Oestradiol administration raises luteal LH receptor levels in intact and hysterectomized pigs

Occupied and unoccupied LH receptors in corpora lutea, and LH and progesterone concentrations in circulating plasma, were measured in non-pregnant gilts that had been treated with oestradiol-17 beta benzoate to prolong luteal function. Oestradiol benzoate (5 mg, administered on Day 12 after oestrus) delayed luteal regression and the decline in LH receptor levels at luteolysis and raised unoccupied receptor levels from 11.8 +/- 1.14 fmol/mg protein on Days 10--15 after oestrus to 31.8 +/- 3.26 fmol/mg protein on Days 15--21. There was no simultaneous rise in occupied receptor levels and occupancy decreased from 29.8 +/- 3.01 to 11.5 +/- 1.26%. Basal plasma LH concentrations were unchanged by oestradiol, but mean corpus luteum weight and plasma progesterone concentrations were slightly reduced. Oestradiol benzoate on Day 12 caused a similar increase in unoccupied receptor levels in gilts hysterectomized on Days 6--9 after oestrus, from 17.0 +/- 5.83 to 34.5 +/- 6.00 fmol/mg protein, determined on Days 15--18. Plasma concentrations of LH and progesterone were unchanged by oestradiol. Unoccupied receptor levels in corpora lutea and plasma LH and progesterone were unaltered by hysterectomy in untreated gilts. Occupied receptor levels were not influenced by hysterectomy or oestradiol. It is concluded that oestradiol-17 beta raises luteal LH receptor levels by a mechanism independent of the uterus.     

Comparison of oestrous synchronization regimens for lactating dairy cows.

The objective of this experiment was to evaluate various programmes for synchronization of oestrus. The focus of the study was to evaluate rates of detection of oestrus, synchrony of oestrus, pregnancy rate, and effect of ovarian status at initiation of the programmes on rates of detection of oestrus and pregnancy rate. Spring-calving, lactating dairy cows (n = 2009) were allocated at random to one of six treatments: (1) A (n = 335), progestogen (controlled intravaginal drug release; CIDR) inserted per vaginum 10 d before breeding season for 8 d, 10 microg of buserelin at CIDR insertion, PGF2alpha treatment on the day prior to CIDR removal, and AI of cows detected in oestrus within 6 d after CIDR withdrawal; (2) B (n = 330), as in A, plus 1 mg of oestradiol benzoate i.m. 10 h post CIDR withdrawal; (3) C (n = 347), as in A, except buserelin was replaced by 10 mg of oestradiol benzoate; (4) D (n = 335), as in A, plus PGF2alpha and oestradiol benzoate at CIDR insertion; (5) E (n = 332), CIDR containing a 10 mg oestradiol benzoate capsule inserted per vaginum for 12 d; or (6) F (n = 330), as in E, plus PGF2alpha on the day prior to CIDR withdrawal. The oestrous detection rate (number of cows detected in oestrus within 6 days of CIDR withdrawal as a proportion of the number of cows submitted for synchronization of oestrus) and oestrous synchrony (oestrous detection rate within 2 d of CIDR withdrawal), respectively, were greater (P<0.05) following B (95.7% of 330, 98.7% of 316) compared with any of the other programmes for synchronization of oestrus (A: 87.5 of 335, 79.4% of 293; C: 86.7% of 347, 80.0% of 301; D: 90.1% of 335, 89.8% of 302; E: 74.4% of 332, 70.4% of 247; F: 76.4% of 330, 78.5% of 252). The oestrous detection rate was reduced (P<0.05) among cows in metoestrus administered E (64.0% of 50) relative to similar cows administered F (82.8% of 64). Pregnancy rate was greater (P<0.05) following B (57.9% of 330) than A (48.9% of 335, P = 0.06), C (43.2% of 347), E (40.0% of 332), and F (35.1% of 330) but not D (59.3% of 302), when based on those cows presented for oestrous synchronization programmes. In conclusion, 1 mg of oestradiol benzoate administered 10 h post CIDR withdrawal (B) resulted in the best overall oestrous detection, oestrous synchrony, and pregnancy rates, which would be beneficial to a fixed-time AI program.     

Response of sows to oestradiol benzoate treatment after weaning at two stages of lactation

The timing and dosage of oestradiol benzoate injected after weaning was critical with respect to the pattern of behavioural oestrus and the ovarian stimulation achieved; treatment on the day of weaning (Day 0) and Day 1 with 60 micrograms oestradiol benzoate/kg body wt produced poor ovulatory responses and abnormal oestrous behaviour. Treatment on Day 2 with 30 micrograms oestradiol benzoate/kg resulted in consistent oestrus and ovulatory responses although the ovulation rates (10 . 6 +/- 1 . 1 in 3-week and 12 . 2 +/- 1 . 7 in 5-week weaned sows) were below those expected in fertile untreated sows weaned at these times. The timing of the preovulatory LH surge (53 . 6 +/- 2 h after oestradiol benzoate) was closely synchronized in all sows and a similar synchronous rise in plasma progesterone concentrations 100 +/- 4 h after oestradiol benzoate suggests a similar synchrony of ovulation. The magnitude of the LH and FSH responses to oestradiol benzoate were similar to those that occur in untreated sows and similar differences also existed in gonadotrophin secretion related to the length of lactation.     

