Plasma oestrogen and progesterone in relation to superovulation and egg recovery in the cow.

Pregnant mares serum gonadotrophin (PMSG) was used in combination with prostaglandin F2alpha or its analogues to induce superovulation in 25 heifers. Total unconjugated oestrogen and progesterone were determined in peripheral plasma of these superovulated animals, and the levels compared with those found during the normal oestrous cycle. A very high level of oestrogen was found between day 3 and 6 after superovulation, and it seems likely that large unovulated follicles were responsible for the excess steroid. Similarly, progesterone levels were raised in the superovulated animal presumably due to production by the numerous corpora lutea. In two heifers, in which overstimulation of follicular development had occurred, there were no ovulations in one of the animals while in the other animal there were 16 ovulations but early regression of corpora lutea was indicated. It is concluded that the poor recovery of eggs on day 6 after superovulation could have been due to deleterious effects of high levels of oestrogen on either the motility of the genital tract causing the premature transport of eggs, or the properties of the zona pellucida.     

不同药物对荷斯坦青年母牛超排效果的研究

本研究以青年荷斯坦母牛为试验对象,在供体母牛发情周期的任意一天(发情当天除外),于供体牛阴道放置CIDR(孕酮的缓释装置).同时肌注Eb 2 mg和P4激素100 mg,在放置阴道栓的第五天开始按常规4天递减法肌肉注射FSH超数排卵.结果发现,应用进口FSH超排组,有23头发生卵巢囊肿,同时乳房有不同程度的发育,应用国产FSH超排组,只有3头牛发生卵巢囊肿,且其乳房并无发育.表明在超数排卵时,应根据所选药物及超排牛群内牛只个体的不同,选择适宜的超排剂量.     

莱芜黑山羊发情周期中FSH、LH、E2和P的分泌规律

莱芜黑山羊在发情期和间情期，血浆内的卵泡刺激素（FSH）和黄体生成素（LH）均呈脉冲式分泌，雌激素（E2）和孕嗣（P）为波动式分泌。发情期FSH的脉冲周期较间情期长，两者之间显著差异（P〈0．05）。发情期LH的脉冲周期短于间情期，两者之间差异不显著（P〉0．05）。在整个发情周期中，FSH和LH均先后出现4个分泌峰，FSH和LH的第1个分泌峰分别出现在第7天和第5天，其余3个分泌峰均同时出现（分别为第10、15和20天）。E2和FSH、LH均在发情周期的第20天迭最高峰。P在间情期一直维持在一个较高水平。     

非繁殖季节太行山羊胚胎移植方案研究

对48只太行山羊(供体羊)、40只太行山羊和120只奶山羊(受体羊)进行了同期发情和超数排卵胚胎移植试验。其结果如下:(1)CIDR PMSG对太行山羊同期发情,有效发情率为75%;CIDR FSH对奶山羊同期发情,有效发情率为73%。(2)CIDR FSH LH组平均可用胚胎数分别与CIDR PMSG组和CIDR PMSG LH组之间差异达到极显著水平(P<0.01),而与CI-DR FSH组之间差异显著(P<0.05)。(3)CIDR FSH LH超排时,用CIDR FSH对奶山羊进行同期发情,受体妊娠率为56%;CIDR PMSG对太行山羊同期发情,受体妊娠率为60%水平。证明在非繁殖季节对太行山羊采用CIDR FSH LH超数排卵和以太行山羊及奶山羊为受体分别用CIDR PMSG和CIDR FSH同期发情来进行胚胎移植的技术方案是可行的。     

Monoamine oxidase activity in some brain areas of sheep after hormonal stimulation

The influence of hormonal superovulatory preparations Folistiman (450 IU FSH, Spofa, Prague) and serum gonadotropin (1500 IU PMSG, Spofa, Prague) on monoamine oxidase (MAO), the degradative enzyme of catecholamines, was investigated in some areas of the brain regulating reproductive functions (area preoptica of the hypothalamus, pituitary gland, and pineal gland) in ewes with synchronized oestrus (20 mg chlorsuperlutin) during the oestrous period using a radiochemical method. After intramuscular administration of 1500 IU PMSG, marked increase of MAO activity was found in the area preoptica (p < 0.05) and in the pituitary gland (p < 0.01) in comparison with the control group. No change occurred in MAO activity after ovarian stimulation with FSH. Administration of the above superovulatory preparations failed to induce MAO activity in the pineal gland of sheep.     

