Stallion-Like Behavior in Male Castrated Thoroughbred with Non-Secretory Inguinal Mass

A six-year-old castrated male Thoroughbred was presented to the North Carolina State Theriogenology Service for stallion-like behavior and a serum estrone sulfate concentration of 17.50 ng/ml (reference: gelding <5 ng/ml; stallion/cryptorchid >10 ng/ml), consistent with cryptorchidism. Transrectal ultrasonography detected no structures resembling a retained testicle. A human chorionic gonadotropin (hCG) stimulation test was performed and blood collected before and two hours after administration of 6000 IU of hCG intravenously. Serum was submitted to University of Caifornia- Davis Clinical Endocrinology Laboratory for measurement of anti-Mullerian hormone (AMH) and testosterone concentrations. The concentration of AMH was 0.1 ng/ml (reference: cryptorchid >0.15 ng/ml) and testosterone concentrations pre-hCG and post-hCG stimulation were 7.7 ng/ml and 17.7 ng/mL, respectively (reference: gelding <15 ng/ml; inconclusive 50-100 ng/ml; cryptorchid 100-500 ng/ml). [...]