Mature gilts classified by low (12 to 16 corpora lutea [CL], n = 6) or high (17 to 26 CL, n = 5) ovulation rate (OR) were compared for plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol-17beta, and inhibin during an estrous cycle. Gilts were checked for estrus at 8-h intervals beginning on d 18. Blood samples were collected at 8-h intervals beginning on d 18 of the third estrous cycle and continued for one complete estrous cycle. Analysis for FSH and LH was performed on samples collected at 8-h intervals and for ovarian hormones on samples collected at 24-h intervals. The data were standardized to the peak of LH at fourth (d 0) and fifth estrus for the follicular phase and analyzed in discrete periods during the periovulatory (-1, 0, +1 d relative to LH peak), early-luteal (d 1 to 5), mid-luteal (d 6 to 10), late-luteal (11 to 15), periluteolytic (-1, 0, +1 d relative to progesterone decline), and follicular (5 d prior to fifth estrus) phases of the estrous cycle. The number of CL during the sampling estrous cycle was greater (P < 0.005) for the high vs low OR gilts (18.8 vs 14.3) and again (P < 0.001) in the cycle subsequent to hormone measurement (20.9 vs 14.7). For high-OR gilts, FSH was greater during the ovulatory period (P = 0.002), the mid- (P < 0.05) and late-luteal phases (P = 0.01), and tended to be elevated during the early-luteal (P = 0.06), but not the luteolytic or follicular periods. LH was greater in high-OR gilts during the ovulatory period (P< 0.005), but not at other periods during the cycle. In high-OR gilts, progesterone was greater in the mid, late, and ovulatory phases (P < 0.005), but not in the follicular, ovulatory, and early-luteal phases. Concentrations of estradiol-17beta were not different between OR groups during the cycle. Inhibin was greater for the high OR group (P < 0.005) during the early, mid, late, luteolytic, and follicular phases (P < 0.001). The duration of the follicular phase (from last baseline estrogen value to the LH peak) was 6.5 +/- 0.5 d and was not affected by OR group. These results indicate that elevated concentrations of both FSH and LH are associated with increased ovulation rate during the ovulatory phase, but that only elevated FSH during much of the luteal phase is associated with increased ovulation rate. Of the ovarian hormones, both inhibin and progesterone are highly related to greater ovulation rates. These findings could aid in understanding how ovulation rate is controlled in pigs.

Advances in porcine in vitro fertilization have been impaired by low normal fertilization rates resulting from a high rate of polyspermy. The present study was undertaken to determine the effects of porcine follicular fluid (pFF) and oviductal explant-conditioned medium on maturation and fertilization of porcine oocytes in vitro. Oocytes and pFF were collected from small, medium, and large follicles and pooled within size category. Maturation and fertilization media were supplemented (10%) with either fetal calf serum (FCS) or pFF (either fresh or snap-frozen). Snap-frozen pFF from small (3.1-5.0 mm) and medium (5.1-7 mm) follicles, respectively, increased maturation rates of oocytes from small and medium follicles by nearly 36% (p < 0.05) compared with those treated with FCS or fresh pFF. Supplementing media with either fresh or snap-frozen pFF from medium follicles reduced (p < 0.05) polyspermy of oocytes from small follicles by 30% compared with supplemental FCS. Snap-frozen pFF increased (p < 0.05) normal fertilization compared to that in fresh pFF (29% vs. 18%). Supplementing oocytes from medium follicles with snap-frozen pFF yielded the lowest (18%, p < 0.05) polyspermy rate. Oocytes from both small and medium follicles supplemented with pFF and/or conditioned medium (CM) from oviducts of periovulatory gilts exhibited a 95% improvement in normal fertilization rate and a 34% decrease in polyspermy rate compared to those treated with FCS (p < 0.05). CM from oviducts of luteal gilts did not improve rates of polyspermy and normal fertilization (p > 0.05). We conclude that snap-frozen follicular fluid from medium follicles and CM from cultured oviducts of periovulatory gilts improve in vitro maturation, reduce polyspermy, and increase normal fertilization rates in vitro.

In situ hybridization was used to map anatomical patterns of insulin-like growth factor (IGF) system gene expression in the gilt ovary through the estrous cycle. IGF-I, IGF-II< and IGF-I receptor messenger RNAs (mRNAs) were coexpressed in granulosa cells of developing and dominant follicles through the follicular phase. IGF-I and IGF-I receptor mRNAs were selectively concentrated in healthy follicles, whereas IGF-II mRNA was found in all follicles regardless of incipient or overt atresia. IGF-binding protein-1 (IGFBP-1) was not detected in the gilt ovary at any stage. IGFBP-2 mRNA was most abundant in granulosa cells of small follicles and in the ovarian vasculature regardless of cycle stage. IGFBP-2 mRNA persisted in granulosa cells of preovulatory follicles and corpora lutea. IGFBP-3 mRNA was not detected in developing follicles, but was detected in all luteal phase corpora lutea, apparently expressed by theca lutein cells. IGFBP-4 demonstrated a highly dynamic pattern of gene expression, closely tracking LH receptor gene expression throughout the follicular and luteal phases of the estrous cycle. IGFBP-4 mRNA was concentrated in the theca of medium to large growing follicles, but was not detected in granulosa cells until the emergence of dominant follicles in the late follicular stage, when the granulosa cells showed morphological evidence of luteinization as well as LH receptor gene expression. IGFBP-4 mRNA expression continued in granulosa cells of corpora lutea during the luteal phase and was not detected in atretic follicles. IGFBP-5 mRNA was concentrated in the surface or germinal epithelium and in capillary endothelium, particularly in capillaries of corpora lutea. In summary, there is selective expression of IGF-I, IGF-I receptor, and IGFBP-2 and -4 mRNAs during the process of follicular selection in the gilt ovary, with IGFBP-4 expression being closely associated with follicular selection and luteinization. These observations support an important role for autocrine/paracrine IGF action modulated by IGFBP-2 and -4 in both follicular growth and differentiation in the porcine ovary.