Control of proceptive and receptive behavior by ovarian hormones in the Syrian hamster (Mesocricetus auratus)

Two studies examined the roles of estrogen with progesterone and of estrogen alone on the proceptive and receptive behavior of female hamsters. Proceptivity was measured in terms of proximity (approaching, leaving, and following by the female) and in time spent sniffing the male partner. During the 4-day natural estrous cycle, these measures change systematically although lordosis is seen only on Day 1 (estrus). With a constant dose of progesterone, both proceptive and receptive behavior were found to be estrogen dose dependent in ovariectomized females. At estrogen levels too low to induce lordosis, changes in proceptive behavior were seen; at the two highest levels of estrogen, lordosis was maximal but proceptive behavior continued to increase. With estrogen alone, levels of proceptive behavior were attained characteristic both of estrus and of the higher estrogen and progesterone dosage but were not accompanied by spontaneous lordosis. Factors indicating that proceptivity and receptivity may be under separate hormonal and neural control are discussed.     

Differential estradiol requirement for the induction of estrus behavior and the luteinizing hormone surge in two breeds of sheep

For a better understanding of the mechanisms that lead to the preovulatory GnRH/LH surge and estrus behavior, the minimum estradiol (E) requirements (dose and duration) to induce each of these events were determined and compared between two breeds of ewes having either single (Ile de France) or multiple (Romanov) ovulations. The ewes were initially studied during a natural estrus cycle, and were then ovariectomized and run through successive artificial estrus cycles. For these artificial cycles the duration and amplitude of the follucular phase E increase were manipulated by E implants. Under all conditions, the onset of estrus behavior was similar in the two breeds, although its duration was longer in Romanov ewes. While a moderate E signal (6 cm for 12 h) induced an LH surge in 10/10 Ile de France ewes, a larger E signal (12 cm for 12 h) was minimally effective in Romanov ewes (4/10). Additional studies revealed that a small E signal (3 cm for 6 h) induced full estrus behavior in all Romanov ewes but was completely ineffective in Ile de France animals (0/10). Higher doses and mostly longer durations of the E signal (12 cm for 24 h) were required to induce a surge in all the Romanov ewes. These results demonstrate a clear difference in the E requirement for the induction of estrus behavior and the LH surge between breeds of ewes that have different ovulation rates. These data provide compelling evidence that, in one breed, the neuronal systems that regulate both events require different estrogen signals.     

Psychosocial stress suppresses attractivity, proceptivity and pulsatile LH secretion in the ewe

Various stressors suppress pulsatile secretion of luteinizing hormone (LH) in ewes and cortisol has been shown to be a mediator of this effect under various conditions. In contrast, little is known about the impact of stress and cortisol on sexual behavior in the ewe. Therefore, we tested the hypothesis that both psychosocial stress and stress-like levels of cortisol will reduce the level of attractivity, proceptivity and receptivity in addition to suppressing LH secretion in the ewe. In Experiment 1, a layered stress paradigm of psychosocial stress was used, consisting of isolation for 4 h with the addition of restraint, blindfold and noise of a barking dog (predator stress) at hourly intervals. This stress paradigm reduced LH pulse amplitude in ovariectomized ewes. In Experiment 2, ovariectomized ewes were artificially induced into estrus with progesterone and estradiol benzoate treatment and the layered stress paradigm was applied. LH was measured and sexual behavior was assessed using T-mazes and mating tests. Stress reduced pulsatile LH secretion, and also reduced attractivity and proceptivity of ewes but had no effect on receptivity. In Experiment 3, ewes artificially induced into estrus were infused with cortisol for 30 h. Cortisol elevated circulating plasma concentrations of cortisol, delayed the onset of estrus and resulted in increased circling behavior of ewes (i.e. moderate avoidance) during estrus and increased investigation and courtship from rams. There was no effect of cortisol on attractivity, proceptivity or receptivity during estrus. We conclude that psychosocial stress inhibits LH secretion, the ability of ewes to attract rams (attractivity) and the motivation of ewes to seek rams and initiate mating (proceptivity), but cortisol is unlikely to be the principal mediator of these effects.     

