Resumption of follicular activity in the early post-partum period of dairy cows

Lactating Friesian dairy cows (2nd-4th parity) which calved in spring (N = 7) or autumn (N = 15) were used. Their ovaries were examined by ultrasound scanning and blood samples were obtained daily for progesterone and oestradiol concentrations from the 5th day after calving until the first post-partum ovulation occurred. Five autumn-calving cows selected at random were bled every 15 min over a 6-h period on 1 day each week for 4 weeks after calving to assess the patterns of LH secretion. Follicular development during the post-partum anoestrous period was characterized by the growth and regression of small (less than or equal to 4 mm) and medium-sized (5-9 mm) follicles, until a dominant follicle (greater than 10 mm) was detected. The first detected dominant follicle ovulated in 14 cows, became cystic in 4 cows (all in autumn), and failed to ovulate in 1 cow. It was not possible to detect a dominant follicle in 3 cows due to scanning difficulties. The post-partum interval to detection of the first dominant follicle (mean +/- s.d.) was shorter (P less than 0.05) in autumn (6.8 +/- 1.8 days) than in spring (20 +/- 10.1 days). However, there was no significant difference between the respective intervals to first ovulation (autumn 27.4 +/- 25.9 and spring 27.3 +/- 18.9 days). Autumn-calved cows which had cysts had longer (P less than 0.001) intervals to first ovulation (58.2 +/- 23.5 days) than did normal cows (12.0 +/- 2.5 days). All cows with cysts had twin ovulations at their first post-partum ovulation. A pulsatile pattern of LH secretion was detected in the first week post-partum and LH pulse frequency was 2-3 per 6-h period in Weeks 1 and 2 post partum and increased to 5-7 pulses per 6-h period in the presence of a dominant or cystic follicle. Concentrations of progesterone in plasma during post-partum anoestrus were usually low (less than 0.2 ng/ml); oestradiol concentrations were also low (less than 5 pg/ml), but higher values (5-110 pg/ml) were observed in cows that had a dominant or a cystic follicle.     

Systemic and intraovarian effects of dominant follicles on ovine follicular growth

The objective was to study the endocrine activity in sheep with large ovarian follicles and the effects of dominant follicles on other follicles, looking for possible intraovarian differences. Induction of dominant follicles was achieved using controlled exogenous LH pulses every 90 min over 14 days in eight Scottish Blackface ewes. During this period, follicular development was assessed by daily transrectal ultrasonography and jugular venous blood samples were collected every 12 h for FSH, LH inhibin and oestradiol assay. The exogenous LH pulses caused the appearance of large follicles in all the ewes, which reached a maximum mean diameter of 7.2 +/- 0.5 mm on Day 5.5 +/- 2.6 after first detection. In the presence of a dominant follicle, no other follicle grew to a diameter larger than 4 mm and there was a decrease in the number of new growing follicles (P < 0.05) and in the number of smaller follicles (P < 0.01). This effect of dominance was mediated by changes in FSH concentration, since FSH level decreased (P < 0.05) as dominant follicles grew and the decrease in FSH levels was related to a decline in the number of remaining follicles (P < 0.05). However, the greatest decrease in the number of small follicles growing to larger sizes was observed in the ovary ipsilateral to the dominant follicle (P < 0.05). These data confirm that the presence of a large follicle depresses the recruitment and growth of other follicles by systemic factors and provide some evidence of local inhibitors blocking the final development of other putative large follicles.     

Effect of treatment with progesterone and oestradiol benzoate on ovarian follicular turnover in postpartum anoestrous cows and cows which have resumed oestrous cycles.

