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K. F. Breuel, P. E. Lewis, E. K. Inskeep and R. L. Butcher

This study investigated whether treatment with progestagen, which improves fertility after early weaning in postpartum cows, altered concentrations of gonadotrophins or development and function of follicles. Patterns of luteinizing hormone (LH), oestradiol and follicle-stimulating hormone (FSH) and of follicular growth before first postpartum ovulation were compared in two experiments. At 17 to 25 days post partum, suckled anoestrous beef cows received an ear-implant containing 6 mg progestagen (norgestomet) for 9 days or served as untreated controls. Calves were weaned from all cows 7 days after initiation of treatment. Cows were observed for oestrous behaviour twice a day until 10 days after weaning. As expected, the proportion of anoestrous cows that formed a corpus luteum with a normal lifespan was greater (P < 0.01) in cows treated with norgestomet (Expt 1, 17 of 24; Expt 2, 18 of 22) than in control cows (Expt 1, 2 of 16; Expt 2, 3 of 18). In general, patterns of secretion of LH and oestradiol and of final growth of the preovulatory follicle did not differ between control and norgestomet-treated cows. However, there was a transient rise in FSH in association with weaning in control cows that did not occur in norgestomet-treated cows. In addition, mean LH increased more rapidly and mean oestradiol was higher during the 3 days immediately before the preovulatory surge of LH in the norgestomet-treated cows (P < 0.01). These alterations in LH, FSH and follicular function, in the absence of any difference in rate of final growth of the preovulatory follicle, may mean that there was a lack of synchrony between follicular maturation and the LH surge in control cows which resulted in ovulation of a follicle that was not at an optimal stage of maturation. In comparison, treatment with norgestomet may partially synchronize follicular maturation and the LH surge.

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A. Lopez-Sebastian, A. Gomez-Brunet, A. W. Lishman, S. K. Johnson and E. K. Inskeep

Five experiments were conducted with the objective of developing a method to induce superovulation in ewes with a single i.m. injection of FSH. This was achieved by injection of 10 mg FSH-P in propylene glycol at the same time as luteolysis was induced by cloprostenol on day 13 of the oestrous cycle (day 0 = oestrus). Experiments 1, 2, 3 and 5 were conducted in a single flock of Manchega ewes in Spain during the breeding season. Ovulation rates were determined at laparoscopy. In Expt 1, FSH-P was diluted in saline, and neither 5 mg FSH on day 1 nor 5 or 10 mg FSH-P on day 13 changed the ovulation rate after cloprostenol treatment on day 13. In Expt 2, FSH-P was diluted in propylene glycol and data were collected over 2 years. Ten milligrams FSH-P, on day 13 only, increased (P < 0.01) the mean number of corpora lutea to 5.5 compared with a control value of 1.5. Five milligrams FSH-P on day 13 only had no effect; however, 5 mg FSH-P on day 1 reduced the mean number of corpora lutea formed in ewes receiving 10 mg FSH-P on day 13 to 2.6 (P < 0.01). Saline and propylene glycol, as vehicles for 10 mg FSH-P, were compared directly at two times of injection in Expt 3. FSH-P increased the mean number of corpora lutea when injected on day 13 in propylene glycol (4.7) but not in saline (2.5; P < 0.5). Ovulation rate did not differ between diluents when FSH-P was injected 24 h before cloprostenol (1.3; day 12). Experiments 4 and 5 were conducted to examine possible mechanisms by which propylene glycol improved the response to FSH. In Expt 4, conducted during anoestrus in a crossbred flock in West Virginia, concentrations of FSH in plasma were measured for 58 h after injection of 10 mg FSH-P in saline or propylene glycol. Propylene glycol did not delay the time of maximum concentration of FSH in plasma after i.m. injection (2.7 ± 0.7 h) when compared with saline injection (3.6 ± 0.5 h). Maximum concentration was reached later when FSH-P was injected s.c. in propylene glycol (7.6 ± 0.7 h; P < 0.05). In Expt 5, ovulation rate was greater (P < 0.05) in ewes treated with 10 mg FSH-P in propylene glycol than in ewes treated with FSH-P in saline and an injection of propylene glycol at a separate site. The number of corpora lutea did not differ in ewes treated with FSH-P in saline and in ewes treated with FSH-P in saline and propylene glycol at a separate site. Thus neither delayed absorption nor an augmentation effect could account for the benefit of propylene glycol as a vehicle for delivery of FSH to superovulate ewes.

