Anoestrous Females Research Articles

Induction of oestrus by administering Inhibin antiserum along with equine chorionic gonadotropin in anoestrous bitches.

As dogs experience oestrus only once or twice a year, it is necessary to establish an effective method of oestrous induction for efficient breeding. In the present study, we evaluated inhibin antiserum (IAS) on oestrous induction in anoestrous females. Bitches were administered 0.5ml/kg IAS or a mixture of 50IU/kg equine chorionic gonadotropin (eCG) and 0.5ml/kg IAS and 500IU human chorionic gonadotropin (hCG) administered 7days after the mixture injection. As a control, bitches received 50IU/kg eCG, with 500IU hCG administered 7days after eCG injection. Blood-tinged vaginal discharge, vulvar swelling, plasma progesterone concentrations and ovarian follicular development were assessed from day 0 to day 14. IAS alone injection did not induce oestrus in bitches at the anoestrous stage. Conversely, vulvar swelling, blood-tinged vaginal discharge and an estimated luteinizing hormone (LH) surge appeared on days 3-7, days 3-6 and days 7-9 after the IAS+eCG mixture injection, respectively, in all five bitches at the anoestrous stage. The average number of developing and ovulated follicles in bitches administered IAS+eCG was 8.8 and 9.6 respectively. A single eCG injection followed by hCG induced oestrous signs, with an average of 8.3 developing follicles and 4.5 ovulated follicles. This study revealed that IAS alone did not induce oestrus, but when IAS was used in combination with eCG, it induced oestrus and promoted a considerable number of ovulations in anoestrous dogs.

Social isolation does not inhibit sexual behaviour and testosterone secretion in sexually inexperienced photo-stimulated bucks in contact with seasonally anoestrous goats

The aims of this study were to determine: (i) whether sexually inexperienced photo-stimulated males housed individually in pens display less intense sexual behaviour than sexually inexperienced photo-stimulated males housed in a group, and (ii) whether these treatments vary the sexual response in anoestrous goats. Five males were housed either individually in pens (2 × 2 m) or together in a pen (5 × 6 m) and received artificially long days (16 h/light/day/2.5 months). Males were exposed to females (n = 50/group) for 15 days. Plasma testosterone did not differ between males. Male sexual behaviour was recorded on days 0-2 after introduction to females. On days 0-2, nudging was higher in males in group than those individual. On days 0 and 2 anogenital sniffing were higher in males in group, on day 1 was similar between males. Mounting attempts were similar between groups. On day 1 mounts with intromission did not differ but on day 2 were more in males in group. On day 0 self-urination were more in males in group, but on days 1 and 2 were similar between groups. On day 0 flehmen were more in males individually but on days 1-2 were similar between groups. Interval increases the words to first oestrus differ significantly between females, whereas ovulatory responses were similar. Thus, sexually inexperienced photo-stimulated males housed individually showed less sexual behaviour that those photo-stimulated housed in group but did not show reduced ability to induce ovulatory responses in anoestrous females; these responses resembled those induced by group-housed males. Highlights Plasma testosterone concentration is high in sexually inexperienced photo-stimulated males housed in group or individually during the rest sexual. Sexually inexperienced photo-stimulated males housed in group or individually display sexual behaviour in spring. Sexually inexperienced photo-stimulated males housed in group or individually induce sexual response in anoestrous female goats.

Synchronization of ovulation in goats using prostaglandin F2α based protocols during the breeding season

Goats and ewes show a marked reproductive seasonality mainly due to a photoperiod effect. The annual variation of the daily luminosity duration is perceived by the retina of these animals and a neurohormonal pathway involving suprachiasmatic nucleus, sympathetic neurons, and the pineal gland was responsible for production of melatonin, a key hormone, during short days/darkness periods[1-3]. Consequently, melatonin stimulates a neuronal network which modulates the hypothalamic secretion of gonadotropinreleasing hormone (GnRH)[3], and the hypothalamic-pituitarygonadal axis is stimulated. From a latitude > 25°, most of the local breeds progressively present an anoestrous period with variations in duration (3 to 7–8 months) and intensity (originating up to 100% of anoestrous females), during the natural long days[4,5]. In order to inseminate females out of season, several hormonal, natural or mixed protocols were developed for estrus and ovulation synchronization. These protocols were recently reviewed[6]. However, a demand of artificial inseminations also occurs during breeding season. Moreover, from regions at latitude less than 45° towards the equator, a progressive percentage of females remain (Spain; latitude 37° N) or can remain (Mexico; latitude 26° N) cyclic during whole year[5,7]. In fact, parturitions of goats can occur in all months under natural circumstances of mating (Figure 1). Although classical hormonal protocol used during anoestrous season can also synchronize ovulations during the breeding season, other protocols more cost-effective can be used in cyclic goats during the breeding season, mainly in regions showing less marked seasonal reproductive activity of small ruminants. The main aim of the present review was to describe useful methods for ovulation synchronization in goats, based on prostaglandin F2α (PGF2α) protocols during breeding season and to suggest the pathways for a more rational use of hormones for ARTICLE INFO ABSTRACT

