A comparative study of induction of estrus and ovulation by three different intravaginal devices in ewes during the non-breeding season

The aim of the present study was to compare three methods of estrus synchronization in ewes during the non-breeding season. Forty-two ewes were randomly grouped for three treatments with different intravaginal devices for 12 days: Group A) CIDR, Group B) Self-made P sponge, Group C) MAP (medroxyprogesterone acetate) cream sponge. Furthermore, all groups were divided into two treatments with (R) or without ram presence to examine the "ram effect". Blood was collected from all treated ewes, and progesterone (P(4)), estradiol 17-beta (E(2)) and luteinizing hormone (LH) concentrations were measured by enzyme-immunoassay. All ewes showed estrus behavior between Day 0 to 3 after device removal, and the mean onset times of their estrus were 23.0, 33.0 and 21.0 h for Groups AR, BR and CR, respectively. On Day 5 as examined by laparoscopy, the ovulation rates (and number of ovulated ewes) were 1.45 (11/11), 1.25 (12/14) and 1.21 (14/14) for Groups A, B and C, respectively. In Group C, the time to LH surge was significantly (P<0.05) later (32.4 h) than those in Groups A (27.0 h) and B (25.5 h). Ram presence did not affect the number of ovulated ewes, ovulation rate or time to LH surge. The ram introduction group had significantly (P<0.05) lower E(2) concentrations during the period from 0 h to 36 h than the groups without ram presence. These results suggest that the self-made P sponge or MAP cream sponge was effective as well as CIDR, and ram introduction was not necessary, for induction of estrus and ovulation during the non-breeding season.     

Inhibition by progesterone of IUD-induced luteal regression in the ewe

A U.S. Department of Agriculture study at Beltsville, Maryland investigated the effect of progesterone on IUD-induced luteal regression in 95 ewes. The IUD was a plastic spiral with diameter 9 mm and length 30 mm. The first experiment suggested that IUD-induced regression of a corpus luteum (CL) is dependent upon the stage of the estrous cycle but unrelated to the age of the CL. When ovulation was induced on Cycle Day 5 in 4 ewes and an IUD was inserted on Day 7, neither the original CLs, about 6 days old, nor the induced CLs, about 1 day old, regressed. Experiment 2 provided evidence that exogenous progesterone generally prevents IUD-induced luteal regression. 29 ewes were injected twice daily on Days 1-4 of a cycle with 10 mg of progesterone in corn oil or with corn oil alone. An IUD was inserted on Day 3. Sacrifice was on Day 9. Early CL (ovaries ipsilateral to IUD) regression occurred in 7 in the corn-oil group but in only 2 in the progesterone group. In Experiment 3 the administration of progesterone to estradiol- and IUD-treated ewes tended to reduce the percentage of ewes with regressed CL's (p=.10, ovaries ipsilateral to IUD). Estradiol itself extends the stage during which the insertion of an IUD causes luteolysis.     

Effects of feed restriction on reproductive and metabolic hormones in ewes

The goal of this study was to determine the effects of short-term feed withdrawal on reproductive and metabolic hormones during the luteal phase of the estrous cycle in mature ewes. Mature ewes observed in estrus were assigned randomly to control and fasted groups (n = 10 per group Trials 1 and 2). For Trials 1 and 2, control ewes had ad libitum access to feed, whereas fasted ewes were not fed from d 7 through 11 of their estrous cycle; on d 12, all ewes were treated with 10 mg of PGF2alpha, and fasted ewes were gvien ad libitum access to feed. For Trial 1, blood samples were collected daily through fasting and at 2-h intervals following PGF2alpha for 72 h. Serum concentrations of insulin (P < or = 0.002) and IGF-I (P < or = 0.01), but not GH (P > or = 0.60), were decreased during fasting compared with fed ewes. Serum concentrations of 29 (P = 0.02) and 34 kDa (P = 0.04) IGFBP were greater in fasted ewes at 96 h after initiation of fasting than in control ewes. Two control and four fasted ewes in Trial 1 did not exhibit a preovulatory surge release of LH by 72 h. Therefore, Trial 2 was conducted so that the timing of the LH surge could be predicted following the collection of blood samples at 2-h intervals for 112 h and then at 6-h intervals until 178 h following PGF2alpha administration and realimentation. The magnitude of the preovulatory LH surge in Trial 2 was decreased (P = 0.009) and delayed (P = 0.04), and serum concentrations of estradiol were diminished (P < or = 0.03) 12 h before the LH surge in fasted ewes. Ovulation rates were not influenced (P > or = 0.32) by fasting in Trials 1 and 2. Serum concentrations of progesterone in both Trials 1 and 2 were, however, greater (P < 0.001) in fasted than in control ewes. A third trial with ovariectomized ewes was conducted to determine whether the increased serum concentrations of progesterone observed in fasted ewes during Trials 1 and 2 were ovarian-derived. Ovariectomized ewes were implanted with progesterone-containing intravaginal implants and allotted to control (n = 5) or fasted (n = 5) treatment groups and fed as described for Trials 1 and 2. Similar to intact ewes, serum concentrations of progesterone were approximately twofold greater (P < 0.001) in fasted than in control implanted ovariectomized ewes. In summary, feed withdrawal for 5 d during the luteal phase of the estrous cycle increased serum concentrations of progesterone and evoked endocrine changes that could perturb the subsequent estrous cycle.     