Oestradiol and the preovulatory surges of luteinising hormone and follicle stimulating hormone in ewes during the breeding season and transition into anoestrus

This study was designed to see if giving exogenous oestradiol, during the follicular phase of the oestrous cycle of intact ewes, during the breeding season or transition into anoestrus, would alter the occurrence, timing or magnitude of the preovulatory surge of secretion of luteinising hormone (LH) or follicle stimulating hormone (FSH). During the breeding season and the time of transition, separate groups of ewes were infused (intravenously) with either saline (30 ml h⁻¹; n = 6) or oestradiol in saline (n = 6) for 30 h. Infusion started 12 h after removal of progestin-containing intravaginal sponges that had been in place for 12 days. The initial dose of oestradiol was 0.02 μg h⁻¹; this was doubled every 4 h for 20 h, followed by every 5 h up to 30 h, to reach a maximum of 1.5 μg h⁻¹. Following progestin removal during the breeding season, peak serum concentrations of oestradiol in control ewes were 10.31 ± 1.04 pg ml⁻¹, at 49.60 ± 3.40 h after progestin removal. There was no obvious peak during transition, but at a time after progestin removal equivalent to the time of the oestradiol peak in ewes at mid breeding season, oestradiol concentrations were 6.70 ± 1.14 pg ml⁻¹ in ewes in transition (P < 0.05). In oestradiol treated ewes, peak serum oestradiol concentrations (24.8 ± 2.1 pg ml⁻¹) and time to peak (41.00 ± 0.05 h) did not differ between seasons (P > 0.05). During the breeding season, all six control ewes and four of six ewes given oestradiol showed oestrus with LH and FSH surges. The two ewes not showing oestrus did not respond to oestrus synchronisation and had persistently high serum concentrations of progesterone. During transition, three of six control ewes showed oestrus but only two had LH and FSH surges; all oestradiol treated ewes showed oestrus and gonadotrophin surges (P < 0.05). The timing and magnitude of LH and FSH surges did not vary with treatment or season. In blood samples collected every 12 min for 6 h, from 12 h after the start of oestradiol infusion, mean serum concentrations of LH and LH pulse frequency were lower in control ewes during transition than during mid breeding season (P < 0.05). Oestradiol treatment resulted in lower mean serum concentrations of LH in season and lower LH pulse frequency in transition (P < 0.05). We concluded that enhancing the height of the preovulatory peak in serum concentrations of oestradiol during the breeding season did not alter the timing or the magnitude of the preovulatory surge of LH and FSH secretion and that at transition into anoestrus, oestradiol can induce oestrus and the surge release of LH and FSH as effectively as during the breeding season.     

Effect of age and time of day on the timing of the surge in luteinizing hormone, behavioural oestrus and mating in red deer hinds (Cervus elaphus).

The oestrous cycles of fourteen red deer hinds (six yearling; eight more than 2 years old) were synchronized during the early breeding season by removal of a progesterone-containing intravaginal device and blood samples were taken at intervals of 3 h commencing 13 or 25 h later and continued for 54 h. The controlled internal drug release devices (CIDRs) were removed at 08:00 h (group 1; three yearlings and four adults) or 12 h later at 20:00 h (group 2; three yearlings and four adults). There was no significant effect of time of removal of CIDR on the interval to the onset of oestrus (group 1, 34.5 +/- 4.05 h; group 2, 42.14 +/- 7.8 h) on the time of peak concentration (group 1, 41.81 +/- 5.69 h; group 2, 41.71 +/- 7.81 h) or on duration of the luteinizing hormone (LH) surge (group 1, 15.00 +/- 0.95 h; group 2, 14.57 +/- 0.78 h). The six yearling animals exhibited oestrus and LH surge significantly later than the adults (55 +/- 4.2 versus 32 +/- 6.3 h for the LH surge for yearling and adult females, respectively). In a further experiment, 20 hinds were synchronized during the breeding season by removal of CIDR at two times of day 12 h apart and placed with a stag. Mating took place at a mean time of 42.1 +/- 2.4 h and 37.0 +/- 1.3 h later in the two groups. There was no significant effect of time of removal of CIDR upon time to onset of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Progesterone, oestradiol-17 beta and LH during the oestrous cycle of muskoxen (Ovibos moschatus)

