An XY agonadal Oldenburg warmblood horse exhibiting a male phenotype.

In a 1.5-year-old Oldenburg horse, a clitoris-like structure instead of a penis was identified in the prepuce. The external genital organs did not show any abnormalities at visual inspection except that exteriorization of the penis was not possible, not even under general anesthesia. The horse's owner observed a continuous dripping of urine and a tendency to mild colics beginning 2 weeks after birth. Testosterone concentration was 0.01 ng/ml and therefore under the threshold for geldings, and the horse did not respond to the application of gonadotropin-releasing hormone (GnRH). The inner genital consisted of a male urinary tract. Gonads and accessory male glands were missing. Residual structures of a female genital tract were not observed. Abnormalities of the mesentery could be found which might explain the recurrent colics of this horse. A cytogenetic examination revealed a 2n = 64,XY-karyotype and a positive result for the SRY-PCR. This is the first report on an agonadal horse with a male karyotype and a pseudohermaphrodite phenotype.