Investigations on the detrimental effect of prostaglandin F2α-regulated estrus on the number and condition of sperm in the reproductive tract of the ewe

Ewes in the luteal phase of the estrous cycle were treated with prostaglandin F₂α (PGF), mated to rams at the ensuing estrus 2 days later, and necropsied at 2 or 23 hr after mating. At 2 hr after mating, ewes in PGF-regulated estrus had significantly fewer sperm in the middle and anterior one-thirds of the cervix and in the uterus than did ewes mated during natural estrus. At 23 hr, soon after ovulation, significantly fewer ewes in PGF-regulated estrus had sperm in the oviducts than did ewes in natural estrus.In Experiment 2, ewes in PGF-regulated or natural estrus were laparotomized, inseminated by deposition of semen in the uterine lumen, and necropsied 2 or 23 hr later. Intrauterine insemination prevented most of the reduction in sperm numbers in the reproductive tract at PGF-regulated estrus.In Experiment 3, ewes in PGF-regulated or natural estrus were either mated to rams or inseminated in the uterine lumen and necropsied 2 hr later. Sperm were recovered from three segments of the cervix and were counted and evaluated for motility, response to live-dead staining, and acrosomal morphology. Intrauterine insemination again reduced the detrimental effect of PGF-regulated estrus on sperm numbers. However, the percentages of sperm recovered from the cervix that were motile, live, and had normal acrosomes were much lower in ewes in PGF-regulated estrus than in ewes in natural estrus. Compared with natural mating, intrauterine insemination reduced but did not eliminate the detrimental effects of PGF-regulated estrus on the viability and morphology of sperm. Regulating estrus with PGF resulted in damage to sperm in the cervix regardless of whether sperm reached the cervix from the vagina or from the uterus.     

Hormonal control of proceptive and receptive sexual behavior and the preovulatory LH surge in the ewe: reassessment of the respective roles of estradiol, testosterone, and progesterone

When estrous behavior is induced in ovariectomized ewes by subjecting them to progestagen priming followed by a dose of estrogen large enough to guarantee estrus in all animals, an abnormally long period of estrus in induced, suggesting that the regime of steroid replacement needs modification. Using quantitative tests for proceptivity and receptivity, we studied the patterns of sexual behavior of intact ewes and then attempted to reproduce them in the same animals after they had been ovariectomized. We used various combinations of exogenous estrogen, androgen, and progestagen and compared the behavioral responses with an endocrine response, the preovulatory surge of luteinizing hormone (LH). In intact ewes, sexual behavior and the LH surge were closely synchronized and their characteristics differed slightly between the middle and the end of the breeding season. Proceptive behavior was not greatly affected by the frequency of tests, but the duration of receptivity was significantly reduced by frequent testing. In ovariectomized ewes, we found that: (a) progesterone priming is essential for normal patterns of receptive and proceptive behavior, and for synchronizing the behavioral and endocrine responses to estrogen; (b) androgens do not play a major role in the control of either receptive or proceptive behavior; and (c) the inclusion of a low dose of estrogen with the progestagen in the 'priming' regime improves the responses to estradiol-17 beta. Under these conditions, the timing, intensity and duration of the behavior are very close to those observed in the same ewes when they were intact and cycling spontaneously.     

Altered motility of myometrium from estrous ewes after the regulation of estrus with progestagen or prostaglandin

The $\text{in}$$\text{vitro}$ motility of strips of myometrium was studied in estrous ewes after administration of melengestrol acetate (MGA), medroxyprogesterone acetate (MAP) or prostaglandin F_2α (PG) to regulate estrus. Ewes were killed during estrus, 2 to 4 days after the end of progestagen or PG treatment. The contractions of strips of myometrium were recorded by kymograph and compared to contractions of control ewes.Muscle relaxation was indicated by an interval of tracing that was nearly horizontal and close to the baseline. A major contraction was indicated by a sharp upward movement of the tracing pen and an interval of tracing above the baseline.Treating ewes with MAP by intravaginal sponge lengthened contraction time. Feeding MGA or MAP tended to shorten relaxation time, and injecting PG tended to both lengthen contraction time and shorten relaxation time. As a result of these effects, the proportion of time that myometrium spent in contraction averaged 74% for 42 ewes treated with progestagen or prostaglandin and 56% for 24 control ewes. These results indicate that treatments that inhibit sperm transport when used to regulate estrus also affect the nature of myometrial contractions $\text{in}$$\text{vitro}$.     