Role of experience in the neuroendocrine control of ewes' sexual behavior

We assessed the role of learning in the expression of female sexual behavior and evaluated the relative importance of age versus experience. Two studies were conducted with ovariectomized ewes submitted to steroid treatment that mimicked an estrus cycle. We compared behavioral (experiments 1 and 2), neurochemical (experiment 1), and endocrine (experiment 2) responses of sexually naive young and adult ewes versus sexually experienced adults when exposed to males. In a third study, we compared their performance in an instrumental learning test and the extent to which it was affected by stress. These experiments showed that proceptivity is affected both by age and sexual experience. In experiment 1 only experienced adults were proceptive and displayed an increase in hypothalamic norepinephrine. By the second estrus cycle (experiment 2) naive adults performed similarly to experienced adults but proceptive behavior was still inferior in young ewes. Receptivity was also different between groups but affected more by age than by sexual experience. All ewes mated during the first interaction with a male, although males' latency to ejaculation was shorter with experienced females than naive adults or naive young. Young ewes found food as readily as adults in experiment 3 but were more affected by stress. Together, these experiments show that both experience and age influence sexual activity and that sensitivity to stress may also be involved. This may contribute to the deficient reproductive performance that is often observed in young female mammals.     

Induction of ovulation in the acyclic postpartum ewe following continuous, low-dose subcutaneous infusion of GnRH

Pituitary and ovarian responses to subcutaneous infusion of GnRH were investigated in acyclic, lactating Mule ewes during the breeding season. Thirty postpartum ewes were split into 3 equal groups; Group G received GnRH (250 ng/h) for 96 h; Group P + G was primed with progestagen for 10 d then received GnRH (250 ng/h) for 96 h; and Group P received progestagen priming and saline vehicle only. The infusions were delivered via osmotic minipumps inserted 26.6 +/- 0.45 d post partum (Day 0 of the study). Blood samples were collected for LH analysis every 15 min from 12 h before until 8 h after minipump insertion, then every 2 h for a further 112 h. Daily blood samples were collected for progesterone analysis on Days 1 to 10 following minipump insertion, then every third day for a further 25 d. In addition, the reproductive tract was examined by laparoscopy on Day -5 and Day +7 and estrous behavior was monitored between Day -4 and Day +7. Progestagen priming suppressed (P < 0.05) plasma LH levels (0.27 +/- 0.03 vs 0.46 +/- 0.06 ng/ml) during the preinfusion period, but the GnRH-induced LH release was similar for Group G and Group P + G. The LH surge began significantly (P < 0.05) earlier (32.0 +/- 3.0 vs 56.3 +/- 4.1 h) and was of greater magnitude (32.15 +/- 3.56 vs 18.84 +/- 4.13 ng/ml) in the unprimed than the primed ewes. None of the ewes infused with saline produced a preovulatory LH surge. The GnRH infusion induced ovulation in 10/10 unprimed and 7/9 progestagen-primed ewes, with no significant difference in ovulation rate (1.78 +/- 0.15 and 1.33 +/- 0.21, respectively). Ovulation was followed by normal luteal function in 4/10 Group-G ewes, while the remaining 6 ewes had short luteal phases. In contrast, each of the 7 Group-P + G ewes that ovulated secreted progesterone for at least 10 d, although elevated plasma progesterone levels were maintained in 3/7 unmated ewes for >35 d. Throughout the study only 2 ewes (both from Group P + G) displayed estrus. These data demonstrate that although a low dose, continuous infusion of GnRH can increase tonic LH concentrations sufficient to promote a preovulatory LH surge and induce ovulation, behavioral estrus and normal luteal function do not consistently follow ovulation in the progestagen-primed, postpartum ewe.     