Two experiments were carried out to determine the effect of a low dose of progesterone (P) with and without the addition of an injection of oestradiol benzoate (ODB) on ovarian follicle dynamics, oestradiol production and LH pulsatility in postpartum anoestrous cows, compared with cows which had resumed oestrous cycles (cycling cows). In the first experiment, anoestrous Jersey cows were treated with (AN+P, n=8) or without (AN-3, n=3) a previously used intravaginal progesterone releasing (CIDR) device for 10 days, commencing 3 or 4 days after emergence of a new dominant follicle (DF1) as determined by transrectal ultrasonography. Contemporary cycling cows (CYC+P, n=8) were similarly treated with used CIDR devices and injected with prostaglandin F(2alpha) (PGF) at the time of device insertion. Follicle turnover was monitored by daily ultrasonography and pulsatile release of LH was measured on the ninth day after device insertion. During the period of CIDR device insertion, a second dominant follicle emerged in 4/8 of the CYC+P group and 7/8 of the AN+P group (P=0.14). Maximum diameter of DF1 was greater in cows in the CYC+P compared with the AN+P group (P=0.02), but did not differ between cows in the AN+P and AN-P groups (P>0.1). Frequency of LH pulses was greater in cows in the CYC+P than AN+P group (P=0.06), and in cows in the AN+P than AN-P group (P=0.02).In the second experiment, anoestrous (n=20) and cycling (n=11) Friesian cows were treated with a new CIDR device for 6 days commencing 3 days after emergence of a new dominant follicle (DF1). Cycling cows were also injected with PGF on the day of device insertion. Half of the cows in each group were injected with 2mg ODB on the day of device insertion. Daily ultrasonography was used to monitor follicular dynamics throughout the experimental period. Follicular turnover was increased by ODB in cycling (5/5 versus 1/6; P<0.05), but not anoestrous cows (5/9 versus 4/11). Persistence of DF1 was reduced by ODB treatment in both cycling and anoestrous cows (P<0.001). Maximum diameter of DF1 was influenced by ODB treatment and reproductive status (P<0.05). In anoestrous cows in which a second dominant follicle did not emerge during the period of device insertion, the interval from emergence of DF1 to emergence of a second dominant follicle was significantly delayed by treatment with ODB (P=0.04).In conclusion, P treatment of anoestrous cows increased pulsatile release of LH, but did not induce the development of persistent follicles. Injection of ODB in association with P treatment reduced the persistence of dominant follicles in both cycling and anoestrous cows, but delayed subsequent follicular development in a proportion of anoestrous cows.     

Influence of deslorelin (GnRH-agonist) implant on plasma progesterone, first wave dominant follicle and pregnancy in dairy cattle

The objectives of this study were to investigate the effect of a synthetic GnRH-agonist (Deslorelin) implant on CL function and follicle dynamics when administered 48 h after PGF2 alpha, in a timed-insemination protocol, and to determine if the incorporation of a Deslorelin implant into a timed-insemination protocol to synchronize ovulation would be beneficial to the establishment of pregnancy. In Experiment 1, 15 non lactating cyclic Holstein cows received Buserelin (8 micrograms, i.m.) on Day-9, Lutalyse (25 mg, i.m.) on Day-2, and then on Day 0 received either a Deslorelin implant (700 micrograms, s.c.; n = 5), Buserelin (8 micrograms, i.m.; n = 5), or no treatment (control; n = 5). Blood samples were collected on Days-9, -2, 0 and thereafter daily until the next ovulation. Ovaries were scanned by ultrasound on Days-9, -2, 0, 1 (day of ovulation) and 3 times a week thereafter until a subsequent ovulation. From Days 0 to 15, the rate of increase of plasma progesterone (P4) was greater (P < 0.01) for Deslorelin than for control and Buserelin. Establishment of the first-wave dominant follicle (FWDF) as a Class 3 (> 9 mm) follicle was delayed (P < 0.01) with Deslorelin (14.2 +/- 1.3 d) compared with the control (4.6 +/- 1.3 d) and Buserelin (5.0 +/- 1.5 d) treatments. The FWDF resumed growth after Day 13 in all 5 Deslorelin-treated cows, and 2 cows ovulated spontaneously. In 1 Deslorelin-treated cow, the FWDF regressed, and a second-wave dominant follicle ovulated, while 2 other Deslorelin cows failed to ovulate until after Day 36. The cumulative numbers of Class 2 and 3 follicles was lowest in the Deslorelin group (P < 0.01), while the cumulative number of Class 1 follicles was highest (Deslorelin > Buserelin > Control; P < 0.01). The number of days to CL-regression and days to subsequent estrus did not differ (P > 0.05) among treatments. In Experiment II, 16 lactating potentially subfertile (body condition score 2.25) cows received Cystorelin (100 micrograms, i.m.; Day-9), Lutalyse (25 mg, i.m.; Day-2), and either a Cystorelin injection (100 micrograms, i.m.; n = 8) or Deslorelin implant (700 micrograms, s.c.; n = 8) on Day 0 and inseminated 16 h later. Deslorelin-treated cows had a higher plasma P4 concentration between Days 0 and 16 (P < 0.05) than the 2 other groups, and 5 of the 8 cows in this group were pregnant (Day 45, palpation) compared with 1 of 8 cows in the Cystorelin group (P < 0.05). Incorporation of a Deslorelin implant into a timed-insemination protocol enhanced the pregnancy rate in cows of poor body condition. The results support the hypothesis that enhanced CL function and delayed establishment of the first-wave dominant follicle may enhance embryo survival.     

