Undergraduate Thesis Or Project
 

Methods of Reproductive Control in Domestic and Free-Roaming Horses and the Behavioral Implications

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  • The current American free-roaming horse (Equus caballus) population far exceeds the appropriate population limit set by the Bureau of Land Management (BLM) to preserve resources on public lands. Several techniques have been tested to assist in decreasing repopulation rates. The purpose of the present study was to analyze two contraceptive techniques, one that is reversible and targets domestic mares and one that is irreversible and targets free-roaming stallions. Administration of exogenous progesterone or progestin have been shown to suppress estrous behavior in mares. Five regularly cycling domestic mares were treated with 2 g of long-acting progesterone two days after luteolysis. Daily stallion exposure was used to score estrous behavior, and blood serum progesterone concentrations were tested every other day. Serum progesterone concentrations were significantly elevated (>2 ng/mL) for 10 days following treatment with a long-acting injectable progesterone. Behavioral estrus suppression during this period was minimal and not significant. All mares developed local injection site reactions following treatment. Due to the side effects associated with this treatment, long-acting formulations of injectable progesterone are not appropriate for use in performance horses. In many species, male social rank has been found to correlate with testosterone concentration, with more dominant males having higher circulating testosterone. Fifteen free-roaming stallions gathered for the purpose of castration were behaviorally evaluated for two days to assess social hierarchy status. These males were categorized into three groups. Mane hair and serum samples were collected from each stallion and testosterone and cortisol concentrations were evaluated. There were no significant differences found between hair and serum hormone concentrations and observed behavior. There was also no correlation found between serum and hair testosterone or cortisol concentrations. The present study could be used across various free-roaming horse ranges where range managers are making decisions about population control tactics with the most regard to animal welfare.
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  • Ongoing Research
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  • 2019-05-31 to 2019-12-31

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