11 15 15

Requires remote dart delivery of GonaCon-Equine

Measure: foaling proportions, injection site reactions, body condition

• National Park Service

• Animal Reproduction and Biotechnology

Laboratory, Colorado State University

• Bureau of Land Management

• Morris Animal Foundation

• National Wildlife Research Center

• Deb Carson Photography

• Field Research Technicians and Volunteers – the unsung heroes

Acknowledgements:

Questions?