The Badly Behaved Gelding – Hormonally Driven or Not?

The Badly Behaved Gelding“That is a badly behaved gelding – he must be ‘proud cut'” or “I bet they left some testicular tissue in that badly behaved gelding” are two not infrequently-heard comments, or variations thereof, but how often is residual stallion-like or bad behaviour in a castrated stallion actually hormonally-driven? Omyla et al presented a retrospective review of hormonal profile results from the UC Davis Endocrinology Laboratory which had been requested between 2011-2020. This involved 1,202 animals which were suspected cryptorchids and had associated behavior complaints.

Unsurprisingly, the most commonly-requested assay was for testosterone – requested in 1,056 cases. Anti-Müllerian hormone (AMH) – a useful and definitive marker for cryptorchidism – was requested in a further 877 cases, with both profiles being tested in 790 cases.

The results were not, we are sure, what many of those “badly behaved gelding” owners were expecting!

82.8% (875/1,056) of testosterone assays showed levels below the range indicating a cryptorchid, with similar results for AMH, where 77.8% (682/877) indicated absence of cryptorchid levels. When both levels were evaluated in the same animal, 77% (608/790) were below the cryptorchid/stallion-like concentrations. These threshold levels are indicative of the presence or absence of retained testicular tissue.

A further sub-set of behavioural responses, where aggression was shown towards other animals or humans, but without sexual-like responses produced similar results. In those 54 animals, 79.6% returned levels lower than that which would indicate testicular tissue presence.

The results of this study produce statistically similar figures in all categories. With approximately 80% of tested animals which displayed what was described as inappropriately aggressive behavior to either humans or other animals showing an absence of hormonal levels which would be expected to drive such behaviour, other causes obviously need to be considered. Such causes may be likely to include later castration, where learned behaviour has occurred, as well as simply the manner in which the animals are routinely handled or managed being encouraging of such responses. It should also be considered that the definition of a “badly behaved gelding” will tend to be subjective and could well vary from one person to another. The overall point however was that in the vast majority of such animals, there is no retention of testicular tissue leading to the elevation of those behaviour-inducing hormones. The so called “proud cut gelding” is therefore quite a rarity!

(Omyla K, Conley A, Dini P. 2023. Persistent stallion-like behavior is rarely associated with changes in hormonal markers in the equine cryptorchid suspects: a retrospective study. JEVS 125:104607)