CUMULUS AND OOCYTE MATURATION AND IN-VITRO AND IN-VIVO FERTILIZATION OF OOCYTES IN RELATION TO FOLLICULAR STEROIDS, PROLACTIN, AND GLYCOSAMINOGLYCANS THROUGHOUT THE ESTROUS PERIOD IN SUPEROVULATED HEIFERS WITH A NORMAL LH SURGE, NO DETECTABLE LH SURGE, AND PROGESTIN INHIBITION OF LH SURGE

Crossbred heifers (n = 103) were synchronized to estrus with prostaglandin (PGF(2 alpha)) and superovulated with follicle stimulating hormone (FSH-P). Animals were ovariectomized every 12 hr after the PGF(2 alpha) injection (n = 7 to 9/time) up to 108 hr to monitor the follicular, hormonal, and oocyte changes associated with follicular development and ovulation. Twenty-eight animals were implanted with Norgestomet implants 12 hr before PGF(2 alpha) and ovariectomized at 72, 84, 96, and 108 hr post PGF(2 alpha) injection to monitor effects of progesterone and suppression of the luteinizing hormone (LH) surge on oocyte maturation and quality. Follicular fluid was collected and analyzed for progesterone, estradiol, prolactin, and glycosaminoglycan content in conjunction with cumulus maturation and nuclear stage of oocyte maturation. Analysis of in vivo matured oocytes by in vitro fertilization was carried out at 60, 72, 84, and 96 hr post PGF(2 alpha) and in vitro matured oocytes at 12 to 108 hr post PGF(2 alpha). No developmental changes in cumulus cells surrounding the oocyte of small follicles was noted (less than or equal to 4 mm dia) indicating a static population. Medium (> 4 less than or equal to 8 mm) and large size (> 8 mm) follicles developed to the corona radiata and loose cumulus stages in animals in which an LH surge was detected but cumulus status remained primarily in the tight cumulus stage for animals without an LH surge. The estradiol-to-progesterone ratio for tight cumulus (TC), corona radiata (CR), and loose cumulus (LC) stages was 1.8 +/- .1, 1.0 +/- .1, and.4 +/- .2, respectively (P < .01). Nuclear maturation of oocytes in small follicles from animals without a detectable LH surge seem to indicate early maturation (48 to 72 hr post PGF(2 alpha)) in conjunction with a high percent of degenerate oocytes not seen in animals exhibiting an LH surge. Oocytes from medium size follicles matured to germinal vesicle breakdown (GVBD) and early meiosis (metaphase I; MI) stages of development in all treatments. Most oocytes were degenerate in Norgestomet-implanted animals. Oocytes from large follicles (> 8 mm dia) from animals exhibiting an LH surge were in MI and metaphase II (MII) stages (48 to 84 hr post PGF(2 alpha)) in preparation of ovulation whereas oocytes from animals not exhibiting an LH surge had oocytes that early matured to MII (48 to 72 hr post PGF(2 alpha)), later regressing to degenerate oocytes (84 to 108 hr). Follicular progesterone, estradiol, and prolactin increased with oocyte maturation, particularly in medium and large follicles. In vivo matured oocytes for fertilization (60, 72, 84, and 96 hr post PGF(2 alpha)) were nude (from the oviduct) and primarily CR from follicles. Tubal oocytes (37%) were fertilized more frequently by a single sperm than follicular oocytes (14.3%; P < .01) and single sperm penetration peaked at 72 hr post PGF(2 alpha). Follicular hormone concentrations were not related to sperm penetration. Oocytes (n = 101) matured in vivo had lower fertilization potential from ovaries producing < 14 or > 50 follicles (39.3%) as compared to 21 to 45 aspirated follicles (68.2%; P < .05), with a peak penetration at 32 follicles (86.7% penetration). No treatment differences (LH surge or no detectable LH surge) were noted in relation to in vivo matured oocytes. Oocytes with single sperm penetration had the lowest estradiol/progesterone ratio of 2.2 vs polyspermic penetration of 13.7.