The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial. RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning. CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.     

The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs.

METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial.

RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning.

CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.     

Direct Effects of Luteal Regression on Anterior Pituitary Response To GnRH

The preovulatory period of the ewe is marked by a dramatic decrease in concentrations of progesterone in serum during the late luteal phase, followed by elevated luteinizing hormone (LH) secretion, final follicular maturation and ovulation. This experiment was designed to ascertain the extent to which removal of endogenous progesterone negative feedback at the anterior pituitary gland, independent of effects at the hypothalamus, promotes increased secretion of LH in the hours immediately after induction of luteolysis. Estrus was synchronized in ovary-intact ewes with two injections of prostaglandin F₂α (PGF₂α) analog given 10 d apart (Day 0 = second day after the second PGF₂α injection). Ewes were subjected to hypothalamic-pituitary disconnection (HPD; n = 6) on Day 3 and were pulsed with gonadotropin-releasing hormone (GnRH). Ewes were used during the estrous cycle or received approximately 400 IU pregnant mare serum gonadotropin (PMSG) on Day 2 to stimulate ovulation; there was no difference (P < 0.10) in ovulation rate or progesterone production between these two groups. Luteal regression was induced by injection of PGF₂α analog on approximately Day 10 of the estrous cycle. Blood samples were collected around exogenous GnRH pulses before and at 2- or 4-hr intervals after PGF₂α administration and concentrations of LH and progesterone determined. At 4, 12 and 24 hr after PGF₂α administration, mean serum progesterone levels in all ewes had decreased by 54.7%, 66.2% and 89.4%, respectively (P < 0.05) from pre-injection levels. The decrease in progesterone was associated with an increase (P < 0.01) in LH pulse amplitude with means at 4-hr post-PGF₂α ranging from 190% to 288% of pre-PGF₂α values. Mean serum LH levels were also increased (P < 0.01) within 4 hr of PGF₂α administration and remained elevated at all but the 24-hr time point. The timing of this increase (within 4 hr) indicates that it is independent of changes in serum estradiol concentrations, which do not increase for at least 16 hr after induction of luteolysis. Thus, removal of endogenous progesterone negative feedback at the anterior pituitary gland in the hours immediately after induction of luteolysis seems to play a role in facilitating LH release independently of hypothalamic action.     

Efficient production of pronuclear embryos in breeding and nonbreeding season for generating transgenic sheep overexpressing TLR4

Background: Brucella is a zoonotic Gram-negative pathogen that causes abortion and infertility in ruminants and humans. TLR4 is the receptor for LPS which can recognize Brucella and initiate antigen-presenting cell activities that affect both innate and adaptive immunity. Consequently, transgenic sheep over-expressing TLR4 are an suitable model to investigate the effects of TLR4 on preventing Brucellosis. In this study, we generated transgenic sheep overexpressing TLR4 and aimed to evaluate the effects of different seasons(breeding and non-breeding season) on superovulation and the imported exogenous gene on growth.Results: In total of 43 donor ewes and 166 recipient ewes in breeding season, 37 donor ewes and 144 recipient ewes in non-breeding season were selected for super-ovulation and injected embryo transfer to generate transgenic sheep.Our results indicated the no. of embryos recovered of donors and the rate of pronuclear embryos did not show any significant difference between breeding and non-breeding seasons(P 0.05). The positive rate of exogenous TLR4 tested were 21.21 % and 22.58 % in breeding and non-breeding season by Southern blot. The expression level of TLR4 in the transgenic sheep was 1.5 times higher than in the non-transgenic group(P 0.05). The lambs overexpressing TLR4 had similar growth performance with non-transgenic lambs, and the blood physiological parameters of transgenic and non-transgenic were both in the normal range and did not show any difference.Conclusions: Here we establish an efficient platform for the production of transgenic sheep by the microinjection of pronuclear embryos during the whole year. The over-expression of TLR4 had no adverse effect on the growth of the sheep.     

