Anoestrous Ewes Research Articles

Effect of central administration of indomethacin on anandamide-induced GnRH/LH secretion in the hypothalamus of anoestrous ewes.

It is suggested that cannabinoids (CBs) may disturb reproduction through action on hypothalamic gonadotropin-releasing hormone (GnRH) neurons directly or indirectly through intermediates such as prostaglandins. The study aimed to determine the influence of intracerebroventricular (i.c.v.) injection of the endogenous cannabinoid anandamide (N-arachidonoylethanolamine - AEA), alone or with the prostaglandin synthesis inhibitor indomethacin (IND), on GnRH/luteinising hormone (LH) secretion. The purpose of the research was to clarify the role of endocannabinoids and their interaction with prostaglandins in the regulation of reproduction at the level of the hypothalamus and pituitary in anoestrous sheep. The study was performed on 24 anoestrous ewes divided into four experimental groups: a control group receiving i.c.v. injection of Ringer-Locke solution, an AEA group that received i.c.v. injection of 30 μM of AEA, an IND group receiving i.c.v. injection of 5 μM of IND and an AEA + IND group that received i.c.v. injections of 30 μM of AEA and 5 μM of IND. Anandamide stimulated GnRH protein and gene expression in the median eminence and protein expression in the preoptic area without influencing GnRH messenger RNA (mRNA) in this structure. Indomethacin reversed the changes in GnRH secretion after AEA administration. It was also found that AEA stimulated LH mRNA in the pituitary without influencing LH release. Our results support the role of endogenous cannabinoids in the regulation of reproductive processes at the central nervous system level. They may act directly on the hypothalamic GnRH neurons or indirectly through intermediates such as prostaglandins.

The effect of human menopausal gonadotropin and equine chorionic gonadotropin on the reproductive performance of treated ewes with short-term progesterone injections and sponge during the non-breeding season.

This study investigated the effect of human menopausal gonadotropin (hMG) on reproductive efficiency of synchronized ewes with the sponge and progesterone (P4) injection-based protocols. In study 1, anoestrous ewes (n = 120) were used. Sixty ewes were treated with sponge (S) for 12 days. The injection of eCG (SeCG group, n = 30) or hMG (ShMG, n = 30) was given at the time of sponge removal. Thirty ewes received IM injection of P4, three times every 48 h and the injection of hMG was given 24 h after the third P4 injection (3PhMG group, n = 30), and 30 ewes were used as control group. Pregnancy was diagnosed on day 50 after the release of ram. In study 2, 60 ewes were randomly divided into two equal groups. In the treated group with antibiotics (n = 30), before inserting, the sponges were impregnated with the antibiotic penicillin G sodium (5,000,000 IU) and in the control group (n = 30), there was no added antibiotics. Before inserting and after removing sponges, a vaginal cytology sample was taken with a sterile cotton swab. The number of neutrophils in each sample was counted and analysed. The rate of oestrus and total pregnancy was greater in SeCG (96.7, 93.3%), ShMG (82.8, 93.1%) and 3PhMG (67.9, 89.3%) groups compared with the control group (13.8, 41.4%) (p < .05). No significant difference was found in single, twin and total lambing and pregnancy rates after injection of eCG and hMG during the non-breeding season (p > .05). A higher percentage of control ewes had the vaginal smear with neutrophils more than 50% (96.7% vs. 76.7%; p < .05). In conclusion, a single dose of hMG can induce fertile oestrus in synchronized ewes with P4 administered by either injection or intravaginally. Purulent discharge and percentage of neutrophils were significantly reduced in the synchronized ewes by the impregnated sponges with the antibiotic penicillin.

