Effects of thermal stress on plasma concentrations of luteinizing hormone, progesterone, prolactin and testosterone in the cycling ewe

Naturally cycling white faced ewes were utilized to study the effects of continuously elevated environmental temperature and/or humidity on plasma concentrations of luteinizing hormone (LH), prolactin (PRL), progesterone (P4) and testosterone (TE) during the estrous cycle. Fourteen ewes were randomly allocated on the day of estrus (day 0) to either thermoneutral conditions (21.1 degrees C, 65% relative humidity) or elevated ambient temperature/humidity conditions (36.1 degrees C, 71% relative humidity) producing an average 1.4 degrees C hyperthermia. Animals remained in their respective environments and blood samples were collected daily until the next estrus or day 20, whichever occurred first. Starting at noon on day 14, blood was sampled every 2 hours. Concentrations of LH, PRL, P4 and TE were quantified using validated radioimmunoassays. Hyperthermic ewes exhibited 1) a significant decrease (P<0.05) in the incidence of behavioral estrus and a preovulatory LH surge at the expected time of the estrous cycle, 2) significantly lower (P<0.05) plasma P4 between days 7 and 13 of the cycle, 3) a six-fold increase of PRL levels (P<0.01). Plasma levels of TE were not significantly affected by hyperthermia. The only two experimental ewes which exhibited estrus and an LH surge also showed an unusual and significant peak in plasma P4 two days before estrus. These results confirm that elevated environmental temperatures that result in hyperthermia can induce endocrine imbalances in the ewe which may contribute to decreased reproductive efficiency in the heat-stressed female.     

Estrous activity in different breeds and breed crosses of sheep

Estrus was monitored in 715 straightbred and crossbred ewes during spring lactation, postweaning, summer and/or late summer breeding periods. Straightbred ewes were comprised of seven breeds, and crossbreds consisted of Rambouillet- and Finnsheep-sired ewes of the seven breeds. Estrus was detected in 5.4% of the Rambouillet and Finnsheep crossbred ewes during lactation. After weaning, the incidence of estrus was 1.1% in all crossbred and straightbred ewes. The incidence of estrus was 5.2% for all ewes during the summer period. During late summer (July 28 to August 17), 42% of all ewes showed estrus and both breed of sire and breed of dam influenced estrous activity (P<0.01). Straightbred Rambouillet, Targhee, Dorset and most Rambouillet-sired crossbred ewes showed the greatest estrous activity and could be the genetic stock of choice for early lamb production. Straightbred Hampshire, Suffolk and most Finnsheep crossbred ewes showed estrous activity later in the season. Results support the conclusion that certain sheep breeds and breed crosses show estrous activity during August, while other breeds and breed crosses begin estrous activity later and continue until March or April. Thus, lambs may be produced from January through September each year by maintaining several different breeds or breed crosses in the breeding flock.     

Effects of prostaglandin F(2alpha) dosage of synchronizing ovine estrus using a modified single injection regimen

Two dosages of prostaglandin F(2alpha) (PGF) were tested to evaluate their efficacy to synchronize estrus in ewes. A selectively administered single injection regimen was used. A total of 329 Targhee, Suffolk x Targhee and Finn x Targhee ewes 3 to 6 yr of age were allotted within breed type to one of three treatment groups: control, 10 mg PGF or 15 mg PGF. Trials were conducted over a 2-yr period and were replicated twice within each year. In each trial, epididymectomized rams were placed together with the ewes (1 ram:40 ewes) for 2 wk prior to a 35-d breeding exposure. Fertile, semen-tested rams were introduced (1 ram:10 ewes) on Day 1 of the breeding period. All ewes that had not mated by Day 5 received one of the three randomly assigned treatments. Treatment with PGF-10 or PGF-15 increased the percentage of ewes mating (and the percentage of those conceiving) 32 to 56 h following treatment compared with the control ewes (P<0.01). Within 56 h following treatment, 11.7, 56.2 and 65.5% of the control and the PGF-10 and PGF-15 treated groups, respectively, had mated. The percentage of ewes that conceived within 56 h was 10.7, 42.3 and 47.8, respectively. Treatment did not affect fertility, prolificacy or fecundity (P>0.05), irrespective of breed. A treatment by breed interaction was found: Finn x Targhee ewes treated with PGF-15 had a lower (P<0.01) lambing rate than those treated with PGF-10 or those in the control group. Lamb birth weight and lamb mortality were not affected by treatment (P>0.05). The cumulative lambing percentage was higher (P<0.01) at 157 d following the introduction of rams for ewes treated with PGF than for the controls. These results indicate that at a dose of 10 or 15 mg i.m. PGF was effective in synchronizing estrus in ewes within 56 h post treatment.     