Examination of the relative role of FSH and LH in the mechanism of ovulatory follicle selection in sheep

The GnRH-antagonist suppression-ovarian autotransplant model (n = 18) was used to examine the relative roles of temporal changes in FSH and LH stimulation on follicle development and selection. Follicle development was stimulated by infusion with oFSH for 3 days and treatments applied for 60 h after progestagen sponge withdrawal and before delivery of an ovulatory stimulus. In Expt 1, there was continuous infusion of FSH with or without small amplitude high frequency LH pulses, or withdrawal of FSH with or without pulsatile LH. In Expt 2, there was acute or gradual withdrawal of FSH at sponge withdrawal with pulsatile LH. The patterns of follicle development and basal and pulsatile ovarian hormone secretion were determined. The maintenance of FSH throughout the artificial follicular phase resulted in multiple follicle development and ovulation (3.3 +/- 0.3). Pulsatile LH stimulated steroid secretion (P < 0.001) but had little effect on ovulation rates (3.8 +/- 0.8) when FSH was maintained. However, withdrawal of FSH in the absence of LH resulted in atresia of the ovulatory follicles and anovulation whereas, when FSH was withdrawn in the presence of LH, preovulatory follicle development was maintained in some animals (3/6 and 5/9 in Expts 1 and 2, respectively) and these ewes had lower (P < 0.05) ovulation rates (1-2 ovulations per ewe). When FSH was withdrawn gradually in the presence of pulsatile LH, 9/9 animals ovulated with ovulation rates in the normal range. These results indicate that ovulatory follicles can transfer their gonadotrophic dependence from FSH to LH. It is hypothesized that the ability of a follicle to respond to this switch in gonadotrophic support is central to the mechanism of follicle selection.     

Modification of follicular dynamics by exogenous FSH and progesterone, and the induction of ovulation using hCG in postpartum beef cows

Follicular growth and ovulation in response to FSH, progesterone and hCG were evaluated in postpartum beef cows. In Experiment 1, on Day 21 post partum, cows received an injection of either saline (control; n = 6), FSH (200 mg; n = 6), or a PRID (n = 5) for 10 d. Both FSH and PRID prolonged maintenance of a dominant follicle (15.5 +/- 1.16 and 14.4 +/- 1.29 d, respectively, vs 8.4 +/- 1.22 d in control; P < 0.01), and increased the maximum diameter of the dominant follicle (14.0 +/- 0.91 and 16.4 +/- 1.01 mm, respectively, vs 10.9 +/- 0.95 mm in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 60% of cows, followed by normal estrous cycles (vs 0% in control; P = 0.01), whereas the dominant follicle ovulated in 33% of FSH-treated cows (P = 0.08). The PRID regimen shortened the interval to first ovulation preceding a normal cycle and continued cyclicity (44 +/- 4.1 vs 60 +/- 4.4 d in control; P = 0.02). In Experiment 2, on Day 21 post partum, cows received either saline (control), saline + PRID, or FSH + PRID (n = 16/group). Sixty hours after PRID withdrawal, cows received either saline or hCG (1,500 IU, n = 8/treatment). The FSH + PRID regimen increased the number of large (> 10 mm in diameter) follicles (3.6 +/- 0.43 vs 1.9 +/- 0.39 in control; P = 0.005). Both PRID and FSH + PRID prolonged maintenance of the largest follicle (11.0 +/- 0.82 and 11.2 +/- 0.91 d, respectively, vs 8.7 +/- 0.81 d in control; P < 0.05). The PRID-maintained dominant follicle ovulated in 50% of cows, followed by normal estrous cycles. The FSH + PRID-maintained largest follicle had become atretic at PRID withdrawal and was anovulatory. The FSH + PRID + hCG regimen increased the incidence of ovulation preceding a cycle of normal duration and continued cyclicity (100 vs 50% in PRID; P = 0.03), and reduced the interval to first ovulation preceding a cycle of normal duration and continued cyclicity (38 +/- 6.5 vs 58 +/- 6.3 d in control; P = 0.04). The area under the progesterone curve during the induced cycle was reduced after (PRID +/- FSH) + hCG than after PRID +/- FSH (P = 0.002). These results indicate that PRID alone or with FSH/hCG has the potential to modify the dominant follicle and initiate cyclicity in postpartum beef cows.     

Influence of the type of energy supply on lh secretion, follicular growth and response to estrus synchronization treatment in feed-restricted suckler beef cows