Dopaminergic control of LH secretion by the Al5 nucleus in anoestrous ewes

Dopaminergic control of LH secretion by the Al5 nucleus in anoestrous ewes

Efficacy of two different oestrus synchronization protocols for enhancing reproductive efficiency of anoestrous ewes

Efficacy of two different oestrus synchronization protocols for enhancing reproductive efficiency of anoestrous ewes

Stress and behavioural responses to winter shearing differ between pregnant and non-pregnant ewes

High progesterone concentrations reduce the stress responses in several mammals. Therefore, it may be expected that pregnant ewes have lower responses to stressors than anoestrous ewes. Our aims were to compare the stress response and the behavioural changes of pregnant and non-pregnant ewes sheared during winter. Two trials were with 20 were pregnant (group PR) and 17 non-pregnant ewes (group NP). In the first trial blood samples were collected immediately before and during the first 180 min after shearing, and cortisol, total protein, and albumin concentrations were measured, and globulin concentrations were calculated. In the second trial, the frequency in which each ewe was observed standing, lying down, walking and grazing were recorded from Day −3 to Day −1 (Day 0 = shearing), from Day 1 to Day 5, on Days 13 and 20–21 during 8 h/day. Scan observations were done every 10 min from 8:00 h to 12:00 h and from 14:00 h to 18:00 h (total = 50 recordings.day). Non-pregnant ewes had greater cortisol concentrations than PR ewes (P = .007). Non-pregnant ewes also had greater total protein concentrations than PR ewes (P = .029). Albumin concentration tended to be greater in NP than PR ewes (P = .064). Globulin concentration 30 min after shearing was greater in PR than in NP ewes (P = .047). Pregnant ewes were observed more frequently standing than NP ewes (P = .013). Non-pregnant ewes were observed more frequently lying down and walking than PR ewes (P = .039 and P = .009, respectively). Before shearing, on Day 2 and Day 4, NP ewes walked more frequently than P ewes (P = .007, P < .0001, P = .007 respectively). Pregnant ewes were observed grazing more frequently than NP ewes (P = .009). Pregnant ewes grazed more than NP ewes on Days 1 and 5 (P = .005 and P < .0001 respectively). Overall, we concluded that shearing was a strong stressor that provoked sustained changes in the behavioural pattern, physiological status and gregariousness intensity despite being or not pregnant. Some responses, as cortisol concentration, changes in the time walking and grazing and the decrease of the cohesiveness after shearing seem to be less pronounced in pregnant than in non-pregnant ewes.

Stress and reproduction in farm animals

Transport of post-partum cows or sheep before an oestradiol-induced LH surge delayed gonadotrophin secretion possibly by affecting hypothalamic activity but not via an opioid mediated mechanism as the effect could not be reversed by naloxone. In addition, reduced LH responses to GnRH were observed in cattle during transport. In sheep, adrenocorticotrophic hormone (ACTH) also diminished the LH response to GnRH, but only when GnRH was administered 3 h after ACTH, not after 0.5 h. This finding suggests that very early suppression of LH secretion by stressors is not mediated by ACTH action at the pituitary but that immediate activation of the sympathetic nervous system may be involved. In ewes during the breeding season, repeated exposure to GnRH at intervals of 2 h during transport resulted in lower LH responses to the second and third injections. When anoestrous ewes were treated with oestradiol and GnRH while being restrained and isolated, the onset of the LH surge was delayed. The effects of hypothalamus-pituitary-adrenal hyperactivity on LH release may involve suppression of GnRH receptor activity, a reduction in releasable LH, or both factors. Studies in vitro with perifused ovine pituitaries showed that ACTH or corticotrophin releasing hormone markedly suppressed LH secretion in response to the second of two exposures to GnRH. This occurred with pituitaries obtained from anoestrous ewes irrespective of prior treatment with oestradiol, suggesting that compounds from the hypothalamus-pituitary-adrenal do not exert effects on the oestradiol-sensitizing mechanisms on the pituitary. In conclusion, stressors affect reproductive function via actions at the hypothalamus as well as impairing pituitary LH release induced by GnRH.