Endocrine alterations that underlie endotoxin-induced disruption of the follicular phase in ewes

Two experiments were conducted to investigate endocrine mechanisms by which the immune/inflammatory stimulus endotoxin disrupts the follicular phase of the estrous cycle of the ewe. In both studies, endotoxin was infused i.v. (300 ng/kg per hour) for 26 h beginning 12 h after withdrawal of progesterone to initiate the follicular phase. Experiment 1 sought to pinpoint which endocrine step or steps in the preovulatory sequence are compromised by endotoxin. In sham-infused controls, estradiol rose progressively from the time of progesterone withdrawal until the LH/FSH surges and estrous behavior, which began approximately 48 h after progesterone withdrawal. Endotoxin interrupted the preovulatory estradiol rise and delayed or blocked the LH/FSH surges and estrus. Experiment 2 tested the hypothesis that endotoxin suppresses the high-frequency LH pulses necessary to stimulate the preovulatory estradiol rise. All 6 controls exhibited high-frequency LH pulses typically associated with the preovulatory estradiol rise. As in the first experiment, endotoxin interrupted the estradiol rise and delayed or blocked the LH/FSH surges and estrus. LH pulse patterns, however, differed among the six endotoxin-treated ewes. Three showed markedly disrupted LH pulses compared to those of controls. The three remaining experimental ewes expressed LH pulses similar to those of controls; yet the estradiol rise and preovulatory LH surge were still disrupted. Our results demonstrate that endotoxin invariably interrupts the preovulatory estradiol rise and delays or blocks the subsequent LH and FSH surges in the ewe. Mechanistically, endotoxin can interfere with the preovulatory sequence of endocrine events via suppression of LH pulsatility, although other processes such as ovarian responsiveness to gonadotropin stimulation appear to be disrupted as well.     

Follicular growth, endocrine response and embryo yields in sheep superovulated with FSH after pretreatment with a single short-acting dose of GnRH antagonist

The objective of this study was to characterize follicular development, onset of oestrus and preovulatory LH surge, and in vivo embryo yields of sheep superovulated after treatment with a single dose of 1.5mg of GnRH antagonist (GnRHa). At first FSH dose, ewes treated with GnRH antagonist (n=12) showed a higher number of gonadotrophin-responsive follicles, 2-3mm, than control ewes (n=9, 13.5+/-3.8 versus 5.3+/-0.3, P<0.05). Administration of FSH increased the number of >or=4mm follicles at sponge removal in both groups (19.3+/-3.8, P<0.0005 for treated ewes and 12.7+/-5.4, P<0.01 for controls). Thereafter, a 25% of the GnRHa-treated sheep did not show oestrous behaviour whilst none control sheep failed (P=0.06). The preovulatory LH surge was detected in an 88.9% of control ewes and 66.7% of GnRHa-treated sheep. A 77.8% of control females showed ovulation with a mean of 9.6+/-0.9 CL and 3.3+/-0.7 viable embryos, while ewes treated with GnRHa and showing an LH surge exhibited a bimodal distribution of response; 50% showed no ovulatory response and 50% superovulated with a mean of 12.2+/-1.1 CL and 7.3+/-1.1 viable embryos. In conclusion, a single dose of GnRHa enhances the number of gonadotrophin-dependent follicles able to grow to preovulatory sizes in response to an FSH supply. However, LH secretion may be altered in some females, which can affect the preovulatory LH surge and/or can weak the terminal maturation of ovulatory follicles.     