Studies on factors affecting superovulation and embryo transfer in Hungarian merino ewes

The objectives of this study were (a) to assess the ovulatory response and embryo production of Hungarian Merino ewes after superovulation, (b) to investigate the factors influencing the efficiency of embryo transfer (ET) in Hungarian Merino ewes, (c) to compare the results of two ovarian stimulation protocols (PMSG and PMSG + FSH treatment) in Hungarian Merino ewes, and (d) to study how superovulation, laparoscopic insemination and surgical embryo retrieval (ER) affect the subsequent reproduction of Hungarian Merino donor females after an ET programme. There was no significant difference between the ovarian stimulation protocols in the ratio of donor ewes responding to superovulation nor in the average number of corpora lutea. However, the number of transferable embryos recovered per donor ewe was higher in the PMSG + FSH group. The proportion of transferable embryos, unfertilized oocytes and degenerated embryos did not differ between the treatment protocols. The total pregnancy rate was 53.4% (179/335). Neither the developmental stage of the embryo nor the number of transferred embryos affect the implantation of embryos. However, the increased number of transferred embryos positively influenced the pregnancy rate. No difference was found in the pregnancy rate between synchronised and non-synchronised groups of recipients. Thirty-six out of 45 donor ewes (80%) became pregnant within one year after the ET programme, indicating that ovarian stimulation and surgical ER did not affect adversely their reproduction.     

The effect of GnRH supplement of FSH and PMSG treatments for prepubertal swamp buffalo calves (Bubalus bubalis)

The objective of the experiment was to improve the multifollicle stimulation technique and the ovarian response examination in prepubertal swamp buffalo calves. Six animals were stimulated by gonadotropin hormone 7 days after a progesterone ear-implant. The first stimulation was done by giving 24 mg FSH + 100 microg GnRH (FSH+GnRH) and the second, one month after by giving 2,000 IU PMSG + 100 microg GnRH (PMSG+GnRH). Twenty-four hours after GnRH, the ovarian responses were checked using rectal palpation and real-time B mode ultrasonography. Five out of six animals (83.3%) responded to both treatments and were selected for oocyte collection. The oocytes were aspirated directly following a caudal midline laparotomy. The results of ovarian responses to FSH+GnRH and PMSG+GnRH averaged 17.6+/-12.1 (L-9.8+/-8.7, R=7.8+/-6.2) and 17.4+/-5.6 (L-9.4+/-2.9, R=8.0+/-3.7), respectively. The average number of recovered oocytes per animal was 9.0+/-6.4 and 8.4+/-1.1, respectively which represented a recovery rate of 56.3 (+/- 9.2)% and 51.9 (+/- 10.3)%. More than eighty percent of the recovered oocytes were in an immature stage with more than 2-3 layers of compact cumulus mass. The present study showed that the oocytes were collected successfully in prepubertal buffalo calves after the FSH+GnRH or PMSG+GnRH stimulation and most of the recovered oocytes were immature, which made them suitable for in vitro maturation and fertilization.     

