Equine welfare during breeding is a topic that has historically received limited discrete attention in academic literature, despite its critical importance. This article delves into the existing knowledge surrounding welfare issues in horse breeding, encompassing both traditional “natural cover” methods and modern Artificial Reproduction Techniques (ARTs). While all breeding methods carry potential welfare concerns, ARTs, when judiciously applied, can sometimes offer solutions to these challenges. This review aims to identify negative welfare effects, explore ways to mitigate them, and maximize positive welfare outcomes for horses involved in breeding. Further research is essential to establish a robust evidence base on the stress and pain associated with various breeding procedures and the long-term welfare implications of ARTs for future generations.
The breeding of horses, whether through natural processes or ARTs, presents a complex landscape of welfare considerations. While specific welfare issues related to breeding practices have occasionally been discussed in conference proceedings, a comprehensive academic review has been lacking. This paper addresses this gap by examining the current understanding of welfare challenges in equine breeding and highlighting areas where more data is needed. For the purpose of this review, “horse breeding” is defined as the processes leading to conception, pregnancy, and the management of stallions, mares, and foals until weaning.
This review does not encompass welfare issues arising from heritable conditions or selective breeding for extreme traits. Furthermore, it excludes welfare concerns related to horse abandonment and neglect, often linked to overbreeding. The focus remains on the welfare implications directly associated with the methods of breeding, whether through natural cover or ARTs, assuming the legitimacy of using horses for breeding.
The concept of welfare in this context extends beyond merely preventing negative experiences such as pain, discomfort, fear, and stress. It also includes maximizing positive welfare effects, such as the fulfillment of social interaction needs and the ability to express normal behaviors. While quantifying positive welfare can be speculative, identifying opportunities to enhance it is crucial.
Welfare and health are intrinsically linked in veterinary medicine, particularly in breeding. While vaccinations and disease control are vital for safeguarding welfare, this article concentrates on direct welfare insults—those that cause pain, discomfort, fear, stress, or other reductions in welfare—rather than issues arising from infectious diseases.
Literature Search Methodology
A thorough literature search was conducted using terms such as ‘horse breeding and welfare,’ ‘broodmares and welfare,’ ‘stallions and welfare,’ ‘foals and welfare,’ ‘welfare effects of assisted reproductive technologies,’ ‘equine embryo transfer,’ ‘equine artificial insemination,’ and ‘equine assisted reproductive technologies.’ Searches were performed using the Royal Veterinary College’s SCOUT system, PubMed, CAB Direct, Biomed Central journals, and the Web of Science. Additionally, non-peer-reviewed sources were included in the search.
Welfare Issues Associated with Breeding Techniques
Natural Cover
In natural settings, a stallion and his harem of mares interact continuously throughout the year. Equine courtship and copulatory behaviors are intricate, often initiated by the mare. However, in domesticated breeding, especially within the Thoroughbred industry, breeding practices differ significantly from natural behavior. Mares are typically restrained, and stallions are led to mount with limited opportunity for pre-coital interaction. This controlled environment, while aimed at preventing injury, may lead to frustration by preventing the animals from fulfilling natural behavioral needs. Studies assessing the frustration or stress levels in horses subjected to these controlled breeding systems are notably absent.
Intensified breeding schedules for successful stallions, including covering up to 200 mares per season, can lead to reduced libido, indicating potential mental or physical stress. The practice of “shuttling” stallions between hemispheres for year-round breeding can further compromise their welfare due to the stress of long flights, unfamiliar environments, and potential exposure to novel pathogens.
The artificial time limitation of the Thoroughbred breeding season also has welfare implications. To gain a competitive advantage in racing, where foals are given a nominal January 1st birthday, there is significant economic pressure for mares to foal early. This often necessitates the use of artificial lighting, high nutrition, and hormonal treatments to stimulate reproductive cycles outside the natural breeding season. Foals born early may be confined indoors due to inclement weather or lack of access to pasture, hindering the expression of normal behaviors.
Artificial Insemination (AI) offers potential solutions to many welfare concerns associated with natural cover. AI allows for semen collection, division, and distribution without requiring the stallion to travel extensively or the mare and foal to be transported to a stud. This significantly reduces stress and exposure to pathogens.
