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Experiments were conducted in beef cows without a primary CL, in which pregnancy had been maintained with exogenous progestogen. In preliminary trials, replacement CL induced ipsilateral to the embryo and after, rather than before, d 36 of pregnancy, maintained more pregnancies after withdrawal of exogenous progestogen (13/13 vs 2/6; P < 0.05). In Exp. 1, in cows with replacement CL induced by treatment with hCG on d 28 of pregnancy, treatment with flunixin meglumine on d 31 through 37 did not increase maintenance of pregnancy. Experiment 2 was conducted to evaluate directly the effects of concentrations of PGF2alpha and estradiol-17beta during d 31 through 35 of pregnancy on maintenance of pregnancy by replacement CL induced between d 28 and 31. In cows that maintained pregnancy while progestogen was provided, maintenance of pregnancy after withdrawal of exogenous progestogen tended to be greater with high (5/5) than with low (2/6; P < 0.10) concentrations of PGF2alpha and greater with low (6/7) than with high (2/6; P = 0.10) concentrations of estradiol-17beta. Secretion of progesterone by replacement CL was greater (P < 0.05) in cows with high than in those with low concentrations of PGF2, during d 31 through 35. Prostaglandin F2alpha may facilitate attachment of the bovine embryo (d 30 to 40) in a manner similar to that reported for implantation in other species. Cows that did not form CL in response to hCG on d 28 to 31 responded well when retreated after d 36. Again, maintenance of pregnancy was greater when replacement CL were induced after (9/9) rather than before d 36 (8/16; P < 0.05).

Effects of day of estrous cycle and induced luteal regression on follicular dynamics in ewes were examined. In Exp. 1, ewes received PGF2 alpha (i.m.) on d 5, 8, or 11 after estrus (d 0) or saline on d 14 (n = 27, 27, 31, and 29, respectively). Ewes were laparotomized before treatment and again 48 h after induced estrus to record numbers, sizes, and locations of follicles > or = 2 mm and corpora lutea (CL). The two largest follicles (designated F1 and F2) and any of equal size (F1.5 and F2.5) were marked with India ink in stroma around the follicle. Ewes treated on d 8 ovulated fewer F1 and F1.5 (39%) than ewes treated on d 5 (69%; P < .05); d 11 (51%) and 14 (56%) were intermediate. In Exp. 2, ewes received PGF2 alpha on d 5 or 8 (n = 15/d). Ovaries were examined with transrectal ultrasonography daily from 4 d before PGF2 alpha until ovulation, and on d 5 and 8 after ovulation. Diameters, locations, and ranks (at time of PGF2 alpha) of follicles > or = 2 mm and CL were recorded. Ewes treated on d 8 ovulated fewer F1 and F1.5 (35%) than ewes treated on d 5 (86%; P < .05). Ovulatory follicles at time of PGF2 alpha were larger on d 5 (4.7 +/- .2 mm) than on d 8 (4.0 +/- .2 mm; P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

This study was conducted to determine the effects of the corpus luteum (CL) of pregnancy and(or) the previously gravid uterine horn (g-UH) on the incidence and site of ovulation and the duration of luteal function in postpartum (PP) ewes. Ewes were laparotomized at d 60 to 80 of gestation and assigned to one of four groups: 1) single g-UH, CL left intact (SI, n = 35); 2) single g-UH, CL removed (SR, n = 30); 3) twin g-UH, CL on both ovaries left intact (TI, n = 21); and 4) twin g-UH, CL removed from one ovary (TR, n = 32). On d 20 PP, the number of follicles on each ovary was determined at laparoscopy, and ewes received (i.m.) 750 IU of hCG. Ovarian structures were determined at laparoscopy on d 24 PP. Blood samples were collected daily from d 20 to 40 PP and assayed for progesterone. more follicles (P < .05) were observed at laparoscopy on d 20 PP in SI/TI than in SR/TR groups (8.4 vs 6.0, respectively; SE = .4). Overall, 52% of the ewes had visible CL 4 d after hCG, and 73% of the ewes had elevated levels of progesterone by 7 d after hCG. The number of g-UH (S vs T) or status of the CL (I vs R) did not affect these responses. For SR ewes with hCG-induced CL on a single ovary, the incidence of CL formation on the ovary adjacent to g-UH was less (P < .05) than that for SI ewes (0 vs 57, respectively). Removal of the CL from S ewes, but not from T ewes, reduced follicular development and ovulation in response to hCG. Perhaps there is a positive systemic effect of the CL of pregnancy on postpartum ovarian function in ewes.