Expression of prostaglandin E 2 receptor subtypes in the canine lower urinary tract varies according to the gonadal status and gender

Locally-synthesised prostaglandin E 2 (PGE 2) is pivotal for the function of the lower urinary tract (LUT). This study aimed at investigating the expression and distribution pattern of the four PGE 2 receptor (EP) subtypes in the LUT of intact and gonadectomised male and female dogs. Expression for EP1, EP2, EP3, and EP4 and their mRNA (EP2, EP3, and EP4) was investigated. Twenty clinically healthy dogs were allotted into 4 groups based on their gonadal status and gender including 5 intact males, 5 anoestrous females, 4 castrated males, and 6 spayed females. In situ hybridization and immunohistochemistry showed variation in the expression of mRNA and protein for the EP subtypes among tissue layers (epithelium, sub-epithelial stroma, and muscle), regions (body and neck of the bladder as well as proximal and distal urethra) and between gonadal statuses and genders. The expression for the four EPs was intense in the luminal epithelium, intermediate to low in the muscle and the sub-epithelial stroma regardless of gonadal status or gender. Higher expression of all EPs and their mRNAs was observed in the proximal urethra compared to other regions in intact dogs. However, in gonadectomised dogs, the expression did not differ among different regions and was generally lower than in intact dogs particularly in the proximal urethra. Differences in the expression between genders were found and depended on EP subtypes. In conclusion, the results have shown that four subtypes of EP receptors and their mRNAs are present in the canine LUT and their expression was affected by the gonadal status and the gender. The results lead to suggest that an impaired LUT function post-neutering may partly be associated with differences in PGE 2 receptor expression between intact and gonadectomised dogs.

Male Effect Pheromone Tickles the Gonadotrophin‐Releasing Hormone Pulse Generator

In sheep and goats, the primer pheromone produced by the male induces out-of-seasonal ovulation in anoestrous females, the so-called 'male effect.' Because the initial endocrine event following reception of the pheromone is the stimulation of pulsatile luteinising hormone (LH) secretion, the central target of the pheromone is considered to be the putative gonadotrophin-releasing hormone (GnRH) pulse generator. Using electrophysiological techniques to record multiple-unit activity (MUA) in close proximity to kisspeptin neurones in the arcuate nucleus (ARC) of Shiba goats, we found that bursts (volleys) of MUA occur at regular intervals, and repetitive bursts are invariably associated with discrete pulses of LH, suggesting that the ARC kisspeptin neurones may be the intrinsic source of the GnRH pulse generator. A brief exposure of female goats to the pheromone immediately elicited an instantaneous rise in MUA, which is followed by an MUA volley and an accompanying LH pulse, indicating that the pheromone signal is transmitted to a subset of the ARC kisspeptin neurones to activate them. Because it has been suggested that the neurokinin B and dynorphin coexpressed in those neurones play critical roles in generating rhythmic bursts, they may be involved in the intracellular pheromone actions that are responsible for inducing the GnRH pulse.

Modulation of Gonadotrophin‐Releasing Hormone Pulse Generator Activity by the Pheromone in Small Ruminants

In small ruminants, such as goats and sheep, a primer pheromone produced by males induces an out-of-seasonal ovulation in anoestrous females, a phenomenon known as the male effect. The male effect is unique in that an external chemical stimulus can immediately modulate the activity of the hypothalamic gonadotrophin-releasing hormone (GnRH) pulse generator. We have established a monitoring method of the GnRH pulse generator activity in Shiba goat. Using this method as a sensitive bioassay to assess the male effect pheromone activity, we have shown that the male effect pheromone is synthesised in an androgen-dependent manner in the sebaceous glands or their vicinity in specific body regions in goats. Although chemical identity of the pheromone is yet to be determined, analyses of male goat hair extracts by gas chromatography fractionation suggest that the male effect pheromone is a volatile substance with relatively small molecular weight. From morphological and molecular biological studies in goats, it is suggested that the pheromone molecule is detected by a member of the V1R family located on both the olfactory neurones and the vomeronasal sensory neurones, and the pheromone signal is conveyed to the medial nucleus of amygdala via the main olfactory and vomeronasal pathways and, subsequently, to the hypothalamic GnRH pulse generator to enhance its activity.