The oxytocin receptor, luteolysis and the maintenance of pregnancy

During luteal regression episodic pulses of oxytocin secretion become coupled to the release of prostaglandin F2 alpha (PGF2 alpha) following synthesis of endometrial oxytocin receptors, but in early pregnancy the inhibition of oxytocin receptor formation by the conceptus prevents the development of the pulsatile pattern of PGF2 alpha release needed to achieve luteolysis. Oxytocin receptors are present on the luminal epithelium in ovariectomized and anoestrous ewes, in pregnant animals throughout most of gestation (day 21 to term) and in explants of endometrial tissue cultured in vitro. These receptors can be downregulated for a brief period by progesterone (10-12 days in sheep, 12-14 days in cattle). This period of inhibition can be extended by infusion of interferon tau (IFN-tau) (which probably inhibits oxytocin receptor gene transcription) or of oxytocin into the systemic circulation (which may act further downstream, possibly at the level of translation). Oxytocin receptors also develop on the caruncular stroma and deep glands at oestrus, but these need positive upregulation and appear dependent on an oestrogenic environment. Only epithelial receptors are needed to achieve a maximal PGF2 alpha response to an oxytocin challenge, but the presence of oxytocin receptors does not necessarily confer responsiveness as other factors may influence intracellular coupling mechanisms and precursor availability. The duration of the luteal phase is regulated by the time of the initial post-ovulatory rise in progesterone and the duration of exposure to progesterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics and causes of the inadequate corpus luteum

An inadequate luteal phase occurs in domestic ruminants in several physiological situations (e.g. puberty, post partum), and also following the induction of ovulation in anoestrous ewes with GnRH treatment. The induced corpora lutea (CL) initially developed, but then regressed rapidly after Day 4, unless the animals had been primed with progesterone before GnRH therapy or hysterectomized. Significant increases in prostaglandin F-2 alpha metabolite (PGFM) secretion and coincident peaks of oxytocin and PGFM occurred around the time of premature regression. Endometrial oxytocin receptors were also detectable at this time in ewes which had abnormal luteal phases, but not in ewes which had been progesterone primed and thus had normal luteal phases. This suggests that the presence or otherwise of the oxytocin receptor during the early luteal phase may be crucial in determining whether the CL has a short or normal lifespan. These results show that an inadequate luteal phase is often caused by the premature induction of luteolysis and the presence of the endometrial oxytocin receptor in necessary for this occurrence. This receptor in turn is controlled by the steroid environment to which the uterus has previously been exposed.

Dopaminergic control of LH secretion by the Al5 nucleus in anoestrous ewes

Dopaminergic control of LH secretion by the Al5 nucleus in anoestrous ewes

Treatments with eCG and courtship behaviour in rams during the breeding and the non-breeding seasons

Equine chorionic gonadotrophin (eCG or PMSG) is a hormone with FSH/LH effect that has been widely used in ewes and cows to induce follicle development. However, the possible positive effects of its administration to males have been rarely studied. ECG stimulates testosterone secretion and increases rams’ ability to stimulate ovulation in anoestrous ewes (the ‘ram effect’), but it is still not known if this effect is at least partially explained by an enhancement of a ram’s sexual behaviour. Thus, the aim was to determine if the administration of eCG induces an increase in testosterone concentration, and thus improves sexual behaviour of Saint Croix rams during both the breeding and the non-breeding seasons. Two doses of 1000 IU of eCG were administered separated by 4 days to 10 rams during the breeding and five rams during the non-breeding seasons, with the same number of animals as untreated controls. Administration of eCG increased testosterone concentration during the breeding (P = 0.008) and the non-breeding (P = 0.0009) seasons. The number of ano-genital sniffings, lateral approaches, as well as total courtship behaviours were greater in treated than untreated rams during the breeding season. Treated rams also tended to mount and mate more during the breeding season. During the non-breeding season, treated rams tended to display more ano-genital sniffs, lateral approaches and total courtship behaviours than untreated rams 6 days after the first dose. Overall, eCG increased testosterone concentrations the breeding and the non-breeding seasons, and was associated with a greater display of sexual behaviours during the former.

Biosynthesis of gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) in hypothalamic-pituitary unit of anoestrous and cyclic ewes.

