MEASURING FECAL ESTROGENS FOR THE DIAGNOSIS OF CRYPTORCHIDISM IN HORSES

The measurement of androgens and estrogens in blood has been widely utilized to differentiate geldings from horses with testicular tissue. Estrogens are excreted in part via feces and can be quantified by immunoassay. Therefore a diagnosis of cryptorchidism based on the determination of fecal estrogens was established. The concentration of unconjugated estrogens was measured in fecal samples of normal stallions (n=63), cryptorchid horses (n=34) and geldings (n=125). In addition the concentration of conjugated estrogens and testosterone in blood samples was measured. Mature stallions had fecal estrogen concentrations in the range of 59 to 398 nmol/kg (median: 130) whereas that of geldings ranged from I to 38 nmol/kg (median: 12). Stallions with one undescended testis (n=18) had concentrations of 60 to 322 nmol/kg (median: 113), which were indistinguishable from those of normal stallions. Fecal estrogen concentrations of bilateral (n=9) and hemicastrated (n=7) cryptorchid horses ranged from 34 to 222 nmol/kg (median: 64) and differed (p<0.001) from those of stallions and geldings. By measuring fecal estrogens it was possible to detect testicular tissue in mature horses with good accuracy, similar to that by using steroid determinations in blood. Therefore this study suggests that the determination of estrogens in feces is a useful tool for the diagnosis of equine cryptorchidism with an easy, noninvasive collection of samples.