Endocrine alopecia is caused by ovarian cysts, very common in guinea pigs even though not always secretory, which induce symmetrical hair loss starting from the flanks and extending to the rear quarters. The skin appears glabrous and without other lesions. If the cysts are big they can be detected by palpation of the abdomen. The diagnosis is made by radiography or ultrasonography. The degree of alopecia is not related to the size of the cysts.
Pregnancy-related alopecia occurs at the end of the pregnancy, when the sow loses hair from the lumbar-sacral area and flanks, and is due to hair shedding in the telogen phase. It is often associated with over-intensive reproduction. The alopecia resolves spontaneously after delivery but can recur in a more severe form in subsequent pregnancies if these occur at too short intervals.
A congenital form of alopecia has been described, with complete or almost complete absence of hair from the whole body. The diagnosis can be confirmed, if considered necessary, by biopsy.