Hormonal Response of Female Goats to Active Immunization against a Recombinant Human Inhibin α-subunit, and establishment of an Enzyme-linked Immunosorbent Assay for Caprine Follicle-stimulating Hormone

The effect of selective immunosuppression of endogenous inhibin in goats on FSH, LH, progesterone and estradiol-17β profiles was studied during the breeding and nonbreeding seasons. Eighteen adult female Boer goats were immunized against the recombinant human inhibin α-subunit (hINH-α). With the exception of estradiol, which was determined by radio-immunoassay (RIA), all plasma hormone concentrations were determined by ELISA. The ELISA for FSH presented in this paper was established in the authors' laboratory, based on an existing RIA. Mean basal concentrations of FSH were not affected by immunosuppression of endogenous inhibin, nor was there a difference in the amplitude of the pre-ovulatory FSH surge. Immunization against inhibin appears to eliminate the slight secondary rise of FSH occurring 12–20 h after the major surge associated with ovulation. The LH profiles of the immunized goats were characterized by lower basal concentrations both before and after the pre-ovulatory LH surge which itself was reduced by 50% in immunized does. By contrast, concentrations of circulating estradiol were significantly elevated after inhibin-immunization. Progesterone profiles were not affected. Extending immunization into the anoestrous season by a booster injection of hINH-α, implicating oestrus induction with a progestagen and eCG, produced no discernible differences in FSH and LH profiles in comparison with nonimmunized control goats. The findings suggest that in goats, paracrine factors may play a more significant role in controlling follicular activity than a feedback mechanism acting via the pituitary.     

Changes in the hypothalamus and adjacent ependyma after hormonal stimulation of the ovaries in ewes]

Superovulation treatment leaves alternations in the controlling regions of the hypothalamus and in the adjacent ependyme after ovulation. The test ewes were synchronized with Agelin (20 mg chlorsuperlutin in one vaginal sponge) and stimulated (after the removal of the sponges) with 750 IU PMSG + 750 IU HCG and with 1000 IU HCG and 750 IU PMSG + 5 ml Antisergon (goat antiserum against PMSG), administered 68 hours after PMSG (i.e. 40 hours after HCG). The control ewes were in different stages of the ovarial cycle. The experimental ewes were killed 120 to 130 hours after the start of stimulation. Routine histological techniques were used to treat the brain samples; this treatment was followed by assessment under light microscope. The ependyme epithelium of the third cerebral chamber was studied under scanning microscope. Preparations with different FSH:LH ratios had different effects on the nucleus ventromedialis. Antisergon administration influenced the secretion of NPV (prevented persistent stimulation), which was observed after administration of PMSG + HCG. On the surface of the lower part of the third cerebral chamber the administration of Antisergon slowed the formation of the miniblebs. Supraependyme cells disappeared after stimulation for superovulation.     

Endocrine Profiles and Embryo Quality in Japanese Black Cattle Superovulated with Human Menopausal Gonadotrophin and Porcine Follicle Stimulating Hormone

Induction of superovulation using human menopausal gonadotriphin (hMG) in Japanese Black cattle can result in the recovery of a higher percentage of high quality embryos compared with that using porcine follicle stimulating hormone (FSH). In order to clarify the endocrinological mechanism involved in this discrepancy, 30 superovulation sessions of 17 Japanese Black cattle were studied. Fifteen cattle were super‐stimulated with hMG (total 600 IU), and the remaining 15 cattle were given FSH (total 20 mg). The plasma profiles of LH, estradiol‐17β (E₂) and progesterone (P₄) were correlated, and the embryo quality was investigated. The total number of ova recovered and the number of transferable embryos tended to be larger in the hMG‐treated group than in the FSH‐treated group. The percentage of excellent embryos tended to be higher in the hMG‐treated group than in the FSH‐treated group (54.3 and 28.7%, respectively, p < 0.10). The E₂ level increased during the first 3 days after the initial administration of either hMG or FSH and was higher in the hMG‐treated group than in the FSH‐treated group (p < 0.05). During this period, the E₂ level could be categorized into one of the following three types according to whether it increased or decreased and according to the degree of increase or decrease: (1) increase by a factor of 1.2 or more (quick increase type) (2) slight increase by a factor less than 1.2 (slow increase type), and (3) no increase (unstable increase type). In the group treated with hMG, 66.7% of the animals (10 of 15 cattle) showed a quick increase in the E₂ level. However, in the FSH‐treated group, 40% (six of 15) of the animals showed a slow increase in the E₂ level. The plasma LH level increased dramatically 8 h prior to the peak level in both the hMG‐ and FSH‐treated groups, and then it returned to the basal level 12 h later. After the administration of prostaglandin (PG)F_2α, the LH peak level was attained within 44 h in 80% of the animals in the hMG‐treated group, whereas in the FSH‐treated group, the LH peak level tended to be reached later. The P₄ level did not increase during the period of hMG or FSH treatment and decreased drastically following administration of PGF_2α. After the onset of oestrus, the P₄ level was higher in the hMG group than in the FSH group, and 5 to 7 days after oestrus, the level remained higher in the hMG group than in the FSH group (p < 0.05). After the first 3 days of hMG administration, the E₂/P₄ ratio was higher than that after FSH administration. Furthermore, on the day following PGF_2α administration, the ratio was significantly higher in the hMG group than in the FSH group (p < 0.05). These results indicate that superovulation in cattle given hMG results in a significant increase in plasma E₂ during the first 3 days and that the increase in the plasma P₄ level is larger a few days after oestrus and thereafter compared with FSH‐induced superovulation. Therefore, such plasma level profiles may be related to the increased recovery rate of high quality embryos.     

