Presumptive diagnosis by ultrasound should be confirmed cytogenetically. Many of the fetuses diagnosed prenatally with Turner's syndrome are electively terminanted. X Chromosome Monosomy in Mice XO mice have been reported to be fertile and have histologically normal ovaries. However, quantitative histology on such ovaries collected between 12 and 200 days of age revealed that they had approximately half the number of oocytes as their XX siblings - even at day 12 of life, the population of growing follicles was clearly retarded. Turner's Syndrome in Mares X monosomy appears to be a relatively common cytogenetic disorder in mares.
Affected animals appear normal externally, but with a smaller than normal vulva.
The uterus is also small, the cervix usually open and flaccid and the ovaries range in size from small to very small. Most XO mares fail to cycle, although some show sporadic or indistinct periods of estrous behavior. This abnormality should definitely be put on a list of differential diagnoses for any cases of unexplained reproductive failure, particularly if associated with genital tract infantilism. Gonadal dysgenesis in the mare.