Progesterone, oestradiol-17 beta and LH were measured in plasma from 6 non-pregnant, captive, female muskoxen during the 1984 and 1985 breeding seasons. Jugular blood samples were taken on an alternating 3/4-day schedule in 1984 and daily or at 4-h intervals over oestrus, via indwelling jugular cannulae, for 6 weeks in 1985. Oestrous cycle length was 19.6 +/- 0.96 (s.d.) days (n = 19) and did not vary between the first and subsequent cycles of the season. Progesterone was lowest at oestrus (less than or equal to 0.1 ng/ml), began to rise on Days 4-5, peaked on Days 10-12 (mean = 2.6 ng/ml) and returned to baseline 2-5 days before the next oestrus. A small rise in progesterone before the first cycle of the breeding season was observed on 7 of 12 occasions. Oestradiol-17 beta was significantly higher (P less than 0.001) 1-4 days before, or coincident with, oestrus. The average duration of the LH peak was 24.6 h (n = 7) and coincided with observations of behavioural oestrus. In one animal behavioural oestrus and an LH peak preceded a small progesterone rise at the beginning of the breeding season. The temporal relationship of these three hormones during the muskox oestrous cycle is very similar to that seen in domestic ruminants.     

Control of oestrus in cattle using progesterone coils

Four experiments were conducted to determine the effect of length of treatment, stage of cycle at start of treatment and administration of oestradiol benzoate or progesterone at the start of treatment with intravaginal progesterone coils on oestrous response and fertility. In Experiment 1, the number of heifers in oestrus was affected neither by injection of 5 mg oestradiol benzoate alone or with 200 mg progesterone nor by length of treatment. More heifers (P < 0.05) were in oestrus on day 2 after treatment following a 12-day treatment compared to a 9-day treatment.In Experiment 2, heifers between days 17 and 20 of the oestrous cycle received an injection of either 5 mg oestradiol benzoate alone or with 200 mg progesterone at the start of a 9-day treatment with progesterone coils. Neither the number of heifers in oestrus nor the pattern of onset were affected after treatment. In Experiment 3, heifers between days 0 and 3 of the oestrus cycle received progesterone coils for 9, 12 or 14 days. In addition, animals received (i) no further treatment, (ii) a gelatin capsule adhered to the coil containing 10 mg oestradiol benzoate (iii) a gelatin capsule adhered to the coil containing 200 mg progesterone. Following a 9- or 12-day treatment period heifers receiving the coil with the oestrogen capsule had a high oestrous response ( compared to , P < 0.05). When oestrogen was not given, there was a significant linear effect of duration of treatment on the number in oestrus (9 days, ; 12 days ; 14 days, ; P < 0.05).In Experiment 4, post-partum cows were used to compare a 9- and 12-day treatment period and half the animals in each group received either 5 mg oestradiol benzoate and 200 mg progesterone at the start of treatment or a 10 mg gelatin capsule adhered to the coil. The length of treatment affected the number of heifers in oestrus since were in oestrus after a 12-day treatment period compared with after a 9-day period (P < 0.001). There were no significant differences in the number of cows in oestrus after injection of oestrogen and progesterone ( ) or after the use of the gelatin capsule ( ).     

Effect of adrenocorticotrophic hormone (ACTH1-24) on ovine pituitary gland responsiveness to exogenous pulsatile GnRH and oestradiol-induced LH release in vivo.

The present experiment was designed to determine if and how exogenous ACTH replicates the effects of stressors to delay the preovulatory LH surge in sheep. Twenty-four hours after oestrous synchronisation with prostaglandin in the breeding season, groups of 8-9 intact ewes were injected with 50 microg oestradiol benzoate (0 h) followed 8 h later by 3 injections of saline or GnRH (500 ng each, i.v.) at 2 h intervals (controls). Two further groups received an additional 'late' injection of ACTH (0.8 mg i.m.) 7.5 h after oestradiol, i.e., 0.5 h before the first saline or GnRH challenge. To examine if the duration of prior exposure to ACTH was important, another group of ewes was given ACTH 'early', i.e. 2.5 h before the first GnRH injection. The first GnRH injection produced a maximum LH response of 1.9+/-0.4 ng/ml which was significantly (p < 0.01) enhanced after the second and third GnRH challenge (7.1+/-1.5 ng/ml and 7.0+/-1.7 ng/ml, respectively; 'self-priming'). Late ACTH did not affect the LH response after the first GnRH challenge (1.9+/-0.4 vs. 1.8+/-0.3 ng/ml; p > 0.05) but decreased maximum LH concentrations after the second GnRH to 35% (7.1+/-1.5 vs. 4.6+/-1.1 ng/ml; p = 0.07) and to 40% after the third GnRH (7.0+/-1.7 vs. 4.0+/-0.8 ng/ml; p = 0.05). When ACTH was given early, 4.5 h before the second GnRH, there was no effect on this LH response suggesting that the effect decreases with time after ACTH administration. Concerning the oestradiol-induced LH surge, exogenous GnRH alone delayed the onset time (20.5+/-2.0 vs. 27.8+/-2.1 h; p > 0.05) and reduced the duration of the surge (8.5+/-0.9 vs. 6.7+/-0.6 h; p > 0.05). The onset of the LH surge was observed within 40 h after oestradiol on 29 out of 34 occasions in the saline +/- GnRH treated ewes compared to 11 out of 34 occasions (p < 0.05) when ACTH was also given, either late or early. In those ewes that did not have an LH surge by the end of sampling, plasma progesterone concentrations during the following oestrous cycle increased 2 days later suggesting a delay, not a complete blockade of the LH surge. In conclusion, we have revealed for the first time that ACTH reduces the GnRH self-priming effect in vivo and delays the LH surge, at least partially by direct effects at the pituitary gland.     

