The breeding of horses, whether through natural cover or advanced artificial reproduction techniques (ARTs), has often overlooked specific welfare implications. While discussions surrounding these practices occur sporadically in academic circles and industry presentations, a comprehensive and discrete consideration within the broader academic literature remains largely absent. This review aims to bridge that gap by examining the existing knowledge on welfare issues in horse breeding, identifying areas where data is lacking, and exploring how negative welfare effects can be mitigated while maximizing positive ones. The scope of this paper focuses on the welfare issues directly associated with the breeding process itself, from conception to weaning, excluding heritable conditions, selective breeding for extreme traits, and issues related to abandonment and neglect stemming from overbreeding.
Understanding Equine Welfare in Breeding
Welfare in the context of horse breeding encompasses both the prevention of negative experiences—such as pain, discomfort, fear, and stress—and the promotion of positive ones. While assessing positive welfare effects, like a mare’s potential pleasure in raising a foal, can verge on conjecture, associating breeding practices with the fulfillment of an animal’s needs for social interaction and the expression of normal behaviors can indicate positive welfare. Health and welfare are intrinsically linked in veterinary medicine, particularly in breeding, where routine vaccinations and disease control are crucial for safeguarding well-being. This article, however, concentrates on direct welfare insults that can cause pain, discomfort, fear, or stress to the animals involved or their offspring, rather than issues arising from infectious diseases.
Literature Review and Technique-Specific Welfare Concerns
A thorough literature search using terms such as ‘horse breeding and welfare,’ ‘artificial insemination,’ and ‘equine assisted reproductive technologies’ was conducted across various academic databases. This review highlights distinct welfare concerns associated with both natural cover and ARTs.
Natural Cover and its Welfare Implications
In natural settings, horses exhibit complex courtship and copulatory behaviors. However, domesticated breeding practices, particularly within the Thoroughbred industry, often deviate significantly from these natural patterns. Mares are frequently restrained, and stallions are presented to them with limited opportunity for natural interaction. This emphasis on restraint, while aimed at preventing injury, may lead to frustration by preventing the animals from fulfilling natural behavioral needs. The intensive breeding schedules for successful stallions, sometimes involving covering up to 200 mares in a season, can also lead to a loss of libido, indicative of potential mental or physical stress. Furthermore, the practice of “shuttling” stallions between hemispheres exposes them to the stress of long-distance travel and unfamiliar environments.
The artificial limitation of the breeding season in Thoroughbred racing also presents welfare challenges. To gain a competitive advantage, there is significant economic pressure for mares to foal early, necessitating reproductive stimulation outside their natural cycles. This can involve artificial lighting, specialized nutrition, and hormonal treatments. Early-born foals may then face confinement due to inclement weather or a lack of pasture, hindering the expression of normal behaviors.
Artificial Insemination (AI) offers potential welfare improvements by reducing the frequency of collection for stallions and eliminating the need for transporting horses, thereby minimizing stress and pathogen exposure.
Assisted Reproductive Techniques (ARTs) and Their Welfare Considerations
While most non-Thoroughbred studbooks now permit ARTs, these techniques also carry their own set of welfare considerations, affecting both the animals undergoing the procedures and those conceived through them. These implications can be short-term or long-term.
Artificial Insemination (AI): While generally considered minimally painful or stressful for mares, AI can lead to an attenuation of normal reproductive behaviors for stallions, as they may not directly interact with mares. However, AI significantly reduces the number of times a stallion needs to ejaculate, minimizes risks during breeding, and eliminates the need for transporting horses. The ability to freeze semen also facilitates castration, simplifying social management for male horses.
Embryo Transfer (ET): ET procedures, particularly embryo flushing, may cause stress or discomfort to mares. While ET can be beneficial for mares at high risk of injury during pregnancy, it involves more invasive examinations and pharmacological interventions compared to AI. The need to synchronize donor and recipient mares often increases the number of examinations and potential for drug administration.
Oocyte Retrieval and Transfer: Transvaginal ultrasound-guided follicular aspiration, a common method for oocyte retrieval, is known to be associated with pain in other species. While studies specifically on pain perception in mares undergoing this procedure are limited, it is standard practice to restrain, sedate, and provide analgesia to mares, suggesting a clinical recognition of potential discomfort. Concerns about pathogen transmission and vaginal rupture are also associated with this technique. The welfare implications for foals conceived via these methods are less understood, though some studies in cattle suggest potential issues related to fetal size and placental function, which may be linked to in-vitro culture conditions.
Cloning: Equine cloning, while rare, is associated with recognized welfare problems observed in other species. These include higher embryo loss rates, increased risks of abnormalities at birth, and a greater need for intensive neonatal care. While mares may regulate fetal size differently than cattle, potentially mitigating some issues like fetal oversize, data on the long-term welfare of cloned horses remains sparse.
Mitigating Negative Welfare Effects in Equine Breeding
The judicious use of ARTs can offer significant welfare benefits by reducing the stress and disease exposure associated with long-distance transportation of horses. Innovations like allowing geldings with frozen semen to be registered as breeding animals can also improve welfare by reducing the need to keep male horses entire, thus facilitating better social management.
However, a significant knowledge gap exists regarding the specific welfare impacts of newer ARTs. The current practice of providing analgesia for some procedures without definitive evidence of pain, while withholding it for others where pain is suspected, highlights the need for more evidence-based decision-making. Research incorporating valid measures of pain, discomfort, fear, and stress, combining physiological parameters with behavioral indicators, is crucial. Developing specific pain scales for equine gynecological procedures would be highly beneficial.
Furthermore, understanding the long-term welfare implications of ARTs on future generations is essential. While AI and ET have been used for decades with no apparent long-term adverse effects, more extensive, long-term studies are needed for techniques like intracytoplasmic sperm injection (ICSI) and cloning.
Conclusion
A general lack of comprehensive data on the welfare of breeding horses necessitates the inclusion of these animals in broader welfare assessments. Careful management practices that allow for the expression of normal behaviors, alongside a thoughtful consideration of how ARTs can mitigate stressors associated with natural cover and transportation, are paramount. Future research must focus on establishing an evidence base for the stress and pain associated with various ARTs and their lifetime implications for subsequent generations. Only with such information can sound ethical judgments be made regarding the balance between potentially stressful procedures and the welfare benefits derived from reduced travel, mixing, and natural cover techniques.