Effects of repeated removal of large ovarian follicles and treatment with progestin on ovarian function in the ewe

Preovulatory follicles were removed from ewes during estrus to determine hormonal, ovarian and behavioral responses. In Experiment 1, new follicles were recruited and ovulated within 4 days, and a second estrous period was observed in most ewes. In Experiment 2, follicles were removed at Day 0 (estrus), Day 3.5 and Day 7.0 to determine responses to repeated follicular removal in the absence of a corpus luteum (CL). Ewes in two groups were given exogenous progestin at the time of first or second surgery. Each follicular removal was followed by a surge of follicle-stimulating hormone (FSH) and follicular growth, and in many cases, behavioral estrus and/or a surge of luteinizing hormone (LH) was detected around the time of the next follicular removal. Although not necessary for display of estrus, treatment with progestin during follicular maturation increased the number of ewes showing estrus. When the newly developing follicles were allowed to ovulate, resulting corpora lutea produced low levels of progesterone or had a short life span.     

Passive immunization of the pig against gonadotropin releasing hormone during the follicular phase of the estrous cycle

Three experiments were conducted to determine the effects of passively immunizing pigs against gonadotropin releasing hormone (GnRH) during the follicular phase of the estrous cycle. In Experiment 1, sows were given GnRH antibodies at weaning and they lacked estrogen secretion during the five days immediately after weaning and had delayed returns to estrus. In Experiment 2, gilts passively immunized against GnRH on Day 16 or 17 of the estrous cycle (Day 0 = first day of estrus) had lower (P<0.03) concentrations of estradiol-17beta than control gilts, and they did not exhibited estrus at the expected time (Days 18 to 22). When observed three weeks after passive immunization, control gilts had corpora lutea present on their ovaries, whereas GnRH-immunized gilts had follicles and no corpora lutea. The amount of GnRH antiserum given did not alter (P<0.05) serum concentrations of LH or pulsatile release of LH in sows and gilts. In Experiment 3, prepuberal gilts were given 1,000 IU PMSG at 0 h and GnRH antiserum at 72 and 120 h. This treatment lowered the preovulatory surge of LH and FSH, but it did not alter serum estradiol-17beta concentrations, the proportion of pigs exhibiting estrus, or the ovulation rate. These results indicate that passive immunization of pigs against GnRH before initiation of or during the early part of the follicular phase of the estrous cycle retards follicular development, whereas administration of GnRH antibodies during the latter stages of follicular development does not have an affect. Since the concentration of antibodies was not high enough to alter basal or pulsatile LH secretion, the mechanism of action of the GnRH antiserum may involve a direct ovarian action.     

Plasma follicle stimulating hormone and luteinizing hormone patterns during the estrous cycle of ewes

Fifteen Suffolk ewes were used in three experiments to compare plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) patterns during the estrous cycle and to determine whether FSH levels undergo changes in pulse frequency. Luteinizing hormone changed inversely with progesterone levels whereas FSH and progesterone concentrations revealed no obvious relationship. Unlike LH, FSH levels did not pulsate during the follicular phase. Higher FSH levels were detected on days 1, 6 and 12 and lower levels on days 0, 4 and 16. Coincident preovulatory LH and FSH surges were observed and this was the only time FSH and LH levels appeared to be jointly controlled.     

Effects of indomethacin, luteinizing hormone (LH), prostaglandin E(2) (PGE(2)), trilostane, mifepristone, ethamoxytriphetol (MER-25) on secretion of prostaglandin E (PGE), prostaglandin F(2alpha) (PGF(2alpha)) and progesterone by ovine corpora lutea of pregnancy or the estrous cycle

Two experiments were conducted to determine the luteotropin of pregnancy in sheep and to examine autocrine and paracrine roles of progesterone and estradiol-17 beta on progesterone secretion by the ovine corpus luteum (CL). Secretion of progesterone per unit mass by day-8 or day-11 CL of the estrous cycle was similar to day-90 CL of pregnancy (P >/= 0.05). In experiment 1, secretion of progesterone in vitro by slices of CL from ewes on day-8 of the estrous cycle was increased (P /= 0.05) while PGE(2) increased (P /= 0.05) detectable quantities of PGF(2alpha) or PGE while day-90 ovine CL of pregnancy secreted PGE (P /= 0.05). Trilostane, mifepristone, or MER-25 did not affect secretion of progesterone, PGE, or PGF(2alpha) by day-11 CL of the estrous cycle or day-90 CL of pregnancy (P >/= 0.05). It is concluded that PGE(2), not LH, is the luteotropin at day-90 of pregnancy in sheep and that progesterone does not modify the response to luteotropins. Thus, we found no evidence for an autocrine or paracrine role for progesterone or estradiol-17 36 on luteal secretion of progesterone, PGE or PGF(2alpha).     