Regulation of follicular activity and ovulation in ewes by exogenous progestagen

The success of estrus synchronization programs using progestagen sponges, particularly for fixed-time AI, varies considerably. In view of the recent evidence in cattle that exogenous progestins alter follicular dynamics, it may be that the stage of the estrous cycle at which the synchronization protocol is begun affects the synchrony of ovulation. The goal of this study was to evaluate the effect of medroxyprogesterone acetate (MAP) intravaginal sponges on follicular dynamics, luteal function and interval to ovulation when inserted at 3 stages of the estrous cycle. Sponges were inserted for 12 d beginning on either Day 0, 6 or 12 (n = 5) following ovulation. Ovarian activity was monitored using real-time ultrasound imaging during the treatment and the post-treatment estrous cycles. Information from the post-treatment cycle was used as a baseline to compare with the treatment cycle. Most ewes (79%) in the post-treatment cycle exhibited 3 follicular waves in an estrous cycle of 16 d, with the second wave follicles having smaller diameter (P < 0.001). Treatment with MAP increased the number of follicular waves from 3 to 4 or 5 when sponges were inserted on Days 6 and 12, respectively. Size of the largest follicle was smaller (P > 0.01) in waves in the early and middle of the 12-d MAP treatment period when compared with the last 4 days. This effect was most pronounced when endogenous progesterone concentrations were elevated concurrently with the presence of the sponge. Persistence of the ovulatory follicle was increased (P < 0.001) when sponges were inserted on Day 12, the only treatment where these follicles were under the influence of MAP in the absence of functional corpora lutea. Follicles were regressing at sponge removal in the Day 6 treatment, which resulted in a delay in emergence of ovulatory follicles, the LH surge and ovulation (P < 0.08) in relation to Day 0 and Day 12. Treatment with MAP sponges does not adequately synchronize estrus and ovulation among cyclic ewes due to the different follicular patterns that result depending on the stage of cycle at the time of sponge insertion.     

Endocrine events during the periestrous period and the subsequent estrous cycle in ewes after estrus synchronization

The aim of the present study was to investigate the endocrinology of the periestrus period and that of the subsequent estrous cycle in ewes synchronized during the breeding season. Animals were treated for 14 days with either MAP intravaginal sponges or subcutaneous progesterone implants, followed by administration of 500 IU PMSG at the time of withdrawal. The time to estrus occurrence following progestagen withdrawal differed significantly between groups (45.3+/-2.7h for the MAP and 21.5+/-1.2h for the implant group, P<0.001). Estradiol levels around estrus did not differ between groups, but a significant difference was detected for the interval from peak estradiol to estrus, with a shorter interval for the implant group (26.7+/-0.7 and 2.7+/-0.9h, P<0.001). Progesterone implants shortened the interval from removal to LH surge, compared to the MAP group (31.2+/-4.4 and 56.5+/-3.6h, respectively, P<0.05). An earlier response was also observed for the interval from estradiol peak to LH peak in the implant group (12.1+/-3.3 and 37+/-2h, respectively, P<0.005), but no difference was observed for the interval from estrus to LH surge. Progesterone levels, particularly during the Days 6 to 10 of the subsequent estrous cycle were significantly higher (P<0.05) in the implant group. It is concluded that the kind of progesterone treatment may affect the time of estrus and the LH peak as well as the progesterone levels of the subsequent cycle.     