Induction of sexual receptivity in the female broad-headed skink, Eumeces laticeps, by estradiol-17 beta

Sexual receptivity in the female scincid lizard Eumeces laticeps occurs naturally only during the spring breeding season, which is also when maximal follicular development occurs. The presumption that high estrogen levels are coincidentally present and the need for a reliable method of inducing sexual receptivity for behavioral studies prompted tests of the hypothesis that estrogen induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual behavior. A series of experiments established that estradiol-17 beta induces sexual receptivity within 4 days when injected every other day at 2.0 micrograms in 20 microliters peanut oil in intact or ovariectomized females. In behavioral tests conducted during August, all control females (intact or ovariectomized injected with vehicle only) rejected courtship whereas all females receiving estrogen copulated. Estrogen injections also induced a statistically significant change from rejection to receptivity within individuals. Initial attempts to implant estradiol-17 beta in Silastic tubes killed all females so treated.     

Female effect in sheep. I. The effects of sexual receptivity of females and the sexual experience of rams

When in contact with receptive or non-receptive ewes, the presence of females increased LH peak frequency both in experienced and inexperienced rams (P less than 0.05). The highest response was found in experienced rams stimulated by sexually receptive ewes. In this group only, the mean testosterone levels increased during stimulation (P less than 0.05). Sexual behavior did not differ between experienced and inexperienced males. The sexual receptivity of the females and the sexual experience of rams appear to interact and thus facilitate the rams' LH and testosterone responses to the presence of ewes.     

Female sex behaviors in the South African clawed frog, Xenopus laevis: gonadotropin-releasing, gonadotropic, and steroid hormones

The goals of this study were to characterize sex behaviors of female South African clawed frogs, Xenopus laevis, and to explore the behavioral effects of endocrine manipulation. The responses of females to clasp assaults by sexually active males were observed. Two patterns of female responses predominated. In one, females exhibited extreme leg extension and ticking vocalizations when clasped (unreceptive behaviors). In the other, females responded to being clasped by adduction of the thighs and increased flexion at the knee; ticking vocalizations were absent (receptive behaviors). When the female was unreceptive, clasps by males generally lasted less than 1 min. With a receptive female, on the other hand, amplexus could last up to 2 days. In intact females, injection of human chorionic gonadotropin (HCG) or of luteinizing hormone-releasing hormone (LHRH) into the dorsal lymph sac results in significant increases in receptivity. These hormones do not promote receptivity in ovariectomized females. Neither estradiol (E) nor progesterone (P) when administered alone was effective in restoring receptivity to ovariectomized females. In combination, E + P increased sexual receptivity. The releasing hormone, LHRH, when given to ovariectomized, E + P-treated females, further increased receptivity and led to the prolonged amplexus otherwise observed with an HCG-injected intact female. The behavioral effects of LHRH may be independent of action on the pituitary since they are not mimicked by gonadotropin.     

Effect of transport on pulsatile and surge secretion of LH in ewes in the breeding season.

The aim of this study was to elucidate the mechanism(s) involved in stress-induced subfertility by examining the effect of 4 h transport on surge and pulsatile LH secretion in intact ewes and ovariectomized ewes treated with steroids to induce an artificial follicular phase (model ewes). Transport caused a greater delay in the onset of the LH surge in nine intact ewes than it did in ten ovariectomized ewes (intact: 41.0 +/- 0.9 h versus 48.3 +/- 0.8 h, P < 0.02; ovariectomized model: 40.8 +/- 0.6 h versus 42.6 +/- 0.5 h, P < 0.02). Disruption of the hypothalamus-pituitary endocrine balance in intact ewes may have reduced gonadotrophin stimulation of follicular oestradiol production which had an additional effect on the LH surge mechanism. In the ovariectomized model ewes, this effect was masked by the exogenous supply of oestradiol. However, in these model ewes, there was a greater suppression of maximum LH surge concentrations (intact controls: 29 +/- 4 ng ml-1 versus intact transported 22 +/- 5 ng ml-1, P < 0.02; ovariectomized model controls: 35 +/- 7 ng ml-1 versus model transported 15 +/- 2 ng ml-1, P < 0.02). Subsequent exposure to progesterone for 12 days resulted in the resumption of a normal LH profile in the next follicular phase, indicating that acute stress leads to a temporary endocrine lesion. In four intact ewes transported in the mid-follicular phase, there was a suppression of LH pulse amplitude (0.9 +/- 0.3 versus 0.3 +/- 0.02 ng ml-1, P < 0.05) but a statistically significant effect on pulse frequency was not observed (2.0 +/- 0.4 versus 1.7 +/- 0.6 pulses per 2 h). In conclusion, activation of the hypothalamus-pituitary-adrenal axis by transport in the follicular phase of intact ewes interrupts surge secretion of LH, possibly by interference with LH pulsatility and, hence, follicular oestradiol production. This disruption of gonadotrophin secretion will have a major impact on fertility.     