Endocrine patterns in the postpartum beef cow associated with weaning: a comparison of the short and subsequent normal cycles

Levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone and estradiol-17 beta were measured in five Polled Hereford cows. Blood samples were collected once or twice daily for 5 d, then every 6 h from 1 d before weaning (d 28 to 38 postpartum) until 10 d after the second postweaning estrus. Blood samples were again collected at daily intervals until the third postweaning estrus. All cows exhibited estrus within 4 d after weaning, a second estrus 8 to 10 d after the first and a third estrus 16 to 23 d after the second. All cows had peaks in serum concentrations of LH during the first (22.6 to 81.7 ng/ml) and second (4.4 to 149.0 ng/ml) postweaning estrus. Mean levels of LH in serum during the peak and the area under the LH curve during the first and second postweaning estrus did not differ. Serum levels of LH and FSH during the first 4 d of the short cycle did not differ from LH and FSH levels the first 4 d of the subsequent normal cycle. Levels of LH in serum for 4 d before the first LH surge, associated with the first postweaning estrus, did not differ from levels of LH found 4 d before the second Lh surge, associated with the second postweaning estrus. However, serum levels of FSH during the 4 d before the first ovulatory LH surge were lower (P = .05) than those observed during the 4-d period before the second ovulatory surge of LH. Progesterone levels were similar the first 6 d after the first and second estrous periods, but were lower after d 6 of the first (short) cycle than after d 6 of the second (normal) cycle. Estradiol peaks of 1.2 to 2.8 pg/ml were detected during the first postweaning estrus and 1.4 to 12.5 pg/ml during the second postweaning estrus, but due to the variability among cows mean levels of estradiol during first estrus did not differ from second estrus. These data agree with previous reports that postpartum anestrous cows had short cycles if they exhibit estrus in response to weaning. The early decline of progesterone after the first estrus apparently did not stem from lack of LH in serum, but the lower levels of FSH observed before this first ovulation may have been an important factor contributing to the reduced life span of the subsequent corpus luteum.     