Effect of breeding season on fertility of sheep following estrus synchronization and fixed-time artificial insemination under field conditions in semi-arid tropical region

Accelerated lambing system is heavily reliant on reproductive technologies meant to enable off the season breeding in sheep. Therefore, the present study was programmed to assess the effect of breeding season (BS) on fertility of sheep following estrus synchronization (ES) and fixed time artificial insemination (FTAI). A total of 248 and 365 ewes were synchronized and inseminated during the BS (Febuary–March and July–September) and non-breeding season (NBS) respectively, during 2012–14. Synchronization of estrus was done by AVIKESIL-S, intra-vaginal progesterone sponges kept in situ in vagina for 12 days. 200 IU eCG was administered intramuscularly on 12th day after sponge withdrawal. FTAI was performed twice in ewes exhibiting signs of estrus at 48 and 56h after sponge removal, using liquid chilled semen of Patanwadi/Malpura rams containing 100 million sperm. Breeding season had no significant (p<0.05) effect on estrus synchronization. The estrous responses during the BS and NBS were 84.68% and 83.29% respectively. The lambing percentage during BS was 66.67%, which is significantly (p<0.05) higher than the lambing percentage of NBS (57.57%). Although, the lambing percentage in NBS maneuvered ewes were lower than the BS ewes but still the technology can be used to offset the effect of anestrus and to augment production in sheep.     

Effect of exogenous progestogens on plasma concentrations of the oxytocin-associated neurophysin and 13,14-dihydro-15-keto-prostaglandin F in intact and ovariectomized ewes over the time of expected luteal regression

Plasma concentrations of the prostaglandin F metabolite 13,14-dihydro-15-keto-prostaglandin F (PGFM), the oxytocin-associated neurophysin (OT-N) and progesterone were monitored by radioimmunoassay (RIA) in five ewes sampled from the jugular vein at hourly intervals between 0700-1900 h from Days 12-16 of the estrous cycle. These hormones were also determined in plasma samples collected at similar times from five intact and five ovariectomized ewes given twice daily injections of medroxyprogesterone acetate (MPA) over Days 10 to 20 after the last observed estrus. In both the control and intact MPA-treated ewes, coincident surges of OT-N and PGFM were observed in jugular plasma during the time of luteal regression. No significant differences were noted in the number and amplitude of OT-N and number of PGFM peaks between the control and intact MPA-treated animals, although in the latter the amplitude of the PGFM peaks was significantly reduced (P less than 0.01). No marked surges in the plasma concentrations of PGFM or OT-N were observed in the ovariectomized ewes given exogenous MPA. This latter finding is consistent with previous proposals, suggesting that the ovaries are a major source of oxytocin in the ewe. In addition, the observation that exogenous progestogens in the intact ewes did not influence the number and peak height of the OT-N surges, indicates that a fall in progesterone levels during the normal cycle is not obligatory for oxytocin release although it may facilitate the release of uterine PGF2 alpha.     

Effects of an opioid antagonist on pulsatile luteinizing hormone secretion in the ewe vary with changes in steroid negative feedback

In ewes during the breeding season, estradiol (E) and progesterone (P) synergistically regulate pulsatile luteinizing hormone (LH) secretion. E primarily inhibits LH pulse amplitude and P inhibits LH pulse frequency. To determine if endogenous opioid peptides (EOP) mediate these negative feedback effects, we administered the long-acting opioid antagonist WIN 44,441-3 (WIN) to intact ewes during the luteal and follicular phases of the estrous cycle and to ovariectomized ewes treated with no steroids, E, P, or E plus P. Steroid levels were maintained at levels seen during the estrous cycle by Silastic implants placed shortly after surgery. WIN increased LH pulse frequency, but not amplitude, in luteal phase ewes. In contrast, during the follicular phase, LH pulse amplitude was increased by WIN and pulse frequency was unchanged. Neither LH pulse frequency nor pulse amplitude was affected by WIN in long-term ovariectomized ewes untreated with steroids. In contrast, WIN slightly increased LH pulse frequency in short-term ovariectomized ewes. WIN also increased LH pulse frequency in ovariectomized ewes treated with P or E plus P. WIN did not affect pulse frequency but did increase LH pulse amplitude in E-treated ewes. These results support the hypothesis that EOP participate in the negative feedback effects of E and P on pulsatile LH secretion during the breeding season and that the inhibitory effects of EOP may persist for some time after ovariectomy.     

