Changes in circulating concentrations of testosterone and estrone sulfate after human chorionic gonadotropin administration and subsequent to castration of 2-year-old stallions.

The research examined the optimal times for sampling levels of testosterone (T) and estrone sulfate (E1S) in stallions after the administration of human chorionic gonadotropin (hCG) and post-castration. It found that T concentration peaked 72 hours after hCG administration and levels were significantly reduced 24 hours after castration.

Objective

• The researchers aimed to determine the optimal sampling times for T and E1S after hCG administration and the half-life of these steroids after castration. This is important for diagnosing cryptorchidism in horses (the condition in which one or both of the testes fails to descend) and confirming complete removal of testicular tissue after castration.

Methodology

• The study subjects were eight pony stallions divided into control or treatment groups. The treatment group was administered a 5000 IU dosage of hCG. Blood samples were collected after the hCG administration and following castration.

Findings

• The T concentrations peaked at 72 hours after hCG administration, with levels significantly higher in the treated group than in the control group.
• No significant changes in E1S concentrations were observed after the administration of hCG.
• The T response to hCG administration was found to be biphasic (having two phases), with a maximum response occurring between 48-96 hours after administration.
• The half-lives of T and E1S post-castration were revealed to be 1.1 and 0.7 hours, respectively.
• Concentrations of T and E1S were similar to those of castrated male horses (geldings) 24 hours post-castration. Based on these results, the researchers suggest that this 24 hour post-castration time-point should be considered optimal for testing to ensure complete castration has occurred.

Conclusion

• The study provides valuable insights for veterinary practitioners regarding the optimal times to assess levels of T and E1S for diagnosing cryptorchidism and verifying complete castration in stallions. It also contributes to a better understanding of the physiological responses to hCG administration and castration in horses.