This study was performed to explain how the molecular processes governing the biosynthesis of gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) in the hypothalamic-pituitary unit are reflected by luteinizing hormone (LH) secretion in sheep during anoestrous period and during luteal and follicular phases of the oestrous cycle. Using an enzyme-linked immunosorbent assay (ELISA), we analyzed the levels of GnRH and GnRHR in preoptic area (POA), anterior (AH) and ventromedial hypothalamus (VM), stalk-median eminence (SME), and GnRHR in the anterior pituitary gland (AP). Radioimmunoassay has also been used to define changes in plasma LH concentrations. The study provides evidence that the levels of GnRH in the whole hypothalamus of anoestrous ewes were lower than that in sheep during the follicular phase of the oestrous cycle (POA: p < 0.001, AH: p < 0.001, VM: p < 0.01, SME: p < 0.001) and not always than in luteal phase animals (POA: p < 0.05, SME: p < 0.05). It has also been demonstrated that the GnRHR amount in the hypothalamus-anterior pituitary unit, as well as LH level, in the blood in anoestrous ewes were significantly lower than those detected in animals of both cyclic groups. Our data suggest that decrease in LH secretion during the long photoperiod in sheep may be due to low translational activity of genes encoding both GnRH and GnRHR.

Priming anoestrous Corriedale ewes with progesterone and gonadotrophin-releasing hormone causes cervical tissue remodelling due to metalloproteinase-2 (MMP-2) activity

The aim was to obtain experimental evidence of cervical collagen degradation in anoestrous Corriedale adult ewes induced to ovulate with progesterone (P) and gonadotrophin-releasing hormone (GnRH), at the expected time of induced ovulation and early luteal phase. In Experiment 1, anoestrous ewes were treated with P for 10 days (P, n = 4), with nine micro-doses of GnRH followed by a GnRH bolus injection (GnRH, n = 4) or with P plus GnRH treatments (P+GnRH, n = 3), and cervices were obtained either without treatment (A, n = 4), when P was removed, or 24 h after the GnRH bolus injection. In Experiment 2, cervices were obtained 1 (group P+GnRH, n = 5) or 5 (P+GnRH 5, n = 6) days after the GnRH bolus injection with P pretreatment. MMP-2 activity was detected in all samples; however, MMP-9 activity was only detected in 15% of the samples. The activity of the latent (L) form of MMP-2 in the cranial zone of group A was higher than in the cranial zone of groups P, GnRH and P+GnRH, and was also higher than that in the caudal zone of the same group (P &lt; 0.05). The collagen concentration was lower in group P+GnRH 1 than in group P+GnRH 5 (P &lt; 0.04). The activity of the activated (A) form of MMP-2 and the A/L MMP-2 ratio were higher in group P+GnRH 1 than in group P+GnRH 5 (P &lt; 0.05). Data suggest that the L form of MMP-2 was expressed mainly in a constitutive form in the cervix of anoestrous ewes and that an oestrogen-dependent activation mechanisms due to the GnRH treatment may be responsible for the lowest collagen content at the moment of the induced ovulation. This work provides evidence about cervical collagen remodelling in anoestrous ewes treated with P + GnRH.

The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep.

During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the “ram effect” in ewes that had a “precocious” LH surge (starting within 6 hours), a “normal” surge (between 6 and 28h) and “late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. “Precocious” LH surges were not preceded by a large increase in E2 unlike “normal” surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the “precocious” LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the “ram effect”. Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators.

Progesterone pretreatment increases the stress response to social isolation in ewes.

In rodents, progesterone (P4) pretreatment increases anxiety and response to stressors. Social isolation is a stressor that generates physiological and behavioural stress responses in sheep. The aim of the study was to compare the stress response of anoestrous ewes previously treated or not with P4 to the social isolation test. Ten ewes received P4 treatment during 13 d (group P4-W) and another 10 remained untreated as controls (group Con). The ewes were individually isolated in a novel place during 10 min, 24 h after the end of P4 pretreatment and their behaviours were recorded. Cortisol and P4 concentrations as well as body surface temperature were recorded before and after the test. Ewes of the P4-W group presented higher cortisol levels 0, 10, 20 and 30 min after the social isolation and had greater area under the curve of cortisol compared to Con ewes (41,785%±4,156% vs. 25,682%±4,565% during 75 min). Progesterone and body surface temperature increased after social isolation, with no differences between P4-W and Con ewes. There were no differences in behavioural responses to social isolation. P4 pretreatment appears to augment the stress response to social isolation in anoestrous ewes.