The introduction of rams induces an increase in pulsatile LH secretion in cyclic ewes during the breeding season

Application of the ram effect during the breeding season has been previously disregarded because the ewe reproductive axis is powerfully inhibited by luteal phase progesterone concentrations. However, anovulatory ewes treated with exogenous progestagens respond to ram introduction with an increase in LH concentrations. We therefore tested whether cyclic ewes would respond to ram introduction with an increase in pulsatile LH secretion at all stages of the estrous cycle. We did two experiments using genotypes native to temperate or Mediterranean regions. In Experiment 1 (UK), 12 randomly cycling, North of England Mule ewes were introduced to rams midway through a frequent blood-sampling regime. Ewes in the early (EL; n=3) [corrected] and late luteal (LL; n=6) phase responded to ram introduction with an increase in LH pulse frequency and mean and basal concentration [corrected] of LH (at least P<0.05). In Experiment 2 (Australia), the cycles of 32 Merino ewes were synchronised using intravaginal progestagen pessaries. Pessary insertion was staggered to produce eight ewes at each stage of the estrous cycle: follicular (F), early luteal (EL), mid-luteal (ML) and late luteal (LL). In all stages of the cycle, ewes responded to ram introduction with an increase in LH pulse frequency (P<0.01); EL, ML and LL ewes also had an increase in mean LH concentration (P<0.05). In conclusion, ram introduction to cyclic ewes stimulated an increase in pulsatile LH secretion, independent of ewe genotype or stage of the estrous cycle.     

Concentrations of progesterone,follistatin, and follicle-stimulating hormone in peripheral plasma across the estrous cycle and pregnancy in merino ewes that are homozygous or noncarriers of the Booroola gene

The circulating concentrations of progesterone, FSH, and follistatin across the estrous cycle and gestation were compared in Australian merino sheep that were homozygous for the Booroola gene, FecB, or were noncarriers. The Booroola phenotype is due to a point mutation in the bone morphogenetic protein receptor 1B. Progesterone concentrations began to rise earlier and were higher in the Booroola ewes than in the noncarriers on most days of the luteal phase but not during the follicular phase of the cycle. Follistatin concentrations remained unchanged across the estrous cycle in both groups of ewes, with no differences between genotypes. FSH concentrations were higher in Booroola ewes than in noncarrier ewes on most days of the estrous cycle, with a significantly higher and broader peak of FSH around the time of estrus. Progesterone concentrations were significantly higher in early and midgestation in Booroola ewes but were lower toward the end of gestation than those in noncarriers. FSH declined in both groups across gestation, with lower concentrations of FSH in Booroola ewes during midgestation. Follistatin remained unchanged across gestation in Booroola ewes and noncarrier ewes with a twin pregnancy but declined across gestation in noncarrier ewes with a singleton pregnancy. These results suggest that follistatin concentration is not regulated by the FecB gene during the estrous cycle and pregnancy but is influenced by the number of fetuses. However, the FecB gene appears to positively affect both progesterone and FSH during the estrous cycle and across pregnancy, which suggests that bone morphogenetic proteins play an important role in the regulation of both hormones.     

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.     

Control of endometrial oxytocin receptor and uterine response to oxytocin by progesterone and oestradiol in the ewe

