The stimulation of testosterone and LH secretion by synthetic GnRH in the male Cape porcupine

The effects of GnRH stimulation on plasma testosterone and luteinizing hormone (LH) levels in Cape porcupine males were examined by analysing plasma collected before and after an intravenous injection of GnRH. In six mature males and one subadult, which were given an intravenous injection of 0,5 ml saline, levels of plasma testosterone and LH did not increase. Four weeks later an intravenous GnRH challenge (40 μ?) caused plasma testosterone to rise three-fold and LH to rise 10-15-fold within 180 min in five of the mature males. Peaks of plasma testosterone and LH occurred 90 and 120 min, respectively, after stimulation, and baseline and peak levels of both hormones were significantly related.     

Pituitary responsiveness to GnRH, hypothalamic content of GnRH and pituitary LH and FSH concentrations immediately preceding puberty in gilts

To determine whether pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) or hypothalamic content of gonadotropin releasing hormone (GnRH) change before puberty, 40 prepubertal gilts averaging 7 mo of age were slaughtered before or on the second, third or fourth day after relocation and boar exposure. Some gilts responded to relocation and boar exposure as indicated by swollen vulvae, turgid uteri and enlarged ovarian follicles at the time of slaughter. Pituitary concentrations of LH and FSH and hypothalamic content of GnRH were similar between gilts that responded to relocation and boar exposure and gilts that did not respond. In addition, boar exposure and relocation had no effect on pituitary concentrations of LH and FSH or on hypothalamic content of GnRH. To determine whether pituitary responsiveness to GnRH changes before puberty, a third experiment was conducted in which 72 gilts were injected with 400 micrograms of GnRH either before or on the second, third or fourth day after relocation and boar exposure. In gilts that subsequently responded (i.e., ovulated) as a result of relocation and boar exposure, pituitary responsiveness to GnRH was reduced as compared with gilts that failed to ovulate after relocation and boar exposure. Peak concentrations of serum LH after GnRH injection were 4.6 +/- 1.3 vs 9.8 +/- .8 ng/ml for responders vs nonresponders. Peak serum FSH after GnRH injection was also lower for responders than for nonresponders (29.5 +/- 4.2 vs 41.2 +/- 2.4 ng/ml). When compared with controls, relocation and boar exposure did not significantly affect GnRH-induced release of LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given GnRH

The effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given 100 microg of GnRH im were determined in three experiments. In Experiment 1, heifers were given GnRH 3, 6 or 9 days after ovulation; 8/9, 5/9 and 2/9 ovulated (P<0.02). Mean plasma concentrations of progesterone were lowest (P<0.01) and of LH were highest (P<0.03) in heifers treated 3 days after ovulation. In Experiment 2, heifers received no treatment (Control) or one or two previously used CIDR inserts (Low-P4 and High-P4 groups, respectively) on Day 4 (estrus=Day 0). On Day 5, the Low-P4 group received prostaglandin F(2alpha) (PGF) twice, 12 h apart and on Day 6, all heifers received GnRH. Compared to heifers in the Control and Low-P4 groups, heifers in the High-P4 group had higher (P<0.01) plasma progesterone concentrations on Day 6 (3.0+/-0.3, 3.0+/-0.3 and 5.7+/-0.4 ng/ml, respectively; mean+/-S.E.M.) and a lower (P<0.01) incidence of GnRH-induced ovulation (10/10, 9/10 and 3/10). In Experiment 3, 4-6 days after ovulation, 20 beef heifers and 20 suckled beef cows were given a once-used CIDR, the two largest follicles were ablated, and the cattle were allocated to receive either PGF (repeated 12h later) or no additional treatment (Low-P4 and High-P4, respectively). All cattle received GnRH 6-8 days after follicular ablation. There was no difference between heifers and cows for ovulatory response (77.7 and 78.9%, P<0.9) or the GnRH-induced LH surge (P<0.3). However, the Low-P4 group had a higher (P<0.01) ovulatory response (94.7% versus 61.1%) and a greater LH surge of longer duration (P<0.001). In conclusion, although high plasma progesterone concentrations reduced both GnRH-induced increases in plasma LH concentrations and ovulatory responses in beef cattle, the hypothesis that heifers were more sensitive than cows to the suppressive effects of progesterone was not supported.     