Gonadotrophin secretion during the periovulatory period in Galway and Finnish Landrace ewes and Finnish Landrace ewes selected for high ovulation rate

Rates of ovulation differed significantly (P less than 0.01) among ewes of the different genetic lines. However, of the reproductive characteristics studied, only progesterone concentration at the height of luteal function, duration of oestrus, and interval from onset of oestrus to peak of the preovulatory gonadotrophin surge showed significant positive association with rate of ovulation. The pattern of secretion of LH during the periovulatory period did not differ in the Galway and Finnish Landrace breeds. The total amount of LH secreted during the preovulatory surge did not differ amongst lines. Similarly, no difference in the plasma concentration of LH at the height of the preovulatory surge was noted among Galway and reference Finnish Landrace lines. However, the concentration of LH at the height of the surge was significantly (P less than 0.05) reduced in the selected Finnish Landrace line. Plasma concentrations of FSH during the preovulatory period were significantly (P less than 0.05) elevated in the breed (Galway) with the lowest prolifcacy. When contrasted with either of the Finnish Landrace lines, the magnitudes of the preovulatory surge of FSH and the secondary surge of FSH were significantly greater (P less than 0.05) in Galway ewes. These results suggest that genetic difference in rate of ovulation among sheep breeds is not tightly coupled to quantitative differences in plasma concentration of gonadotrophic hormones during the periovulatory period.     

An ultrasound-aided study of temporal relationships between the patterns of LH/FSH secretion, development of ovulatory-sized antral follicles and formation of corpora lutea in ewes

To characterize the pulsatile secretion of LH and FSH and their relationships with various stages of follicular wave development (follicles growing from 3 to > or =5 mm) and formation of corpora lutea (CL), 6 Western white-faced ewes underwent ovarian ultrasonography and intensive blood sampling (every 12 min for 6 h) each day, for 10 and 8 consecutive days, commencing 1 and 2 d after estrus, respectively. Basal serum concentrations of LH and LH pulse frequency declined, whereas LH pulse duration and FSH pulse frequency increased by Day 7 after ovulation (P<0.05). LH pulse amplitude increased (P<0.05) at the end of the growth phase of the largest ovarian follicles in the first follicular wave of the cycle. The amplitude and duration of LH pulses rose (P<0.05) 1 d after CL detection. Mean and basal serum FSH concentrations increased (P<0.05) on the day of emergence of the second follicular wave, and also at the beginning of the static phase of the largest ovarian follicles in the first follicular wave of the cycle. FSH pulse frequency increased (P<0.05) during the growth phase of emergent follicles in the second follicle wave. The detection of CL was associated with a transient decrease in mean and basal serum concentrations of FSH (P<0.05), and it was followed by a transient decline in FSH pulse frequency (P<0.05). These results indicate that LH secretion during the luteal phase of the sheep estrous cycle reflects primarily the stage of development of the CL, and only a rise in LH pulse amplitude may be linked to the end of the growth phase of the largest follicles of waves. Increases in mean and basal serum concentrations of FSH are tightly coupled with the days of follicular wave emergence, and they also coincide with the end of the growth phase of the largest follicles in a previous wave, but FSH pulse frequency increases during the follicle growth phase, especially at mid-cycle.     

