Merck Manual

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Professional Version

Cystic Ovary Disease in Mares


Jonathan Statham

, MA, VetMB, DCHP, MRCVS, Bishopton Veterinary Group

Last full review/revision Feb 2015 | Content last modified Feb 2015
Topic Resources

When diagnosing the reproductive status of mares, it must be remembered that follicles during estrus are normally 4–6 cm in diameter. Ovulation failure can also be seen in mares having irregular estrous cycles during the spring or fall transition phases of the reproductive cycle, but this state is not treated in the same way as the cystic ovary disease condition of cattle. The granulosa cell tumor condition in mares causes marked enlargement of one ovary but differs from cystic ovary disease of cattle.

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