The present experiment aimed to compare the efficiency of supplementation (+17.5 MJ Net Energy/d starting 47 +/- 4 days after calving) with concentrate (CS, maize grain, n = 10) or with forage (FS, maize silage, n = 10) in estrus-synchronized (Norgestomet implant 10 days inserted 60 +/- 4 days postpartum + PMSG at implant removal) beef cows previously restricted (47 MJ Net Energy/d, 785 g CP/d, 70% of requirements). The type of diet had no significant effect on basal LH concentrations (CS: 0.18 +/- 0.12 vs FS: 0.11+/- 0.02 ng/mL), LH pulse frequency (CS : 0.7 +/- 0.3 vs FS: 0.8 +/- 0.2 pulse/10 h), LH pulse amplitude (CS: 0.55 +/- 0.50 vs FS : 0.62 +/- 0.50 ng/mL) or estradiol (E2) concentrations (CS: 3.3 +/- 0.8 vs FS: 4.6+ /- 0.8 pg/mL) 13 days after the beginning of energy supplementation. No differences between CS and FS cows were observed for the number of small, medium and large follicles nor on the size of the largest follicle from 11 days before implant insertion to implant removal (IR). After IR, an LH surge was observed in 2 of the CS and 4 of the FS cows. The type of energy supplementation had no significant effect on LH (CS: 0.16 +/- 0.06 ng/mL vs FS 0.48 +/- 0.06 ng/mL; P > 0.05) or on estradiol concentrations (CS : 7.8 +/- 0.2 vs FS : 8.9 +/- 0.2 pg/mL, P > 0.10) measured hourly from 29 to 49 h after IR. Cows that ovulated after IR tended to have higher E2 concentrations than cows that did not ovulate (9.4 +/- 0.2 vs 6.3 +/- 0.2 pg/mL, P = 0.08). Similar ovulation and pregnancy rates were observed in CS and FS cows (CS: 6/10 vs FS: 7/10 and CS: 6/10 vs FS: 5/10 respectively, P > 0.05). To conclude, energy supplementation with forage was as effective as energy supplementation with concentrate to influence follicular growth, ovulation and pregnancy percentage after estrus synchronization treatment in diet-restricted beef cows.     

Ovarian function in nutritionally induced anoestrous cows: effect of exogenous gonadotrophin-releasing hormone in vivo and effect of insulin and insulin-like growth factor I in vitro

Ovarian function of nutritionally induced anoestrus cows was evaluated in vivo (Expt 1) and in vitro (Expt 2). In Expt 1, 32 nutritionally induced anoestrous beef cows were divided into four treatment groups receiving: (1) saline infusions at one pulse every 4 h for 13 days (control); (2) 2 micrograms GnRH at one pulse every 4 h (2 micrograms infused in 1.8 ml saline over 5 min) for 13 days (GnRH-4); (3) 2 micrograms GnRH at one pulse every 1 h for 13 days (GnRH-1); and (4) continuous infusion of 2 micrograms GnRH (a total of 2 micrograms in 34 ml h-1) for 13 days (GnRH-C). On the last day of treatment, cows were killed, ovaries were removed and follicular fluid samples (n = 149) were collected. The percentage of cows with luteal activity on day 13 was significantly different (P < 0.01) among treatments (0, 25, 75 and 25% for control, GnRH-4, GnRH-1 and GnRH-C cows, respectively). Owing to the large percentage of ovulatory cows in the GnRH-1 group (n = 6), anovulatory cows (n = 2) were removed from this treatment group for statistical analysis, as were cows with luteal tissue from the GnRH-4 (n = 2) and GnRH-C (n = 2) groups. The numbers of small (1.0-4.9 mm) and medium plus large (> or = 5 mm) follicles were not affected (P > 0.10) by treatment. However, GnRH-4 cows (n = 6) had greater (P < 0.05) concentrations of oestradiol in follicular fluid than did control (n = 8) but not GnRH-1 (n = 6) or GnRH-C (n = 6) cows. Concentrations of insulin-like growth factor I were greater (P < 0.05) in the follicular fluid of GnRH-1 cows than in all other treatment groups. Concentrations of androstenedione and progesterone in follicular fluid were not affected (P > 0.10) by treatment or follicle size. The binding activity of insulin-like growth factor binding proteins was not affected by GnRH treatment. However, the binding activity of insulin-like growth factor binding protein 2, 29-32 kDa and 22 kDa insulin-like growth factor binding proteins were greater (P < 0.05) in small versus medium plus large follicles. In Expt 2, granulosa cells were collected from nutritionally anoestrous cows to determine whether ovarian cells from anoestrous cows have the capacity to respond to insulin-like growth factor I or insulin in vitro. Both insulin-like growth factor I (20 and 200 ng ml-1) and insulin (10, 100 and 1000 ng ml-1) increased (P < 0.05) granulosa cell proliferation and progesterone production. In conclusion, pulsatile infusion of 2 micrograms GnRH (every 1 or 4 h) for 13 days into nutritionally induced anoestrous cows results in increased intrafollicular oestradiol and insulin-like growth factor I concentrations and can stimulate ovulation without markedly affecting concentrations of androstenedione or progesterone, or the binding activity of insulin-like growth factor binding proteins, in follicular fluid. In addition, granulosa cells from nutritionally induced anoestrous cows have the capacity to respond to insulin-like growth factor I and insulin in vitro, indicating that the decrease in trophic factors observed with restricted feeding does not reduce the response of the ovary to insulin-like growth factor I and insulin.     