Inter-breed variation in the postpartum ewe response to continuous low dose infusion of GnRH

During the nonbreeding season the pituitary and ovarian responses to a subcutaneous GnRH infusion were investigated in acyclic, lactating Mule ewes which exhibit a deep seasonal anestrus and in Finn x Dorset ewes in which seasonal anestrus is ill-defined. Each breed received 10 d of progestagen priming before being subdivided into 3 groups. In Group L + G, 5 lactating ewes received GnRH (250 ng/h sc) for 96 h; in Group D + G, 5 dry ewes received GnRH (250 ng/h sc) for 96 h; in Group L, 5 lactating ewes received saline vehicle for 96 h. The infusions began when lactating and dry ewes were approximately 28 d and 120 d post partum, respectively. Blood samples were collected for LH, progesterone and estradiol analysis. Estrous behavior was monitored between Day -4 and Day +7. On Day +7 the reproductive tract was also examined. In the Mule ewes the mean plasma LH concentration increased (P < 0.05) following minipump insertion in each treatment group, although mean LH levels were greater (P < 0.05) in Group D + G, than in either Group L + G or Group L. Following the GnRH infusion, mean plasma estradiol levels increased (P < 0.05) in Group D + G but not in Group L + G. A preovulatory LH surge and subsequent ovulation occurred in 5 5 , 2 5 and 0 5 ewes from Group D + G, L + G and L, respectively, and estrus was recorded in 5 5 , 1 5 and 0 5 of these ewes, respectively. The LH surges began earlier (P < 0.05) (43.2 +/- 6.8 h vs 77.0 +/- 1.0 h) and the ovulation rate was greater (2.2 +/- 0.37 vs 1.00 +/- 0.00) in Group D + G than Group L + G. In the Finn x Dorset ewes mean LH concentrations increased (P < 0.05), to a similar level following minipump insertion in Groups D + G and L + G, but not Group L. The elevated LH levels were accompanied by increased (P < 0.05) plasma estradiol levels in Group D + G, but not in Group L + G. The GnRH infusion culminated in an LH surge and estrous behavior in 5 5 , 1 5 and 0 5 ewes from Groups D + G, L + D and L, respectively. The interval to the LH surge was similar between Group D + G (48.4 +/- 6.6 h) and Group L + G (46.0 h). Ovulation was evident in those ewes which exhibited an LH surge plus one additional ewe from Group L + G. The mean ovulation rate was greater in Group D + G (4.00 +/- 1.05) than in Group L + G (1.5 +/- 0.50). These data show that continuous GnRH infusion can consistently induce out of season breeding in the nonlactating Mule and Finn x Dorset ewe but can not break combined seasonal and lactational anestrous in these breeds. Further, between-breed differences are evident in the site along the hypothalamic-pituitary-ovarian axis at which reproduction is compromised in ewes at the same chronological stage post partum.     

Differential estradiol requirement for the induction of estrus behavior and the luteinizing hormone surge in two breeds of sheep

For a better understanding of the mechanisms that lead to the preovulatory GnRH/LH surge and estrus behavior, the minimum estradiol (E) requirements (dose and duration) to induce each of these events were determined and compared between two breeds of ewes having either single (Ile de France) or multiple (Romanov) ovulations. The ewes were initially studied during a natural estrus cycle, and were then ovariectomized and run through successive artificial estrus cycles. For these artificial cycles the duration and amplitude of the follucular phase E increase were manipulated by E implants. Under all conditions, the onset of estrus behavior was similar in the two breeds, although its duration was longer in Romanov ewes. While a moderate E signal (6 cm for 12 h) induced an LH surge in 10/10 Ile de France ewes, a larger E signal (12 cm for 12 h) was minimally effective in Romanov ewes (4/10). Additional studies revealed that a small E signal (3 cm for 6 h) induced full estrus behavior in all Romanov ewes but was completely ineffective in Ile de France animals (0/10). Higher doses and mostly longer durations of the E signal (12 cm for 24 h) were required to induce a surge in all the Romanov ewes. These results demonstrate a clear difference in the E requirement for the induction of estrus behavior and the LH surge between breeds of ewes that have different ovulation rates. These data provide compelling evidence that, in one breed, the neuronal systems that regulate both events require different estrogen signals.     