Interactions of photoperiod, testosterone, and naloxone on GnRH and LH pulse parameters in the male sheep

This study tested the hypothesis that the effects of the opiate antagonist naloxone on GnRH (and LH) secretion is affected by photoperiod length and testosterone (T) concentrations. The effect of infusing naloxone on GnRH and LH pulse patterns was determined in four groups of orchidectomized sheep: long day (LD) photoperiod treated with T, LD without T (LDC), short day photoperiod (SD) with T, SDC (n = 5-7/group). Hypophyseal-portal and jugular blood samples were collected at 10 min intervals for 4 h before and 4 h during naloxone infusion (1 mg/kg/h). Neither photoperiod nor T affected either mean GnRH or LH whereas naloxone (P < 0.01) increased both. LD photoperiod (P < 0.01), T (P < 0.01) and naloxone (P < 0.01) all increased LH pulse amplitude whereas only naloxone increased GnRH pulse amplitude (P < 0.01). There was an interaction (P < 0.01) between steroid and naloxone on LH, but not GnRH, pulse amplitude. Both LD photoperiod and T increased both LH and GnRH (P < 0.01) interpulse-interval (IPI). Naloxone decreased GnRH IPI (P < 0.01). The LH/GnRH pulse amplitude ratio was (P < 0.02) increased by T--likely a secondary response to the T-induced increase in IPI. These results are interpreted as showing that in the ram the endogenous opiate peptides regulate both GnRH pulse frequency and amplitude, but that their specific role is modulated by photoperiod and T. These results do not support the concept that the opiate peptides are the primary mediators of the negative feedback effects of T.     

Basal and GnRH induced secretion of FSH and LH in ovariectomized ewes treated with bovine follicular fluid

Ovariectomized (OVX) ewes were injected with 5 ml of either bovine serum, charcoalextracted bovine follicular fluid (FF), or whole bovine FF. Five hours after this pretreatment, ewes on each pretreatment were injected with either 0, 1, or 5 μg of GnRH. Ewes that were pretreated with either type of FF had decreased concentrations of FSH regardless of dose of GnRH when compared to ewes pretreated with bovine serum. There was no effect of charcoal extraction. There were no differences among the pretreatment groups in LH response to GnRH. In a second experiment, OVX ewes were pretreated (4 ml) with either bovine serum or bovine FF 5 hr prior to GnRH or with bovine FF 42, 30 and 18 hr prior to GnRH. Ewes were injected with either 0 or 5 μg of GnRH. Pretreatment with FF for 5 or 42 hr prior to GnRH resulted in significantly decreased concentrations of FSH both at the time of GnRH treatment and during the following 2 hr. Concentrations of LH did not differ among pretreatment groups. In a third experiment, OVX ewes were pretreated with either bovine serum or bovine FF 30, 18 and 5 hr prior to GnRH. Ewes were injected with either 0, 5 or 50 μg of GnRH. Pretreatment with FF resulted in decreased concentrations of FSH both at the time of GnRH treatment and during the following 2 hr. Concentrations of LH were also decreased at the time of GnRH treatment.     

Effect of GnRH Dose on Occurrence of Short Oestrous Cycles and LH Response in Cyclic Dairy Heifers

Prostaglandin F_2α (PGF_2α) and GnRH treatments given 24 h apart have been shown to result in short oestrous cycles (8–12 days) in some cows and heifers. The differences in responses may depend on the dose of GnRH. Therefore, the effect of the dose of GnRH on occurrence of short cycles and LH response was studied here. Oestrus was induced with dexcloprostenol (0.15 mg) in two groups of Ayrshire heifers. A second luteolysis was induced similarly on day 7 after ovulation; 24 h after PGF_2α treatment, the heifers were administered either a high (0.5 mg, n = 15, group T500) or low (0.1 mg, n = 10, group T100) dose of gonadorelin. Blood samples for progesterone analyses were collected daily from the second PGF_2α administration to the second ovulation after the PGF_2α injection. Beginning 24 h after the GnRH treatment, ovaries were examined by transrectal ultrasonography every 6 h until ovulation, and daily between day 4 and the next ovulation. Five heifers from both groups were sampled for LH analyses via a jugular catheter every 30 min from 1 h before to 6 h after the GnRH administration. Short oestrous cycles were detected in 7 of 10 cases in group T100 and in 12 of 15 cases in group T500. No significant differences in LH responses were detected between the groups. In group T500, the rise in LH concentration tended to be somewhat slower than in group T100. The dose of GnRH (0.1 vs 0.5 mg) did not affect the occurrence of short oestrous cycles and LH response.     