Development of preovulatory follicles expected to form short-lived corpora lutea in beef cows

Oestrus, expected to be followed by a short luteal phase, was induced in post-partum cows by weaning their calves at 35 days after parturition. Ovaries containing the first preovulatory follicles (Type F) formed after parturition were collected 3 h after the onset of oestrus. For comparison, preovulatory follicles (Type C) were collected 3 h after the onset of oestrus in normally cycling cows. The number of granulosa cells was determined and the concentrations of receptors for follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in granulosa cells and for LH in theca cells were measured. Concentrations of oestradiol-17 beta, testosterone, androstenedione and progesterone in follicular fluid were also measured. Type F follicles contained about twice the number of granulosa cells (based on DNA) as did Type C follicles (45.8 +/- 11.3 and 24.5 +/- 3.9 micrograms DNA/follicle, respectively; P less than 0.05) but these cells had fewer receptors for LH (0.13 +/- 0.02 vs 0.29 +/- 0.03 fmol/micrograms DNA; P less than 0.01) and FSH (0.61 +/- 0.08 vs 1.3 +/- 0.29 fmol/micrograms DNA; P less than 0.08) than did those from Type C follicles. Additionally, there were fewer receptors for LH in theca tissue from Type F than from Type C follicles (28.3 +/- 5.2 vs 51.3 +/- 6.1 fmol/follicle; P less than 0.01). Concentrations of oestradiol-17 beta (475.8 +/- 85.6 vs 112.9 +/- 40.0 ng/ml; P less than 0.01) and androstenedione (214.1 +/- 48.7 vs 24.7 +/- 7.7 ng/ml; P less than 0.01) in follicular fluid were higher in Type C than in Type F follicles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Postpartum acyclicity in suckled beef cows: a review

Prolonged postpartum acyclicity in suckled beef cows is a source of economic loss to beef cattle producers. Duration of postpartum acyclicity is influenced by suckling status, nutritional status, calving season, age, and several other factors. Although uterine involution begins and ovarian follicular waves resume soon after parturition, dominant follicles of these waves fail to ovulate, due to a failure to undergo terminal maturation. As a result, postpartum anovulatory dominant follicles are smaller than the ovulatory follicles in cyclic cows. Failure of postpartum dominant follicles to undergo terminal maturation is due to absence of appropriate LH pulses, a prerequisite for follicular terminal maturation prior to ovulation. Absence of LH pulses early post partum is primarily due to depletion of anterior pituitary LH stores, although GnRH pulses are also absent during this period due to suckling. Following replenishment of LH stores between Days 15 and 30 post partum, absence of LH pulses is due to continued sensitivity of the hypothalamic GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta, which results in absence of GnRH pulses. This negative feedback effect of estradiol-17beta is modulated by suckling which stimulates release of endogenous opioid peptides from the hypothalamus. As the postpartum interval increases, sensitivity of the GnRH pulse-generator to the negative feedback effect of ovarian estradiol-17beta decreases. This is followed by an increasing frequency of GnRH discharges and LH pulses, terminal follicular maturation, ovulation, and continued cyclicity. The first ovulation post partum is usually followed by a short cycle due to premature luteolysis because of premature release of PGF2alpha from the uterine endometrium, which is possibly intensified by the suckling-induced oxytocin release from the posterior pituitary. A model for the postpartum ovulatory acyclicity and for the resumption of cyclicity is presented.     

Secretory patterns of LH and FSH and follicular growth following administration of PGF(2)alpha during the early luteal phase in cattle

Two studies were conducted to determine the changes in gonadotropin secretion associated with growth and development of the largest follicle and the ability of the largest ovarian follicle present on Day 5 following estrus to ovulate if luteal regression is induced. In both studies, cows received either saline (i.m.) or prostaglandin F(2)alpha (PGF(2)alpha; 25 mg i.m.) on the fifth day post estrus. Frequency of LH pulses declined (P<0.01) with increasing day of cycle, while pulse amplitude and duration increased (P<0.05) in saline-treated cows. In PGF(2)alpha-treated cows, LH remained as high frequency-low amplitude pulses. Secretory patterns of FSH were similar between the two groups. In Experiment 2, the largest ovarian follicle present was marked around its periphery with sub-epithelial injections of charcoal. In saline-treated cows, the size of the charcoal marked follicles generally decreased, indicating atresia. A corpus luteum was present within the area of a previously marked follicle in three PGF(2)alpha-treated cows. The size of the marked follicles either decreased or increased in the remaining PGF(2)alpha-treated cows, with ovulation occurring at a different site. In summary, PGF(2)alpha-induced luteal regression on the fifth day of estrus subsequently alters the frequency, amplitude and duration of LH pulses, but not FSH pulses, and the largest follicle present on Day 5 either increases or decreases in size or ovulates when PGF(2)alpha is given on Day 5 following estrus.     