Duration of the breeding season and response to reproductive manipulation in five breeds of sheep under northern prairie conditions

The breeding season was 157, 154, <126, 210 and 217 days for Rambouillet, Columbia, Suffolk, Rambouillet x Finnish Landrace and Columbia x Finnish Landrace ewes respectively. Treatment of cyclic ewes with pregnant mare serum gonadotropin (PMSG) (500 IU), following a 12-day treatment with progestin-containing intravaginal sponges, did not affect fertility, but did decrease the time from sponge removal to estrus, (control 48.0 +/- 3.1 hr; PMSG 39.4 +/- 1.8 hr) to the preovulatory surge of LH (control 52.7 +/- 2.8 hr; PMSG 39.0 +/- 1.7 hr) and FSH (control 52.3 +/- 2.9 hr; PMSG 42.8 +/- 1.6 hr) and caused an elevation of serum LH levels prior to the preovulatory surge (control 1.25 +/- 0.18 ng/ml; PMSG 2.31 +/- 0.22 ng/ml). Exposure of the purebred ewes to 18 hours of daylight in January, decreasing by 30 minutes a week subsequently, counteracted the seasonal reduction in the number of ewes lambing following induced breeding under natural daylight in May. Prolificacy was greatest in crossbred ewes and their fertility was not affected by season. Gestation period was longer for fall-bred ewes and varied with breed.     

Ovarian response to gonadotropin treatment initiated relative to wave emergence in ultrasonographically monitored ewes

Follicular recruitment and luteal response to superovulatory treatment initiated relative to the status of the first wave of the ovine estrous cycle (Wave 1) were studied. All ewes (n = 25) received an intravaginal progestagen sponge to synchronize estrous cycles, and ewes were monitored daily by transrectal ultrasonography. Multiple-dose FSH treatment (total dose = 100 mg NIH-FSH-P1) was initiated on the day of ovulation (Day 0 group) in 16 ewes. In the remaining 9 ewes, FSH treatment was started 3 d after emergence of the largest follicle of Wave 1 (Day 3 group). Ewes received PGF(2alpha) with the last 2 FSH treatments to induce luteolysis. Daily blood samples were taken to determine progesterone profiles and to evaluate the luteal response subsequent to superovulation. The ovulation rate was determined by ultrasonography and correlated with direct observation of the ovaries during laparotomy 5 to 6 d after superovulatory estrus when the uterus was flushed to collect embryos. Results confirmed that follicular recruitment was suppressed by the presence of a large, growing follicle. In the Day 0 and Day 3 groups, respectively, mean numbers (+/- SEM) of large follicles (>/= 4 mm) recruited were 6.4 +/- 0.6 and 2.7 +/- 0.7 (P < 0.01) at 48 h after the onset of treatment, and 6.7 +/- 0.5 and 5.1 +/- 0.6 (P = 0.08) at 72 h after the onset of treatment. Ovulation rates were 5.6 +/- 0.8 and 3.3 +/- 0.8 in the respective groups (P < 0.05). The number of transferable embryos was 1.8 +/- 0.5 and 0.3 +/- 0.2 in the respective groups (P < 0.05). Short luteal phases (相似文献   

The relationship between vaginal mucous impedance and serum concentrations of estradiol and progesterone throughout the sheep estrous cycle

The objective of this experiment was to assess the relationship between electrical resistance of the vaginal mucosa and serum concentrations of estradiol (E2) and progesterone (P4) during the estrous cycle in ewes. Vaginal impedance was recorded daily using a 2-electrode impedometer in 10 nonprolific Western white-faced and 7 prolific Finn ewes, during the mid-breeding season (October to December). Transrectal ultrasonography of ovaries was performed once a day to confirm ovulation and monitor follicle growth (follicles > or =3 mm in diameter) and development of corpora lutea (CL). Jugular blood samples were collected daily for radioimmunoassay (RIA) of estradiol and progesterone. In all ewes, a decline in vaginal impedance (to <40 ohms) was closely associated with the onset of behavioral estrus. In both breeds of sheep, there was no significant correlation between daily serum concentrations of estradiol and vaginal impedance throughout the estrous cycle. Daily serum concentrations of progesterone and the E2:P4 ratio were correlated with vaginal impedance during the period of luteolysis and follicular phase in both breeds (Western white-faced ewes: r = 0.62, P = 0.0002 and r = -0.56, P = 0.0002; Finn ewes: r = 0.61, P = 0.001 and r = -0.45, P = 0.03, respectively) and early in the cycle (Days 0 to 2, Day 0 = day of ovulation) in white-faced ewes (r = 0.61, P = 0.0003 and r = -0.36, P = 0.052, respectively) but not during the remaining portion of the luteal phase in either breed. In conclusion, vaginal mucous impedance appears to be primarily controlled by progesterone, but it also changes in response to shifts in the E2:P4 ratio when progesterone concentrations are low. Impedometric characteristics of the vaginal mucosa in cyclic ewes are an indicator of serum concentrations of progesterone and E2:P4 ratios during the terminal stage of the estrous cycle.     