Endocrine and Ovarian Changes in Response to the Ram Effect in Medroxyprogesterone Acetate-primed Corriedale Ewes During the Breeding and Nonbreeding Season

Two experiments were performed to determine the endocrine and ovarian changes in medroxyprogesterone acetate (MAP)-primed ewes after ram introduction. Experiment 1 was performed during the mid-breeding season with 71 ewes primed with an intravaginal MAP sponge for 12 days. While the control (C) ewes (n = 35) were in permanent contact with rams, the ram effect (RE) ewes (n = 36) were isolated for 34 days prior to contact with rams. At sponge withdrawal, all ewes were joined with eight sexually experienced marking Corriedale rams and estrus was recorded over the next 4 days. The ovaries were observed by laparoscopy 4–6 days after estrus. Four weeks later, pregnancy was determined by transrectal ultrasonography. In eight ewes from each group, ovaries were ultrasonographically scanned; FSH, LH, and estradiol-17β were measured every 12 hours until ovulation or 96 hours after estrus. The response to the rams was not affected by the fact that ewes had been kept or not in close contact with males before teasing. No differences were found in FSH, LH, estradiol-17β concentrations, growth of the ovulatory follicle, onset of estrus, ovulation rate, or pregnancy rate. Experiment 2 was performed with 14 ewes during the nonbreeding season. Ewes were isolated from rams for 1 month, and received a 6-day MAP priming. Ovaries were ultrasonographically scanned every 12 hours, and FSH, LH, estradiol-17β, and progesterone were measured. Ewes that ovulated and came into estrus had higher FSH and estradiol-17β levels before introduction of the rams than did ewes that had a silent ovulation. The endocrine pattern of the induced follicular phase of ewes that came into estrus was more similar to a normal follicular phase, than in ewes that had a silent ovulation. The follicle that finally ovulated tended to emerge earlier and in a more synchronized fashion in those ewes that did come into estrus. All ewes that ovulated had an LH surge and reached higher maximum FSH levels than ewes that did not ovulate, none of which had an LH surge. We conclude that (a) the effect of ram introduction in cyclic ewes treated with MAP may vary depending on the time of the breeding season at which teasing is performed; (b) patterns of FSH, and estradiol-17β concentrations, as indicators of activity of the reproductive axis, may be used to classify depth of anestrus; and (c) the endocrine pattern of the induced follicular phase, which is related to the depth of anestrus, may be reflected in the behavioral responses to MAP priming and the ram effect.     

Investigations on spermicidal activity in the sheep vagina.

This study was conducted to elucidate some of the effects of a synthetic progestagen and natural ovarian hormones on spermicidal activity in the sheep vagina. In the first experiment, parous ewes were treated for 17 days either intravaginally with medroxyprogesterone acetate (MAP) or subcutaneously with progesterone. They were inseminated artificially either on the last day of progestagen treatment or during estrus after progestagen withdrawal. Their vulvovaginal junctions were ligated to prevent the loss of sperm cells by drainage to the exterior. Untreated control ewes were inseminated during either estrus or the luteal phase of the estrous cycle. The ewes were killed 22 hr. after insemination, their vaginas flushed, and intact sperm cells and tailless sperm heads counted. In the second and third experiments, some of the ewes were bilaterally ovariectomized and inseminated several weeks later. Other ewes were ovariectomized and given subcutaneous injections of estradiol, progesterone, or both hormones.In the first experiment, most sperm cells were recovered intact from estrous or luteal phase control ewes. The intravaginal administration of MAP increased both the breakage of sperm cells into heads and tails and the disappearance of sperm cells. The spermicidal effects of MAP were just as great in ewes inseminated on the last day of treatment. as in those inseminated during the ensuing estrus; these results indicated that the peak estrogen secretion that occurs near the beginning of estrus was not necessary for the intensification of spermicidal activity.In the second experiment, ovariectomized ewes were compared to estrous and luteal phase ewes in regard to vaginal spermicidal activity. Sperm breakage and disappearance occurred least in estrous ewes, to a somewhat greater degree in luteal phase ewes, and to the greatest extent in ovariectomized ewes. The results suggested that endogenous ovarian hormones, particularly those in estrous ewes, suppress spermicidal mechanisms in the vagina.In the third experiment, the administration of estradiol and progesterone to ovariectomized ewes prevented the increase in sperm cell disappearance. Neither hormone alone prevented the increase.     

