Equine Inhibin Testing

Equine Inhibin Testing

Implementation of a New Inhibin (inhibin-B) Assay for Horses

For over 2 decades now, the Clinical Endocrinology Laboratory has been the only laboratory in the world offering inhibin as a test to aid in diagnosing equine reproductive problems including most notably, granulosa-theca cell tumors (GCTs). This test was established using reagents purchased decades ago which have finally run out. In an effort to maintain this diagnostic aid, we partnered with a commercial supplier of hormone assays and have been able to validate a new inhibin assay for horses. Our studies show that the new test is more specific for certain isoforms of inhibin, and that GCTs primarily secrete the isoform called inhibin-B. Inhibin-B circulates in blood in a much lower concentration range and as a result we have had to re-establish our reference ranges that are now very different.

               The results of our assay development studies suggest that the new inhibin-B assay is equally useful diagnostically, as sensitive as the old assay, especially when coupled with AMH and testosterone. As with all assays, our ability to distinguish false positives (inhibin is high at ovulation in mares that are still cycling) from true positives in GCT cases relies on case history and clinical findings in consultation with the attending veterinarian. As always, we are grateful for any and all information and feedback we receive from clients as regards final diagnostic confirmation on submitted cases. This helps us to build our data base of cases with the greatest accuracy retrospectively. We are proud of our efforts and ability to develop new or better tests of clinical value that enable us to continue serving the equine industry, and thank you for your support over the years.

Dr. Alan J. Conley, BVSc, MS, PhD, FRCVS


UC Davis Endocrinology Laboratory 1089 Veterinary Medicine Dr. 3230 VM3B Davis, CA 95616 Phone: (530) 752-0298 Fax: (530) 752-6318

Recommendations for sample submission for new inhibin test, effective the week of August 21st,2017

  1. Serum requirements will be the same: we suggest 1 ml for inhibin alone, and 3 ml per panel.
  2. Inhibin is a heat sensitive protein. Store the separated serum in the fridge or freezer if you are not able to ship immediately. Please send overnight on an ice pack, and don’t ship to arrive on weekends or holidays. We also close the lab for one week between Christmas and New Year’s.
  3. We suggest progesterone testing for cases of high inhibin in cyclic mares.
  4. We recommend a panel including AMH, inhibin and testosterone for the most accurate interpretation of test results.
  5. We have not yet established reference ranges for stallions or geldings but will soon. 
  6. We have not established reference ranges for mules, donkeys or pregnant mares but have plans to do so.
  7. We have not established reference ranges for cattle, alpacas, or goats.