Mare behaviour can sometimes be unpredictable and challenging to manage, leaving horse owners and veterinarians searching for potential causes. Hormonal imbalances, particularly those associated with ovarian abnormalities such as granulosa cell tumours (GCTs), are often suspected. These suspicions arise from the well-known role of ovarian hormones in regulating behaviour, but is the connection as strong as we think? A recent retrospective study by Huggins et al. (2023) takes a closer look, providing critical insights into the true prevalence of hormonal associations with behavioural changes in mares.
This study analysed hormone profiles in thousands of mares presenting with behavioural issues, questioning the commonly held assumption that ovarian hormone imbalances are a leading cause of behavioural abnormalities. The findings may shift how we approach diagnosing and managing these issues in mares.
Study Overview: Searching for Connections
The retrospective study reviewed 2,914 hormonal profile submissions where behavioural concerns were a primary or contributing factor. Submissions included notes containing terms such as “behave,” “behaviour,” or “behaving,” signalling that the owners or veterinarians associated the behaviour with a possible hormonal cause. The samples were evaluated for concentrations of key ovarian hormones: testosterone, anti-Müllerian hormone (AMH), inhibin A, and progesterone. These hormones are significant markers for diagnosing granulosa cell tumours (GCTs) and other ovarian abnormalities.
The primary aim was to identify patterns linking hormone levels with reported behaviours. By doing so, the researchers sought to clarify the true role of hormonal imbalances in behavioural abnormalities and whether these behaviours are often indicative of underlying ovarian pathology.
Key Findings: Breaking Down the Myths
- Lack of Correlation Between Hormones and Behaviour
One of the study’s most striking findings was the lack of a consistent correlation between behavioural abnormalities and elevated levels of ovarian hormones. Hormones such as testosterone, AMH, and inhibin A, which are typically elevated in mares with GCTs, were not consistently elevated in the majority of cases presenting with behavioural concerns. This suggests that behaviours often attributed to ovarian dysfunction may have other underlying causes, unrelated to hormonal changes. - Progesterone Levels Show No Clear Patterns
Progesterone levels varied widely among the samples. However, the study found no consistent pattern linking progesterone concentrations to the reported behavioural issues. While progesterone plays a role in regulating reproductive and behavioural cycles, its variability among mares without concurrent hormonal disorders suggests it is not a primary driver of abnormal behaviours. - Incidence of GCTs in the Sample Population
The study confirmed that GCTs were relatively rare among the sample population, further supporting the notion that most behavioural abnormalities in mares are not related to ovarian tumours. Elevated levels of the hormones typically associated with GCTs (testosterone, AMH, and inhibin A) were observed in only a small subset of cases. - Implications for Diagnosis and Management
The findings suggest that relying solely on hormonal assays to diagnose the causes of behavioural abnormalities in mares is insufficient. Instead, a more holistic approach, which includes thorough physical and behavioural assessments, is needed. The study highlights the importance of considering other potential factors such as pain, training issues, environmental stressors, and general health when addressing behavioural concerns.
Behaviour and Hormonal Misattributions: The Broader Implications
The study’s findings have significant implications for equine health management, especially in challenging behavioural cases. Historically, hormonal imbalances have often been blamed for a wide range of abnormal behaviours in mares, including aggression, unpredictability, and unwillingness to work. However, the data shows that these associations are likely overestimated.
Veterinarians: A Call for Comprehensive Diagnostics
For veterinarians, this study reinforces the value of a comprehensive diagnostic approach. Instead of focusing heavily on hormonal assays, veterinarians should consider factors such as:
- Pain or discomfort
- Environmental stressors (e.g., inadequate turnout or stabling conditions)
- Nutritional deficiencies
- Behavioural or psychological causes, including improper handling or training
Incorporating broader diagnostic protocols can ensure more accurate treatment plans and avoid unnecessary interventions.
Shifting the Diagnostic Paradigm: A Holistic View
The findings from Huggins et al. advocate for a paradigm shift in diagnosing behavioural abnormalities in mares. This shift moves away from focusing solely on hormonal imbalances and toward a more integrated, evidence-based approach.
- Behavioural Observation
Careful observation of the mare’s behaviour in various settings, such as under saddle, in-hand, and at liberty, can reveal valuable insights. For instance, reluctance to work may stem from physical discomfort rather than hormonal fluctuations. - Physical Examination
A full physical examination is critical to rule out pain or lameness as underlying causes of behavioural changes. Back pain, joint issues, or subtle signs of discomfort may explain aggression or resistance. - Environmental and Social Factors
Stress related to housing, feeding practices, or social interactions with other horses can profoundly affect a mare’s behaviour. Investigating these factors can provide clues to behavioural changes. - Targeted Hormonal Testing
Hormonal testing remains an essential tool, particularly in cases where ovarian abnormalities are suspected. However, this study shows that these tests should be used judiciously and not as a first-line diagnostic tool in all behavioural cases.
Future Directions in Research and Practice
The study opens the door for future research into the root causes of behavioural abnormalities in mares. Areas for further investigation include:
- The role of pain and discomfort in behavioural changes
- Psychological or neurological factors influencing behaviour
- Genetic predispositions to certain behavioural traits
- Advanced imaging and diagnostic techniques to detect subtle musculoskeletal or internal issues
For practitioners, this research highlights the need to educate clients about the multifactorial nature of equine behaviour. Veterinarians and equine behaviourists can work together to implement practical solutions tailored to the individual horse’s needs.
Practical Advice for Horse Owners
For horse owners dealing with behavioural challenges in mares, this study provides several takeaways:
- Stay Open-Minded: Don’t jump to conclusions about hormonal imbalances as the root cause of behavioural changes.
- Work with Professionals: Engage both a veterinarian and, if necessary, an equine behaviourist to explore the full range of potential causes.
- Observe and Document: Keep a journal of your mare’s behaviours, including when they occur and any potential triggers. This information can be invaluable for diagnostic purposes.
- Evaluate the Environment: Ensure your mare’s stabling, feeding, and social environment supports her mental and physical well-being.
Conclusions
This study by Huggins et al. challenges long-standing assumptions about the link between ovarian hormones and behavioural abnormalities in mares. The findings underscore the importance of broadening our diagnostic lens to include physical, environmental, and psychological factors.
By moving away from a narrow focus on hormonal imbalances, veterinarians and horse owners can achieve a deeper understanding of mare behaviour and provide more effective care. Whether managing a high-performance athlete or a beloved companion, this holistic approach promises better outcomes for mares and their handlers alike.