Poor reproductive response of anestrous Suffolk ewes to ram exposure is not due to failure to secrete luteinizing hormone acutely

Twenty Polypay-sired ewes (Group P) and 14 Suffolk ewes (Group S) were bled at 48-h intervals for 10 d beginning on April 6, 1989, and the serum was assayed for progesterone to determine which ewes were anestrous; 9/20 Group P ewes were anestrous, compared with 14/14 Group S ewes (P less than .001). Catheters were placed into the jugular vein of anestrous ewes from both breed groups (eight of Group P, seven of Group S), and samples of serum were collected at 12-min intervals for 4 h. Then, the ewes were exposed to mature, intact rams, and additional samples were taken at 12-min intervals for 4 h after ram exposure. The serum was later analyzed to determine the secretion of LH in response to ram introduction. After the acute bleeding period, all Group P and Group S ewes were commingled and exposed to a ram continuously for 42 d. Samples of serum were collected thrice weekly and analyzed for progesterone to monitor ovulatory response to ram introduction through the 42-d period. In addition, breeding activity and lambing data were recorded. When all Group P ewes were compared to Group S ewes, a greater proportion (P less than .001) of Group P ewes were mated (20/20 vs 3/13; one Group S ewe died during the 42-d mating period) by the end of the 42-d period and more (P less than .001) ewes lambed in the fall (17/20 Group P vs 2/13 Group S).(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteotropic influence of the ovine uterus.

Preliminary observations indicated that the ovine uterus might play a contributing role in the development of the corpus luteum. In order to better define this putative relationship, we monitored luteal function in mature ewes that were hysterectomized or sham-operated at different intervals following induction of ovulation. Corpora lutea formed following hysterectomy carried out immediately after ovulation were subnormal. Circulatory concentrations of progesterone in these animals began to ascend normally, but then achieved a plateau level less than that of control animals. This was attributed to reduced size of the luteal gland, and not to anomalies per unit tissue in morphology or content of progesterone. Luteal activity was not altered in ewes hysterectomized later in the estrous cycle (Day 5). However, when such a luteal phase was terminated by exogenous luteolysin, corpora lutea formed subsequently were defective. It appears that the ovine uterus produces a hormonal factor during metestrus that augments the growth potential of the corpus luteum.     

Comparison of estrus induction and subsequent fertility with two different intravaginal devices in ewes during the non-breeding season

Two experiments were conducted to compare the effect of estrus induction by controlled internal drug release (CIDR) and intravaginal cream containing 500 mg progesterone (P cream) in ewes during the non-breeding season. In the first experiment, twenty-four ewes were randomly grouped for two treatments with the different intravaginal devices for 12 days: Group A was the CIDR group and Group B was the P cream group. Blood was collected from all treated ewes, and progesterone (P(4)), estradiol 17-beta (E(2)) and luteinizing hormone (LH) concentrations were measured by enzyme immunoassay. In the second experiment, the conception rates from natural mating, estrus-detected AI (inseminated 12 h after estrus detection), or fixed-time AI (inseminated 42 h after removal of an intravaginal device) in 127 ewes treated with CIDR or P cream were compared. In Experiment 1, the rate of estrus induction and the time of estrus onset after device removal were 91.7% and 36.3 +/- 15.7 h in Group A, and 100% and 35.0 +/- 12.6 h in Group B, respectively. There were no significant differences between the devices. The mean plasma P(4) concentration in Group B was significantly (P < 0.01) lower than Group A between day -9 and day -1 (Day 0: the day of device removal). However, no significant differences were found in the mean E(2) concentrations of the two groups after treatment. The mean time of estrus onset in ewes with an observed LH surge and the time of LH surge after treatment were 23.3 +/- 8.7 h and 30.3 +/- 5.0 h for Group A and 27.6 +/- 6.5 and 26.3 +/- 8.0 h for Group B, respectively, and there were no significant differences. However, a significant difference (P < 0.05) was found in the mean time from the time of estrus onset to LH surge between Group A (6.4 +/- 6.7 h) and Group B (-1.3 +/- 4.1 h). In Experiment 2, the conception rates for natural mating, estrus-detected AI, and fixed-time AI were 55.0, 29.4, and 25.0% for Group A and 40.7, 25.0, and 42.1% for Group B, respectively, and there were no significant differences. These results suggest that the effect of induction of estrus and ovulation and the rate of conception after treatment were comparable to CIDR even though the plasma P(4) concentration of the P cream method tended to be low during the insertion period.     

