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 WITHA NORMAL LH SURGE, NO DETECTABLE LH SURGE, AND PROGESTIN INHIBITION OF LH SURGE

Crossbred heifers (n = 103) were synchronized to estrus with prostagla ndin (PGF(2 alpha)) and superovulated with follicle stimulating hormon e (FSH-P). Animals were ovariectomized every 12 hr after the PGF(2 alp ha) 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 im plants 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 matur ation and quality. Follicular fluid was collected and analyzed for pro gesterone, estradiol, prolactin, and glycosaminoglycan content in conj unction with cumulus maturation and nuclear stage of oocyte maturation . Analysis of in vivo matured oocytes by in vitro fertilization was ca rried out at 60, 72, 84, and 96 hr post PGF(2 alpha) and in vitro matu red oocytes at 12 to 108 hr post PGF(2 alpha). No developmental change s in cumulus cells surrounding the oocyte of small follicles was noted (less than or equal to 4 mm dia) indicating a static population. Medi um (> 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 estrad iol-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 foll icles from animals without a detectable LH surge seem to indicate earl y maturation (48 to 72 hr post PGF(2 alpha)) in conjunction with a hig h percent of degenerate oocytes not seen in animals exhibiting an LH s urge. Oocytes from medium size follicles matured to germinal vesicle b reakdown (GVBD) and early meiosis (metaphase I; MI) stages of developm ent in all treatments. Most oocytes were degenerate in Norgestomet-imp lanted animals. Oocytes from large follicles (> 8 mm dia) from animals exhibiting an LH surge were in MI and metaphase II (MII) stages (48 t o 84 hr post PGF(2 alpha)) in preparation of ovulation whereas oocytes from animals not exhibiting an LH surge had oocytes that early mature d to MII (48 to 72 hr post PGF(2 alpha)), later regressing to degenera te oocytes (84 to 108 hr). Follicular progesterone, estradiol, and pro lactin increased with oocyte maturation, particularly in medium and la rge follicles. In vivo matured oocytes for fertilization (60, 72, 84, and 96 hr post PGF(2 alpha)) were nude (from the oviduct) and primaril y CR from follicles. Tubal oocytes (37%) were fertilized more frequent ly by a single sperm than follicular oocytes (14.3%; P < .01) and sing le sperm penetration peaked at 72 hr post PGF(2 alpha). Follicular hor mone 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 aspir ated follicles (68.2%; P < .05), with a peak penetration at 32 follicl es (86.7% penetration). No treatment differences (LH surge or no detec table LH surge) were noted in relation to in vivo matured oocytes. Ooc ytes with single sperm penetration had the lowest estradiol/progestero ne ratio of 2.2 vs polyspermic penetration of 13.7.