Expression of cyclooxygenase-2 in the canine lower urinary tract with regard to the effects of gonadal status and gender

As pituitary gonadotrophins can induce prostaglandin (PG) synthesis and receptors for LH and FSH are present in the canine lower urinary tract (LUT), the objectives of this study were to (i) investigate the expression of COX-2, a key rate-limiting enzyme in PG production, in the canine LUT and (ii) determine if COX-2 expression differs between gender, gonadal status (intact and gonadectomised) and LUT regions. Four regions (body and neck of the bladder as well as proximal and distal urethra) of the LUT were obtained from 20 clinically healthy dogs (5 intact males, 5 intact anoestrous females, 4 castrated males, 6 spayed females). In situ hybridization and immunohistochemistry were performed to determine the presence of COX-2 mRNA and protein, respectively. The mRNA and protein expression was semi-quantitatively assessed. The scoring system combined both the distribution and intensity of positive staining and was carried out separately on the three tissue layers (epithelium, sub-epithelial stroma and muscle) for each of four regions of the LUT. In comparison to intact dogs, lower expression ( P < 0.001) of COX-2 and its mRNA in gonadectomised males and females was observed in all tissue layers of each region of the LUT except in the distal urethra where there was no difference in mRNA expression between gonadal statuses. Regardless of region and tissue layer, intact females expressed more ( P < 0.05) COX-2 and its mRNA than intact males. However, in gonadectomised dogs, mRNA expression of COX-2 did not differ between genders; males had higher ( P < 0.001) protein level of COX-2 compared to females. In conclusion, both COX-2 and its mRNA were expressed in the canine LUT and COX-2-regulated PG synthesis in the canine LUT may differ between gonadal statuses and genders. The lower expression of COX-2 in gonadectomised dogs may impair normal function of the LUT and probably implicated in the development of neutering-induced urinary incontinence in the dog.

Evidence of mate choice copying in Norway rats, Rattus norvegicus

In the literature, nonindependent mate choice of females is frequently referred to as ‘mate choice copying’. The label seems particularly appropriate when the probability that a focal female will mate with a male increases after she has watched him engage in sexual behaviour with another female. However, the classic definition of mate choice copying requires only that a male’s attractiveness to a female change following his acceptance or rejection by another female regardless of whether such alteration in a female’s response results from seeing him mate or from some other process. Here, we provide evidence that female Norway rats prefer to affiliate with a male that has recently engaged in sexual activity, even when they did not observe the male’s previous mating. Furthermore, when we provided oestrous females with access to two males tethered some distance apart, the male that had recently copulated also mounted and achieved intromission and ejaculation sooner and more frequently than the male that had not recently copulated. We also provide evidence that increased attractiveness of male rats that had recently copulated was mediated by olfactory cues, and that female rats tended to affiliate with males that had engaged in sexual activity but not with males that had spent time with anoestrous females.

The influence of oestrous swellings on the grooming behaviour of chimpanzees of the Budongo Forest, Uganda

Allogrooming among primates has been suggested as a strategy for enhancing reproductive success, by allowing males to enhance their proximity to oestrous females, or by influencing female choice through the development of affiliative relationships with males. Female chimpanzees have swollen anogenital regions signalling receptivity and by adapting their grooming investment accordingly, males could increase their copulatory success whilst females may increase chances of copulations with preferred males. Five and a half years of data from chimpanzees in the Budongo Forest, Uganda, were examined to investigate how sexual swellings influence grooming behaviour between males and females of different age classes. Based on the availability of oestrous females, significantly less grooming than expected occurred between anoestrous females and adult males, as well as between adult (anoestrous and oestrous) females and subadult males, but significantly more grooming than expected occurred between oestrous females and adult males or subadult males. Both oestrous adult and subadult females devoted more time to grooming interactions with adult males than did anoestrous females. Grooming interactions between adult males and oestrous adult females were initiated and terminated significantly more often by males, but those between anoestrous subadult females and adult males were initiated significantly more frequently by females.