Temporal Relationships Between Oxytocin and 13,14-Dihydro-15-Keto-Prostaglandin F2α Pulses in Ovariectomized Ewes

The primary objective was to evaluate the role of non-ovarian oxytocin in the initiation of pulses of PGF_2α, as measured by peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F_2α (PGFM). A 2 × 2 factorial arrangement of estradiol and progesterone treatments was administered to groups of five ewes after ovariectomy on Day 12. Progesterone (10 mg) was administered at 0700 and 1900 hr on Day 12, and then either progesterone or its vehicle was administered on Days 13 and 14. Silastic implants, either empty or containing estradiol, was administered at ovariectomy. Oxytocin and PGFM were measured in jugular blood samples withdrawn from an indwelling catheter at 5-min intervals for 8 hr on Day 15. Statistically significant pulses of oxytocin, presumably of posterior pituitary origin, were detected in all ewes. Approximately one-half of the oxytocin pulses preceded a pulse in PGFM concentrations by 10 min or less. These pulses tended (P = 0.09) to have a longer duration than those not linked to pulses of PGFM. The number of PGFM pulses that followed or did not follow an oxytocin pulse by 10 min or less was similar (P > 0.2). The amplitude and duration of oxytocin-linked PGFM pulses were greater (P = 0.05) than non-linked pulses. Although several explanations for the lower than anticipated temporal relationship between oxytocin and PGFM pulses are possible, the finding that oxytocin-related PGFM pulses are distinguishable from other pulses is consistent with the concept that oxytocin initiates robust pulses in PGF_2α secretion.     

Response of Corriedale ewes to the "ram effect" after priming with medroxyprogesterone, fluorogestone, or progesterone in the non-breeding season

One hundred eighty-nine Corriedale ewes were used during the non-breeding season to study the "ram effect" stimulus after priming with progestogens. Intravaginal sponges containing either medroxyprogesterone acetate (MAP group, n = 49), fluorogestone acetate (FGA group, n = 49), or progesterone devices (CIDR group, n = 46) were inserted on Day-6 (Day 0 = introduction of the rams). Forty-five ewes were untreated and kept as a control group. On Day 0 the sponges were removed and rams provided with marking harnesses for oestrous detection were placed with the ewes. Onset of estrus was monitored until Day 25, and conception was determined by transrectal ultrasonography. Ewes came into heat during 4 periods: Days 0-3, 5-7, 17-20, and 21-23. The overall number of oestrus ewes were 29%, 53%, 35%, and 50% for the control, MAP, FGA, and CIDR groups, respectively (MAP and CIDR > control, p < 0.05). Control ewes presented oestrus only on Days 17-20 and 21-23. Oestrus in the progestogen-primed ewes was concentrated during Days 0-3 and 17-20, and some ewes came into oestrus on Days 5-7. There were no differences between different primings neither in oestrous response nor in conception rate. The conception rate from matings occurring on Days 0-3 was higher than on those occurring on Days 17-20. We conclude that MAP, FGA, and CIDR is equally effective in improving the response to the ram effect, and the pattern of oestrus in primed ewes was different than previously reported.     

Effects of exogenous estradiol-17 beta on luteinizing hormone, progesterone, and estradiol-17 beta concentrations before and after prostaglandin F2 alpha-induced termination of pregnancy and pseudopregnancy in gilts.