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D. J. Tortonese, P. E. Lewis, H. Papkoff and E. K. Inskeep

Summary. Prepubertal crossbred beef heifers were injected (i.v.) with 50 μg bovine LH every 2 h for 48 h (first injection at 0 h). At 28 h, number and diameter of ovarian follicles were determined by ultrasonic scanning, and unilateral removal of either the ovary bearing the largest follicle (Group UL, N = 5) or the opposite ovary (Group UO, N = 4) was performed; control animals remained intact (Group I, N = 5). Blood samples were taken every 2 h (starting at 0 h) for a 60-h period to assess concentrations of gonadotrophins and oestradiol. Preovulatory-like surges of LH occurred in 0/5, 4/4 and 5/5 heifers for Groups UL, UO and I respectively; the time of the LH surge did not differ between animals in Groups I and UO (mean = 40 h). FSH in Group UL heifers rose to a plateau immediately after unilateral ovariectomy; this pattern was not observed in the other two groups (P < 0·01). The area under the curve for FSH was significantly different (P < 0·05) among groups after 28 h. Preovulatory-like surges of FSH occurred coincidently with those of LH, except for one Group I heifer. An increase in the concentrations of oestradiol between 0 and 28 h was detected in all animals. Profiles of oestradiol during this period did not differ between heifers that had an LH surge (Groups UO and I) and those that did not (Group UL). After 28 h, concentrations of oestradiol declined to basal levels in Group UL heifers, but in the other two groups it was not possible to characterize, by linear, quadratic or cubic regression, any particular pattern of oestradiol before the LH surge. Ovulation, as determined by rectal palpation and concentrations of progesterone, occurred in 0/5, 4/4 and 4/5 animals for Groups UL, UO and I, respectively. All induced luteal phases were of short duration (<9 days). It is concluded that: (1) repeated injections of LH in the prepubertal heifer are able to induce surges of gonadotrophins and formation of a corpus luteum, (2) the ovary containing the largest follicle is required to mediate the stimulatory effect leading to the LH and FSH surges, and (3) the opposite ovary plays no important role in this mechanism.

Keywords: LH; FSH; oestradiol; dominant follicle; prepubertal heifers

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D. A. Cooper, D. A. Carver, P. Villeneuve, W. J. Silvia and E. K. Inskeep

Summary. The role of PGF-2α in determining the lifespan of corpora lutea in the post-partum beef cow was investigated. In control cows (N = 5) induced to ovulate at Day 28 to 36 post partum by injection of 1000 i.u. hCG, corpora lutea had an average lifespan of only 8 days. In cows pretreated with 6 mg implants of a progestagen (norgestomet, N = 4) for 9 days, with implant removal 2 days before injection of hCG, luteal lifespan averaged 17·5 days. Concentrations of PGF-2α in 9 hourly samples of plasma collected from the posterior vena cava via indwelling catheters were higher on Days 4 through 9 after injection of hCG (P < 0·05) in the cows with short-lived corpora lutea. Greater release of PGF-2α could therefore be a major factor in premature luteal regression. Concentrations of PGFM and oxytocin did not differ between cows with corpora lutea of short or normal lifespan.

In a second experiment, concentrations of PGF-2α in plasma from the posterior vena cava were examined during treatment with norgestomet (N = 8) or in contemporary controls (N = 7). In progestagen-treated cows, PGF-2α was higher than in control cows (P < 0·05), beginning on Day 3 of treatment and peaking on Day 5. It is concluded that the post-partum uterus increases secretion of PGF-2α very early after first exposure to endogenous or exogenous progestagen.

Keywords: PGF-2α; abnormal corpus luteum; PGFM; oxytocin; progestagen

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G. W. Asher, I. C. Scott, K. T. O'Neill, J. F. Smith, E. K. Inskeep and E. C. Townsend

Ovarian follicular dynamics were monitored in 12 surgically modified red deer hinds (ovaries adhered to vaginal wall) by transvaginal real-time ultrasonography during the luteal cycle, anoestrus and induction of superovulation. All 12 hinds showed evidence of regular luteal (plasma progesterone) cyclicity during the breeding season, although luteal tissue was not observed on the ultrasonograms. During the normal luteal cycle (14–22 days) total numbers of follicles > 3 mm did not vary significantly by day (range of means: 1.8–3.4; P > 0.05). A single large (≥ 6 mm) follicle was usually present on all days except immediately after ovulation (day 0). However, the appearance of new follicles (≥3 mm) was not random, and was greatest on day 1 and day 14 (P < 0.05). Tracking of individual follicles revealed irregular waves of emergence and disappearance of the largest follicle, with either one (n = 1), two (n = 3) or three (n = 5) waves observed across nine luteal cycles. New follicles (≥ 3 mm) emerged after regression or ovulation of a large follicle, suggesting a dominance effect. There were no significant differences in the overall mean numbers of follicles during early, mid- and late anoestrus (September, November and April, respectively) but follicle turnover was more rapid during mid-anoestrus as evidenced by a significantly greater number of new small (> 3 mm) follicles (P < 0.001). Administration of superovulatory doses of ovine FSH during the breeding season resulted in a marked increase in the appearance of new follicles within 48 h of initiation of the injection regimen. By termination at 96 h, the time of progesterone withdrawal, the mean number of follicles > 3 mm was significantly higher than for control hinds (9.8 versus 3.0; P < 0.001). While most follicles ovulated progressively 2–7 days later, about 40% persisted beyond this period. The study demonstrated the presence of discrete patterns of antral follicle growth and regression during the breeding and non-breeding seasons, with the luteal cycle characterized by a variable number (1–3) of dominant follicle waves. Anoestrus represents a period of dynamic changes in follicular turnover.