猪胚胎移植中同期发情母猪的内分泌研究

〗本研究选用猪胚胎移植的３头供体母猪，依次用前列腺素（ＰＧ），孕马血清促性腺激素（ＰＭＳＧ）和人绒毛膜促性腺激素（ＨＣＧ）作同期发情和超数排卵处理，于处理第１１天做剖腹手术采集胚胎，在整个处理过程中多次采血，监测了血清中孕酮（Ｐ４），雌二醇（Ｅ２），促黄体素（ＬＨ）和硫酸雌酮（Ｅ１Ｓ）四种激素浓度的变化，并据此来讨论同期发情和超数排卵处理成功和失败的原因。     

The effects of progesterone and oestrogen treatment in heifers on oestrous cycle control and plasma progesterone levels

Data are presented on the effects of a short-term progesterone treatment for oestrous cycle control in cattle. Progesterone was administered by intravaginal sponge pessaries inserted for a 10-day period. Progesterone pessaries alone did not affect oestrous cycle length or corpus luteum function at either early (day 2) or midluteal (day 12) cycle stages. However, when progesterone (250 mg) and oestradiol benzoate (7-5 mg) were given intramuscularly on the day of pessary insertion corpus luteum development was inhibited in animals treated at day 2 and was regressed in animals at day 12. This combined oestrogen-progesterone treatment efficiently controlled oestrous cycle length.     

Effect of prostaglandin F2alpha on ovarian, adrenal, and pituitary hormones and on luteal blood flow in mares

The effect of a single injection of prostaglandin F2alpha (PGF) during mid-diestrus on systemic concentrations of progesterone, LH, FSH, estradiol, and cortisol and on blood flow to the corpus luteum was studied in 10 controls and 10 PGF-treated mares. Blood flow was assessed by estimating the percentage of corpus luteum with color-Doppler signals of blood flow during real-time scanning of the entire structure and by the diameter of the vascular pedicle near its attachment to the ovary. Treatment was done 8 days after ovulation and 0 h was immediately before the treatment. Examinations and collection of blood samples were done at 0 h, every 5 min until 1h, and then at 1.5, 2, 4, 8, 12, 24, 48, and 72 h. The concentrations of estradiol did not change, but progesterone, LH, FSH, and cortisol increased significantly within 5 min. Concentrations of LH and FSH in the PGF group remained elevated until a temporarily lower concentration at 8 or 4h, respectively, rebounded to 12h, and then slowly decreased. Cortisol remained elevated, until a decrease between 1 and 4h. Progesterone in the PGF group increased significantly until 10 min after 0 h and then decreased by 40 min to below the concentrations in controls. Within the PGF group, progesterone decreased significantly by 45 min to below the concentrations at 0 h. The values for each of the two indicators of blood flow did not differ significantly between the PGF and control groups until a decrease at 24h in the PGF group. Results did not support the hypothesis that the immediate transient post-PGF increase in progesterone was associated with an increase in luteal blood flow. Luteolysis, as indicated by decreasing progesterone, began well before the beginning of a decrease in luteal blood flow.     

α-Adrenergic control of gonadotropin secretion in the ewe

The effect of the centrally acting α-adrenoceptor agonist, clonidine, on plasma LH and FSH was studied in oestradiol-primed and unprimed ewes and in oestrous ewes. In unprimed anoestrous ewes, clonidine stimulated LH and FSH release after a lag period of 18 h, and noradrenaline intracarotid injection or i.v. infusions immediately stimulated LH release. In oestradiol-infused anoestrous ewes, clonidine produced either a delay or inhibition of the gonadotrophin surge and noradrenaline i.v. infusion advanced the LH surge. In oestrous ewes treated with clonidine, there was marked delay in the LH surge, but the magnitude of the LH and FSH surges were unaffected. Intravenous administration of α-adrenoceptor blockers, phentolamine and phenoxybenzamine, blocked the oestradiol-induced gondotrophin surge in anoestrous ewes. The effect of phenoxybenzamine on gonadotrophin surge was dose dependent in oestrous ewes. Small doses (4 mg/kg i.v.) of phenoxybenzamine delayed the synchronous LH and FSH surges. There was complete blockade of the LH surge and partial blockade of FSH surges in ewes given phenoxybenzamine (8 mg/kg i.v.) before the expected synchronous gonadotrophin surges. After this experiment, the initial rise of plasma progesterone concentrations did not occur until day 6 of oestrous cycle. Administration of phenoxybenzamine before the expected second FSH surge had no effect on the second FSH surge. Gonadotrophin release induced by gonadotrophin-releasing hormone was attenuated by phenoxybenzamine, but not by clonidine. The results suggest that the LH surge is under α-adrenergic control and the first FSH surge is under partial α-adrenergic control, but the second FSH surge is not under α-adrenergic control. The results also suggest oestradiol modulation of α-adrenergic receptor action.     

