Recipient Organization
UNIVERSITY OF NEVADA
(N/A)
RENO,NV 89557
Performing Department
Ag Nutrition and Vet Sciences
Non Technical Summary
Feral horse populations in Nevada are managed so that they have minimal environmental impacts on the land, yet they continue to overpopulate several rangelands within the state. Currently, wild horse populations in Nevada are over appropriate management levels (AML) in 49% of herd management areas (BLM 2009). Most management practices involve removing horses from the range and adopting these out to members of the public. Horses found to be unadoptable are maintained in long term sanctuaries at great expense to the public (approximately $29 million) (BLM 2009). Questions have been raised over the effectiveness and humanness of removals for adoption or long term holding, thus requiring a new way to manage these horses. An alternative management method would be to limit the fertility of the horses, rather than remove horses from the land, which is expensive and difficult. Contraceptive technologies are being developed that are safe, effective, long-acting and reversible. However, most formulations do not last longer than 1-2 years after treatment, which limits their practicality in most management situations. In addition to a contraceptive being long-lasting, it should have minimal impacts to behavior and ecology of treated individuals. We treated mares in 2005 with two formulations that were developed to last for several years with one injection. We found that most mares were infertile for four years post-treatment, but many have not returned to fertility and it is unknown how long these contraceptive vaccines last in free-roaming horses. During the first three years of the study, we found no major changes to the social behavior of females, but in the fourth year, it appeared that some treated females were changing bands more often than control females. These changes could have welfare implications as well as ecological repercussions. We are proposing a study where we continue to investigate the impact of contraceptive treatment on fertility, mare behavior, and social group stability over the next three years with feral horses in the Virginia Range. The results of this study would impact all feral horse populations, as well as other overabundant species, as a way to properly manage horses by reducing the need for constant gathers and having minimal impact on social behavior. Management of horses at appropriate population levels would increase the productivity of rangelands and benefit local wildlife and grazing livestock.
Animal Health Component
90%
Research Effort Categories
Basic
10%
Applied
90%
Developmental
(N/A)
Goals / Objectives
This will be the first study to investigate long term efficacy and behavioral side effects in feral horses treated with contraception and a continued collaboration with experts in the fields of equine behavior and contraception. We aim to understand how long these contraceptive formulations last and when females return to fertility. Our long term goals are to understand how to better manage feral horse populations that minimizes behavioral or physiological side effects, which will most likely produce a shift in management away from gathers and towards contraception (see Figure 1). Our expected results should increase the use and research of contraceptive technologies. Ultimately, we hope to demonstrate the effectiveness and safety of long term contraceptive use in order to shift public perspectives towards a more positive view of using contraception as a management tool in feral horses and other overabundant species. Better management will result in lower costs, while maximizing horse and rangeland health, which benefits other wildlife and agricultural practices.
Project Methods
Mares were monitored on an at least weekly basis from the ground to determine foaling rates for the last four years. We will continue this monitoring effort for the next three years. Fertility status will be determined if a foal is present any time during the year or if a female is noticeably pregnant, judged conservatively by an enlarged belly and swollen teats. If females are not seen until after the foaling season and no foal is present, they will be recorded as unknown and excluded from the analysis. The sex of each foal will be recorded shortly after birth, and they will be monitored for survival until weaning. Fecal samples from known individuals will be collected on an opportunistic basis in order to analyze for pregnancy hormones (e.g., progesterone and estrodial). These samples will be used to supplement and verify our visual observations of pregnancy status. Fecal samples will be extracted according to protocol of Asa et al. 2001. Samples will be run using radioimmunoassay for both hormones. Once a female has been located in the field, her fertility status will be recorded as well as body condition and band membership. Body condition scores are visually estimates of fat deposits around the neck, ribs and rump using an 11 point scale from 0-5, with 0.5 gradations (Carroll and Huntingdon 1988, Rudman and Keiper 1991). These scores are used as a measurement of energy reserves and are correlated with fat percentage in horses (Henneke et al. 1983). These scores will give us an indication of overall health in treated mares. For band fidelity, we will record all present band members to note any changes (e.g., deaths, births, dispersals). A band change will be classified as immigration into a new band that lasts for more than a day.