Persistent stallion-like behavior is rarely associated with changes in hormonal markers in the equine cryptorchid suspects: a retrospective study

Abstract

Listen

Translate article

Persistent stallion-like and/or aggressive behavior is a common symptom of cryptorchidism or incomplete castration in supposed geldings. Hormones secreted by Leydig and Sertoli cells in testicular tissues, such as testosterone and/or anti-Müllerian hormone (AMH), can be used to evaluate the possible presence of testicular tissues in suspected cryptorchids. Currently, there is little known about the association between the presence of testicular tissue and the prevalence of persistent stallion-like behavior in cryptorchids. In the current study, we evaluated the association between abnormal behaviors and concentrations of AMH and testosterone. From the samples submitted to the UC Davis Endocrinology Laboratory between 2011-2020, 1,202 cases were suspected cryptorchids with behavior complains. These cases included the words “behavior”, “behave”, and/or “behaving” in their submitted histories. Testosterone was the most frequently requested hormone among all the samples. Of the 1,202 cases, testosterone was measured in 1,056 samples (∼88%). Interestingly, in the majority of these cases (875/1,056; 82.8%), the measured concentrationof testosterone was below the laboratory range for cryptorchids (>100pg/ml). Similarly, among 877 samples submitted for AMH measurement, 682 (77.8%) did not reach cryptorchid/stallion-like concentrations (>0.15 ng/ml), indicating an absence of any testicular tissue. Both hormones were measured in 790 cases and both values were below the cryptorchid/stallion-like concentration in 608 of the cases (77%). There was a significant correlation between the concentration of both hormones among the samples (r=0.84; P<0.0001). Additionally, 54 samples that were submitted with a history of aggressive behavior towards people or other horses, but without reported sexual/‘stud-like’ behavior, were analyzed. In 43 cases (79.6 %) both hormones (AMH and testosterone) did not reach cryptorchid-like concentrations. Among the remained 11 horses, all had elevated concentrations of AMH and three cases had elevated concentrations of both AMH and testosterone. The results of this study demonstrate that undesirable behaviors in geldings are rarely associated with presence of testicular tissue as indicated by biomarkers such as AMH and testosterone.