In at least one study, however, cows with cysts averaged 1.2 years older than cows without cysts and, therefore, would be expected to produce more milk. Other studies have found no relationship between cystic ovarian disease and level of production. Some cystic follicles continued to grow without producing estrogen, and less estrogen was found in follicular fluid from cystic follicles compared to normal follicles. In another study, there was no relationship between content of estrogen in fluid from cystic follicles and behavior of the cow. Thus the relationship between ovarian cysts and level of production of milk still is not well documented.
Incidence increases up to the fourth or fifth lactation in dairy cows.
Beef cows develop cysts after 4 to 6 years of age even if never bred. Yet, no relationship was found between lactation number and incidence of cystic ovaries in 324 cows in the university herd in another study. Presumably, different culling practices for reproductive inefficiency removed many cows predisposed to cystic development before it occurred. The greatest incidence of ovarian cysts occurs Within the first 45 to 60 days postpartum and during October through February. The functional relationship between the ovaries and the pituitary gland was established in the 1920s.