This study evaluated the influence of exogenous estradiol-17 beta (E2) administration on LH concentrations and the number of animals returning to estrus after the termination of pregnancy or pseudopregnancy in gilts. Gilts were mated (pregnant; n = 11) on the 1st d of estrus or received 5 mg of estradiol valerate i.m. at d 11 to 15 after the onset of estrus (pseudopregnant; n = 9). Gilts were treated with prostaglandin F2 alpha (PGF2 alpha, 15 and 10 mg) at 12-h intervals on d 44 of pregnancy or pseudopregnancy. The day of abortion or luteolysis (progesterone less than .2 ng/mL) was considered d 0. Six pregnant and four pseudopregnant gilts received s.c. an E2 capsule (24 mg of E2) on d -20 and additional E2 capsules on d -13 and -6. The E2 capsules were removed on the day after PGF2 alpha administration. Blood samples were collected at 12-h intervals from d -21 to -3, at 6-h intervals from d -2 to 21 or the onset of estrus, and at 15-min intervals for 8 h on d -2, 1, 4, 7, 10, 14, and 18. After each 8-h sampling period, gilts were treated i.v. with GnRH at .5 micrograms/kg of BW and blood samples collected at 10-min intervals for 3 h. A greater (P less than .05) proportion of sham-treated gilts than of E2-treated gilts exhibited a preovulatory-like LH surge after abortion/luteolysis. It was evident that E2 supplementation before luteolysis reduced the ability of pregnant and pseudopregnant gilts to return to estrus.     

Effect of cerebroventricular infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in diet-restricted ewes

The objective was to determine the effect of central infusion of insulin and (or) glucose on hypothalamic expression of leptin receptor and pituitary secretion of LH in the ewe. Twenty-two ovariectomized ewes (32 wk of age) were fitted with two lateral cerebroventricular (LCV) cannulae and fed 33% of NRC requirements for 8 wk. Ewes (n> or =5/group) were then infused, via LCV cannulae, with artificial cerebrospinal fluid (aCSF) or aCSF containing physiological concentrations of insulin (INS), glucose (GLU), or INS + GLU; the mass of each increasing linearly from Day 0 (mass = 0 units/h) to Day 8 (mass of INS = 80 mIU/hr and GLU = 10 mg/hr). Jugular serum was collected every 12 min for 4 hr on Days 0, 2, and 4. Ewes treated with INS or INS + GLU had greater (P<0.06) mean concentrations of LH than aCSF treated ewes on Day 2 (13.8+/-1.8 and 12.5+/-1.3 > 8.0+/-3.3 ng/ml). Furthermore, on Day 4, concentrations of LH in INS treated ewes exceeded that (P<0.07) of aCSF treated ewes (14.8+/-2.0 > 7.4+/-3.0 ng/ml). Expression of NPY mRNA did not differ between treatments (P = 0.87). Leptin receptor mRNA expression was dramatically reduced (P<0.0002) in INS+GLU versus aCSF treated ewes. These data provide evidence to suggest that insulin may be an important component of hypothalamic mechanisms regulating secretion of LH and expression of leptin receptors in undernourished ruminants.     

Effect of peripheral concentrations of progesterone on follicular growth and fertility in ewes

The effects of progesterone (P₄) on follicular growth and fertility in ewes were examined. In Experiment 1, 22 ewes received either one or three packets of P₄ (5 g/packed) or an empty packet subcutaneously (sc) from Days 5 to 15 of the estrous cycle (estrus = Day 0). On Day 6, P₄-treated ewes received 12.5 mg of prostaglandin F₂α. Follicles ⩾3 mm in diameter were observed via transrectal ultrasonography daily from Day 4 through estrus, corpora lutea (CL) were observed 5 to 7 d after estrus. Ewes with low (LOW; ⩽1 ng/ml; n = 5), intermediate (MED; > 1 and <2 ng/ml; n = 10), or normal (NOR; ⩾2 ng/ml; n = 7) P₄ in jugular plasma on Days 7 through 15 differed in follicular development. The largest follicle at estrus was larger in ewes with LOW vs. MED and NOR P₄ (7.8 ± 0.3 vs. 6.9 ± 0.2 mm; P < 0.05). Treatments differed in proportions of multiple-ovulating ewes, in which the oldest ovulatory follicle was first observed before Day 10 (LOW: 3 of 3, MED: 6 of 10, NOR: 0 of 5, respectively; P < 0.05). Estradiol was higher early in the treatment period in LOW ewes than in MED and NOR ewes (day × treatment; P < 0.05). In Experiment 2, ewes received 5 mg of P₄ in corn oil (low progesterone [LP]; n = 51) or 2 ml of corn oil (CON; n = 49) sc every 12 hr on Days 6 through 14 of the estrous cycle before mating. LP ewes received 15 mg of prostaglandin F₂α on Day 6. Mean serum P₄ on Days 7 through 15 was 0.6 ± 0.1 ng/ml in LP and 1.9 ± 0.1 ng/ml in CON ewes. Eleven LP and 12 CON ewes were scanned daily from Day 4 through mating, and in all ewes (n = 93), CL were counted 10 d after mating and embryos were counted at 25, 40, and 60 d of gestation. In multiple-ovulating ewes, day of cycle of appearance was earlier for the oldest (Day 6.1 ± 0.8 vs. 10.4 ± 0.8) but not second oldest (Day 11.7 ± 1.0 vs. 12.2 ± 0.9) ovulatory follicles in LP compared with CON ewes. The conception rate was lower in LP (72%) than in CON ewes (98%; P < 0.01). However, numbers of CL 10 d after mating, and in pregnant ewes, numbers of embryos 25 d after mating and lambs born, did not differ with treatment. In summary, low P₄ increased the size of the largest follicles and the age of the oldest ovulatory follicles. Embryos resulting from the ovulation of older and younger follicles in the same ewe did not differ in their ability to survive.     