The effects of administration of progesterone and oestradiol on ovine endometrial oxytocin receptor concentrations and plasma concentrations of 13,14-dihydro-15-keto prostaglandin F-2 alpha (PGFM) after oxytocin treatment were determined in ovariectomized ewes. Ewes received progestagen pre-treatment, progesterone and/or oestradiol in 11 different treatment schedules. Progestagen pre-treatment decreased oxytocin receptor concentrations in endometrium from ewes treated subsequently with either progesterone for 5 days or progesterone for 5 days plus oestradiol on Days 4 and 5 of progesterone treatment. Oestradiol increased endometrial oxytocin receptor concentrations when administered on Days 4 and 5 of 5 days progesterone treatment. Progestagen pre-treatment followed by progesterone treatment for 12 days caused a large increase in oxytocin receptors and no further increase occurred when ewes were given oestradiol on Days 11 and 12, or when progesterone was withdrawn on Days 11 and 12, or these two treatments were combined. Oxytocin administration caused an increase in plasma PGFM concentrations in ewes which did not receive progestagen pre-treatment, and subsequently received progesterone treatment for 5 days and oestradiol treatment on Days 4 and 5 of progesterone treatment. Similarly treated ewes which received progestagen pre-treatment did not respond to oxytocin. Oxytocin administration also increased plasma PGFM concentrations in ewes which received progestagen pre-treatment followed by progesterone treatment for 12 days, progesterone treatment for 12 days plus oestradiol on Day 11 and 12 of progesterone treatment, progesterone withdrawal on Day 11 and 12, or progesterone withdrawal and oestradiol treatment combined. The results indicate that (1) progesterone pre-treatment affects oxytocin receptor concentrations in the endometrium and uterine responsiveness to oxytocin and (2) progesterone treatment alone for 12 days after a treatment which mimics a previous luteal phase and oestrus is sufficient to induce oxytocin receptors and increase oxytocin-induced PGF release. These results emphasize the importance of progesterone and provide information which can be used to form an hypothesis for control of luteolysis and oestrous cycle length in the ewe.     

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   

Effects of chronic infusion of dibutyryl c-AMP or adenosine on luteal function in sheep

Adenosine or vehicle; dibutyryl c-AMP, a c-AMP analogue, or vehicle in two separate experiments were infused through an indwelling cannula every four hours around the ovarian vascular pedicle of ewes unilaterally ovariectomized on day 8 postestrus. Adenosine or vehicle was infused from day 8 through 22 postestrus and dibutyryl-cAMP was infused from day 8 through 20 postestrus or until the ewes returned to estrus. Interestrous intervals were greater (p less than or equal to 0.05) in ewes receiving adenosine (27.3 +/- 2.4 days) than in control ewes (17.2 +/- 1.3 days). The length of the estrous cycle of ewes receiving dibutyryl c-AMP was greater (22.4 +/- 1.1; p less than or equal to 0.05) than in control ewes which averaged 16.7 +/- 0.6 days. Profiles of progesterone were different (p less than or equal to 0.05) for ewes receiving adenosine or dibutyryl c-AMP when compared to their respective controls. In addition, the overall mean concentrations of progesterone were greater (p less than or equal to 0.05) in dibutyryl c-AMP or adenosine-treated ewes than in controls. In a third experiment, infusions of adenosine or dibutyryl c-AMP intrauterine every 4 hours through a cannula from day 8 through 22 postestrus had no effect (p less than or equal to 0.05) on the interestrous interval or profiles of progesterone. It is concluded that dibutyryl c-AMP or adenosine in vivo can delay luteolysis and adenosine and c-AMP may play roles in luteal secretion of progesterone in sheep but are probably not the uterine embryonic antiluteolysin of early pregnancy in sheep.     

Effects of adrenalectomy on serum concentrations of progesterone during the luteal phase of sheep

An experiment was conducted to test the hypothesis that the adrenal gland influences luteal activity in sheep. Twelve Finnish Landrace x Southdown ewes were either bilaterally adrenalectomized (n = 6) or sham adrenalectomized (n = 6) during the breeding season. At approximately 37 and 47 d after surgery, all ewes received intramuscular injections of cloprostenol to synchronize estrus. Blood samples were taken via jugular venipuncture at 48-h intervals between 1 and 19 d after the last cloprostenol treatment. Serum concentrations of progesterone were determined in each of these samples. Analysis of variance showed that concentrations of progesterone during the luteal phase were lower (P<0.05) in adrenalectomized ewes than in sham-operated controls, but that patterns of progesterone were similar for both groups of sheep. Based on these results, we conclude that the adrenal gland does not appear to be necessary for initiation of luteal regression in ewes.     