Concentrations of luteinizing hormone, follicle stimulating hormone and prolactin following transection of the pituitary stalk in ovariectomized ewes

Two experiments (Spring and Fall) were conducted in ovariectomized ewes to determine changes in pituitary hormone secretion immediately after pituitary stalk-transection. Ewes underwent either pituitary stalk-transection (SS), sham-transection (SH) or administration of anesthesia only (AO). Stalk-transected, but not sham-operated or anesthetized ewes had polyuria and polydipsia for 7 to 14 days after surgery. Concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin were measured in peripheral blood samples collected every 10 minutes for a six-hour period. Results were comparable for each season. During the six hours following surgery or removal from anesthesia, concentrations of LH declined in all ewes, but more slowly in SS ewes. No differences in patterns or mean concentrations of FSH were observed. Immediately after surgery, concentrations of prolactin were elevated, then declined in SH and SS ewes. The decrease was greater in SH than SS ewes. Data are consonant with the view that hypothalamic inhibition as well as LHRH stimulation regulate gonadotropin release by the pituitary.     

Plasma Inhibin Levels in Relation to Steroids and Gonadotrophins during Oestrous Cycle in Buffalo

The study was conducted on six Murrah buffalo synchronized and induced to oestrus. An indwelling catheter was placed in the jugular vein of each buffalo 4 days before the expected onset of the oestrus following the induced oestrus and blood samples were collected at 8 h intervals from each animal throughout the oestrous cycle. Plasma immunoreactive inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17β and progesterone were estimated by radioimmunoassay to study the variations in the peripheral levels of these hormones and their inter-relationships in order to elucidate the feedback systems controlling them during the oestrous cycle of buffalo. Plasma inhibin levels ranged between 391.25 and 631.97 pg/ml during various phases of the oestrous cycle and were found to be higher than reported in cows. Peak LH and FSH levels during oestrus were 38.40 ± 9.21 and 24.04 ± 4.75 ng/ml, respectively and estradiol-17β and progesterone were 19.50 ± 5.51 pg/ml and 0.61 ± 0.25 ng/ml, respectively. The mean plasma inhibin concentration on the day of oestrus was 562.5 ± 18.9 pg/ml. Levels of FSH in the plasma showed three mid-cycle elevations which corresponded to comparatively lower inhibin and elevated estradiol-17β levels during the same period. From this observation it was deduced that both inhibin and estradiol-17β have a feed-back regulatory effect on FSH secretion in buffalo.     

Ovarian response to pregnant mare serum gonadotropin and porcine pituitary extract in gilts actively immunized against gonadotropin releasing hormone

Two experiments were conducted to determine the effect of exogenous gonadotropins on follicular development in gilts actively immunized against gonadotropin releasing hormone (GnRH). Four gilts, which had become acyclic after immunization against GnRH, and four control gilts were given 1,000 IU pregnant mare serum gonadotropin (PMSG), while four additional control gilts were given saline. Control animals were prepuberal crossbred gilts averaging 100 kg body weight. Control gilts given saline had ovaries containing antral follicles (4 to 6 mm in diameter). Control gilts given PMSG exhibited estrus and their ovaries contained corpora hemorrhagica and corpora lutea. PMSG failed to stimulate follicular growth in gilts immunized against GnRH, and ovaries contained regressed corpora albicantia and small antral follicles (less than 1 mm in diameter). Concentrations of luteinizing hormone (LH) and estradiol-17 beta (E2) were non-detectable in gilts immunized against GnRH and given PMSG. In the second experiment, five gilts actively immunized against GnRH were given increasing doses of PMSG every third day until unilateral ovariectomy on d 50. PMSG failed to stimulate follicular growth, and concentrations of follicle stimulating hormone (FSH), E2 and LH were not detectable. Six weeks later, gilts were given a booster immunization and then were given 112 micrograms LH and 15 micrograms FSH intravenously every 6 h for 9 d. The remaining ovary was removed on d 10. Although LH and FSH concentrations were elevated, administration of gonadotropins did not stimulate follicular growth or increase E2 concentrations. These results indicate that neither PMSG or exogenous LH and FSH can induce E2 synthesis or sustain follicular development in gilts actively immunized against GnRH.     

