Equine breeding practices, whether through natural cover or advanced artificial reproduction techniques (ARTs), present a complex landscape of potential welfare challenges and opportunities. While often overlooked in academic discourse and industry discussions, these issues are critical for ensuring the well-being of horses involved in breeding. This article delves into the existing knowledge surrounding welfare concerns in horse breeding, highlights areas where data is scarce, and proposes strategies for identifying and mitigating negative welfare effects while maximizing positive ones. The focus remains on the breeding process itself, excluding heritable conditions, selective breeding for extreme traits, and issues arising from abandonment or neglect due to overbreeding.
The welfare of breeding horses encompasses both the prevention of negative experiences, such as pain, fear, and stress, and the promotion of positive states, like the fulfillment of social needs and the ability to exhibit normal behaviors. While the latter can be subjective, it is intrinsically linked to the overall health and well-being of the animals. This review primarily concentrates on direct welfare insults arising from breeding procedures, rather than those stemming from infectious diseases, though the two are often interconnected.
Literature Review and Technique-Specific Welfare Concerns
A comprehensive search of academic literature was conducted using terms related to horse breeding and welfare, including specific ARTs. This review examines the welfare implications of both traditional natural cover and various ARTs.
Natural Cover: Traditional Practices and Welfare Implications
In natural settings, horses engage in complex courtship and copulatory behaviors, often initiated by the mare. However, domesticated breeding, particularly in the Thoroughbred industry, frequently deviates from these natural patterns. Thoroughbred breeding is restricted to “natural cover” for studbook registration, involving restrained mares and stallions. This controlled environment, while aimed at preventing injury, may lead to frustration by preventing the animals from expressing normal behavioral needs. The intense breeding schedules for successful stallions, sometimes covering up to 200 mares per season, can lead to a loss of libido, indicating potential stress. Furthermore, the practice of “shuttling” stallions between hemispheres for year-round breeding exposes them to the stresses of long flights and unfamiliar environments.
The artificial limitation of the Thoroughbred breeding season also has welfare implications. The economic pressure for early foaling, to give foals a competitive advantage due to the industry’s nominal January 1st birth date, necessitates the use of artificial lighting, nutrition, and drugs to stimulate mares’ reproductive cycles outside their natural breeding season. Early-born foals may also face confinement due to inclement weather and limited access to pasture, restricting their ability to express normal behaviors.
Artificial insemination (AI) offers potential welfare benefits by reducing the frequency of a stallion’s ejaculations, minimizing injury risks, and eliminating the need for extensive transportation of horses. AI also allows for the collection, division, and shipment of semen, reducing stress and pathogen exposure for mares and foals.
Assisted Reproductive Techniques (ARTs): Innovations and Welfare Considerations
The majority of non-Thoroughbred studbooks permit the use of ARTs, with AI and embryo transfer (ET) being the most common. While these techniques can alleviate some welfare concerns associated with natural cover, they introduce their own set of potential welfare issues.
Artificial Insemination (AI): While generally considered minimally stressful for mares, AI can attenuate normal reproductive behaviors for stallions. However, there is anecdotal evidence suggesting no long-term welfare effects on animals conceived via AI. The ability to freeze semen also facilitates castration, simplifying social management of male horses.
Embryo Transfer (ET): ET is common in many breeds and can be crucial for mares at high risk of injury if they were to carry a foal to term. Preserved embryo shipping reduces the need for transporting mares and foals. However, ET requires more invasive examinations and pharmacological manipulation than AI. The embryo flushing process may cause stress or discomfort, and repeat superovulation attempts can be taxing for donor mares. The increased frequency of rectal and ultrasound examinations for recipient mares, along with potential pharmacological synchronization, also raises welfare considerations.
Oocyte Retrieval and Transfer: Techniques like oocyte retrieval, often used when ET is unsuccessful, are less common but still carry potential welfare implications. While not extensively studied in mares, similar procedures in other species have been linked to increased heart rate, elevated cortisol levels, and the development of adhesions. Although mares undergoing oocyte retrieval are typically restrained, sedated, and given analgesia, the precise level of pain or discomfort experienced remains an area requiring further research. The welfare of foals conceived through these methods also warrants investigation, though current data does not indicate significant negative short-term effects.
Cloning: Equine cloning, while still rare, presents recognized welfare challenges seen in other species. High embryo loss rates and an increased incidence of abnormalities at birth, requiring intensive neonatal care, have been reported. While some issues seen in cloned cattle, such as fetal oversize, appear less prevalent in horses due to physiological differences, ongoing research is crucial to understand the long-term welfare implications for cloned animals and their offspring.
Mitigating Negative Welfare Effects and Future Research
A significant lack of data exists regarding the welfare of breeding horses. Addressing this requires the inclusion of breeding horses in broader equine welfare data-gathering initiatives. Careful management practices that allow horses to express normal behaviors, within safety constraints, can improve welfare by reducing negative experiences and enhancing positive ones. ARTs can be valuable tools for improving welfare by reducing the need for stressful transportation and potentially enabling the use of geldings for breeding through frozen semen, thus diminishing the incentive for cloning.
However, further research is imperative to establish a robust evidence base on the stress and pain associated with various ARTs. Studies should incorporate valid measures of pain, discomfort, fear, and stress, combining physiological parameters with subtle behavioral indicators. Developing specific pain scales for equine gynecological procedures would greatly enhance our understanding.
Long-term cohort studies are also needed to assess the lifetime welfare implications of ARTs on future generations, particularly for newer techniques like ICSI and cloning. While common-sense suggests AI and ET likely have no significant long-term effects due to their long history of use, this assumption needs rigorous validation for more recent advancements. Only with comprehensive data can informed ethical judgments be made regarding the balance between the potential welfare costs of ART procedures and the benefits derived from reduced stress associated with travel, animal mixing, and natural cover techniques.
Conclusion
The welfare of horses involved in breeding is a multifaceted issue demanding greater attention. While ARTs offer significant potential to mitigate negative welfare impacts, particularly those related to transportation and physical stress, they also introduce new concerns that require thorough investigation. Continued research, coupled with careful management and ethical consideration, is essential to ensure that equine breeding practices prioritize the well-being of these animals throughout their lives and for generations to come.
Acknowledgments
The authors acknowledge the funding support and valuable advice received from various institutions and individuals during the preparation of this review.