Early pregnancy alters the metabolic responses to restricted nutrition in sheep

This study investigated whether a 27-day period of nutrition at half-maintenance during early pregnancy (up to Day 14) could alter maternal endocrine responses. Forty-six ewes were fed all or half of their maintenance requirements and slaughtered on Day 14 of the oestrous cycle or pregnancy. We used real time RT-PCR to study gene expression of growth hormone receptor (GHR) and leptin in adipose tissue and GHR, GHR1A and of the insulin-like growth factor I (IGF-I) in the liver. Blood profiles of metabolites and metabolic hormones were also determined. Throughout the experiment, underfed animals presented lower body weight and body condition, greater plasma concentrations of non-esterified fatty acids (NEFA), and lower plasma concentrations of leptin, compared to adequately fed animals. Undernutrition affected the patterns of gene expression in adipose and hepatic tissues, and the responses differed between pregnant and non-pregnant ewes. In adequately fed ewes, pregnancy up-regulated leptin mRNA expression in adipose tissue, a response that was impaired in underfed ewes. The hepatic expression of IGF-I mRNA was increased by pregnancy in underfed animals while no effect was observed in adequately fed ewes. It remains to be determined whether the changes in the endocrine milieu are paralleled by modifications in uterine gene expression that could alter the environment of the embryo during early pregnancy.     

笼养丹顶鹤繁殖行为和粪样中性激素水平变化的关系

2007年3月～2008年2月,在哈尔滨北方森林动物园,选2对健康的成年丹顶鹤,采用目标取样和扫描取样相结合的方法进行了行为观测,同时收取粪便提取激素,利用放射免疫分析法（RIA）测定了笼养丹顶鹤粪样中睾酮、孕酮、雌二醇的浓度。试验结果表明：笼养丹顶鹤繁殖行为呈显著的季节变化,其对鸣、炫耀行为的高发期在3、4月（P〈0．05）,营巢行为在3月极显著高于其他月份（P〈0．01）,丹顶鹤的交尾行为集中出现在3、4月（P〈0．05）;繁殖期雄性丹顶鹤粪便中睾酮平均水平为（259．59±149．70）ng／dl,非繁殖期为（84．81±27．35）ng／dl,二者差异显著,繁殖期雄鹤求偶炫耀、交尾、卧巢等的发生频次与粪便中睾酮呈极显著相关（P〈0．01）,其对鸣、警戒以及营巢都与睾酮变化水平呈显著相关（P〈0．05）。繁殖期雌性丹顶鹤粪便中的孕酮平均浓度为（9．65±7。15）rig／m1,非繁殖期为（2．76±0．97）ng／ml,差异显著,繁殖期雌鹤粪便中的孕酮激素水平与其卧巢行为呈显著性相关（R=0．8848,P〈0．05）;繁殖期雌性丹顶鹤粪便中雌二醇平均浓度为（30．50±61．77）pg／ml,非繁殖期为（8．17±3．72）pg／ml,二者差异显著,繁殖期雌鸟雌二醇变化水平与其繁殖行为的相关性不显著（P〉0．05）;雌性丹顶鹤粪样中雌二醇激素的变化水平与其产卵时间有着较为密切的关系。     

