Just because a particular type of anomaly in a horse is rare doesn't mean it's not important to investigate and understand better: Take granulosa cell tumors (GCTs), for instance. While these only represent about 2.5% of all equine tumors and usually are benign, GCTs are most common neoplasm (tumor) found in the equine reproductive tract; further, GCTs are difficult to diagnose and can cause a host of problems in affected mares including pregnancy prevention and behavioral problems (i.e., stallion-like behavior).
Veterinarians often detect a GCT during a routine palpation or rectal ultrasound, and currently veterinarians rely on endocrine tests--measuring blood levels of certain hormones such as inhibin, testosterone, and progesterone--to confirm suspicions of a GCT.
However, Barry A. Ball, DVM, PhD, Dipl. ACT, Albert G. Clay Endowed Chair in Equine Reproduction at the University of Kentucky's Maxwell H. Gluck Equine Research Center, described an alternate blood test that involves measuring the anti-Müllerian hormone (AMH) in his presentation at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.
"My colleagues and I recently discovered that high levels of AMH are produced by GCTs, which circulate in the bloodstream," relayed Ball.
To determine AMH levels were significantly different in mares with and without GCTs, Ball et al. collected blood samples from six mares during estrus, six pregnant mares, six mares that had undergone ovariectomy (had both ovaries removed), and 74 mares with GCTs. Subsequently, the researchers compared the groups' AMH levels and also compared the accuracy of using AMH levels to diagnose GCTs to that of the inhibin and testosterone diagnostic assays currently in use.
Key findings of the study were:
- AMH levels were significantly higher in mares with GCTs than in pregnant mares, those in estrus, and those that had undergone ovariectomy; and
- High AMH levels allowed correct diagnosis of GCTs in 70/74 (95%) of mares, whereas inhibin and testosterone assays only correctly diagnosed GCTs in 63 (85%) and 40 (54%) of the 74 mares, respectively.
"This study confirms that AMH is considerably higher in mares with GCTs than all other healthy mares regardless of their reproductive status and that measuring AMH levels is a useful test for GCTs," affirmed Ball.
The AMH test is currently available as a human assay. "We are currently working on assays that might be more affordable for the horse (industry)," said Ball.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.