Follicular cysts in dairy cows

Follicular cysts are the most critical reproductive disorder in dairy cows and disturb normal ovarian cycle, resulting in the prolonged interval from calving to conception. Therefore, this condition causes significant economic losses to the dairy industry. Two direct causal factors of cyst are suggested in this review; the disorder of ovulation and the delay of regression. The disorder of ovulation has been accepted to be a main etiology of cystic follicle. This seems to be caused by the deficiency of positive feedback of estrogen to the hypothalamus, leading to the lack of LH surge. On the other hand, if large anovulatory follicle is regressed immediately after the failure of ovulation, its follicle does not grow more, resulting in no cystic follicle formed. Therefore, it is proposed that another cause of cystic follicle is a delay (lack) of degeneration system of follicle. This review will introduce these two causes separately referring to recent advances about follicular cyst in dairy cows. 5