Endocrinology of the postpartum period in the Pelibuey ewe

The postpartum (PP) period in the Pelibuey ewe was studied. Laparotomies were performed on 14 ewes in the first year at d 10, 20 and 30 PP, and at d 10 and 20 PP in the second year on 17 ewes. Progesterone concentrations were determined in serum taken daily, from 4 to 7 d after parturition until estrus. Temporal fluctuation of luteinizing hormone (LH) was determined in samples taken at 30-min intervals for 4 h weekly. The mean interval from lambing to first ovulation was longer (P less than .001) in 1980 (59 +/- 4.9 d) than 1979 (26 +/- 3.1 d), the mean interval from lambing to first estrus was also longer (P less than .001) in 1980 (91 +/- 5.6 d) than 1979 (51 +/- 5.5 d). Follicles were present on the ovaries of the majority of the ewes at d 10. The mean diameter of the largest follicles on each ovary was reduced (P less than .025) in ewes in 1980 (6 mm) compared with 1979 (7.7 mm). Corpora lutea (CL) occurred in 67 and 75% of the ewes by d 20 and 30, respectively in 1979; no CL were found by d 20 in 1980. Progesterone profiles suggested that the PP period was composed of a period of anestrus, and a period of cyclic ovarian activity with one, two or three ovulations without behavioral estrus. In some ewes, the first cycle was of shorter duration, and its CL secreted less progesterone (P less than .05) relative to CL of silent and regular estrous cycles. Luteinizing hormone peaks were recorded as early as 6 d PP. When progesterone concentrations were elevated to luteal phase levels, the frequency, but not magnitude, of LH peaks per 4-h bleeding period was reduced (P less than .05) relative to anestrus. It is concluded that there are periods of anestrus and of silent cycles, which precede the first postpartum estrus in Pelibuey ewes.     

Synchrony of Ovulation and Follicular Dynamics in Merino Ewes Treated with GnRH in the Breeding and Non-breeding Seasons

The effect of gonadotropin releasing hormone (GnRH) treatment on the time of ovulation and the occurrence of follicular dominance during the non-breeding and breeding seasons (experiment 1), and on fertility after artificial insemination (AI) in the non-breeding season (experiment 2), was examined in Merino ewes. Oestrus was synchronized in 40 nulliparous ewes (experiment 1; n = 20, in the non-breeding and breeding seasons) and in 79 multiparous ewes (experiment 2) using intravaginal sponges and pregnant mare serum gonadotropin. Thirty six hours after sponge removal (SR), half the ewes were injected (i.m.) with 40 microg of synthetic GnRH and the remainder used as controls. GnRH improved the synchrony of ovulation compared with the controls in the breeding (SD = 2.8 vs 5.7 days, p = 0.04) but not the non-breeding season (SD = 3.8 vs 4.4 days, p = 0.69), with ewes ovulating from 42 to 54 h (mean 50.4 +/- 4.08 h) and 42-60 h (mean 54.4 +/- 5.47 h) after SR for GnRH and control, respectively. For both treated and control ewes, ovulation occurred earlier in the non-breeding than the breeding season (50.1 vs 54.6 h; p = 0.002). GnRH had no effect on follicular dominance, as assessed by divergence (D: the time the ovulatory follicle exceeded the average size of the other non-ovulating follicles) or on the interval from D to ovulation (IDO). However, follicular dynamics differed between seasons. The mean follicle diameter increased at a faster rate up to 36 h after SR in the non-breeding compared with the breeding season and then rapidly declined, compared with a later peak (42 h after SR) in mean follicular size during the breeding season. IDO was shorter in the non-breeding than in the breeding season (26.7 +/- 4.30 h vs 39.6 +/- 4.53 h; p = 0.05). In experiment 2, ewes (n = 38 GnRH-treated, n = 40 controls) were inseminated in the uterus by laparoscopy 42 h or 48 h after SR with frozen-thawed sperm. The fertility of ewes treated with GnRH (nine of 39, 23%) was not different to the controls (eight of 38, 21%; p = 0.01). In conclusion the application of GnRH improved synchronization of ovulation but did not improve fertility rates after AI.     

Leptin infusion during the early luteal phase in ewes does not affect progesterone production

Infusion of leptin during the ovine follicular phase has been shown to increase progesterone secretion during the subsequent luteal phase. In this study, we have assessed the effects of infusing leptin during the early luteal phase. Infusion of leptin (2.5 microg/h) into the ovarian artery of ewes with ovarian autotransplants (n=5) on day 3 of the luteal phase for 12h did not affect progesterone estradiol or LH concentrations compared to control ewes (n=5). These results suggest no direct effect of leptin on ovarian function at this stage of the estrous cycle.