Effects of season and phase of the estrous cycle on steroidogenesis and LH-FSH sensitivity of large ovine follicles perfused in vitro

The aims of this study were to compare stero?dogenesis (progesterone, androstenedione and estradiol production) and response to LH and FSH challenge by whole perifused follicles 4 to 5.5 mm in diameter, obtained at different periods of the breeding season (onset, middle, end), during anestrus and the luteal phase. We have observed that all follicles do not have the same stero?dogenetic potential and do not respond with the same intensity to LH and FSH. At the middle of the breeding season, LH and FSH supplementation was ineffective in increasing progesterone secretion by follicles (0.19+/-0.05 vs. 0.20+/-0.03 ng/mL). In contrast, gonadotrophin challenge elicited significant (P<0.05) increases in androstenedione (0.94+/-0.34 vs. 0.35+/-0.09 ng/mL) and estradiol (120+/-11 vs. 49+/-10 pg/mL) production immediately after its administration. At the onset of the breeding season, steroidogenesis was identical under both basal and gonadotrophin-stimulated conditions unlike that in middle of the breeding season. However follicles were more sensitive to the gonadotrophin challenge in terms of estradiol production than those collected at the middle of the breeding season (220+/-45 vs. 120+/-11 pg/mL). Follicles obtained at the end of the breeding season featured higher progesterone (2.61+/-0.81 vs. 0.19+/-0.05 ng/mL; P<0.05) and lower estradiol production (10+/-3 vs. 49+/-10 pg/mL; P<0.05) that was not influenced by LH and FSH. Basal androstenedione secretion was comparable to that observed at the middle of the breeding season (0.42+/-0.10 vs. 0.35+/-0.09 ng/mL), but the response to stimulation was significantly higher (1.82+/-0.61 vs. 0.94+/-0.34 ng/mL; P<0.05). In anoestrus and the luteal phase, follicles presented higher progesterone and androstenedione and lower estradiol concentrations (P<0.05) compared with those obtained during the follicular phase at the middle of the breeding season. In the luteal phase, follicles remained capable of responding to LH-FSH challenge by increasing estradiol secretion (9+/-1 before and 21+/-6 pg/mL after LH-FSH; P<0.05). In contrast, in the luteal phase, estradiol production was not increased by LH-FSH challenge (7+/-2 vs. 12+/-4 pg/mL).     

Effects of oestradiol and some of its esters on gonadotrophin release and ovarian follicular dynamics in CIDR-treated beef cattle

Three experiments were conducted to: (1) compare the effect of three oestradiol formulations on gonadotrophin release in ovariectomised cows; (2) compare the effects of either oestradiol-17beta (E-17beta) or oestradiol benzoate (EB), given at two doses, on the synchrony of ovarian follicular wave emergence in CIDR-treated beef cattle; and (3) determine the timing of ovulation of the dominant follicle of a synchronised follicular wave following administration of E-17beta or EB 24h after progesterone withdrawal. In Experiment 1, ovariectomised cows (n = 16) received a once-used CIDR on Day 0 (beginning of the experiment) and were allocated randomly to receive 5mg of E-17beta, EB or oestradiol valerate (EV) plus 100mg progesterone i.m. The CIDR inserts were removed on Day 7. There were effects of time, and a treatment-by-time interaction (P < 0.0001) for plasma concentrations of both oestradiol and FSH. Plasma oestradiol concentrations peaked 12h after treatment, with highest (P < 0.01) peak concentrations in cows given E-17beta; estradiol concentrations subsequently returned to baseline by 36 h in E-17beta-treated cows and by 96 h in EB- and EV-treated cows. Plasma FSH concentrations decreased by 12h after oestradiol treatment in all groups (P < 0.0001), reached a nadir at 24h, and increased by 60 h in all groups; plasma FSH reached higher (P < 0.02) concentrations in E-17beta-treated than in EB- or EV-treated cows. In Experiment 2, non-lactating Hereford cows (n = 29) received a new CIDR on Day 0 (beginning of the experiment), and were assigned randomly to receive 1 or 5mg of E-17beta or EB i.m. on Day 1. On Day 8, CIDR were removed and PGF was given. Transrectal ultrasonography was done once daily from 2 days before CIDR insertion to 2 days after CIDR removal, and then twice-daily to ovulation. Although there was no difference among groups in the interval from oestradiol treatment to follicular wave emergence (4.2 +/- 0.3 days; P = 0.5), 5mg of E-17beta resulted in the least variable interval to wave emergence (P < 0.005), compared with the other treatment groups which were not different (P = 0.1). For the interval from CIDR removal to ovulation, there were no differences among groups for either means (P = 0.5) or variances (P = 0.1). In Experiment 3, beef heifers (n = 32) received a once-used CIDR on Day 0 (beginning of the experiment) plus 100mg progesterone i.m. and were assigned randomly to receive 5mg E-17beta or 1mg EB i.m. On Day 7, CIDR were removed and all heifers received PGF. On Day 8 (24h after CIDR removal), each group was subdivided randomly to receive 1mg of either E-17beta or EB i.m. There was no effect of oestradiol formulation on interval from treatment to follicular wave emergence (4.1 +/- 0.2 days; P = 0.7) or on the median interval (76.6h; P = 0.7) or range (72-120 h; P = 0.08) from CIDR removal to ovulation. In summary, oestradiol treatments suppressed FSH in ovariectomised cows, with the duration of suppression dependent on the oestradiol formulation. Both E-17beta and EB effectively synchronised ovarian follicular wave emergence and ovulation in CIDR-treated cattle, and the interval from CIDR removal to ovulation did not differ in heifers given either E-17beta or EB 24h after CIDR removal.     