Effect of epinephrine, norepinephrine and(or) GnRH on serum LH in prepuberal beef heifers

Forty prepuberal Simmental X Brahman-Hereford heifers were utilized to determine the effects of epinephrine (E), norepinephrine (NE), gonadotropin releasing hormone (GnRH) or combinations of GnRH + E and GnRH + NE on serum luteinizing hormone (LH) concentrations. Animals were assigned randomly to one of five treatments with four replicates/treatment. Treatments consisted of I) 100 micrograms GnRH at time 0 (n = 8); II) 50 mg NE at time -15 and 0 (n = 8); III) 50 mg E at time -15 and 0 (n = 8); IV) 100 micrograms GnRH at time 0, plus 50 mg NE at time -15 and 0 (n = 8) and V) 100 micrograms GnRH at time 0, plus 50 mg E at time -15 and 0 (n = 8). All treatment compounds were administered im in 2 ml physiological saline and blood samples were collected via tail vessel puncture at -30, -15, 0, 15, 30, 45, 60, 90, 120, 180, 240, 300 and 360 min from GnRH injection. Treatment with NE or E alone had no effect (P greater than .10) on serum LH during the sampling period. The initial LH release to GnRH was altered (P less than .05) by concomitant treatment with NE (treatment IV) or E (treatment V). Magnitude of the LH release was reduced (P less than .01) by treatment V. Area under the LH surge was reduced (P less than .05) by treatment IV (NE) and V (E).     

Theoretical Aspects of the Control of Glossina Morsitans by Game Destruction

One way to avoid potential predators is to be sensitive to odour cues, particularly those in faeces and urine, left by predators. This sensitivity has been demonstrated in many solitary, nocturnal, small mammals which may fall victim to ambush predators.We tested the response of Cape ground squirrels, a diurnal, group-living small mammal, to the presence of predator (black-backed jackal) faeces and non-predator (black wildebeest) dung in baited traps, and also predator faeces and non-predator dung outside their burrows. The squirrels showed a significantly higher avoidance of traps scented with predator faeces than both control and non-predator dung-scented traps. They also took significantly longer to emerge from burrows that had predator faeces outside compared with control burrows and burrows with non-predator dung outside and showed a trend for higher vigilance once they emerged from burrows with predator faeces outside. We argue that as diurnal group-living reduces a reliance on olfactory cues, this species is more likely to rely on visual cues and the vigilance of other individuals than nocturnal solitary species that have been the focus of most studies up till now. As a result, squirrels very quickly return to normal behaviour after exposure to a predator cue. Level of sociality is likely to influence responses to olfactory cues of predators and should be the focus of further studies.     

Effect of Initial GnRH and Duration of Progesterone Insert Treatment on the Fertility of Lactating Dairy Cows

The study compared response to prostaglandin F2α (PG), synchrony of ovulation and pregnancy per AI (P/AI) in a 5‐ vs a 7‐day Ovsynch + PRID protocol and investigated whether the initial GnRH affects P/AI in lactating dairy cows. Two hundred and seventy‐six cows (500 inseminations) were assigned to one of four timed‐AI (TAI) protocols: (i) PRID‐7G; 100 μg GnRH im, and a progesterone‐releasing intravaginal device (PRID) for 7 days. At PRID removal, PG (500 μg of cloprostenol) was given im. Cows received the second GnRH treatment at 60 h after PRID removal and TAI 12 h later. (ii) PRID‐5G; as PRID‐7G except the duration of PRID, treatment was 5 days and PG was given twice (12 h apart). (iii) PRID‐7NoG; as PRID‐7G except the initial GnRH, treatment was omitted. (iv) PRID‐5NoG; as PRID‐7NoG except the duration of PRID, treatment was 5 days. Response to treatments and pregnancy status at 32 and 60 days after TAI was determined by ultrasonography. The percentage of cows ovulating before TAI was greatest in PRID‐7G (17.1%), and the percentage of cows that did not have luteal regression was greatest in PRID‐5G (9.5%). The overall P/AI at 32 and 60 days did not differ among TAI protocols. However, during resynchronization, cows subjected to the 5‐day protocols had greater (p < 0.05) P/AI (45.3% vs 33.6%) than cows subjected to the 7‐day protocols. Pregnancy loss between 32 and 60 days tended (p = 0.10) to be greater in cows that did not receive initial GnRH (14.8%) compared to those that received GnRH (8.2%). In conclusion, the PRID‐5G protocol resulted in fewer cows responding to PG, but P/AI did not differ among TAI protocols. A 5‐day protocol resulted in more P/AI in resynchronized cows, and cows that did not receive initial GnRH tended to experience more pregnancy losses.     