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect.

The proportion of anoestrous ewes ovulating after exposure to a sexually active ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the 'ram effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'ram effect' following exposure to rams for 2 or 12 h. In all ewes, the concentration of E2 increased 2-4 h after rams were introduced and remained elevated for 14.5 ± 0.86 h. The quantity of E2 secreted before the LH surge varied among breeds as did the mean concentration of E2. The granulosa cells of IF ewes collected after 12 h exposure to rams secreted more E2 and progesterone and had higher levels of StAR than the 2 h group but in MV ewes there was no differences between these groups for any of these parameters. These results demonstrate that the LH surge induced by the rams is a result of increased E2 secretion associated with increased levels of STAR in granulosa cells and that these responses varied among breeds. The results suggest that the variable occurrence of a LH surge and ovulation may be the result of variable ovarian responses to the 'ram effect' and insensitivity of the hypothalamus to the E2-positive feedback signal.

Vaginal Histological Changes after Using Intravaginal Sponges for Oestrous Synchronization in Anoestrous Ewes

To characterize the histological and cytological vaginal changes generated by the use of intravaginal sponge (IS) applied in oestrous synchronization treatments in ewes during mid-non-breeding season. Thirty-five multiparous ewes were allocated to three experimental groups according to the moment in which the samples were taken: (i) ewes treated with IS containing 60 mg of medroxyprogesterone acetate for 14 days, sampled the day of IS removal (group ISR; n = 10), (ii) or after sponge removal at time of oestrus or 72 h after removal (group AR; n = 14) and (iii) ewes without sponge treatment that were sampled at the day of IS removal of the other groups (group CG; n = 11). Vaginal biopsies and cytological samples were taken from the anterior vaginal fornix area. The vagina of the CG group had a stratified squamous epithelium with a moderate degree of cellular infiltration with lymphocytes and plasma cells in the lamina propia. Treated ewes (ISR and AR) had epithelial hyperplasia and hypertrophy. ISR ewes had haemorrhage and perivascular infiltrate and an increased number of epithelial cells, neutrophils, macrophages and erythrocytes at IS removal. The use of IS generated histological and cytological alterations in the vaginal wall when used for oestrous synchronization in anoestrous ewes.

Involvement of prolactin in the meloxicam-dependent inflammatory response of the gonadotropic axis to prolonged lipopolysaccharide treatment in anoestrous ewes.

An immune challenge can affect the reproductive process in females. Peripheral administration of bacterial endotoxin (lipopolysaccharide; LPS) decreases LH secretion and disrupts ovarian cyclicity. The aim of the present study was to determine the effects of a cyclo-oxygenase (COX)-2 inhibitor (meloxicam) on gonadotropin-releasing hormone (GnRH) and LH secretion in anoestrous ewes during systemic inflammation induced by LPS. LPS (400ngkg-1 per day) suppressed LH release. In three individuals, meloxicam (500μgkg-1, i.v.) abolished LPS-induced LH suppression. In another three ewes LH was ineffective. Similar changes were observed in hypothalamic GnRH expression. The effect of meloxicam depended on the circulating level of prolactin: meloxicam abolished inflammatory-dependent suppression of GnRH and LH secretion when plasma prolactin levels were similar to those in untreated animals, but was ineffective in those with elevated levels of prolactin. We conclude that COX-2 inhibitors minimise the negative effect of inflammation on the reproductive system but that this effect may be antagonised by prolactin.

Progesterone improves the maturation of male-induced preovulatory follicles in anoestrous ewes.