Dynamic changes in plasma concentrations of gonadotropins, inhibin, estradiol-17beta and progesterone in cows with ultrasound-guided follicular aspiration

To elucidate the effects of ultrasound-guided transvaginal follicular aspiration, plasma concentrations of FSH, LH, inhibin, estradiol-17beta and progesterone, and folliculogenesis were examined in Holstein cows. Four clinically healthy cows with regular estrous cycles were scanned by ultrasound per rectum once a week for 9 weeks before the commencement of follicular aspiration. All visible follicles were divided into 3 categories based on their sizes (2 < or = small < 5 mm; 5 < or = medium < 10 mm, large > or = 10 mm). The follicular aspiration was started at random during the estrous cycle and conducted under epidural anesthesia induced with 5 ml of 2% lidocaine once a week for 6 weeks. The average number of total visible follicles > or = 2 mm in diameter at 7 days after aspiration (21.7 +/- 7.4, n = 24) was similar to that before starting aspiration (26.7 +/- 10.5, n = 36). Plasma inhibin and estradiol-17beta declined and fell to a trough on 1.5 days and returned to pre-aspiration values by 5 days after aspiration. Plasma concentrations of FSH increased and reached peak levels between 1 and 1.5 days after aspirations. Plasma concentrations of LH also increased and reached peak levels between 0.5 and 1.5 days after aspirations. Both plasma FSH and LH had returned to pre-aspiration levels by 5 days after aspirations. Plasma concentrations of progesterone did not change with the follicular aspiration. These results demonstrate that follicular aspiration decreases plasma concentrations of inhibin and estradiol-17beta, which in turn leads to a rise in plasma concentrations of FSH and LH. It is suggested that marked increases in plasma concentrations of FSH and LH after the aspiration stimulate the development and maturation of a new cohort of follicles within one week in cows.     

Dynamics of the Equine Preovulatory Follicle and Periovulatory Hormones: What's New?

Recent studies (2005–2008) on the interrelationships among the preovulatory follicle and periovulatory circulating hormones are reviewed. Close temporal and mechanistic relationships occur between estradiol/inhibin and follicle-stimulating hormone (FSH), between estradiol and luteinizing hormone (LH), and between progesterone and LH. Estradiol from the dominant follicle forms a surge that reaches a peak 2 days before ovulation. Estradiol, as well as inhibin, has a negative effect on FSH, and estradiol has a negative effect on LH. When estradiol decreases, the negative effect diminishes and accounts for the beginning of an FSH increase and a transition from a slow to rapid increase in LH on the day of the estradiol peak. The decrease in estradiol and the reduction or cessation in the growth of the preovulatory follicle beginning 2 days before ovulation are attributable to the development of a reciprocal negative effect of LH on follicle estradiol production when LH reaches a critical concentration. The LH decrease after the peak of the LH surge on the day after ovulation is related to a negative effect of a postovulatory increase in progesterone. Measurable repeatability within mares between consecutive estrous cycles occurs during the preovulatory period in diameter of the ovulatory follicle and concentrations of LH and FSH. Hormone-laden follicular fluid passes into the peritoneal cavity at ovulation and transiently alters the circulating concentrations of LH and FSH. Double ovulations are associated with greater estradiol concentrations and reduced concentrations of FSH.