Insights into the mechanism by which kisspeptin stimulates a preovulatory LH surge and ovulation in seasonally acyclic ewes: Potential role of estradiol

We have previously demonstrated that a constant intravenous infusion of kisspeptin (Kp) for 48 h in anestrous ewes induces a preovulatory luteinizing hormone (LH) surge followed by ovulation in approximately 75% of animals. The mechanisms underlying this effect are unknown. In this study, we investigated whether Kp-induced preovulatory LH surges in anestrous ewes were the result of the general activation of the whole gonadotropic axis or of the direct activation of central GnRH neurons required for the GnRH/LH surge. In the first experiment, a constant iv infusion of ovine kisspeptin 10 (Kp; 15.2 nmol/h) was given to 11 seasonally acyclic ewes over 43 h. Blood samples were taken every 10 min for 15 h, starting 5 h before the infusion, and then hourly until the end of the infusion. We found that the infusion of Kp induced a well-synchronized LH surge (around 22 h after the start of the Kp infusion) in 82% of the animals. In all ewes with an LH surge, there was an immediate but transient increase in the plasma concentrations of LH, follicle-stimulating hormone (FSH), and growth hormone (GH) at the start of the Kp infusion. Mean (± SEM) concentrations for the 5-h periods preceding and following the start of the Kp infusion were, respectively, 0.33 ± 0.09 vs 2.83 ± 0.49 ng/mL (P = 0.004) for LH, 0.43 ± 0.05 vs 0.55 ± 0.03 ng/mL (P = 0.015) for FSH, and 9.34 ± 1.01 vs 11.51 ± 0.92 ng/mL (P = 0.004) for GH. In the first experiment, surges of LH were observed only in ewes that also had a sustained rise in plasma concentrations of estradiol (E₂) in response to Kp. Therefore, a second experiment was undertaken to determine the minimum duration of Kp infusion necessary to induce such a pronounced and prolonged increase in plasma E₂ concentration. Kisspeptin (15.2 nmol/h) was infused for 6, 12, or 24 h in seasonally acyclic ewes (N = 8), and blood samples were collected hourly for 28 h (beginning 5 h before the start of infusion), then every 2 h for the following 22 h. Kisspeptin infused for 24 h induced LH surges in 75% of animals, and this percentage decreased with the duration of the infusion (12 h = 50%; 6 h = 12.5%). The plasma concentration of E₂ was greater in ewes with an LH surge compared to those without LH surges; mean (± SEM) concentrations for the 5-h period following the Kp infusion were, respectively, 2.23 ± 0.16 vs 1.27 ± 0.13 pg/mL (P < 0.001). Collectively, our results strongly suggest that the systemic delivery of Kp induced LH surges by activating E₂-positive feedback on gonadotropin secretion in acyclic ewes.     

Effects of a single injection of GnRH or equine pituitary extract on plasma LH and FSH concentrations in stallions

Plasma LH and FSH concentrations were measured in mature stallions after administration of synthetic GnRH or equine pituitary extract. GnRH caused significant rises in plasma LH (2-fold) and FSH (1.7-fold). Concentrations of LH remained significantly elevated for 4 hours and FSH remained elevated for 2 hours. Similar increases in plasma LH (1.6-fold) and FSH (1.8-fold) occurred after an injection of equine pituitary extract. LH was significantly elevated for 4 hours and FSH was elevated for 6 hours.     