The first ovulation induced by male effect in sheep during seasonal anoestrus usually results in the development of a short cycle that can be avoided by progesterone priming before ram introduction. In elucidating the involvement of the hypothalamic-pituitary-gonadal axis in the occurrence of short cycles, the effects of progesterone and the time of anoestrus on the development of male-induced preovulatory follicles were investigated in anoestrous ewes using morphological, endocrine and molecular approaches. Ewes were primed with progesterone for 2 (CIDR2) or 12 days (CIDR12) and untreated ewes used as controls during early (April) and late (June) anoestrus. The duration of follicular growth and the lifespan of the male-induced preovulatory follicles were prolonged by ∼1.6 days in CIDR12 ewes compared with the controls. These changes were accompanied by a delay in the preovulatory LH and FSH surges and ovulation. Intra-follicular oestradiol concentration and mRNA levels of LHCGR and STAR in the granulosa and theca cells of the preovulatory follicles were higher in CIDR12 ewes than the control ewes. The expression of mRNA levels of CYP11A1 and CYP17A1 also increased in theca cells of CIDR12 ewes. CIDR2 ewes gave intermediate results. Moreover, ewes ovulated earlier in June than in April, without changes in the duration of follicular growth, but these effects were unrelated to the lifespan of corpus luteum. Our results give the first evidence supporting the positive effect of progesterone priming on the completion of growth and maturation of preovulatory follicles induced by male effect in seasonal anoestrous ewes, thereby preventing short cycles.

Equine chorionic gonadotrophin administration to rams improves their effectiveness to stimulate anoestrous ewes (the “ram effect”)

Ewes’ response to ram effect is related to the strength of androgen-dependent ram signals. Experiment 1 aimed to determine if the administration of a single dose of 1000IU of eCG to rams three days before joining them with ewes enhance their ability to stimulate females. Based on the results of Experiment 1, in a second experiment rams received two doses seven and three days before their introduction to females. In Experiment 1, rams treated or not with eCG were joined with ewes, and estrous was recorded until Day 5 (Day 0=rams and ewes were joined), and from Day 15 to Day 23. In addition, serum testosterone concentration was measured in all rams in the first recorded period. Testosterone values were greater in eCG-E1 than in Con-E1 rams on Days 0 and 2. The percentage of ewes in estrus was similar in both groups. In Experiment 2, rams were treated with two doses of eCG on Days −7 and −3 or remained as untreated controls. Estrous was recorded until Day 5, and pregnancy rate on Day 46; testosterone was measured in samples collected from all rams. Testosterone concentration was greater in eCG-E2 than Con-E2 rams from Day −5 to Day 1, and tended to do so on Day 2. More eCG-E2 than Con-E2 ewes came into estrus and became pregnant. It was concluded that treatment of rams with two high doses of eCG before joining them with anestrous ewes, enhanced their ability to induce ewes’ cyclic activity (the “ram effect”).

Short oestrous cycles in sheep during anoestrus involve defects in progesterone biosynthesis and luteal neovascularisation

Anoestrous ewes can be induced to ovulate by the socio-sexual, 'ram effect'. However, in some ewes, the induced ovulation is followed by an abnormally short luteal phase causing a so-called 'short cycle'. The defect responsible for this luteal dysfunction has not been identified. In this study, we investigated ovarian and uterine factors implicated in male-induced short cycles in anoestrous ewes using a combined endocrine and molecular strategy. Before ovulation, we were able to detect a moderate loss of thecal expression of steroid acute regulatory protein (STAR) in ewes that had not received progesterone priming (which prevents short cycles). At and following ovulation, we were able to identify a significant loss of expression of genes coding key proteins involved in the biosynthesis of progesterone (STAR, CYP11A1 and HSD3B1 (HSD3B)) as well as genes coding proteins critical for vascular development during early luteal development (VEGFA and KDR (VEGFR2)), suggesting dysfunction in at least two pathways critical for normal luteal function. Furthermore, these changes were associated with a significant reduction of progesterone production and luteal weight. Additionally, we cast doubt on the proposed uterus-mediated effect of prostaglandin F2α (PGF2α) as a cause of short cycles by demonstrating the dysregulation of luteal expression of the PGF receptor, which mediates the luteal effects of PGF2α, and by finding no significant changes in the circulating concentrations of PGFM, the principal metabolite of PGF2α in ewes with short cycles. This study is the first of its kind to examine concurrently the endocrine and molecular events in the follicular and early luteal stages of the short cycle.