Assisted Reproductive Techniques (ARTs)
While most non-Thoroughbred studbooks now permit ARTs, their use is not without welfare implications. These can be short-term or long-term, affecting animals subjected to or derived from ARTs.
| Technique | Frequency of Use | Negative Welfare Effects | Positive Welfare Effects |
|---|---|---|---|
| Artificial Insemination | Very Common | Lack of controlled studies; anecdotally minimal pain/stress for mares. Attenuation of normal reproductive behaviors for stallions. No apparent long-term welfare effects on offspring. | Reduces collection frequency for stallions. Decreases risk of injury to horses and personnel. Eliminates need for international stallion transport and mare/foal transport to stud. Facilitates castration by enabling semen freezing, simplifying social management. |
| Embryo Transfer | Common | Increased need for invasive examination and pharmacological manipulation. Embryo flushing may be stressful/painful. | Facilitates breeding from mares at high risk of injury during pregnancy. Reduced transport needs for mares and foals via frozen embryo shipping. |
| Oocyte Retrieval & Transfer | Uncommon | Lack of controlled studies in mares. Known to cause increased heart rate and cortisol levels in other species. Potential for adhesions. Unclear long-term welfare effects on offspring. | Enables pregnancy in mares with reproductive pathologies rendering ET unsuccessful. |
| Cloning | Rare | Increased risk of abnormalities, higher neonatal intensive care requirements. | Allows for the genetic replication of desirable individuals. |
For stallions, ARTs like AI can lead to an “attenuation” of normal behaviors, as they may never physically interact with a mare. This can contribute to low libido. However, the primary welfare concerns associated with ARTs generally apply to mares and offspring.
AI involves insemination with fresh, chilled, or frozen semen. While generally considered minimally invasive, mares are often restrained in stocks for safety. Sedation and analgesia practices vary, with a lack of direct studies on pain associated with AI in mares.
Embryo Transfer (ET) also lacks specific studies on pain in mares. Although ET can be more invasive than AI, particularly embryo flushing, it is typically performed non-surgically in mares. Sedation is common, primarily for safety and ease of procedure. Donor mares may experience greater welfare impacts due to flushing and hormonal treatments for superovulation. However, ET can improve welfare by allowing mares at risk of pregnancy complications to avoid carrying a foal to term and by reducing the need for transporting mares and foals.
Oocyte retrieval, often used when ET is unsuccessful, involves transvaginal ultrasound-guided follicular aspiration. While this procedure in humans is known to cause pain, its effects in mares are less understood. Mares undergoing oocyte retrieval are typically restrained, sedated, and given analgesia, suggesting a perceived risk of discomfort or pain. The welfare implications for foals conceived via retrieved oocytes are not well-documented, though concerns in other species related to in vitro culture conditions are noted.
Cloning, an ART with significant welfare implications in other species, is still relatively rare in horses. Studies suggest cloned equine foals may have a higher incidence of abnormalities and require intensive care. However, certain issues seen in cloned cattle, such as fetal oversize, appear less prevalent in horses due to mares’ ability to regulate fetal size in utero.
Mitigating Negative Welfare Effects
The judicious use of ARTs can significantly improve equine welfare. AI and semen transport reduce the stress and disease exposure associated with transporting horses. Using geldings with frozen semen for breeding also offers welfare benefits by simplifying social management.
However, a greater understanding of the potential negative welfare effects of equine ARTs is needed. Currently, there is a paradox where analgesia is provided for some procedures without clear evidence of pain, while other potentially painful procedures are performed without it. Clinical decisions about analgesia are often based on behavioral observations and assumptions.
To make evidence-based judgments, studies are required that incorporate valid measures of pain, discomfort, fear, and stress in mares undergoing ARTs. This should combine physiological measurements with subtle behavioral indicators. Further research is also needed to understand the long-term welfare implications of ARTs, particularly newer techniques like ICSI and cloning, on future generations. While AI and ET appear to have no long-term adverse effects, data on more recent techniques is sparse.
Conclusion
A significant lack of data exists regarding the welfare of horses involved in breeding. This can be addressed by incorporating breeding horses into broader equine welfare data-gathering initiatives. Careful management practices that allow horses to express normal behaviors, alongside the strategic use of ARTs to mitigate stressors associated with travel and natural cover, can enhance welfare. However, robust evidence is required to determine the stress and pain levels associated with various ARTs and their long-term effects on offspring. Only with this information can sound ethical judgments be made regarding the balance between the potential discomfort of certain techniques and the welfare benefits derived from avoiding stressors in other breeding methods.
Acknowledgments
The authors acknowledge the funding and support received, as well as the valuable advice from experts and anonymous referees.