Fertility of a High‐Altitude Sheep Model is Compromised by Deficiencies in Both Preovulatory Follicle Development and Plasma LH Availability

At high altitude, hypoxia and/or oxidative stress may compromise fertility. This study tested the relative effect of short‐ or long‐term exposure to high‐altitude hypobaric hypoxia and oxidative stress in sheep on preovulatory follicle dynamics and gonadotrophin secretion. Thus, growth dynamics, stereidogenic function and competence to ovulate of preovulatory follicles, as well as FSH and LH availability throughout the entire oestrous cycle, were compared among sheep native from low and high altitude, and sheep newcomers to high altitude. The results indicates that short‐term exposure in sheep newcomers to high altitude has a deleterious effect on both the ovarian function (affecting preovulatory follicular development) and the pituitary function (diminishing plasma LH availability). On the other hand, there were no detected differences in the preovulatory follicular development in sheep adapted to high altitude for generations and, conversely, LH secretion was increased, which suggests an adaptive mechanism. The treatment with antioxidant agents during a relative short period for the time of folliculogenesis (approximately 1 month and a half) changed substantially the development of preovulatory follicles in short‐term exposed sheep to similar patterns than in sheep native and living to both high and low altitude. These results highlight the role of oxidative stress in the detriment of the reproductive function in individuals recently exposed to high‐altitude hypoxic environment.     

Aspects on Hormonal Control of Normal and Induced Parturition in the Dog

Average length of gestation on the dog is 63 ± 2 days but may vary between 57-71 days due to the long period of receptivity at oestrus and the extended period of sperm survival in the female genital tract. In contrast to other domestic animals progesterone- and oestrogen concentrations are almost identical in pregnant and non pregnant bitches, except for their rapid decline immediately prior to parturition. Control of luteolysis still poorly understood. Experiments with indomethacin leading to a blockade of the prepartal PgF_2α increase, which commences with the decrease of progesterone, point toward a role of PgF_2α at this stage of pregnancy, which was extended for several days. At physiological conditions first visible signs of parturition were observed at peak-PgF_2α levels, 33.6 ± 17.6 hours after onset of luteolysis, which lasted over 16.8 ± 3.4 hours. Pulse-type releases of oxytocin were only observed after this point of time. To test for the effect of progesterone-withdrawal, four 51-57 days pregnant bitches were treated with the antiprogestin RU 38486 which inhibits the activity of progesterone at the receptor level. In all dogs first visible signs of parturition were observed 33.5 ± 7.5 hours after onset of treatment. However, the process of parturition came to an end after cervical opening and totally only one puppy was born. Different to a normal parturition no increase of PgF_2α was observed. Relaxin levels were not influenced by treatment. These observations suggested that treatment with antiprogestin followed by PgF_2α might be an adequate method to induce parturition in the dog; first experiences seem to confirm this conclusion.     

Noradrenergic Control of GnRH Release from the Ewe Hypothalamus In Vitro: Sensitivity to Oestradiol

The present study investigates the influence of α₁‐adrenoreceptors in GnRH release in vitro and determines whether oestradiol modulates α₁‐adrenoreceptor‐GnRH interaction. Within 10 min after ewe sacrifice, saggital midline hypothalamic slices were dissected, placed in oxygenated Minimum Essential Media‐α (MEM‐α) at 4°C and within 2 h were singly perifused at 37°C with oxygenated MEM‐α (pH 7.4; flow rate 0.15 ml/min), either with or without oestradiol (24 pg/ml). After 4‐h equilibration, 10‐min fractions were collected for 4 h interposed with a 10‐min exposure at 60 min to specific α₁‐adrenoreceptor agonist (methoxamine) or antagonist (thymoxamine) at various doses (0.1–10 mm ). The α₁‐adrenoreceptor agonist (10 mm ) increased (p < 0.05) GnRH release at 90 min both in presence and absence of oestradiol. However, in presence of oestradiol, α₁‐adrenoreceptor agonist (10 mm )‐induced GnRH release remained elevated (p < 0.05) for at least 60 min. The bioactivity of the released GnRH was studied using a hypothalamus–pituitary sequential double‐chamber perifusion. Only after exposure of hypothalamic slices to α₁‐adrenoreceptor agonist (10 mm ), did the hypothalamic eluate stimulate LH release from pituitary fragments (n = 9, 7.8 ± 12.3–36.2 ± 21.6 ng/ml) confirming that the α₁‐adrenoreceptor agonist stimulated release of biologically active GnRH. In summary, GnRH release from the hypothalamus is under stimulatory noradrenergic control and this is potentiated in the presence of oestradiol.     