Effects of follicle-stimulating hormone with and without luteinizing hormone on serum hormone concentrations, follicle growth, and intrafollicular estradiol and aromatase activity in gonadotropin-releasing hormone-immunized heifers

To evaluate the roles of FSH and LH in follicular growth, GnRH-immunized anestrous heifers (n = 17) were randomly assigned (Day 0) to one of three groups (n = 5 or 6). Group 1 received i.m. injections of 1.5 mg porcine FSH (pFSH) 4 times/day for 2 days; group 2 received i.v. injections of 150 microg pLH 6 times/day for 6 days; group 3 received both pFSH and pLH as described for groups 1 and 2. After slaughter on Day 6, measurements were made of follicle number and size, and follicular fluid concentrations of progesterone (P(4)), estradiol (E(2)), and aromatase activity. Injection of pFSH increased (P: < 0.01) the serum concentrations of FSH between 12 and 54 h. Infusion of pLH increased (P: < 0.05) mean and basal concentrations of LH and LH pulse frequency. Serum E(2) concentrations were higher (P: < 0.05) for heifers given pFSH + pLH than those given either pFSH or pLH alone. There was no difference (P: > or = 0.24) between treatments in the number of small follicles (<5 mm). Heifers given pFSH or pFSH + pLH had more (P: < or = 0.02) medium follicles (5.0-9.5 mm) than those that were given pLH alone (none present). Heifers given pFSH + pLH had more (P: = 0.04) large follicles (> or =10 mm) than those given either pLH or pFSH alone (none present). Overall, only 1 of 35 small follicles and 2 of 96 medium follicles were E(2)-active (i.e., E(2):P(4) >1.0), whereas 18 of 21 large follicles (all in the pFSH + pLH treatment) were E(2)-active; of these, 8 of 18 had aromatase activity. Concentrations of E(2) and E(2) activity in follicular fluid were correlated (r > or = 0.57; P: < 0.0001) with aromatase activity in heifers given pLH + pFSH. In conclusion, pLH failed to stimulate follicle growth greater than 5 mm; pFSH stimulated growth of medium follicles that were E(2)-inactive at slaughter and failed to increase serum E(2) concentrations; whereas pFSH + pLH stimulated growth of medium follicles and E(2)-active large follicles, and a 10- to 14-fold increase in serum E(2) concentrations.     

Influence of intrauterine infections and follicular development on the response to GnRH administration in postpartum dairy cows

The effects of intrauterine infections and prior follicular development on the response to gonadotropin releasing hormone (GnRH) administration in postpartum dairy cows were studied. Fifty lactating Holstein cows were assigned at random to one of two groups after calving. Group I (control) consisted of 25 cows given a single intramuscular injection of saline on Day 15 postpartum. Group II (treated) consisted of 25 herdmates given a single i.m. injection of 100 mug of GnRH on Day 15 postpartum. Palpation per rectum and real-time ultrasonography were used to monitor ovarian activity, and endometrial swabs were cultured to determine the presence of uterine infection. Blood samples were collected for progesterone (P(4)) and luteinizing hormone (LH) analysis. Fourteen cows (control, n = 5; treated, n = 9) did not ovulate during the first 60 d postpartum. Ovaries in these cows contained 4 to 8-mm size follicles and both P(4) and LH remained at basal concentrations. Fourteen other cows (control, n = 6; treated, n = 8) ovulated by Day 15 postpartum. Follicles >/= 10 mm were demonstrable in the ovaries of these cows before or by Day 12 postpartum. GnRH treatment had no effect on the lifespan of the existing corpus luteum in these cows. In the remaining cows, 7 of 14 Control and all 8 Treated cows ovulated within 3 d of treatment. All cows ovulating within this period were free of uterine infection and the ovaries contained follicles 相似文献   

Pattern of follicular growth and resumption of ovarian activity in post-partum beef suckler cows

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.     

Follicular deviation and acquisition of ovulatory capacity in bovine follicles.

Selection of dominant follicles in cattle is associated with a deviation in growth rate between the dominant and largest subordinate follicle of a wave (diameter deviation). To determine whether acquisition of ovulatory capacity is temporally associated with diameter deviation, cows were challenged with purified LH at known times after a GnRH-induced LH surge (experiment 1) or at known follicular diameters (experiments 2 and 3). A 4-mg dose of LH induced ovulation in all cows when the largest follicle was > or =12 mm (16 of 16), in 17% (1 of 6) when it was 11 mm, and no ovulation when it was < or =10 mm (0 of 19). To determine the effect of LH dose on ovulatory capacity, follicular dynamics were monitored every 12 h, and cows received either 4 or 24 mg of LH when the largest follicle first achieved 10 mm in diameter (experiment 2). The proportion of cows ovulating was greater (P < 0.05) for the 24-mg (9 of 13; 69.2%) compared with the 4-mg (1 of 13; 7.7%) LH dose. To determine the effect of a higher LH dose on follicles near diameter deviation, follicular dynamics were monitored every 8 h, and cows received 40 mg of LH when the largest follicle first achieved 7.0, 8.5, or 10.0 mm (experiment 3). No cows with a follicle of 7 mm (0 of 9) or 8.5 mm (0 of 9) ovulated, compared with 80% (8 of 10) of cows with 10-mm follicles. Thus, follicles acquired ovulatory capacity at about 10 mm, corresponding to about 1 day after the start of follicular deviation, but they required a greater LH dose to induce ovulation compared with larger follicles. We speculate that acquisition of ovulatory capacity may involve an increased expression of LH receptors on granulosa cells of the dominant follicle and that this change may also be important for further growth of the dominant follicle.     