Comparison of the rate of decline in plasma progesterone concentrations at a natural and progesterone-synchronized oestrus and its effect on tonic LH secretion in the ewe

The pattern of change in plasma progesterone and LH concentrations was monitored in Clun Forest ewes at a natural oestrus and compared to that observed after removal of progesterone implants. The rate of decline in plasma progesterone concentrations after implant withdrawal (1.8 +/- 0.2 ng/ml h-1) was significantly greater (P less than 0.001) than that observed at natural luteolysis (0.2 +/- 0.1 ng/ml h-1), and this resulted in an abnormal pattern of change in tonic LH secretion up to the time of the preovulatory LH surge. This more rapid rate of progesterone removal was also associated with a shortening of the intervals from the time that progesterone concentrations attained basal values to the onset of oestrus (P less than 0.05) and the onset of the preovulatory LH surge (P less than 0.01). However, there were no significant differences in the duration of the LH peak, preovulatory peak LH concentration, ovulation rate or the pattern of progesterone concentrations in the subsequent cycle. It is suggested that the abnormal patterns of change in progesterone and tonic LH concentrations may be one factor involved in the impairment of sperm transport and abnormal patterns of oestradiol secretion known to occur at a synchronized oestrus.     

Effect of transport on pulsatile LH release in ovariectomized ewes with or without prior steroid exposure at different times of year

The initial aim of the present study was to test whether the stress of transport suppresses LH pulsatile secretion in ewes. In a pilot experiment in the late breeding season, transport resulted in an unexpected response in three out of five transported, ovariectomized ewes pretreated with oestradiol and progesterone. Before transport, seasonal suppression of LH pulses had occurred earlier than anticipated, but LH pulsatility suddenly restarted for the period of transport. This finding was reminiscent of unexplained results obtained in ovariectomized ewes infused centrally with high doses of corticotrophin-releasing hormone after pretreatment with low doses of oestradiol with or without progesterone. Hence, an additional aim of the present study was to examine whether these latter results with corticotrophin-releasing hormone could be reproduced by increasing endogenous corticotrophin-releasing hormone secretion by transport. Subsequent experiments used groups of at least eight ovariectomized ewes at different times of the year with or without prior exposure to steroids to assess whether these unexpected observations were associated with season or the prevailing endocrine milieu. In the mid-breeding season, transport for 4 h in the absence of steroid pretreatment for 8 months reduced LH pulse frequency from 7.5 +/- 0.3 to 6.3 +/- 0.4 pulses per 4 h (P < 0.05) and LH pulse amplitude from 2.6 +/- 0.5 to 1.8 +/- 0.3 ng ml-1 (P < 0.05). Similarly, in the mid-breeding season, 34 h after the cessation of pretreatment with oestradiol and progesterone, transport suppressed LH pulse frequency from 6.1 +/- 0.4 to 5.5 +/- 0.3 pulses per 4 h (P < 0.05) with a tendency of effect on amplitude (6.2 +/- 2.7 to 2.61 +/- 0.6 ng ml-1; P = 0.07; note the large variance in the pretransport data). During mid-anoestrus, evidence of a suppressive effect of transport was only observed on LH pulse amplitude (4.7 +/- 0.6 versus 3.0 +/- 0.5 pulses per 4 h; P < 0.05) in ovariectomized ewes that had not been exposed to ovarian steroids for 4 months. Repetition of the pilot experiment with 12 ewes during the transition into anoestrus resulted in one ewe with LH pulses seasonally suppressed but increased by transport; 11 ewes had a distinct pulsatile LH pattern which was decreased by transport in six ewes. In anoestrus, there was no effect of transport on LH pulse frequency or amplitude in intact ewes, or those ovariectomized 2-3 weeks previously, with or without prior oestradiol and progesterone treatment. However, basal concentrations of cortisol were greater in anoestrus than in the breeding season, and the increment in cortisol during transport was similar in anoestrus and the breeding season but greater during the transition into anoestrus (P < 0.05). Progesterone concentrations increased from 0.31 +/- 0.02 ng ml-1 before transport to 0.48 +/- 0.05 ng ml-1 during the second hour of transport (P < 0.05). In conclusion, transport reduced LH pulse frequency and amplitude in ovariectomized ewes that had not been exposed to exogenous steroids for at least 4 months. In most animals, the previously observed increase in LH pulsatility induced by exogenous CRH was not reproduced by increasing endogenous CRH secretion by transport. However, in four ewes, transport did increase LH pulsatility, but only during the transition into anoestrus in ewes with seasonally suppressed LH profiles after withdrawal of steroid pretreatment.     