Mating-induced termination of behavioral estrus in the female lizard, Anolis carolinensis

Mating terminates behavioral estrus in the female lizard, Anolis carolinensis. Postcopulatory sexual inhibition was not observed in females receiving estradiol benzoate (EB) in 10-mm Silastic implants (0.025-in. i.d. × 0.047-in. o.d.). To determine the role of the ovaries in mating-induced inhibition, intact and ovariectomized females received either a 6-mm EB implant or a 0.8-μg EB injection. Ovariectomized females remained sexually receptive after copulation while intact females were no longer receptive. Progesterone was implicated in the regulation of postcopulatory sexual receptivity. Several models are proposed to explain these results, and the adaptive significance of coition-induced sexual inhibition is discussed.     

Facilitation of receptive behavior in estrogen-primed female rats by the anti-progestin, RU 486

The progestin receptor antagonist RU 38486 (henceforth referred to as RU 486) was tested for facilitative effects on female receptive behavior in ovariectomized Long-Evans rats primed with 2 micrograms estradiol benzoate (EB). RU 486 (0, 0.5, 1.6, or 5.0 mg) was administered 48 hr after estrogen priming. The lordosis quotient (LQ) and lordosis score (LS) were assessed 4 hr after RU 486 administration in a standardized test consisting of a 10-mount test by a stimulus male. A significant dose effect was found by both LQ and LS, with those subjects receiving 5 mg of RU 486 being significantly more receptive than vehicle control animals. Thus RU 486 acted as a weak progestin agonist under testing conditions typical for assessment of progestin facilitation of female sexual behavior in rats. Low levels of proceptive behavior (hops and darts) were seen in a minority of the tests, and did not vary systematically as a function of the dose of RU 486 administered. We also examined the effects of RU 486 given before progesterone (P) on receptivity in a blocking paradigm and confirmed previous reports that the antagonist significantly attenuates facilitation of sexual behavior when given in combination with P. A progestin receptor assay of the cytosols of the hypothalamus-preoptic area in estrogen-primed female rats treated with 5 mg RU 486 revealed a significantly greater depletion of available cytosolic P receptors than when rats were treated with a similarly facilitating dose of P (100 micrograms). The results suggest a possible dual mode of action for RU 486--a weak, receptor-mediated agonistic effect on sexual behavior when given alone to estrogen-primed rats, and a competitive blocking effect on receptivity when administered with P.     

The effects of estrogen and progesterone on female rat proceptive behavior

The relative importance of estrogen (EB) and progesterone (P) in stimulating proceptivity in ovariectomized female rats was studied. Proceptive behavior was measured quantitatively, providing a clear measure of response to experimental manipulation. When rats were tested biweekly after daily treatment with 0.4 μg/100 g body wt EB for 4 days, they showed maximal lordosis but low levels of proceptive behavior by the second test. Additional EB (3.0 μg/100 g body wt daily) failed to stimulate additional proceptivity. A graded increase in proceptive behavior resulted from administration of increasing doses of P (50, 100, 500 μg and 1.0 mg) to animals receiving EB priming as described above. The level of “soliciting” was significantly higher than EB-only-treated rats when 500 μg or 1.0 mg P was given. Ovariectomized, adrenalectomized rats, primed with 2.5 μg/100 g body wt EB daily for 7 days and tested on Day 8, were significantly less proceptive than ovariectomized, sham-adrenalectomized rats with the same hormone treatment. Four hours after injection of 1.0 mg P, there was no difference in proceptive or receptive behavior between sham- and adrenalectomized rats. It was concluded that if an EB dose is sufficient to induce maximal receptivity, additional estrogen does not stimulate proceptivity; unlike previous studies, the present data are not consistent with a global effect of ovarian steroids on both components of female behavior. Progesterone is more effective than estrogen in stimulating proceptive behavior, although proceptivity is not absolutely dependent on progesterone for expression. Proceptivity in EB-only-treated rats appears to be facilitated by adrenal P.     