Pituitary and ovarian hormone secretion and ovulation in gilts injected with gonadotropins during and after oral administration of progesterone agonist (Altrenogest)

We determined changes in plasma hormone concentrations in gilts after treatment with a progesterone agonist, Altrenogest (AT), and determined the effect of exogenous gonadotropins on ovulation and plasma hormone concentrations during AT treatment. Twenty-nine cyclic gilts were fed 20 mg of AT/(day X gilt) once daily for 15 days starting on Days 10 to 14 of their estrous cycle. The 16th day after starting AT was designated Day 1. In Experiment 1, the preovulatory luteinizing hormone (LH) surge occurred 5.6 days after cessation of AT feeding. Plasma follicle-stimulating hormone (FSH) increased simultaneously with the LH surge and then increased further to a maximum 2 to 3 days later. In Experiment 2, each of 23 gilts was assigned to one of the following treatment groups: 1) no additional AT or injections, n = 4; 2) no additional AT, 1200 IU of pregnant mare's serum gonadotropin (PMSG) on Day 1, n = 4); 3) AT continued through Day 10 and PMSG on Day 1, n = 5, 4) AT continued through Day 10, PMSG on Day 1, and 500 IU of human chorionic gonadotropin (hCG) on Day 5, n = 5; or 5) AT continued through Day 10 and no injections, n = 5. Gilts were bled once daily on Days 1-3 and 9-11, bled twice daily on Days 4-8, and killed on Day 11 to recover ovaries. Termination of AT feeding or injection of PMSG increased plasma estrogen and decreased plasma FSH between Day 1 and Day 4; plasma estrogen profiles did not differ significantly among groups after injection of PMSG (Groups 2-4). Feeding AT blocked estrus, the LH surge, and ovulation after injection of PMSG (Group 3); hCG on Day 5 following PMSG on Day 1 caused ovulation (Group 4). Although AT did not block the action of PMSG and hCG at the ovary, AT did block the mechanisms by which estrogen triggers the preovulatory LH surge and estrus.     

Ovarian capillary blood flow in seasonally anoestrous ewes induced to ovulate by treatment with GnRH

The microsphere technique was used to obtain estimates of ovarian capillary blood flow near ovulation, in 8 seasonally anoestrous ewes, which were induced to ovulate by GnRH therapy. Plasma progesterone concentrations were monitored in jugular blood sampled between Days 4 and 7 after the onset of the preovulatory LH surge. The ewes were then slaughtered. Three of the ewes were treated with a single injection of 20 mg progesterone before GnRH therapy. In these ewes and 1 other, plasma progesterone values increased after ovulation and reached 1.0 ng/ml on Day 7 following the preovulatory LH surge (normal, functional CL), whilst in the other 4 ewes progesterone concentrations increased initially then declined to 0.5 ng/ml by Day 7 (abnormal CL). In the ewes exhibiting normal luteal function, the mean ovarian capillary blood flow was significantly greater (P less than 0.01) than that for ewes having abnormal luteal function. Irrespective of the type of CL produced, capillary blood flow was significantly greater (P less than 0.05) in ovulatory ovaries than in non-ovulatory ovaries. These findings indicate that the rate of capillary blood flow in ovaries near ovulation may be a critical factor in normal development and maturation of preovulatory follicles and function of subsequently formed CL.     

