Differentiating Rigs From Geldings

Horses showing rig-like behavior can be tested with one of three methods to identify cryptorchidism, depending on the age of the horse.

Anti-Mullerian Hormone

AMH is produced by the Sertoli cells and is therefore a biomarker of testicular tissue, allowing for distinction between cryptorchid and castrated horses. This test is suitable for horses over 18 months of age.

Sample requirements for AMH: 3ml of blood in a plain (clot) tube.

Oestrone Sulphate

In horses 3 years or older, a single test for oestrone sulphate will distinguish between rigs and geldings. The equine testis is unusual in that it produces more than 10 times as much oestrogen as testosterone. In this group it is recommended that oestrone sulphate levels be measured as commercially available testosterone kits are not sensitive enough to detect the small variations in baseline testosterone between geldings and rigs.

Sample Requirements for Oestrone Sulphate

2.5 ml of blood in a plain (clot) tube.

hCG Stimulation Test

In horses 2 years or younger and donkeys of any age, dynamic screening of testosterone with a hCG stimulation test levels is the recommended procedure.

Protocol and Sample Requirements for the hCG Stimulation Test

  1. Collect 5 ml of blood in a plain (clot) tube.
  2. Inject at least 6000 IU of hCG IV (always check the product sheet for accurate dosing rates and precautions).
  3. Wait 30 minutes to 2 hours.
  4. Collect 5 ml of blood in a plain (clot) tube.
  5. Make sure that both tubes are accurately labelled.

Other Species:

The hCG stimulation test can be used to detect cryptorchidism in other species, but the dose of hCG required will vary. Consult the package insert for more dose details and precautions.