Behavioral and endocrine responses of hair sheep ewes exposed to different mating stimuli around estrus

Hair sheep ewes were used to evaluate the influence of various levels of mating stimuli on the duration and timing of estrus and LH concentrations around estrus. Ewes were treated with PGF2alpha (15 mg, im) 10 d apart. At the time of the second PGF2alpha treatment (Day 0) ewes were placed in groups and exposed to different types of mating stimuli. One group of ewes (n = 16) was exposed to an epididymectomized ram (RAM), a second group of ewes (n = 16) was exposed to an epididymectomized ram wearing an apron to prevent intromission (APRON) and a third group of ewes (n = 17) was exposed to an androgenized ovariectomized ewe (T-EWE). Jugular blood samples were collected from ewes at 6-h intervals through Day 5. Plasma was harvested and LH concentration was determined by RIA. The ewes were observed at 6-h intervals to detect estrus. A ewe was considered to be out of estrus when she no longer stood to be mounted by the teaser animal. There was no difference (P > 0.10) in the proportion of ewes expressing estrus (79.6%) or having an LH surge (85.7%) among the treatments. Neither the time to estrus nor the duration of estrus were different (P > 0.10) among APRON, RAM or T-EWE groups (41.6+/-3.8 vs 43.6+/-3.6 vs 46.1+/-3.6 h, respectively, and 26.5+/-2.2 vs 24.8+/-2.3 vs 30.5+/-2.2 h, respectively). The time to LH surge was similar (P > 0.10) among APRON, RAM and T-EWE groups (51.2+/-4.5 vs 51.2+/-4.7 vs 52.7+/-4.5 h, respectively). The magnitude of the LH surge was similar (P > 0.10) in the T-EWE, APRON and RAM ewes (99.7+/-4.9 vs 87.2+/-4.9 vs 85.8+/-5.0 ng/mL, respectively). The time from estrus to the LH surge was not different (P > 0.10) among APRON, RAM or T-EWE ewes (10.1+/-2.2 vs 9.8+/-2.3 vs 11.6+/-2.3 h, respectively). These results show that the expression and duration of estrus are not influenced by different types of mating stimuli in hair sheep ewes. In addition, the timing and the magnitude of LH release does not appear to be influenced by mating stimuli around the time of estrus.     

Sexual orientation, proceptivity, and receptivity in the male rat as a function of neonatal hormonal manipulation

The influence of neonatal androgen on the potential to exhibit feminine sexual behavior was investigated. Male rats castrated on Day 0 but not those castrated on Day 4 or later showed hop/darting, ear wiggling, and lordotic behavior in response to treatment with estrogen and progesterone in adulthood at a frequency equal to that of females. Neonatal treatment with testosterone propionate (1 mg/rat for 4 days) abolished the capacity to show these behaviors. In subsequent experiments, involving castration of male rats at 0 or 4 hr after cesarean delivery, the effect of the postnatal surge of testicular secretions on the expression of female sexual behavior was investigated. No differences were seen in the frequency of hop/darting, ear wiggling, and receptivity between males castrated immediately or 4 hr after delivery. In a preference test where the experimental male could choose between an estrous female and a sexually active male, the neonatally castrated males preferred the company of a male when treated with estrogen and progesterone. The implantation of testosterone resulted in a preference for an estrous female. It was concluded that testicular secretions in the newborn male influence adult sexual orientation and suppress the ability to show proceptive and receptive behaviors.     

