Limited association between stallion-like behavior and hormonal indicators of testicular remnants in geldings.
Authors: Omyla K, Conley A, Varner D, Dini P
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Stallion-like Behaviour in Geldings — Not Always About Hidden Testicular Tissue When a supposedly gelded horse exhibits stallion-like behaviours, cryptorchidism (retained testicular tissue) is often suspected, yet this retrospective analysis of 1,202 geldings with such behaviours reveals a more nuanced picture. The researchers measured serum testosterone and anti-Müllerian hormone (AMH) concentrations — established markers for detecting testicular remnants — finding that over 80% of behaviourally problematic geldings had hormone levels consistent with complete castration. Intriguingly, only 1.8% showed testosterone elevation without corresponding AMH elevation, whilst 4.3% displayed elevated AMH (suggesting cryptorchidism) despite normal testosterone levels, highlighting a concerning disconnect between these biomarkers. Among confirmed cryptorchids, age influenced both hormone concentrations whilst seasonal variation remained negligible. These findings suggest that behavioural issues in geldings warrant investigation beyond hormonal screening alone; factors including learned behaviour, pain, neurological conditions, or incomplete behavioural retraining may warrant equal consideration, fundamentally reshaping how practitioners approach diagnosis and management of these cases.
Read the full abstract on PubMed
Practical Takeaways
- •Stallion-like behavior in geldings is rarely due to missed testicular tissue—investigate other behavioral or management factors before assuming cryptorchidism
- •Hormone testing (testosterone and AMH) can help rule out cryptorchidism but results may not always align; interpret patterns rather than single values
- •Behavioral issues in geldings require a broader diagnostic approach beyond endocrine evaluation, including consideration of learned behavior, environmental triggers, and neurological factors
Key Findings
- •80.6% of geldings with stallion-like behavior had testosterone below cryptorchid reference range (<60 pg/mL), indicating testicular tissue is not present in most behaviorally problematic geldings
- •77.8% of behaviorally affected geldings had AMH below cryptorchid threshold (≤0.15 ng/mL), further suggesting absent testicular tissue
- •4.3% of samples showed elevated AMH suggesting cryptorchidism but normal testosterone, indicating hormonal discordance in some cases
- •Age affected both AMH and testosterone concentrations in presumptive cryptorchid stallions, while season had no effect