Two experiments, each arranged as a 2 x 2 factorial, were conducted in ewes to examine direct effects of bovine follicular fluid (bFF) on follicular development and luteal function and to further characterize follicular development and luteal function after pituitary stalk transection (SS). In Exp. 1, ewes were sham-operated or SS on d 6 of an estrous cycle and received 5 ml of saline or bFF three times daily on d 5 through 11 of the same cycle. In Exp. 2, all ewes were SS on d 6 of an estrous cycle and treated with saline or bFF three times daily on d 5 through 11 and with ovine FSH (60 micrograms; NIADDK-oFSH-16) or saline (1.2 ml) from d 7 to 11. In Exp. 2, ewes were ovariectomized on d 11 to assess effects of treatments on follicular development and luteal function. In both experiments, concentrations (ng/ml) of FSH on d 7 were suppressed (P less than or equal to .005) by bFF compared with saline (.50 +/- .17 vs 1.63 +/- .15) and remained suppressed (P less than or equal to .005) through d 11 (.46 +/- .12 vs 1.54 +/- .12). Replacement therapy (oFSH) restored concentrations of FSH. Concentrations of LH were not affected by bFF but were elevated (P less than or equal to .05) 1 d after SS (d 7; .88 +/- .09 vs .56 +/- .09) and remained elevated (P less than or equal to .05; 1.31 +/- .20 vs .65 +/- .11) from d 6 through 11. Concentrations of progesterone were unaffected by SS.(ABSTRACT TRUNCATED AT 250 WORDS)

Three experiments were conducted to examine the relationship between systemic concentrations of luteinizing hormone (LH) and estradiol-17 beta (E2) after withdrawal of progesterone in cycling ewes. In Exp. 1, ewes were assigned randomly to one of three treatments: laparotomy (C), removal of the luteal ovary (ULO), or ULO plus anesthesia with sodium pentobarbital for 6 h beginning 4 h after surgery. Anesthesia was used in an attempt to block the expected increase in tonic secretion of LH. Patterns of LH and E2 in these three groups did not differ during the 24-h experimental period. In Exp. 2, a longer period of anesthesia was utilized. Forty-eight ewes were assigned at random to one of four treatments: C, ULO, lutectomy or an intrafollicular injection of prostaglandin F2 alpha (PGF2 alpha). One-half of the ewes in each group were anesthetized with sodium pentobarbital from initiation of treatment (0 h) until 10 h after surgery. Sodium pentobarbital did not suppress the increases in LH and E2 after progesterone withdrawal. The regression of concentrations of E2 on concentration of LH was not significant. In Exp. 3, ewes were infused with either saline or dopamine after receiving an im injection of PGF2 alpha. Tonic secretion of LH increased after 4 h in ewes infused with saline, but not in ewes infused with dopamine. Despite the suppression of LH, concentrations of E2 increased in dopamine-treated ewes as in control ewes. Therefore, the initial increase in E2 after a decline of progesterone in cycling ewes is independent of increases in LH.

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.