Pattern of ovarian progesterone secretion during the luteal phase of the ovine estrous cycle

Pulsatile secretion of progesterone has been observed during the late luteal phase of the menstrual cycle in the rhesus monkey and human. As the luteal phase progresses in each of these species, there is a pattern of decreased frequency and increased amplitude of progesterone pulses. The present study was designed to determine the pattern of progesterone secretion during the late luteal phase (Days 10-16) of the normal ovine estrous cycle. Five unanesthetized ewes, each bearing an indwelling cannula in the utero-ovarian vein, were bled every 15 min from 0800 h on Day 10 through 0800 h on Day 16 of the estrous cycle. With the computer program PULSAR, it was determined that progesterone secretion was episodic, with pulsations observed on all days. Analysis of variance was used to determine differences in frequency, amplitude, and interpeak interval (IPI) of progesterone pulses among ewes and days. The ewes averaged 8.0 +/- 0.63 pulses of progesterone per 24 h. Mean frequency of pulses was not different between days but showed differences between ewes. Mean amplitude of progesterone pulses was 7.0 +/- 0.27 ng/ml, with no differences observed either between days or between ewes. Mean IPI was 197 +/- 7.1 min, and, like frequency, the IPI was not different between days, but varied between ewes. No consistent temporal relationship was found between progesterone pulses and luteinizing hormone (LH), as determined by bioassay and radioimmunoassay, on Day 14 of the cycle in one ewe. The results indicate that progesterone secretion is episodic during the luteal phase of the ovine estrous cycle and is independent of LH pulses.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of bovine somatotropin (bST) administration on reproduction, progesterone concentration during lactation and LH secretion during estrus, in dairy ewes.

Twenty-two polytocous lactating Chios ewes were used to test the effects of bovine somatotropin (bST) on reproduction, progesterone concentration and LH secretion during estrus. Half of the ewes were injected every second week with 160 mg bST in a prolonged release vehicle, from the fifth day post partum until the end of lactation, while the remaining ones were used as controls. All animals were fed the same amount of ration. Supplementation with bST resulted in an increase of milk production (P<0.05) and an insignificant trend for delayed resumption of normal estrous cycles. Although there were no differences between groups, there was also a tendency for the bST group to display lower progesterone concentrations during the first three fortnights after the onset of normal estrous cycles and higher ones during the last three fortnights of the experiment, compared with the control group. Duration of the first normal luteal phase after delivery of the bST group was found to be shorter compared with the control group (P<0.05). After estrous synchronization the bST group showed a shorter estrus compared with the control group (P<0.05). Average and baseline LH concentrations during synchronized estrous in the bST group was lower (P<0.001) compared with the control group. Additionally, the conception rate did not differ between the two groups. This study supports the concept that the beneficial effects of bST treatment on milk production outweigh the potential deleterious effects on reproduction.     

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.     

The active immunization of the cyclic ewe against an estrone protein conjugate

Four mature, cyclic ewes were given injections (I.M.) of a conjugate of 1,3,5 (10)-estratrien-3-ol-6,17-dione, 6 carboxyoxime bovine serum albumin (immunized ewes) on day 3 after estrus, and at days 10, 20, 40, 58, 91 and 134 after this initial treatment. Six control ewes treated with carrier emulsion alone continued to cycle normally. Three of the immunized ewes failed to exhibit estrus, an associated preovulatory surge of LH and ovulation. One ewe showed 1 abnormally short estrous period and then became anestrus. Injection of an estrone-protein-conjugate at days 3 and 13 after estrus did not appear to interfere with the rate of structural luteolysis of the corpus luteum present, but plasma concentrations of progesterone reached abnormally high luteal phase levels and in 2 ewes failed, subsequently to decline to normal follicular phase levels. Estrone binding capacity rose as early as day 9 after first treatment, and concentrations of LH rose as early as day 14. Subsequently, plasma levels of LH, estrone and progesterone and antisera titer rose; the only significant cross reaction of the antisera was with estradiol 17beta (11.32 +/- 2.80%).     

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.