# Sheep Reproduction: Cycle and Breeding Sheep are short-day breeders, meaning the breeding season begins as day length shortens, so most breeds cycle in autumn. A ewe cycles every 16 to 17 days, stands in estrus for 24 to 36 hours, and carries a pregnancy for about 147 days (range 142 to 152). Understanding sheep reproduction means understanding a calendar written in light. The ewe's reproductive year is not a continuous loop like that of the cow or the sow. It is a seasonal window, opened and closed by the changing ratio of daylight to darkness, and then fine-tuned by nutrition, body condition, breed, and the presence of a ram. For shepherds, flock managers, and veterinary students, that seasonality is the single most important fact in reproduction in sheep. It determines when rams go in, when ewes lamb, how pregnancy is diagnosed, and how many lambs hit the ground. This article covers the estrous cycle, the breeding season and its photoperiodic control, the ram effect, flushing, teaser rams, pregnancy diagnosis by ultrasound, and a practical management timeline from ram introduction through lambing. Comparative notes on cattle and goats appear only where they sharpen the sheep picture. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## The Estrous Cycle in the Ewe The ewe is a seasonally polyestrous animal. During the breeding season she cycles repeatedly. Outside it, she enters anestrus, a period of ovarian quiescence with no behavioral estrus and no ovulation. The cycle itself is short. A normal ovine estrous cycle runs 16 to 17 days. Estrus, the period of sexual receptivity, lasts 24 to 36 hours. Ovulation occurs late in estrus, typically 24 to 30 hours after the onset of standing heat, which is later relative to the onset of estrus than in the cow. This timing matters for breeding management because it means a single service early in estrus may be too early relative to ovulation. The cycle divides into two phases. **Follicular phase.** Follicles grow under the influence of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both released from the anterior pituitary. Estradiol rises, drives behavioral estrus, and triggers the preovulatory LH surge that ruptures the dominant follicle. The follicular phase is short, roughly two to three days. **Luteal phase.** After ovulation, the ruptured follicle becomes a corpus luteum (CL), which secretes progesterone. Progesterone prepares the uterus for a possible embryo and, through negative feedback, suppresses GnRH and LH release so new follicles do not ovulate. If no pregnancy occurs, the uterus releases prostaglandin F2 alpha (PGF2α), which lyses the CL, progesterone falls, and the next follicular phase begins. In the ewe, luteal regression is uterine-dependent, which is why a ewe with uterine pathology can retain a CL and stop cycling. The neuroendocrine control of this cycle is layered. Kisspeptin neurons are the most potent secretagogues of GnRH secretion, and their activity changes with photoperiod [1]. In ewes moved from long days to short days, the number of kisspeptin neurons per square millimeter doubled in the caudal arcuate nucleus by day 112 after the transition, and the percentage of neurons showing kisspeptin immunoreactivity rose in both the preoptic area and the arcuate nucleus [1]. Other hypothalamic systems modulate the axis. Neuropeptide Y (NPY) neurons in the arcuate nucleus and median eminence region were fewer in ewes killed during anestrus than during the breeding season, while galanin-stained cell numbers did not change with season [2]. Endogenous opioid peptides also act as modulators of reproductive function in the ewe [3]. Somatostatin neurons interact with kisspeptin neurons in the preoptic area and mediobasal hypothalamus, and this crosstalk is not photoperiod dependent, which suggests it is a standing brake rather than a seasonal switch [4]. One peptide that does not appear to matter is spexin. Despite sharing an ancestor gene with Kiss1, in vivo infusion of spexin in ewes did not provide support for a role in control of the gonadotropic axis [5]. ## Why Sheep Are Short-Day Breeders Photoperiod is the master clock. As day length shortens after the summer solstice, the ewe's hypothalamus shifts from a state that suppresses GnRH pulsatility to one that permits it. The result is the onset of ovulatory cycles in autumn. The mechanism runs through the pineal gland and melatonin. Melatonin is secreted at night, so the duration of the nightly melatonin signal encodes day length. The pars tuberalis of the pituitary reads that signal and controls production of thyroid-stimulating hormone (TSH), which in turn governs the opposing seasonal patterns