THE ‘PROUD-CUT’ Patrick M. McCue DVM, PhD, Diplomate American College of Theriogenologists

Misconceptions abound as to the cause of evaluation of level in a single persistent -like behavior in a blood sample may not be sufficient to that has been gelded. The term ‘proud-cut’ differentiate a gelding from a cryptorchid has been used historically for many of these stallion. In those instances, a test called an cases. Traditionally, the term ‘proud-cut’ ‘hCG stimulation test’ may be used. A implies that a part of the epididymis (sperm blood sample is collected just prior to storage site located adjacent to the testes) administration of the hormone human was left in the horse at the time of . chorionic gonadotropin. A second blood Normally each testis and associated sample is collected 1 to 2 hours later. The epididymis is removed during castration. hCG will cause an increase in testosterone However, since the epididymis does not secretion from testicular tissue present in produce testosterone, leaving the structure in cryptorchid (or intact) . No increase a horse would not lead to a continuation of in testosterone will be elicited in true stallion behavior. that are castrated . The table below outlines at an older age may retain some stallion-like testosterone levels prior to and 1 to 2 hours behaviors. Although the source of after administration of hCG in geldings, testosterone has been removed, some cryptorchids and intact stallions. learned behaviors may persist. Testosterone (pg/ml) Hormonal diagnostic tests are available to Horse Pre-hCG Post-hCG determine if a horse is a true gelding or a Gelding < 100 No change cryptorchid stallion. The most commonly Cryptorchid 100-500 Increase used test is the measurement of testosterone Intact Stallion > 500 Increase levels in the blood. Testosterone is produced by cells within the testes. In the While cryptorchid testes continue to produce absence of testicular tissue, testosterone testosterone, sperm production within the levels in the blood should be very low (i.e. cryptorchid testes is inhibited due to the less than 100 pg/ml). Intact stallions with higher temperatures within the as two scrotal testes usually have blood compared to within the . testosterone levels of 500 to 1,000 pg/ml or Consequently, horses with two cryptorchid higher. Testosterone level in cryptorchid testes may tease , gain an , stallions is higher than that of geldings and mount and even ejaculate, but are infertile. usually lower than that of intact stallions (i.e. 100 to 500 pg/ml). Unfortunately,

1 It is generally recommended that the retained testes be removed from cryptorchid stallions. Affected horses may exhibit aggressive or stallion-like behavior and have a slightly increased risk of medical conditions such as testicular tumors and torsion of the spermatic cord.

Ultrasound photo of cryptorchid testis in a horse

Drawing of the testis and epididymis in a horse

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