Prostaglandin F2 alpha (PGF2 alpha) was injected on d 5, 8 or 11 postestrus in ewes to determine how stage of the estrous cycle would affect PGF2 alpha-induced changes in concentrations of ovarian and pituitary hormones and intervals to the onset of estrus and the preovulatory surge of luteinizing hormone (LH). Initial concentrations of progesterone and average values during the 12 h after PGF2 alpha were related positively to the day of cycle on which PGF2 alpha was administered. Patterns of decline in progesterone after injection of PGF2 alpha were similar among the 3 d. Concentrations of LH in plasma increased in a similar manner from 0 to 12 h in all ewes. After 12 h LH continued to increase, plateaued or declined in ewes treated on d 5, 8 or 11, respectively. Initial concentrations of follicle stimulating hormone (FSH) in plasma were related positively to day of treatment. After treatment with PGF2 alpha, FSH increased within 2 h on d 5 but declined by that time on d 8 or 11. Concentrations of estradiol following treatment did not vary with day. The onset of estrus and the preovulatory surge of LH occurred at 36 and 35, 40 and 45, and 48 and greater than 48 h in ewes treated on d 5, 8 or 11, respectively. It is concluded that: 1) the initial increase in LH is dependent on a decrease in plasma progesterone and 2) differences in patterns of secretion of gonadotropins before the preovulatory surge of LH might be caused by differences in progesterone or progesterone:-estradiol ratio when luteal regression is induced on different days of the estrous cycle.

Two experiments were conducted in peripuberal ewe lambs to determine (a) the influence of the first luteal structure [most frequently a transient (i.e., 1 to 4 d) structure] on subsequent ovarian activity and (b) a role for the uterus in its demise. In Exp. 1, 21 lambs were assigned randomly on the day of the first rise in progesterone in the plasma to (1) sham-operation, (2) removal of the nonluteal ovary, (3) removal of the luteal ovary and (4) removal of the luteal ovary plus progesterone replacement (5 mg given three times 12 h apart, initiated at surgery). No effect of treatment on subsequent ovarian activity was observed. In Exp. 2, four of 14 lambs were assigned randomly to be hysterectomized before their first rise in progesterone. The remaining 10 lambs, (five each) were sham-operated or hysterectomized on the day of the first rise in progesterone. All hysterectomized lambs (N = 9) exhibited a rise in progesterone and maintained elevated concentrations of progesterone, whereas sham-operated lambs initiated estrous cycles. Oviducts and uteri collected from lambs hysterectomized on the day of the first rise in progesterone in Exp. 2 were flushed for presence of oocytes and none were found. Similarly, no retained oocytes were found in histological preparations of first luteal structures obtained from eight lambs ovariectomized in Exp. 1. Concentrations of luteinizing hormone (LH) and prolactin were determined in daily samples collected from 19 lambs in Exp. 1. Luteinizing hormone increased and became more variable as lambs matured, whereas prolactin decreased with no detectable change in variability. It is concluded that the transient luteal structure is not required for sexual maturation and that its lifespan is uterine dependent.

The objectives of this study were to determine 1) the ability of charcoal-extracted bovine follicular fluid (bFF) to suppress endogenous follicle stimulating hormone (FSH) at various stages of the estrous cycle and 2) the effects of suppression of FSH on luteal function and lengths of the current and subsequent estrous cycles. Twenty-six mature ewes were assigned randomly to receive 5 ml of either bFF or saline, subcutaneously, at 8-h intervals on d 1 through 5 (bFF n = 6; saline n = 3), d 6 through 10 (bFF n = 6; saline n = 3) or d 11 through 15 (bFF n = 6; saline n = 2) of the estrous cycle (d 0 = estrus). Blood was collected daily beginning at estrus and continued until the third estrus (two estrous cycles) or 40 d; more frequent samples were collected 2 h prior to initiation of treatment (0600), hourly for the first 8 h of treatment, then every 4 h until 0800 on the first day after treatment, and finally at 1600 and 2400 on that day. Plasma concentrations of FSH were lower (P less than .001) in bFF-treated than in saline-treated ewes. Treatment with bFF reduced (P less than .05) plasma concentrations of progesterone during the current but not during the subsequent estrous cycle. Treatment with bFF did not affect plasma concentrations of estradiol-17 beta. Administration of bFF on d 11 through 15 of the estrous cycle lengthened the interval from the decline in progesterone to estrus and the inter-estrous interval by approximately 3 and 4 d, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)