A REVIEW AND AN UPDATE OF CYSTIC OVARIAN DEGENERATION IN RUMINANTS

We reviewed all the reports to date concerning the pathological conditions in the organs integrating the hypothalamic-hypophyseal-gonadal axis in ruminants with cystic follicles as well as the causative factors associated with the disease, emphasizing the role of uterine infections and stress. At the hypothalamic-pituitary level, most data available suggest that neither pituitary sensitivity to GnRH, nor pituitary content of gonadotropins are consistently altered in cows with cystic follicles. However, the scarce information on hypothalamic GnRH content indicates that unbalanced distribution between nuclei involved in basal LH secretion and preovulatory LH surge might be a key factor in the development of cystic follicles. The reports on the altered release of LH and FSH associated with cystic follicles are inconsistent. However, their role is clearer in those studies where cysts are classified according to their histological appearance, their steroidogenic capacities or their response to GnRH treatment. Some relevant histological studies, often overlooked, are reviewed and the correlation between histochemical findings and steroidogenic capacity is emphasized. Metritis and stress are two instances in which high plasma concentrations of cortisol might lead to cyst formation at the pituitary level (suppression of the preovulatory LH surge) and at the follicular level (alteration of steroidogenesis, reduced concentration of LH receptors).