Developmental pattern of small antral follicles in the bovine ovary

The study was designed to characterize the developmental pattern of 1- to 3-mm follicles and to determine the stage at which the future dominant follicle first attains a size advantage among its cohorts. In experiment 1, heifers (n = 18) were examined every 24 h by transrectal ultrasonography for one interovulatory interval (IOI). In experiment 2, cows (n = 9) were examined every 6 h from 5 to 13 days after ovulation to monitor precisely the diameter changes of individual follicles >/=1 mm during emergence of wave 2. Results revealed a change over days (P < 0.05) in the number of 1- to 3-mm follicles, with a maximum (P < 0.05) 1 or 2 days before wave emergence (conventionally defined as the time when the dominant follicle is first detected at 4 mm), followed 3-4 days later by a maximum (P < 0.05) in the number of >/=4-mm follicles. The profiles of small (1-3 mm) and large (>/=4-mm) follicles were inversely proportional (r = -0.79; P = 0.01). The profile of the number of 1- to 3-mm follicles during wave emergence was similar (P = 0.63) between waves in two-wave IOI, but differed (P < 0.01) among waves in three-wave IOI as a result of a greater number of follicles in the ovulatory wave (P < 0.04). As well, the number of follicles in the ovulatory wave tended to be greater (P < 0.06) in three-wave IOI than in two-wave IOI. The future dominant follicle was first identified at a diameter of 1 mm and emerged 6-12 h earlier than the first subordinate follicle (P < 0.01). After detection of the dominant follicle at 1 mm (0 h), its diameter differed from that of the first and second subordinate follicles at 24 h (P = 0.04) and 12 h (P = 0.01), when the dominant follicle was 2.4 +/- 0.17 mm and 1.7 +/- 0.14 mm, respectively. The growth rate of the dominant follicle differed from that of the first and second subordinate follicles at 120 h (P = 0.03) and 108 h (P = 0.02), when the dominant follicle was 9.5 +/- 0.30 mm and 8.8 +/- 0.49 mm, respectively. Emergence of the future dominant (r = 0.71), first (r = 0.73), and second (r = 0.76) subordinate follicles was temporally associated (P < 0.01) with a rise in circulating concentrations of FSH. Transient, nocturnal elevations in plasma FSH concentration were followed within 6 h by an increase in the growth rate of 1- to 3-mm follicles. We conclude that 1) 1- to 3-mm follicles develop in a wave-like manner in association with surges in plasma concentrations of FSH, 2) 1- to 3-mm follicles are exquisitely responsive to transient elevations in FSH, and 3) selection of the dominant follicle is manifest earlier than previously documented and is characterized by a hierarchical progression over a period encompassing the entire FSH surge (5 days).     

Factors regulating the growth of the preovulatory follicle in the sheep and human

Around the time of luteal regression in monovular species a single dominant follicle, which will eventually ovulate, is selected from the population of antral follicles. The dominant follicle is characterized by its progressive increase in diameter due to increase in antral fluid volume as well as an increased number of granulosa cells. The crucial factor in the continued development of the dominant follicle is its ability to synthesize oestradiol under the influence of LH and FSH. In the sheep FSH secretion continues throughout the luteal phase while LH is suppressed. Thus development of large antral follicles continues so that when luteal regression occurs and LH secretion increases the final stages of development of the pre-antral follicle occur within 3 days. In the human, however, both FSH and LH are suppressed during the luteal phase and only rise when the levels of progesterone and oestradiol fall a few days before menstruation. This rise in FSH and LH which occurs at this time stimulates the further development of a small antral follicle (1-2 mm diameter). Within 7 days the favoured follicle establishes dominance over the other asynchronously developing follicles probably by inhibiting the secretion of FSH. As in the sheep, once aromatase enzyme(s) has been fully activated the dominant follicle is able to utilize the increased androgen precursor produced by the theca under LH stimulation.     