Effect of early luteolysis in progesterone-based timed AI protocols in Bos indicus, Bos indicus x Bos taurus, and Bos taurus heifers

The objective of this study was to evaluate the effects of treatment with an intravaginal progesterone-releasing device (CIDR) and estradiol benzoate (EB) on follicular dynamics in Bos indicus (n=23), Bos taurus (n=25), and cross-bred (n=23) heifers. To assess the influence of reduced serum progesterone concentrations during 8 days of treatment with a progesterone-releasing device on follicular dynamics, half of the heifers received PGF at CIDR insertion (Day 0; 3 x 2 factorial design). Mean (+/-S.E.M.) serum progesterone concentrations during CIDR treatment varied (P<0.05) among genetic groups: B. indicus (5.4+/-0.1 ng/mL), B. taurus (3.3+/-0.0 ng/mL), and cross-bred (4.3+/-0.1 ng/mL). Maximum diameter of the dominant follicle (DF) was smaller (P<0.01) in B. indicus heifers (9.5+/-0.5 mm) than in cross-bred (12.3+/-0.4 mm) or B. taurus heifers (11.6+/-0.5 mm). B. indicus experienced lower (P<0.01) ovulation rate (39.1%) than did B. taurus (72.7%) and cross-bred (84.0%). Heifers treated with PGF on Day 0 had lower (P<0.05) serum progesterone concentrations during progesterone treatment. The PGF treatment on Day 0 increased (P<0.01) the diameter of the DF (11.9+/-0.4 mm vs. 10.5+/-0.4 mm). Moreover, greater (P=0.02) ovulation rates (78.8 vs. 54.0%) occurred in heifers treated with PGF on Day 0. In summary, B. indicus heifers had greater serum progesterone concentrations, smaller DF diameter, and a lower ovulation rate compared to B. taurus heifers. Prostaglandin treatment on the day of CIDR insertion reduced serum progesterone during treatment, and resulted in increased maximum DF diameter and ovulation rate.     

Effects of maturity of the potential ovulatory follicle on induction of oestrus and ovulation in cattle with oestradiol benzoate

The effect of maturity of the dominant follicle (DF) on the capacity of oestradiol benzoate (ODB) to induce oestrus and ovulation was examined in cattle. In experiment 1, 31 prepubertal heifers each received an intravaginal progesterone insert (IPI) and 1mg ODB i.m./500kg BW (ODB1). Daily ovarian ultrasonography detected emergence of a new follicular wave 3.1+/-0.1 days after ODB1. The IPI was removed when newly emerged DF were "young" (1.3+/-0.1 days after emergence; YDF; n=15) or "mature" (4.2+/-0.1 days; MDF; n=16), and 24h later, heifers received 0.75mg ODB/500kg BW (ODB2; n=16) or no further treatment (NoODB2; n=15). Most of the heifers receiving ODB2 were observed in oestrus (15/16) and ovulated (12/16), as compared to 0/15 and 1/15 in the NoODB2 group, respectively (P<0.01). In experiment 2, 32 heifers received ODB1 on day 6 of the oestrous cycle, and new follicular wave emergence was detected 3.2+/-0.1 days later. Heifers received an injection of prostaglandin-F2alpha (PGF) when the DF was young (1.1+/-0.1 days after emergence; YDF; n=16) or mature (4 days; MDF; n=16), and then ODB2 24h later or no further treatment (NoODB2). The interval from PGF to oestrus was greater (P<0.01) in the YDF-NoODB2 (70+/-3.9h) as compared to MDF-NoODB2 group (57+/-1.8h). Inclusion of ODB2 reduced (P<0.01) this interval to 47.0+/-0.7h without regard to the maturity of the DF (maturityxODB2, P<0.05) and also reduced (P<0.05) the interval to ovulation. In experiment 3, 21 suckling anoestrous cows received an IPI and ODB1 at 29.3+/-1.7 days postpartum. The IPI were removed either 1 day (YDF; n=9) or 3.9+/-0.1 days (MDF; n=9) after emergence of a new follicular wave and every cow received ODB2. Oestrus was subsequently detected in all but one animal. Ovulation of the newly emerged DF was detected within 48h of ODB2 in nine of nine cows of the MDF group, and in four of nine of the YDF group (P<0.05). During the subsequent ovulatory cycle, luteal size and plasma concentrations of progesterone were greater (P<0.01) in the MDF group compared to the YDF group. We conclude that behavioural oestrus is readily induced by 0.75mg ODB i.m./500kg BW. Maturity of the DF appeared to have little influence on the ability of the DF to ovulate in heifers. In contrast, young DF in lactating anoestrous cows were less likely to respond to the ovulatory cue provided, and luteal development was compromised in those that did ovulate.     