of the deiodinases Dio2 and Dio3 in tanycytes of the mediobasal hypothalamus [6]. That local thyroid hormone switch is a key node in seasonal breeding. Seasonal [gene expression](/blog/guides/gene-expression) in the pars tuberalis is independent of sex steroid status and independent of thyroid hormone, which supports the view that the pars tuberalis acts as a circannual timer [6]. Melatonin's timing, not just its duration, carries information. In Romney Marsh ewes given short nights around the winter solstice, ovarian activity resumed in ewes that received no melatonin infusion and in ewes infused with melatonin in the morning, but not in ewes infused in the afternoon before dark [7]. The phase of the melatonin signal relative to the circadian pacemaker, rather than the total amount of melatonin, appears to be the important cue. Nutrition interacts with photoperiod at the level of the brain. In Ile-de-France ewes kept under a simulated annual photoperiod of 8 to 16 hours of light per day, a restricted nutritional state shortened the season of ovarian activity by shifting the timing of the seasonal transitions into and out of anestrus, and the same effect appeared in the seasonal rhythm of LH in ovariectomized estradiol-treated ewes [8]. The practical reading is straightforward. Thin ewes have shorter breeding seasons and later starts. ### Breed and Latitude Effects Seasonality is not fixed across all sheep. Traditional wool and meat breeds are strongly seasonal. Some breeds, including the Polypay and Dorset, have been selected for reduced seasonality and can lamb year-round, though variation within those breeds persists in the ability to lamb out of season [9]. Genomic work has identified candidate genes for out-of-season lambing related to eye development, reproductive hormones, and neural function [9]. Latitude changes the amplitude of the signal. At higher latitudes, day length swings widely between summer and winter, so the breeding season is sharply defined. Near the equator, photoperiod barely changes, and seasonality weakens or disappears. Hair sheep illustrate this. In a study at roughly 22 degrees south, Santa Inês hair ewe lambs showed no seasonal variation in plasma progesterone, while Romney Marsh and Suffolk wool ewe lambs had higher progesterone in autumn and winter than in spring and summer [10]. All three breeds showed the same annual melatonin pattern, so the difference lay downstream of the photoperiodic signal [10]. Wild and feral sheep show the same architecture. In European mouflon kept under natural photoperiod at about 40 degrees north, first ovulations of the breeding season were highly synchronized and occurred in mid-October, while the end of ovulatory cycles varied from February to May depending on age, with 2-year-old animals showing the longest anovulatory period [11]. ## The Ram Effect The ram effect is the phenomenon in which the introduction of a ram synchronizes and advances ovulation in anestrous ewes. It is the most useful non-hormonal tool in sheep reproduction, and it costs nothing but a fence and a plan. The mechanism is pheromonal. Ram odor stimulates the ewe's olfactory system, which relays to the hypothalamus and increases GnRH and LH pulsatility. The first ovulations after ram introduction are typically silent, meaning the ewe ovulates without showing estrus. A short cycle follows, and the next ovulation is accompanied by a normal, fertile estrus. This is why the timing of ram introduction relative to the desired breeding date matters so much. Ewes bred on the first silent ovulation will not conceive in a normal mating, but ewes bred on the second, behavioral estrus will. The ram effect is most powerful in ewes that are close to the transition into the breeding season. It is weaker in deep anestrus and in ewes that are thin or lactating heavily. Male introduction also works in combination with hormonal protocols. In Lacaune dairy ewes exposed to 77 days of artificial long days (16 hours light, 8 hours dark) during winter followed by increasing natural photoperiod, ewes joined with rams 40 days after the end of photostimulation, and ewes given an additional 6-day progestagen treatment with PGF2α and eCG at insert withdrawal and joined 1 day after removal, both had low mean serum progesterone before joining, indicating they were still largely anestrous at the start of the male exposure [12]. The light program plus male introduction is a recognized pathway to out-of-season breeding in dairy sheep. ## Flushing, Teaser Rams, and Pre-Breeding Management ### Flushing Flushing is the practice of increasing the plane of nutrition in the weeks before and during breeding to raise ovulation