Differences in the expression of luteinizing hormone and follicle-stimulating hormone receptors in the lower urinary tract between intact and gonadectomised male and female dogs

Receptors for LH (LHR) and FSH (FSHR) are expressed in the canine lower urinary tract (LUT). As gonadectomy results in an increase in plasma LH and FSH, the objective of this study was to determine whether there are any differences in the expression of LHR and FSHR in the LUT between intact and gonadectomised dogs. Four regions of the LUT, i.e. body and neck of the bladder as well as proximal and distal urethra, were collected from 20 healthy dogs (5 intact males, 5 intact anoestrous females, 4 castrated males and 6 spayed females). The mRNA and protein expression of receptors was determined by in situ hybridization and immunohistochemistry, respectively, and assessed semi-quantitatively incorporating both the distribution and the intensity of specific staining. Expression of LHR and FSHR was present in all tissue layers (epithelium, sub-epithelial stroma and muscle) of each region with different levels of the expression. Overall mRNA and protein expression for both LHR and FSHR was significantly (P<0.001) lower in gonadectomised dogs. Intact dogs had more (P<0.05) LHR and FSHR mRNA and protein in all tissue layers of the four regions, except for LHR mRNA expression in the sub-epithelial stroma where no differences were observed between the two statuses. Decreases in LHR and FSHR mRNA and protein in gonadectomised dogs appeared to be more consistent in spayed bitches compared to castrated males. Lower expression of LHR and FSHR observed in gonadectomised dogs may adversely affect the normal canine LUT function.

Luteinizing hormone and follicle-stimulating hormone receptors and their transcribed genes (mRNA) are present in the lower urinary tract of intact male and female dogs

In dogs, one of the side effects of neutering is the development of urinary incontinence. The relationship between neutering and urinary incontinence caused by acquired urethral sphincter mechanism incompetence (USMI) has been reported. Recently, GnRH analogue treatment that suppresses elevated plasma gonadotrophin concentrations post-spaying has been successfully used in incontinent bitches. These data and the fact that non-gonadal tissues may contain receptors for LH (LHR) and FSH (FSHR) suggest that there might be a functional relationship between gonadotrophins and the lower urinary tract in dogs. This study aimed to investigate the presence of LHR and FSHR in the lower urinary tract of intact male and female dogs. Four regions of the lower urinary tract, i.e. (i) body of the bladder, (ii) neck of the bladder, (iii) proximal urethra and (iv) distal urethra were collected from 10 healthy dogs (5 males and 5 anoestrous females). In situ hybridization and immunohistochemistry were performed to characterise the presence of receptor mRNA and receptor protein. Staining was rated semi-quantitatively, incorporating both the distribution and intensity of specific staining. The distribution of receptor expression in different tissue layers (epithelium, subepithelial stroma and muscle) in each region was statistically analyzed. Luteinizing hormone receptor and FSHR mRNA and protein were present in all four regions and in three tissue layers of males and females. Irrespective of region and layer, female dogs expressed significantly higher expression for LHR mRNA ( P < 0.001), LHR protein ( P < 0.05) and FSHR protein ( P < 0.001). The expression of LHR and FSHR mRNA and protein was not uniform and depended on region, tissue layer and gender. The expression of LHR mRNA was higher in the bladder, compared to the urethra ( P < 0.05). The FSHR mRNA significantly increased from the bladder to the urethra. Protein expression for LHR and FSHR was highest in the proximal urethra ( P < 0.05). The overall expression for LHR and FSHR at both mRNA and protein levels was highest in the epithelium, intermediate to low in the subepithelial stroma and muscle. A significant interaction between region and tissue layer showed that mRNA and protein expression for LHR and FSHR decreased from the bladder to the urethra in the epithelium and subepithelial stroma. In contrast, it gradually increased from the bladder to the urethra in the muscle. In conclusion, the present study showed that both mRNA and protein for LHR and FSHR were expressed in the canine lower urinary tract, and the expression levels varied between genders and among regions and tissue layers. The presence of these receptors suggests that gonadotrophins have a role in the physiology and/or pathology of the lower urinary tract function in the dog.