Synchronization of estrus with PGF2 alpha administered 18 days after a progesterone treatment in lactating dairy cows

In a previous study we showed that estrus synchronization with 2 treatments of PGF2 alpha 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2 alpha treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2 alpha was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2 alpha (25 mg, i.m., Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2 alpha treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.     

Effects of human chorionic gonadotrophin on contractile activity of steroid-primed pig myometrium in vitro

We examined the effects of (a) oestrogen and progesterone on concentrations of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in uterine smooth muscle in vivo and (b) hCG on spontaneous myometrial contractions in vitro. Ovariectomized gilts received 2 ml corn oil (control; n = 5), 2 mg oestradiol benzoate (n = 6) or 20 mg progesterone (n = 5) for 5 days. Gilts were hysterectomized 8 h after the last injection and longitudinal sections of myometrium were incubated in modified Krebs' solution with 0 or 10 i.u. of hCG (n = 10/gilt) for 4 h at 37 degrees C in 95% O2:5% CO2. After incubation, myometrial sections were placed in a tissue chamber perfused with Krebs' solution and mechanical activity was recorded for 30 min. Cell membrane fractions were prepared from myometrial tissue not used for in-vitro studies and analysed for LH/hCG receptors. Treatment with oestradiol benzoate increased (P less than 0.01) the number of LH/hCG-binding sites compared with gilts receiving corn oil or progesterone. Incubation of myometrium with hCG reduced (P less than 0.01) the frequency and amplitude of spontaneous uterine contractions in gilts treated with oestradiol benzoate. In contrast, hCG had no effect (P greater than 0.05) on the pattern of myometrial contractions in gilts given corn oil or progesterone. These results indicate that oestradiol promotes the synthesis of LH/hCG receptors in pig myometrium and incubation of oestrogen-primed tissue with hCG has a quiescent effect on myometrial contractility.     

Temporal relationship between the onset of oestrus, the preovulatory LH surge and ovulation in farmed fallow deer, Dama dama

A study was conducted to determine the timing of ovulation relative to the onset of oestrus and the preovulatory LH surge in fallow deer. Mature fallow does were randomly allocated to two treatments (N = 10 per treatment) designed to synchronize oestrus on or about 17 May. Does assigned to Group 1 (prostaglandin-induced oestrus) each initially received single intravaginal CIDR [Controlled Internal Drug Release] devices for 13 days followed by an i.m. injection of 750 mg cloprostenol on Day 12 (15 May) of the subsequent luteal cycle. Does assigned to Group 2 (progesterone-induced oestrus) each received CIDR devices for 13 days, with withdrawal occurring on 15 May. All does were run with crayon-harnessed bucks (10:1 ratio) from the start of synchronization (18:00 h 15 May). Ten does (5 per group) were blood sampled via indwelling jugular cannulae every 2 h for 72 h from cloprostenol injection or CIDR device withdrawal and the plasma was analysed for concentrations of progesterone and LH by radioimmunoassay. Does within each treatment were randomly allocated to an ovarian examination time of 12, 16, 20 or 24 h after the onset of oestrus. Laparoscopy was repeated at 12-h intervals until ovulation was recorded. The ovaries of does failing to exhibit oestrus were examined 72 and 86 h after cloprostenol injection or CIDR device withdrawal. A total of 17 does were observed to exhibit oestrus at a mean (+/- s.e.m.) interval from treatment of 44.6 +/- 3.6 h for Group 1 (N = 9) and 34.1 +/- 2.5 h for Group 2 (N = 8).(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between the onset of oestrus, the preovulatory surge in luteinizing hormone and ovulation following oestrous synchronization and superovulation of farmed red deer (Cervus elaphus).