rate and therefore litter size. It works because the ewe's brain integrates metabolic cues with photoperiodic ones [8]. A rising plane of nutrition signals abundance, and the hypothalamus responds with greater GnRH and LH drive. Practical flushing means moving ewes onto better pasture or supplementing with grain for roughly two to three weeks before ram introduction and continuing for two to three weeks into the breeding period. The ewes that respond best are those in moderate body condition, not those already fat and not those severely thin. Overconditioned ewes respond poorly, and very thin ewes may not cycle at all regardless of feed. Nutritional state also shapes the length of the breeding season itself. Restricted nutrition shortened the season of ovarian activity in Ile-de-France ewes [8]. Flushing is therefore not only about ovulation rate for the current cycle. It is about keeping the whole season open long enough for repeat breeding of ewes that fail to conceive on the first service. ### Teaser Rams A teaser ram is a vasectomized or otherwise infertile ram used to stimulate ewes without breeding them. Teaser rams serve three purposes. First, they apply the ram effect on a schedule. A teaser introduced at a known date lets the manager predict when the first fertile estrus will occur, typically about 17 to 25 days later depending on how close the flock is to the natural transition. Second, teaser rams identify ewes in estrus. A ram fitted with a marking harness or a raddle marks the rump of each ewe he serves, giving a daily record of which ewes are cycling and when. Third, teasers reduce the workload on breeding rams. A single fertile ram can be spread over more ewes if the ewes have already been stimulated and their estrus synchronized by prior teaser exposure. Teaser rams should be physically separated from ewes by a fence that allows sight, sound, and smell but not contact, and they should be introduced to the flock as a group rather than one at a time. ### Breeding Soundness of the Ram Ram fertility is half the equation and is often neglected. A breeding soundness examination before the season should assess body condition, feet and legs, scrotal circumference, testicular tone and symmetry, and semen quality. Rams in poor body condition or with foot pain will not serve reliably. The ratio of rams to ewes depends on age, terrain, and whether ewes are synchronized. A mature, sound ram can cover a modest flock under natural conditions, but synchronized ewes bred over a short window require more rams or the use of artificial insemination. ## Pregnancy Diagnosis Pregnancy diagnosis in sheep has moved decisively toward ultrasound. Transabdominal and transrectal ultrasonography can detect pregnancy and, importantly, count fetuses, which is the information that drives late-gestation nutrition and lambing management. Timing matters. Transrectal ultrasound is useful in the earlier part of gestation, when the uterus can be reached. Transabdominal scanning becomes more practical as gestation advances and the uterus descends over the pelvic brim. Fetal counting is most reliable in mid-gestation, when the fetuses are large enough to distinguish but not so crowded that they overlap. Ultrasound is not the only option. A ram can be used to return ewes to service, and a ewe that does not return to estrus within about 17 to 21 days after breeding is presumed pregnant. This method is free but imprecise. Progesterone assays can identify cyclic versus non-cyclic status but do not confirm a viable pregnancy. Radiography is impractical for routine flock use. For commercial flocks, real-time ultrasound is the standard because it answers the two questions that matter: is she pregnant, and how many is she carrying. Pregnancy diagnosis also has a welfare and economic dimension. Ewes carrying twins or triplets need more energy in late gestation than ewes carrying singles, and identifying them early allows targeted feeding. Underfeeding a ewe carrying twins in late gestation leads to pregnancy toxemia and small, weak lambs. Overfeeding a ewe carrying a single leads to dystocia from a large fetus. ## Management Timeline from Ram Introduction Through Lambing The table below lays out a practical flock calendar. Dates are expressed as days relative to ram introduction (Day 0). Because the ram effect advances and synchronizes ovulation, the first fertile estrus after ram introduction often clusters in a window rather than spreading evenly across the season. | Phase | Timing | Key Actions | |--|--|--| | Pre-breeding | Day -21 to Day 0 | Condition score ewes. Begin flushing. Examine rams. Vaccinate and deworm per flock plan. | | Ram introduction | Day 0 | Introduce rams or teaser rams. Record marking. | | Ram effect window | Day 0 to Day 17 | Expect silent ovulations and a short first cycle. Do not judge conception yet. | | First fertile estrus | Roughly Day 17 to Day 25 | Most ewes bred in this window under a strong ram effect. | | Repeat cycles | Every 16 to 17 days | Ewes returning to estrus are rebred. Record each mark. | | Pregnancy diagnosis | Day 45 to Day 90 | Ultrasound for pregnancy and fetal count. | | Mid-gestation | Day 90 to Day 120 | Maintain nutrition. Avoid stress and handling that risks pregnancy loss. | | Late gestation | Day 120 to Day 147 | Increase energy for twin-bearing ewes. Monitor for pregnancy toxemia. Prepare lambing pens. | | Lambing | Day 142 to Day 152 | Attend lambing. Ensure colostrum intake within the first hours. | | Postpartum | After lambing | Monitor ewe for retained placenta and metritis. Plan postpartum anestrus management. | The postpartum interval deserves separate attention. In mouflon ewes, when lambing occurred within the breeding season (February to April), 12 of 26 animals had their first ovulation 25 plus or minus 1.8 days after parturition, while the 14 late-lambing females had their first postpartum ovulation delayed until the next breeding season [11]. Domestic ewes show the same principle. A ewe that lambs late in the season may not cycle again until the following autumn, which is why lambing date and breeding date are locked together in a seasonal system. The diagram below traces the decision path from ram introduction to lambing. ```mermaid flowchart TD A[Ram introduced to ewes] --> B{Ewe cycling} B -->|No| C[Ram effect advances ovulation] B -->|Yes| D[Ewe bred at estrus] C --> D D --> E[Return to estrus in 16 to 17 days] E -->|Yes| D E -->|No| F[Presumed pregnant] F --> G[Ultrasound at 45 to 90 days] G --> H{Fetal count} H -->|Single| I[Standard late gestation feed] H -->|Twins or more| J[Higher energy late gestation feed] I --> K[Lambing at 142 to 152 days] J --> K ``` ## Hormonal Synchronization and Fixed-Time Breeding Natural methods are the backbone of sheep reproduction, but hormonal protocols are common in commercial flocks, especially for artificial insemination and out-of-season breeding. The classic protocol uses an intravaginal progestogen sponge left in place for a set number of days, followed by an injection of equine chorionic gonadotropin (eCG) at sponge removal. In one large study, ewes received a flurogestone acetate sponge for 12 days followed by 330 IU of eCG at sponge removal and were inseminated twice, at 52 and 64 hours after sponge removal [13]. Adding a GnRH agonist at sponge insertion increased pregnancy rate compared with controls and with administration at insemination or day 7 post-insemination, and litter size was higher in the insertion and insemination groups than in controls [13]. Dose and timing of eCG have been studied in hair sheep ewe lambs under dry-tropical conditions. In 216 ewe lambs of Dorper, Katahdin, and Pelibuey breeding given a 12-day progestogen sponge and either 200 or 300 IU eCG at 24 hours before or at sponge withdrawal, 82 percent showed estrus within 48 hours. There was no main effect of eCG dose or application time on overall estrus rate, but a dose-by-time interaction affected the interval to estrus, with a shorter mean interval after the 24-hours-before application (30.2 plus or minus 1.0 hours) than after application at withdrawal (34.6 plus or minus 1.0 hours) [14]. Breed influenced estrus expression and silent ovulation [14]. Prostaglandin-based protocols are also used during the breeding season, when a functional CL is present. In Anatolian Merino ewes treated at day 12 of the cycle, no significant differences appeared in estrus rates or the timing of estrus onset among single, half, or split doses of cloprostenol, but 95 percent of ewes that received split doses exhibited estrus within the first 48 hours [15]. Single-dose treatment produced the highest pregnancy rate, though the difference from other groups was not statistically significant [15]. Newer approaches target the kisspeptin system. In anestrous Corriedale ewes synchronized with a 14-day medroxyprogesterone sponge, a synthetic kisspeptin analogue given 24 hours after sponge removal produced more synchronous ovulations than eCG, with a standard deviation of 4.1 hours versus 10.7 hours for eCG [16]. However, more ewes showed estrus in the eCG group (10 of 10) than in the kisspeptin analogue group (2 of 10) [16]. Synchrony and expression of estrus are not the same thing. Other experimental manipulations have been explored. Letrozole, an aromatase inhibitor, has been tested as an adjunct