Why do river otters scent-mark? An experimental test of several hypotheses

We tested several alternative hypotheses about the function of scent marking by the North American river otter, Lontra canadensis. Otters may mark at latrine sites with spraints (faeces) to (1) signal species identity, (2) advertise their reproductive status, (3) establish and maintain territories, and (4) communicate social status and identity to group members. Olfactory preference tests were conducted at the Alaska Sealife Center in Seward, Alaska, on a group of 15 wild-caught male otters in February 1999. We found that male otters investigated otter scent more than sealion faeces. The male otters also showed a preference for male scent over the scent of anoestrous females. No preference for the scent of unfamiliar males, compared with the scent of familiar males, was observed, and no preference for the scent of close kin was detected. However, an investigation of dominant relationships of the captive otters showed that dominant males spent more time investigating male scent than did subordinate males. Thus, spraints deposited at latrine sites may function to communicate social status of males.

Management of photoperiod to control caprine reproduction in the subtropics

Reproductive seasonality is observed in some breeds originating from or adapted to subtropical latitudes. In ‘photoperiodic flexible breeds’, such as Australian cashmere goats, the annual breeding season can be manipulated through nutrition, whereas in ‘photoperiodic rigid breeds’, such as Creole goats from subtropical Mexico, sexual activity can be controlled by altering the photoperiod. In males from the latter breed, artificial long days, whether or not accompanied by the administration of melatonin, stimulate sexual activity during the non-breeding season. These treated males are able to induce the sexual activity of anoestrous females through the male effect under intensive or extensive conditions. Photoperiodic treatments and the male effect can be easily integrated into different breeding management systems in subtropical latitudes.

Scent-marking behaviour by male prairie voles, Microtus ochrogaster, in response to the scent of opposite- and same-sex conspecifics

We conducted an experiment using the prairie vole ( Microtus ochrogaster) to test predictions associated with the proposed functions of scent marking as a sexual attractant, in reproductive competition, and as a self-advertisement. We allowed an oestrous female, an anoestrous female, and an adult male to scent mark three portions of a clean substrate and then exposed a second male to this substrate for secondary marking. We did not support a sexual attraction hypothesis in that males did not place more scent marks in response to oestrous than anoestrous females. Similarly, we did not support a reproductive competition hypothesis in that males did not place more scent marks in response to marks of males than to those of females or bare substrate. Males did not overmark the scent of males or females and thus we did not support a scent-masking or scent-blending hypothesis. In that males deposited scent similarly in response to males, females, and on bare substrate, our results suggest that the frequency and placement of scent marks by males function primarily to advertise individual identity in an area.

Scent Marking in Female Prairie Voles: a Test of Alternative Hypotheses

We conducted three experiments with females in different stages of reproductive condition to test alternative hypotheses for the function of scent marking in female prairie voles, Microtus ochrogaster. The three reproductive categories were isolated females prior to sexual stimulation (anoestrous), sexually stimulated (oestrous) and lactating. Females in different reproductive condition were given the opportunity to scent mark clean unmarked substrate or areas that had previously been marked by adult females or adult males. The numbers of scent marks deposited by females did not differ statistically for females in different reproductive condition. However, there was a trend for anoestrous females to mark the most, oestrous females less, and lactating females the least. The lack of scent marking by lactating females might be to reduce conspicuousness to conspecifics or predators. Oestrous females tended to mark the most in the area marked previously by males, although the difference was not statistically significant.Our results provide some support for a mate‐attraction hypothesis and a territorial‐defense hypothesis, but were most consistent with a self‐advertisement hypothesis. Over marking was uncommon and did not differ by experiment or sex of previous donor. Our results suggest that the number and placement of scent marks by females are highly variable and function primarily to convey individual identity.

L’effet mâle chez les ovins : une technique actuelle de maîtrise de la reproduction

