Population dynamics and fertility control of feral horses

Collins, Gail H.; Kasbohm, John W.

doi:10.1002/jwmg.21196

Cited by 11 publications

(10 citation statements)

References 38 publications

(51 reference statements)

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“…The BLM and USFS are not permitted to use lethal removal or sell horses to those who would kill otherwise healthy animals (Garrott 2018) as prescribed by annual Department of Interior appropriations acts (BLM 2020 a ). Despite permitted management actions occurring at HMAs range‐wide (BLM 2020 a ), estimates have exceeded AML max every year since 2005, which is largely influenced by population growth (Collins and Kasbohm 2017) that exceeds BLM's ability to pay for an adequate number of animal removals or fertility suppression (Garrott 2018). Horse population estimates, as a whole, are currently >1.97 times above AML max across their range for every state except Arizona.…”

Section: Figurementioning

confidence: 99%

Sage‐Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

et al. 2021

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In recent decades, feral horse (Equus caballus; horse) populations increased in sagebrush (Artimesia spp.) ecosystems, especially within the Great Basin, to the point of exceeding maximum appropriate management levels (AMLmax), which were set by land administrators to balance resource use by feral horses, livestock, and wildlife. Concomitantly, greater sage‐grouse (Centrocercus urophasianus; sage‐grouse) are sagebrush obligates that have experienced population declines within these same arid environments as a result of steady and continued loss of seasonal habitats. Although a strong body of research indicates that overabundant populations of horses degrade sagebrush ecosystems, empirical evidence linking horse abundance to sage‐grouse population dynamics is missing. Within a Bayesian framework, we employed state‐space models to estimate population rate of change (λ) using 15 years (2005–2019) of count surveys of male sage‐grouse at traditional breeding grounds (i.e., leks) as a function of horse abundance relative to AMLmax and other environmental covariates (e.g., wildfire, precipitation, % sagebrush cover). Additionally, we employed a post hoc impact‐control design to validate existing AMLmax values as related to sage‐grouse population responses, and to help control for environmental stochasticity and broad‐scale oscillations in sage‐grouse abundance. On average, for every 50% increase in horse abundance over AMLmax, our model predicted an annual decline in sage‐grouse abundance by 2.6%. Horse abundance at or below AMLmax coincided with sage‐grouse λ estimates that were consistent with trends at non‐horse areas elsewhere in the study region. Thus, AMLmax, as a whole, appeared to be set adequately in preventing adverse effects to sage‐grouse populations. Results indicated 76%, 97%, and >99% probability of sage‐grouse population decline relative to controls when horse numbers are 2, 2.5, and ≥3 times over AMLmax, respectively. As of 2019, horse herds exceeded AMLmax in Nevada, USA, by >4 times on average across all horse management areas. If feral horse populations continue to grow at current rates unabated, model projections indicate sage‐grouse populations will be reduced within horse‐occupied areas by >70.0% by 2034 (15‐year projection), on average compared to 21.2% estimated for control sites. A monitoring framework that improves on estimating horse abundance and identifying responses of sage‐grouse and other key indicator species (plant and animal) would be beneficial to guide management decisions that promote co‐occurrence of horses with sensitive wildlife and livestock within landscapes subjected to multiple uses. Published 2021. This article is a U.S. Government work and is in the public domain in the USA. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

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Section: Figurementioning

confidence: 99%

Sage‐Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

et al. 2021

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“…The laparoscopic vasectomy technique used in this study allowed an adequate excision of a portion of DD, resulting in azoospermia without interferences in the reproductive behaviour of stallions. The procedure Stallion vasectomy can be requested as a contraception technique for the control of feral horse populations, 32 as well as some owners may ask for a contraception method able to preserve the stallion's natural behaviour in the herd. Especially because vasectomy is an elective procedure, risks must be minimised as much as possible.…”

Section: Discussionmentioning

confidence: 99%

“…Stallion vasectomy can be requested as a contraception technique for the control of feral horse populations, 32 as well as some owners may ask for a contraception method able to preserve the stallion's natural behaviour in the herd. Especially because vasectomy is an elective procedure, risks must be minimised as much as possible.…”

Section: Discussionmentioning

confidence: 99%

Application of a laparoscopic technique for vasectomy in standing horses

et al. 2019

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This report describes a technique for standing laparoscopic vasectomy in stallions through a prospective descriptive study. A preliminary study was carried out with two experimental intact male horses and subsequently the procedure was performed in two clinical cases. These horse owners want to keep their animals in the most possible natural way, preserving its stallion behaviour in a herd without generating offspring. The horses were sedated and restrained in stocks and laparoscopic vasectomy was performed using three portal sites in both paralumbar fossae recording surgical times. A 4-cm segment of each ductus deferens (DD) was occluded with laparoscopic vessel sealing devices and subsequently excised. Semen collection was performed using an artificial vagina before the laparoscopic procedure and at 15 and 60 days postoperatively. Sexual behaviour and spermiogram were analysed. Two months after vasectomy, control laparoscopy was performed in experimental horses to assess the surgical site. Bilateral vasectomy could be performed without intraoperative complications in a mean surgical time of 20 min per DD. Success of the procedure was confirmed in all cases by azoospermic ejaculates 60 days after vasectomy. This is the first time that the technique for laparoscopic vasectomy is described in horses.

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“…Furthermore, as new methods of controlling these populations are developed (Ransom et al, 2014;Hall et al, 2016;Collins and Kasbohm, 2017), behavioral consequences for target animals and their associates should be monitored to ensure animal welfare and effective management. Table Table 1.…”

Section: Management Implicationsmentioning

confidence: 99%

Decreased female fidelity alters male behavior in a feral horse population managed with immunocontraception

Jones

Nuñez

2019

Applied Animal Behaviour Science

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In social species like the feral horse (Equus caballus), changes in individual behavior are likely to affect associated animals. On Shackleford Banks, North Carolina, USA, mares treated with the contraceptive agent porcine zona pellucida (PZP) demonstrate decreased fidelity to their band stallions. Here, we assess the effects of such decreased mare fidelity on male behavior and address potential interactions with habitat visibility, a component of the environment shown to significantly affect feral horse behavior. We compared the frequency and escalation of male-male contests, rates of aggressive and reproductive behaviors directed toward females, and the percentage of time spent vigilant among males experiencing varying levels of mare group changing behavior. We found that regardless of habitat visibility, males experiencing more female group changes engaged in contests at a higher rate (P = 0.003) and escalation (P = 0.029) and spent more time vigilant (P = 0.014) than males experiencing fewer group changes. However, while visibility had a positive effect on aggression directed by stallions toward mares (P = 0.013), female group changing behavior did not influence male-female aggressive or reproductive behaviors (P > 0.1), showing that decreases in mare fidelity altered male-male but not male-female interactions. These results have important implications for feral horse management; PZP-contracepted mares demonstrating prolonged decreases in stallion fidelity may have a disproportionate effect on male behavior. Moreover, our results shed light on the relative influences of female behavior and environmental factors like habitat visibility on male behavior. Such findings can ultimately improve our understanding of how the social and physical environments interact to shape male-male and male-female interactions.

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Population dynamics and fertility control of feral horses

Cited by 11 publications

References 38 publications

Sage‐Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

Sage‐Grouse Population Dynamics are Adversely Affected by Overabundant Feral Horses

Application of a laparoscopic technique for vasectomy in standing horses

Decreased female fidelity alters male behavior in a feral horse population managed with immunocontraception

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