to progesterone-based synchronization in suckling Awassi ewes during anestrus [17]. Naloxone, an opioid antagonist, altered the timing and duration of estrus and the preovulatory LH surge in ewes with induced estrus during the non-breeding season, supporting the role of endogenous opioid peptides as modulators of reproductive function [3]. Irisin, a metabolic hormone, increased GnRH, LH, FSH, and estrogen in Kurdish ewes during the breeding season in a dose-dependent manner [18]. Anandamide, an endocannabinoid, affected GnRH synthesis during inflammation in follicular-phase ewes but did not reverse the inflammation-associated reduction in LH secretion [19]. These are research findings, not routine field protocols. ## Clinical Relevance, Limitations and Common Mistakes The most common mistake in sheep reproduction is treating the ewe like a cow. Cattle cycle year-round. Sheep do not. A ewe that is not cycling in late spring is not necessarily infertile. She may simply be in anestrus, and no amount of ram exposure or flushing will reliably overcome deep seasonal anestrus in a strongly seasonal breed. The second common mistake is misreading the ram effect. Ewes stimulated by a ram often ovulate silently on the first cycle. A manager who checks for estrus in the first 17 days and concludes the ewes are not responding may miss the fertile estrus that follows. The correct approach is to leave the ram in and keep recording. The third mistake is neglecting ram fertility. Ewes get the attention because they carry the pregnancy, but a ram with foot pain, poor body condition, or testicular abnormalities will produce an empty flock regardless of how well the ewes are managed. Breeding soundness examination before the season is not optional. The fourth mistake is skipping pregnancy diagnosis or delaying it too long. Fetal counting in mid-gestation allows targeted nutrition. Without it, twin-bearing ewes are fed as singles and lamb as small, weak offspring or develop pregnancy toxemia. The fifth mistake is ignoring body condition. Nutrition centrally modulates the interpretation of photoperiod to affect seasonal reproductive transitions [8]. Thin ewes start later, finish earlier, and ovulate fewer eggs. Flushing works, but it works best on ewes that are already in reasonable condition. Individual animals vary, and a veterinarian should evaluate any ewe or ram with a specific reproductive problem. The general principles above describe flock-level management, not a diagnosis for a single animal. ## Frequently Asked Questions ### How long is the sheep estrous cycle? The estrous cycle in sheep is 16 to 17 days. Estrus itself lasts 24 to 36 hours. Ovulation occurs late in estrus, roughly 24 to 30 hours after the onset of standing heat. ### When is the breeding season for sheep? Sheep are short-day breeders, so the breeding season begins as day length shortens, and most breeds cycle in autumn. Latitude and breed both shift the timing. Hair sheep near the equator may cycle year-round, while strongly seasonal wool breeds at high latitude have a sharply defined season. ### What is the ram effect in sheep? The ram effect is the synchronization and advancement of ovulation in anestrous ewes caused by the introduction of a ram. The first ovulations are often silent, followed by a short cycle, then a normal fertile estrus. It is the most useful non-hormonal tool for tightening a breeding window. ### How long are sheep pregnant? Gestation in sheep is about 147 days, with a normal range of 142 to 152 days. Breed, fetal number, and other factors cause minor variation within that range. ### What is flushing in sheep breeding? Flushing is increasing the plane of nutrition for two to three weeks before and during breeding to raise ovulation rate and litter size. It works best in ewes in moderate body condition and is less effective in very thin or overconditioned ewes. ### What is a teaser ram? A teaser ram is a vasectomized or otherwise infertile ram used to stimulate ewes and identify those in estrus without breeding them. Teaser rams apply the ram effect on a schedule and, when fitted with a marking harness, provide a daily record of which ewes are cycling. ### How is pregnancy diagnosed in sheep? Transabdominal or transrectal ultrasound is the standard method. It confirms pregnancy and allows fetal counting, usually in mid-gestation. Non-return to estrus and progesterone assays are less precise alternatives. ### Can sheep breed out of season? Some breeds can. The Polypay and Dorset have been selected for reduced seasonality and can lamb year-round, though variation persists within those breeds. Out-of-season breeding in strongly seasonal breeds