An ultrasonographic study of luteal function in breeds of sheep with different ovulation rates

Development and demise of luteal structures were monitored using daily transrectal ultrasonography in 2 breeds of sheep differing in ovulation rates (nonprolific Western white-faced cross-bred, n = 12 and prolific pure-bred Finn sheep, n = 7), during 1 estrous cycle in the mid-breeding season. Jugular blood samples were collected once a day for radioimmunoassay (RIA) of progesterone. The mean diameter of ovulatory follicles was higher in Western white-faced than in Finn ewes (6.4 +/- 0.2 and 5.3 +/- 0.2 mm, respectively; P < 0.001). The mean volume of luteal structures was higher (P < 0.05) in Western white-faced compared with Finn sheep from Days 5 to 15 of the cycle (Day 0 = day of ovulation). This accounted for the higher (P < 0.05) total luteal volumes recorded in Western white-faced ewes on Day 7 and from Days 11 to 15, despite the higher ovulation rate in Finn ewes (2.7 +/- 0.3 and 1.7 +/- 0.2, respectively; P < 0.05). Mean serum progesterone concentrations were higher (P < 0.05) in Western white-faced than in Finn ewes from Days 4 to 14. Daily total luteal volumes were positively correlated with daily serum progesterone concentrations throughout the cycle in Finn sheep (r > or = 0.40, P < 0.02), and during luteal growth and regression (r > 0.60, P < or = 0.00001) but not during mid-cycle in white-faced ewes (r = 0.16; P = 0.22). During the growth of the corpora lutea (CL), luteal tissue volume increased faster (P < 0.05) than serum progesterone concentrations in both breeds of sheep. During luteolysis, the decrease in luteal volumes parallelled that in serum progesterone concentrations in Finn (P = 0.11) but not in Western white-faced ewes, where luteal volumes decreased more slowly (P = 0.02) in relation to progesterone secretion. Increased ovulation rate in prolific Finn ewes resulted in more but smaller CL, and lower serum progesterone levels compared with nonprolific Western white-faced ewes. We conclude that breed-specific mechanisms exist to control the formation of luteal tissue and progesterone secretion in cyclic ewes differing in prolificacy. The mechanisms may involve ovulation of Graafian follicles at different sizes and inhibitory paracrine effects of CL on co-existing CL.     

Influence of CIDR treatment during superovulation on embryo production and hormonal patterns in cattle

One of the major sources of success in embryo transfer is timing of AI relative to the LH surge and ovulation. The aim of this study was to compare the embryo production following superovulation during a PGF2alpha (control cycle) or a CIDR-B synchronized cycle (CIDR-B cycle). CIDR-B (CIDR-B ND, Virbac, Carros, France) was inserted on Day 11 of a previously synchronized cycle and left for 5 days. A total dose of 350 microg FSH was administered (eight injections i.m. for 4 days; first on Day 13, decreasing doses) and PGFalpha analog (750 microg i.m.: Uniandine ND, Schering-Plough, Levallois-Perret, France) injected at the time of third FSH injection. Artificial inseminations were performed 12 and 24 h after standing estrus (Day 0). Embryos were collected on Day 7. Luteinizing hormone was measured by EIA (Reprokit Sanofi, Libourne, France) from blood samples collected every 3 h for 36 h, starting 24 h after PGF2alpha (control cycle) or 12 h after CIDR-B removal (CIDR-B cycle). The effects of treatment group and interval between the LH peak and AI (two classes, < 10 and > or = 10 h) on embryo production and quality were analyzed by ANOVA. No effect of treatment was observed on embryo production variables. The intervals between the end of treatment and onset of estrus and between end of treatment and LH surge were greater in heifers treated during a control than a CIDR-B cycle, respectively (45.5 +/- 1.4 versus 31.9 +/- 0.7; 42.0 +/- 1.6 versus 31.0 +/- 1.5; P < 0.05), but maximal LH and estradiol concentrations, at the preovulatory surge were similar in control and CIDR-B synchronized heifers. The numbers of viable and Grade I embryos were significantly increased (P < 0.01) when animals had an interval from LH peak to first AI > or = 10 h (7.2 +/- 0.9 and 3.5 +/- 0.6) when compared to shorter intervals (4.2 +/- 1.1 and 2.0 +/- 0.7) whereas total number of embryos was unchanged (11.8 +/- 1.4 versus 10.3 +/- 1.8). It is concluded that late occurrence of LH peaks in relation to estrous behavior is associated with a lower embryo quality when first AIs are performed systematically 12 h after standing estrus. Further studies are needed to know if results may be improved when making AI at a later time after standing estrus or if LH assays are useful to better monitor AI time.