Effect of estrual stage on complement activity in bovine follicular fluid

Ovaries were excised from 112 cows during specific stages of the estrous cycle and from cows with follicular cysts. Follicular fluid was collected from the largest follicle at estrus (d 1), metestrus (d 2 to 4), early diestrus (d 5 to 8), mid diestrus (d 9 to 14), late diestrus (d 15 to 18), proestrus (d 19 to 21), and from follicular cysts. Complement was measured with a standard hemolytic assay. Complement in follicular fluid varied with stage of cycle and was two to five times higher at estrus than at diestrus. Complement in follicular fluid was 5 to 22-fold higher than in blood serum. Blood complement was not influenced by stage of cycle. Cystic follicular fluid had complement amounts similar to that of metestrus follicles. The relationships of complement to ovulation, sperm maturation, fertilization, and sperm removal from the tract are discussed.