usually requires artificial photoperiod programs, hormonal synchronization, or both. ## Related Articles - [Donkey Breeding and Reproduction Management](/knowledge/animal-farming/alternative-livestock/donkey-breeding-reproduction-management) - [Draft Horse Breeding and Reproduction Management](/knowledge/animal-farming/alternative-livestock/draft-horse-breeding-reproduction-management) - [Water Buffalo Reproduction and Breeding Management](/knowledge/animal-farming/alternative-livestock/water-buffalo-reproduction-breeding) - [Poultry Reproduction: Understanding Breeding and Fertility](/knowledge/animal-farming/poultry/poultry-reproduction-understanding-breeding-and-fertility) - [Dairy Cow Reproduction: Synchronization and Breeding Management](/knowledge/animal-farming/dairy-cattle/dairy-cow-reproduction-synchronization-and-breeding-management) - [Pig Breeding Cycle and Reproductive Management](/knowledge/animal-farming/swine/pig-breeding-cycle-reproductive-management) - [Cell Cycle Control: What Your Results Indicate](/blog/research-skills/cell-cycle-control-what-your-results-indicate) ## Sources 1. [Effects of photoperiod on kisspeptin neuronal populations of the ewe diencephalon in connection with reproductive function.](https://pubmed.ncbi.nlm.nih.gov/20002963/) 2. [Effect of season on neuropeptide Y and galanin within the hypothalamus of the ewe in relation to plasma luteinizing hormone concentrations and the breeding season: an immunohistochemical analysis.](https://pubmed.ncbi.nlm.nih.gov/10849206/) 3. [The effect of low doses of naloxone on the preovulatory surge of LH and on the onset and duration of oestrus in the ewe with induced oestrus during the non-breeding season.](https://pubmed.ncbi.nlm.nih.gov/11267802/) 4. [Crosstalks between kisspeptin neurons and somatostatin neurons are not photoperiod dependent in the ewe hypothalamus.](https://pubmed.ncbi.nlm.nih.gov/28935581/) 5. [No evidence that Spexin impacts LH release and seasonal breeding in the ewe.](https://pubmed.ncbi.nlm.nih.gov/32916519/) 6. [Circuit-level analysis identifies target genes of sex steroids in ewe seasonal breeding.](https://pubmed.ncbi.nlm.nih.gov/32422398/) 7. [The coincidence of light and melatonin with a specific phase of the circadian pacemaker is important for the timing of seasonal breeding in the ewe.](https://pubmed.ncbi.nlm.nih.gov/11106068/) 8. [The interaction between photoperiod and nutrition and its effects on seasonal rhythms of reproduction in the ewe.](https://pubmed.ncbi.nlm.nih.gov/22053094/) 9. [Genomic Approaches Identify Novel Gene Associations with Out of Season Lambing in Sheep.](https://pubmed.ncbi.nlm.nih.gov/30851038/) 10. [Annual pattern of plasma melatonin and progesterone concentrations in hair and wool ewe lambs kept under natural photoperiod at lower latitudes in the southern hemisphere.](https://pubmed.ncbi.nlm.nih.gov/16879314/) 11. [The timing of the onset of puberty, extension of the breeding season, and length of postpartum anestrus in the female mouflon (Ovis gmelini musimon).](https://pubmed.ncbi.nlm.nih.gov/12790426/) 12. [Reproductive performance of Lacaune dairy sheep exposed to artificial long days followed by natural photoperiod without and with additional progestagen treatment during the nonbreeding season.](https://pubmed.ncbi.nlm.nih.gov/25468556/) 13. [Effects of GnRH administration on pregnancy rate and litter size in ewes subjected to a fixed time insemination program during the breeding season.](https://pubmed.ncbi.nlm.nih.gov/41037989/) 14. [Effects of eCG dose and timing on estrus and ovulation in hair ewe-lambs of three breeds under dry-tropical conditions across two breeding seasons.](https://pubmed.ncbi.nlm.nih.gov/42223517/) 15. [Evaluation of luteolytic activity and reproductive outcomes in ewes following single and split dose cloprostenol during the breeding season.](https://pubmed.ncbi.nlm.nih.gov/41677985/) 16. [The Kisspeptin analogue C6 induces more synchronized ovulation than eCG in the transition period to breeding season in Corriedale ewes.](https://pubmed.ncbi.nlm.nih.gov/41385063/) 17. [A novel therapeutic approach: The effect of letrozole-assisted synchronization on reproductive performance in suckling ewes during the non-breeding season.](https://pubmed.ncbi.nlm.nih.gov/41223620/) 18. [Dose- and time-dependent effects of intravenous irisin administration on GnRH, LH, FSH, and estrogen in Kurdish ewes during the breeding season.](https://pubmed.ncbi.nlm.nih.gov/40505589/) 19. [Effect of Central Injection of Anandamide on LPS-Dependent Suppression of GnRH/LH Secretion in Ewes During the Follicular Phase of the Estrous Cycle.](https://pubmed.ncbi.nlm.nih.gov/41373409/)