GABA Control of GnRH Release from the Ewe Hypothalamus In Vitro: Sensitivity to Oestradiol

The present study examines the involvement of GABA_{A or B} receptors in gonadotrophin‐releasing hormone (GnRH) release in vitro and determines whether oestradiol modulates γ‐aminobutyric acid (GABA)–GnRH interaction. Within 10 min after ewe killing, hypothalamic slices were dissected and placed in oxygenated Minimum Essential Media (MEM)‐α at 4°C; within 2 h, slices were singly perifused at 37°C with oxygenated MEM‐α (0.15 ml/min), with or without oestradiol (24 pg/ml). After 4 h equilibration, fractions were collected for 4 h interposed with a 10 min exposure to specific GABA_{A or B} receptor ligands (0.1–10 mm ). The GABA_{A or B} agonists (muscimol or baclofen) did not greatly influence GnRH release. However, GnRH increased (p < 0.05) after exposure to 10 mm GABA_{A or B} antagonists (bicuculline or CGP52432, respectively). The GABA_A antagonist stimulated greater sustained GnRH release (p < 0.05) in the absence of oestradiol than in its presence. The bioactivity of the released GnRH was studied using a hypothalamus‐pituitary sequential double‐chamber perifusion. Only after exposure of hypothalamic slices to the GABA_A antagonist, did the hypothalamic eluate stimulate luteinizing hormone release from pituitary fragments (p < 0.05) confirming that the GABA_A antagonist stimulated release of biologically active GnRH. In summary, GnRH release from the hypothalamus is predominantly under GABA_A receptor inhibitory control and this is attenuated in the presence of oestradiol.     

Effect of CD14/TLR4 antagonist on GnRH/LH secretion in ewe during central inflammation induced by intracerebroventricular administration of LPS

Background: Immune stress induced by lipopolysaccharide(LPS) influences the gonadotropin-releasing hormone(GnRH)/luteinizing hormone(LH) secretion. Presence of LPS interacting Toll-like receptor(TLR) 4 in the hypothalamus may enable the direct action of LPS on the GnRH/LH secretion. So, the aim of the study was to investigate the influence of intracerebroventricular(icv) injection of TLR4 antagonist on GnRH/LH secretion in anestrous ewes during LPS-induced central inflammation. Animals were divided into three groups icv-treated with: Ringer-Locke solution, LPS and TLR4 antagonist followed by LPS.Results: It was demonstrated that TLR4 antagonist reduced LPS-dependent suppression of GnRH gene expression in the preoptic area and in the medial basal hypothalamus, and suppression of receptor for GnRH gene expression in the anterior pituitary gland. It was also shown that TLR4 antagonist reduced suppression of LH release caused by icv injection of LPS. Central administration of LPS stimulated TLR4 gene expression in the medial basal hypothalamus.Conclusions: It was indicated that blockade of TLR4 prevents the inhibitory effect of centrally acting LPS on the GnRH/LH secretion. This suggests that some negative effects of bacterial infection on the hypothalamic-pituitary-gonadal axis activity at the hypothalamic level may be caused by central action of LPS acting through TLR4.     

Heat Stress, the Follicle, and Its Enclosed Oocyte: Mechanisms and Potential Strategies to Improve Fertility in Dairy Cows

Reduced reproductive performance of lactating cows during the summer is associated with decreased thermoregulatory competence due to intensive genetic selection for high milk production. This review examines the immediate and delayed effects of heat stress on follicular function and describes some potential strategies for their alleviation. It focuses on how heat stress affects the follicle and its enclosed oocyte, suggesting that perturbations in the follicular microenvironment, to which the oocytes are exposed for long periods of development, reduce their developmental competence. Among the potential alterations are reduction in gonadotropin secretion, alteration in follicular growth, attenuation of dominance, and disruption of steroidogenesis. Evaporative cooling methods are the most common strategy used to alleviate the effect of heat stress; however, there is a compelling need to find additional ways to improve fertility during the summer and autumn. Hormonal treatment to enhance removal of the impaired follicles by synchronization of follicular waves with GnRH and PGF2α is suggested. An alternative method is stimulation of follicular growth by a brief treatment with bST or FSH. Other strategies, such as timed AI and embryo transfer, have been recently used, making the optimization of embryo cryopreservation procedures highly relevant. Protection of the ovarian pool of oocytes from thermal stress via nutritional manipulations or administration of antioxidants or other survival factors should also be considered. A better understanding of the underlying mechanisms by which heat stress impairs fertility may lead to the development of additional approaches to alleviate these effects.