Natural or hormone-induced sexual and social behaviors in the female brown lemming (Lemmus trimucronatus)

The behaviors of intact or ovariectomized, estradiol benzoate-treated or estradiol benzoate followed by progesterone-treated female brown lemmings were compared. Intact, diestrous females engaged in more social interactions with a male than did ovariectomized females (Experiment 1). In the first 5 min of a 1-hr mating exposure (Experiment 2, Test A) intact females in natural estrus engaged in more social and sexual behaviors than did ovariectomized females in estrogen-induced estrus. However, during the last 5 min of the 1-hr exposure (Test B) ovariectomized females receiving estrogen alone continued to show high levels of sexual activity with a male partner, while intact estrous females or females receiving estrogen followed by progesterone showed an apparent drop in sexual receptivity and an increase in aggressivity. Aggressive behaviors, as indexed by threat-leap behaviors on the part of the female may increase in the presence of progesterone. Declines in sexual activity, occurring within 1 hr of progesterone injection, were apparently dependent on the interaction of progesterone and copulatory events which may affect both the male and female.     

Effects of thermal stress on plasma concentrations of luteinizing hormone, progesterone, prolactin and testosterone in the cycling ewe

Naturally cycling white faced ewes were utilized to study the effects of continuously elevated environmental temperature and/or humidity on plasma concentrations of luteinizing hormone (LH), prolactin (PRL), progesterone (P4) and testosterone (TE) during the estrous cycle. Fourteen ewes were randomly allocated on the day of estrus (day 0) to either thermoneutral conditions (21.1 degrees C, 65% relative humidity) or elevated ambient temperature/humidity conditions (36.1 degrees C, 71% relative humidity) producing an average 1.4 degrees C hyperthermia. Animals remained in their respective environments and blood samples were collected daily until the next estrus or day 20, whichever occurred first. Starting at noon on day 14, blood was sampled every 2 hours. Concentrations of LH, PRL, P4 and TE were quantified using validated radioimmunoassays. Hyperthermic ewes exhibited 1) a significant decrease (P<0.05) in the incidence of behavioral estrus and a preovulatory LH surge at the expected time of the estrous cycle, 2) significantly lower (P<0.05) plasma P4 between days 7 and 13 of the cycle, 3) a six-fold increase of PRL levels (P<0.01). Plasma levels of TE were not significantly affected by hyperthermia. The only two experimental ewes which exhibited estrus and an LH surge also showed an unusual and significant peak in plasma P4 two days before estrus. These results confirm that elevated environmental temperatures that result in hyperthermia can induce endocrine imbalances in the ewe which may contribute to decreased reproductive efficiency in the heat-stressed female.     

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.     

Sexual differentiation of reproductive behavior in pigs: defeminizing effects of prepubertal estradiol

The present study sought to determine (1) whether estrogen by itself can defeminize the behavior of pigs during the late juvenile-early pubertal period, and (2) whether the progressive late defeminization reported for pigs is a true organizational effect, as opposed to an artifact of the time between castration and testing. Male pigs were castrated at 19-22 days or left intact and females were ovariectomized at 3 months. Additional males castrated at 19-22 days and females ovariectomized at 3 months were implanted with estradiol benzoate (EB) from 3 to 5.5 months. After castration of the previously intact males at the age of 5.5 months, all subjects were tested beginning at 6.5 months for proceptivity (choice of a male versus a female in a T-maze) and receptivity (immobilization to a mounting male) following an injection of EB. EB administered during development significantly defeminized proceptivity and receptivity in both sexes. The decrease in proceptivity was more pronounced in males than in females and was more pronounced than the decrease in receptivity, as if differentiation ends earlier for proceptivity than for receptivity; the decrease in receptivity was more pronounced in females. To see whether the capacity to display female-typical behavior is a function of time since castration, we castrated additional males at 4 months and tested for receptivity 9 days later following an injection of EB, then tested again with the other subjects at 6.5 months. The proceptivity and receptivity scores for males castrated at 4 months fell between those for intact males and males castrated at 3 weeks, and thus these animals were not completely defeminized. They were more receptive at 6.5 months than at 4 months, but the difference was not significant. These results indicate that in pigs estradiol defeminizes both receptive and proceptive behavior and that this defeminization can occur relatively late in development.