L’introduction des béliers dans un groupe de brebis en anoestrus anovulatoire induit dans les 2 à 4 jours une ovulation silencieuse, c’est-à-dire non associée à un comportement de chaleur, suivie soit par un cycle ovulatoire de durée ’normale’ (voisine de 17 jours) puis d’une nouvelle ovulation associée à un comportement de chaleur, soit par un cycle ovulatoire de durée courte mais constante (6 jours) suivi d’une nouvelle ovulation silencieuse puis, après un cycle ovulatoire de durée normale, par une nouvelle ovulation associée à un comportement d’oestrus.&#x0D; Il en résulte que les premières chaleurs apparaissent très tardivement chez les femelles dont l’activité sexuelle est induite par l’introduction des béliers, ce qui se traduit par deux pics d’activité sexuelle situés environ 18 à 20 jours et 24 à 26 jours après l’introduction des béliers. Les brebis non gravides reviennent normalement en oestrus sauf si l’anoestrus est intense au moment attendu de ces retours (plus de un mois après induction de la première ovulation).&#x0D; L’article présente les connaissances acquises ces dernières années sur les mécanismes physiologiques impliqués dans l’induction de l’ovulation par l’effet bélier et donne quelques règles d’utilisation de cette méthode dans les élevages, tout en précisant ses limites. Les deux points essentiels pour utiliser efficacement cette technique sont d’une part, la connaissance des aptitudes de reproduction (saisonnement) de la race dans son milieu et, d’autre part, la possibilité de séparer les mâles des femelles pendant une durée minimale de un mois préalablement à leur mise en contact physique.

Follicle development in cyclic, anoestrous and FSH-treated brushtail possums (Trichosurus vulpecula).

The common brushtail possum (Trichosurus vulpecula) is a pest of considerable economic importance in New Zealand. Attempts to develop methods of suppressing reproduction in this species are currently hampered by the lack of reliable methods to synchronise oestrus and ovulation in this species. The objective of this study was to compare antral follicle populations in anoestrous and cyclic brushtail possums and to assess the efficacy of exogenous FSH to induce follicle development in anoestrous animals. Ovaries were recovered from anoestrous possums after administration of either exogenous FSH (1.0 mg/injection) or the saline vehicle alone (0.5 ml/injection) at 12-h intervals for 3 days (n = 6/group), and from cyclic animals (n = 6) that were euthanised in mid-follicular phase (5 days after removal of their pouch young). All antral follicles > or =1.0 mm in diameter were dissected free of extraneous tissue, incubated in vitro to measure oestradiol production, and then processed for histological assessment of health status. Mean weight of ovaries and vaginal cul-de-sac tissues were both significantly greater (P<0.001) in FSH-treated anoestrous females (24.2+/-5.1 mg and 6.50+/-1.34 g, respectively), but did not differ significantly between saline-treated anoestrous possums (12.4+/-3.0 mg and 1.31+/-0.27 g) and cyclic animals (13.5+/-1.6 mg and 2.62+/-0.95 g). Mean uterine weights in both cyclic (889+/-161 mg) and FSH-treated (1098+/-184 mg) animals were significantly heavier(P<0.001) than those of anoestrous possums (414+/-61 mg). The mean number of follicles (> or =1.0-mm diameter) present was significantly greater (P<0.001) in FSH-treated, than in cyclic and anoestrous possums (38.0+/-4.4, 23.2+/-3.2 and 10.7+/-3.4 follicles/animal, respectively). Cyclic animals had significantly more (P<0.01) follicles than anoestrous possums. The proportion of follicles that were classified as healthy, was significantly lower (P<0.01) in cyclic possums(38%) than in anoestrous (69%) and FSH-treated (88%) animals. The mean diameter of the largest healthy follicle present was 2.5+/-0.41, 2.1+/-0.08, and 3.1+/-0.15 mm for cyclic, anoestrous and FSH-treated animals, respectively. None of the follicles harvested from saline-treated anoestrous possums produced measurable levels of oestradiol in vitro, whereas 7% and 59% of those from cyclic and FSH-treated animals did so. In summary, cyclic possums had more antral follicles present than anoestrous animals, but a lower percentage of these follicles were healthy. Less than 10% of healthy follicles from cyclic possums, and none of those from anoestrous animals, were capable of producing oestradiol when incubated in vitro. Treatment with ovine FSH promoted follicle development in anoestrous possums, to significantly increase the number of follicles present, the proportion that were healthy and the percentage capable of producing oestradiol.

Distribution and morphology of luteinising hormone-releasing hormone neurones in a species of wild antelope, the springbok (Antidorcas marsupialis).