The timing of ovulation relative to the onset of oestrus and the preovulatory surge in luteinizing hormone (LH) was studied in red deer following treatments to synchronize oestrus and induce either a monovulatory or superovulatory response. Mature hinds (n = 36) were allocated randomly to two mating groups (n = 16 + 20), with respective treatments staggered by 4 weeks during the 1990 rut (March-April). Each hind was treated with an intravaginal controlled internal drug releasing (CIDR)-type S device for 14 days. Treatments to induce a monovulatory response included CIDR device alone (treatment A; n = 4 + 8) and additional injection of 200 iu pregnant mares' serum gonadotrophin (PMSG) at device removal (treatment B; n = 4 + 4). Treatments to induce a superovulatory response included injections of 200 iu PMSG and 0.5 units ovine follicle-stimulating hormone (FSH) at about time of removal of CIDR devices (treatment C; n = 4 + 4) and further treatment with gonadotrophin-releasing hormone (GnRH) analogue 18 h after removal of CIDR devices (treatment D; n = 4 + 4). The hinds were run with crayon-harnessed stags from insertion of CIDR devices (12 March or 9 April) and blood samples were taken every second day to determine plasma progesterone. Further blood samples were collected for determination of plasma LH and progesterone via indwelling jugular cannulae every 2 h for 72 h from removal of CIDR devices. Hinds were allocated randomly to an initial ovarian examination by laparoscopy at either 16 or 20 h (A and B), or 12 or 16 h (C and D) after the onset of oestrus, with laparoscopy repeated at intervals of 8 h until either ovulation was recorded (A and B), or for four successive occasions (C and D). All hinds received cloprostenol injections 15 days after device removal. A total of 28 hinds (78%) exhibited oestrus and a preovulatory LH surge, with mean (+/- SEM) times to onset of oestrus of 44.6 +/- 1.0 h (A; n = 7), 37.4 +/- 2.0 h (B; n = 7), 16.3 +/- 1.7 h (C; n = 6) or 14.0 +/- 1.7 h (D; n = 8). Failure to exhibit oestrus or LH surge was most prevalent among hinds in treatment A early in the rut.(ABSTRACT TRUNCATED AT 400 WORDS)     

Season affects characteristics of the pre-ovulatory LH surge and embryo viability in superovulated ewes

The aim of this study was to determine whether there are seasonal shifts in ovulatory response, and in the viability of ova recovered from superovulated ewes. Fifty mature ewes underwent a standard oestrous synchronisation (CIDR), superovulation (oFSH) and artificial insemination procedure during October (peak breeding season) and April (transition to anoestrus). In each month peripheral LH and progesterone concentrations were measured around the time of ovulation and embryos were recovered, graded and cryopreserved on day 6 after insemination. During the subsequent breeding season, grade 1 and 2 morulae and unexpanded blastocysts were thawed and transferred singly to synchronous recipients (October, n = 40; April, n = 40) or cultured in vitro for 18-20 h (October, n = 107; April, n = 98). Following culture, viable embryos were stained to count cell nuclei or assayed to measure their capacity for glucose metabolism ([3H]glucose) and protein synthesis ([35S]methionine). Peak LH concentrations were higher in October than in April (38.2 +/- 3.26 ng ml(-1) versus 25.7 +/- 1.99 ng ml(-1), respectively; P < 0.01) and the pre-ovulatory LH surge was advanced by approximately 3 h (P < 0.05). Progesterone concentrations at CIDR withdrawal were lower in October than in April (3.1 +/- 0.16 ng ml(-1) versus 4.3 +/- 0.19 ng ml(-1), respectively; P < 0.001) but were not different at embryo recovery. Season did not affect the numbers of corpora lutea per ewe or the numbers of ova recovered but the proportion of recovered ova that was unfertilised/degenerate was lower in October than in April (0.43 versus 0.58, respectively; P < 0.001). For embryos containing more than 16 cells, there was no effect of season on the median stage of development or morphological grade. The proportions of October and April embryos that established pregnancy following transfer to recipient ewes were 0.78 and 0.70 (not significantly different), and that were viable after in vitro culture were 0.66 and 0.37 (P < 0.05), respectively. Season did not affect the number of nuclei per viable embryo or the capacity for protein synthesis but the glucose uptake of October embryos was approximately double that of April embryos (3163+/-293.4 dpm versus 1550+/-358.9 dpm, respectively; P < 0.05). Results indicate that during the late compared to peak breeding season, there is an increased incidence of fertilisation failure as a possible consequence of seasonal shifts in LH secretion and (or) associated effects on follicular function. Frozen-thawed embryos produced at contrasting stages of the breeding season are equally viable in vivo but those produced during the late, as opposed to the peak breeding season have lower viability following in vitro culture.     

Effects of removal in late pregnancy of the corpus luteum, graafian follicle or ovaries on plasma progesterone, oestradiol, LH, parturition and post-partum oestrus in the tammar wallaby, Macropus eugenii

Concentrations of oestradiol-17 beta, progesterone, and luteinizing hormone (LH) were measured in plasma collected at 6- to 12-h intervals from tammars around the time of parturition and post-partum oestrus. Parturition occurred on Day 26 or 27 after reactivation of lactation-delayed pregnancy and coincided with a precipitous decline in progesterone levels. A sharp rise in oestradiol, from basal concentrations of less than 10 pg/ml to a peak of 13 to 32 pg/ml, as well as oestrus, followed the drop in progesterone by 8.3 and 9.8 h, respectively. The LH surge was dependent on the oestradiol rise and followed it by 7 h. Ovulation followed mating by about 30 h and the LH surge by 24 h. Removal of the ovary with the large Graafian follicle prevented the oestradiol rise, oestrus and the LH surge, but not parturition. Peripartum changes in peripheral oestradiol do not appear to be involved in initiation of parturition but the oestradiol rise and associated change in the oestradiol:progesterone ratio are important signals for post-partum oestrus and the LH surge.