Effects of buserelin injection and deslorelin (GnRH-agonist) implants on plasma progesterone, LH, accessory CL formation, follicle and corpus luteum dynamics in Holstein cows

The influence of Buserelin injection and Deslorelin (a GnRH analogue) implants administered on Day 5 of the estrous cycle on plasma concentrations of LH and progesterone (P4), accessory CL formation, and follicle and CL dynamics was examined in nonlactating Holstein cows. On Day 5 (Day 1 = ovulation) following a synchronized estrus, 24 cows were assigned randomly (n = 4 per group) to receive 2 mL saline, i.m. (control), 8 micrograms, i.m. Buserelin or a subcutaneous Deslorelin (DES) implant in concentrations of 75 micrograms, 150 micrograms, 700 micrograms or 2100 micrograms. Blood samples were collected (for LH assay) at 30-min intervals for 2 h before and 12 h after GnRH-treatment from cows assigned to Buserelin, DES-700 micrograms and DES-2100 micrograms treatments and thereafter at 4-h intervals for 48 h. Beginning 24 h after treatment, ovaries were examined by ultrasound at 2-h intervals until ovulation was confirmed. Thereafter, ultrasonography and blood sampling (for P4 assay) was performed daily until a spontaneous ovulation before Day 45. A greater release of LH occurred in response to Deslorelin implants than to Buserelin injection (P < 0.01). Basal levels of LH between 12 and 48 h were higher in DES-700 micrograms group than in DES-2100 micrograms and Buserelin (P < 0.05). The first wave dominant follicle ovulated in all cows following GnRH treatment. Days to CL regression did not differ between treatments, but return to estrus was delayed (44.2 vs 27.2 d; P < 0.01) in cows of DES-2100 micrograms group. All GnRH treatments elevated plasma P4 concentrations, and the highest P4 responses were observed in the DES-700 micrograms and DES-2100 micrograms groups. The second follicular wave emerged earlier in GnRH-treated than in control cows (9.9 vs 12.8 d; P < 0.01). However, emergence of the third dominant follicle was delayed in cows of DES-2100 micrograms treatment (37.0 d) compared with DES-700 micrograms (22.2 d), Buserelin (17.8 d) or control (19.0 d). In conclusion, Deslorelin implants of 700 micrograms increased plasma P4 and LH concentrations and slightly delayed the emergence of the third dominant follicle. On the contrary, Deslorelin implants of 2100 micrograms drastically altered the P4 profiles and follicle dynamics.     

Body condition influences maintenance of a persistent first wave dominant follicle in dairy cattle

The objective of this study was to determine whether plasma concentrations of progesterone (P4) from a controlled internal drug releasing (CIDR) device (approximately 2 ng/ml) were adequate to sustain a persistent first wave dominant follicle (FWDF) in low body condition (LBC, body condition score [BCS] 1 = lean, 5 = fat [2.3 +/- 0.72, n = 4]) compared with high body condition (HBC, BCS = 4.4 +/- 0.12, n = 4) nonlactating dairy cows. On Day 7 of the estrous cycle (Day 0 = estrus), cows were treated with PGF2 alpha (25 mg i.m. Lutalyse, P.M., and Day 8 A.M.) and a used CIDR device containing P4 (1.2 g) was inserted into the vagina until ovulation or Day 16. Plasma was collected for P4 and estradiol (E2) analyses from Day 5 to Day 18 (or ovulation), and ovarian follicles were monitored daily by ultrasonography. Mean concentrations of plasma P4 were greater in HBC than LBC cows between Days 5 and 7 (4.6 > 3.4 +/- 0.37 ng/ml; P < 0.04). All LBC cows maintained the first wave dominant follicle and ovulated after removal of the CIDR device (18.3 +/- 0.3 d, n = 3; Cow 4 lost the CIDR device on Day 11 and ovulated on Day 15), whereas in the HBC cows ovulation occurred during the period of CIDR exposure (11.3 +/- 0.3 d; n = 3; a fourth cow developed a luteinized first wave dominant follicle that did not ovulate during the experimental protocol on Day 19). Mean day of estrus was 17 +/- 0.4 for LBC (n = 3) and 10 +/- 0.4 for HBC (n = 3) cows. Sustained concentrations of plasma E2 (12.9 +/- 2.8 pg/ml; Days 8 to 17) in LBC cows reflected presence of an active persistent first wave dominant follicle. The differential effect of BCS on concentrations of plasma P4 (y = ng/ml) was reflected by the difference (P < 0.01) in regressions: yLBC = 19.9 - 3.49x + 0.166x2 vs yHBC = 37.3 - 7.04x + 0.340x2 (x = day of cycle, Days 7 to 12). Although P4 concentration was greater for HBC cows prior to Day 8, a greater clearance of plasma P4 released from the CIDR device in the absence of a CL altered follicular dynamics, leading to premature ovulation in the HBC cows. A greater basal concentration of P4 was sustained in LBC cows that permitted maintenance of a persistent first wave dominant follicle.