The distribution and morphology of luteinising hormone-releasing hormone (LHRH) neurones varies between species. The primary purpose of this study was to characterize the distribution and morphology of the LHRH system in a species of antelope, the springbok. This wild antelope has a well-defined social structure in which reproductive activity is confined to a few dominant, territorial rams. We also sought to determine whether social or reproductive status could be accounted for by differences in the distribution or morphology of hypothalamic LHRH neurones. Eleven anoestrous female, nine breeding territorial male (TM) and eight "bachelor" male (BM) springbok were obtained, and their reproductive and body conditions were assessed. By using standard immunocytochemical techniques, the LHRH system was visualised in the brains of four animals from each group. Immunoreactive neurones were located in a continuum from the septum to the arcuate nucleus, with the majority at the level of the organum vasculosum of the lamina terminalis. Neither the distribution nor the number of cells differed among the three groups. Furthermore, the area of LHRH perikarya was similar in both groups of males, suggesting that reproductive differences between TMs and BMs lie at another level of the neuroendocrine axis. The anoestrous females had significantly larger neurones than males (TM plus BM). This may reflect a sex difference in the LHRH system of this wild antelope. However, an alternative explanation is that the male/female difference is related to the comparatively inactive reproductive neuroendocrine state of the females.

The effects of daily exposure to oestrous or anoestrous gilts and sows on the attainment of puberty in the gilt

Seventy Large White/ Landrace crossbred gilts were allocated by litter of origin and liveweight to one of five treatments: (1) no contact with stimulus animals (control); (2) daily exposure to an anoestrous gilt; (3) daily exposure to an oestrous gilt; (4) daily exposure to an anoestrous sow; (5) daily exposure to an oestrous sow. All treatments were imposed for 20 min daily from a mean gilt age of 159 days for 100 days. Fourteen ovariectomised female pigs were used to provide the treatments, seven of these being designated small (mean liveweight 78.9 ± 4.1 kg) and seven designated large (mean liveweight 192.0 ± 15.0 kg). These ovariectomised females were treated on a rotational basis with two daily injections of oestradiol benzoate (OB) to induce oestrus, oestrus being taken as days 4 and 5 following the first injection. Anoestrous females were selected from within the same group, but females that had been treated with the OB were not used from the day of injection for at least 10 days. Results show that a significantly higher proportion of gilts reached puberty within the experimental period when given daily contact with stimulus animals than when not stimulated ( P < 0.05). Exposure to large stimulus females tended to reduce gilt age at puberty (204.2 vs. 216.3 days) and significantly increased ( P < 0.05) the proportion of gilts attaining puberty by days 29 (0.46 vs. 0.15) to 40 (0.54 vs. 0.19) of the experimental period compared with exposure to small stimulus females. The sexual status of the exposure female exerted no influence on the timing of gilt puberty (mean age at puberty 210.3 vs. 207.7 days and proportion pubertal within the experimental period 0.82 vs. 0.85 for treatments involving exposure to anoestrous and oestrous females respectively). These data indicate that exposure to ‘strange’ females can induce early puberty in the gilt. They further suggest that differences in the stimulus value to prepubertal gilts of exposure to ‘strange’ female pigs may occur, and that any differences that do occur are likely to be due to the size, rather than the sexual status, of the exposure female.

Male influence on oestrous cycles in female woolly opossum (Caluromys philander)

Plasma progesterone concentrations and the occurrence of oestrous cycles were studied in isolated woolly opossums subsequently subjected to male influences during a 40-day period. Pairing (N = 48) or exposure to male urine (N = 15) resulted in all females exhibiting oestrous during the stimulation phase, providing evidence that the activation of ovarian activity in the woolly opossum involves pheromonal cues from males. The latency of occurrence of oestrous in stimulated females depended upon their sexual state before male stimulation. In anoestrous females, the mean latency was 20.7 +/- 0.9 days (N = 35), a value which agrees with the duration of the follicular phase. In females which first entered oestrous before male stimulation, the latency of induced oestrous was inversely correlated to the date of occurrence of the previous oestrous. The inter-oestrous interval was normal (38.1 +/- 1 days, N = 5) when females were in oestrous at the beginning of male stimulation. In contrast, the inter-oestrous interval was significantly shortened (28.7 +/- 2 days, N = 7) or lengthened (51.1 +/- 1.7 days, N = 16) depending on whether females were in the luteal or follicular phases at the beginning of male stimulation. During pairing several females became pregnant and gave birth 24 +/- 0.9 days (N = 13) after copulation. In the woolly opossum, the response to male influences involves mechanisms similar to those observed in eutherians and results in enhancement and synchronization of oestrous cycles in females. Pheromonal interactions could play an important role in synchronizing oestrous cycles in wild females during the dry season, a period when animals regroup to feed on spatially localized food resources.