Seasonal effects on the endocrine pattern of semi-captive female Asian elephants (Elephas maximus): timing of the anovulatory luteinizing hormone surge determines the length of the estrous cycle

Better breeding strategies for captive Asian elephants in range countries are needed to increase populations; this requires a thorough understanding of their reproductive physiology and factors affecting ovarian activity. Weekly blood samples were collected for 3.9 years from 22 semi-captive female Asian elephants in Thai elephant camps to characterize LH and progestin patterns throughout the estrous cycle. The duration of the estrous cycle was 14.6+/-0.2 weeks (mean+/-S.E.M.; n=71), with follicular and luteal phases of 6.1+/-0.2 and 8.5+/-0.2 weeks, respectively. Season had no significant effect on the overall length of the estrous cycle. However, follicular and luteal phase lengths varied among seasons and were negatively correlated (r=-0.658; P<0.01). During the follicular phase, the interval between the decrease in progestin concentrations to baseline and the anovulatory LH (anLH) surge varied in duration (average 25.9+/-2.0 days, range 7-41, n=23), and was longer in the rainy season (33.4+/-1.8 days, n=10) than in both the winter (22.2+/-4.5 days, n=5; P<0.05) and summer (18.9+/-2.6 days, n=8; P<0.05). By contrast, the interval between the anLH and ovulatory LH (ovLH) surge was more consistent (19.0+/-0.1 days, range 18-20, n=14). Thus, seasonal variation in estrous cycle characteristics were mediated by endocrine events during the early follicular phase, specifically related to timing of the anLH surge. Overall reproductive hormone patterns in Thai camp elephants were not markedly different from those in western zoos. However, this study was the first to more closely examine how timing of the LH surges impacted estrous cycle length in Asian elephants. These findings, and the ability to monitor reproductive hormones in range countries (and potentially in the field), should improve breeding management of captive and semi-wild elephants.     

Use of genital inspection and female urine tests to detect oestrus in captive Asian elephants

Captive Asian elephant (Elephas maximus) populations are decreasing due to low birth rates compared to wild elephants. Improving oestrous detection in female elephants is required to ensure successful mating in captive and semi-captive herds. Responsive behaviours of eight semi-captive bull elephants to the uro-genital area (genital inspection test) or urinary pheromones (urine test) of 14 female elephants throughout the oestrous cycle were evaluated. Weekly blood samples were collected for 27 consecutive months (14 months for the genital inspection test and 13 months for the urine test) from female elephants to characterize the patterns of circulating progestagen. Responsive behaviours of bulls were compared between females in the follicular versus the luteal phase of the cycle. The sensitivity and specificity of the genital inspection test were 65% and 68%, while those of the urine test were 52% and 61%, respectively. The bulls showed significantly higher “genital inspection”, “flehmen from genital area” and “trunk on back” behaviours during the genital inspection test, and “flehmen” behaviours during the urine test in oestrous than in non-oestrous females. In sum, this study showed that monitoring sexual behaviours of Asian elephant bulls towards females or their urine can be used to detect the oestrous period. Although the sensitivity and specificity of both tests were not as high as expected, still, these methods appear to be more efficient at detecting oestrous than traditional methods based on mahout estimations of female receptivity. The use of genital inspection and urine tests may lead to more successful matings and thus to creating self-sustaining populations of captive elephants in range countries.     

Fecal progesterone metabolites and ovarian activity in cycling and pregnant mountain gazelles (Gazella gazella)

Fecal reproductive progestagen monitoring in the mountain gazelle (Gazella gazella) provided a non-invasive method for tracking reproductive cycling, estimating age of sexual maturity and diagnosing pregnancy in this species of gazelle. Fresh fecal samples were collected from eight female mountain gazelle (Gazella gazella) for a period of two months. Two of the animals were pregnant while the other six were not. Using the progestagen profile the luteal phase, interluteal (follicular) phase and estrous cycle in adult female gazelles were determined to be 12.5 ± 1.2, 5.9 ± 0.59 and 18.8 ± 0.98 days respectively. Significant inter-animal differences in fecal progestagen concentration were observed in both the luteal and follicular phases. Significant differences were observed in the levels of fecal progestagen between cycling females and females in late pregnancy. Low concentrations of fecal progestagen in females aged less than 18 months old indicated that sexual maturity in captivity is not attained before that age.     

Reproductive cycle of the elephant

The combination of a few factors, including poor captive reproduction, secession of importation from the wild and advances in hormone detection and ultrasonography, has contributed to the current knowledge on the elephant reproductive cycle. Several reproductive features in elephants differ markedly from other mammals. These include the urogenital tract anatomy, length and structure of the reproductive cycle, the formation of multiple corpora lutea and the type and secretion pattern of reproductive hormones. Being 13-18 weeks in length, the elephant estrous cycle is the longest amongst all studied non-seasonal mammals to date. Progesterone increases 1-3 days after ovulation, indicating the start of the luteal phase, which lasts 6-12 weeks. This is followed by a 4- to 6-week follicular phase that is concluded by two, precisely spaced and timed, LH surges. In general, the first, anovulatory LH surge occurs exactly 19-21 days before the second, ovulatory surge. Normally, a single follicle is ovulated. However, beside a corpus luteum (CL) forming on the site of ovulation, multiple accessory CLs can be found on the ovaries. Unlike many other species, the predominant progestagen secreted by luteal tissues is not progesterone, but rather its 5-alpha-reduced metabolites. The currently known aspects of the unique estrous cycle in Asian and African elephants, covering estrous behavior, circulating hormones, ultrasonography and anatomy of the reproductive organs as well as hormonal manipulation treatment possibilities, will be reviewed here.     

Behavioral indices of estrus in a group of captive African elephants (Loxodonta africana)

This study investigated behavioral signals of estrus by systematically monitoring the interactions of one male with four female African elephants housed in a naturalistic outdoor enclosure at Disney's Animal Kingdom over a period of 11 months. We measured changes in five spatial behaviors and 22 tactile‐contact behaviors, as well as changes in serum progestagen and LH concentrations, across three ovarian cycles for each female. Two females did not cycle during the study. Three different phases of the ovarian cycle were identified: mid luteal, anovulatory follicular, ovulatory follicular. The male followed more and carried out more genital inspections, flehmen, and trunk‐to‐mouth behaviors toward cycling females during their ovulatory phase. Genital inspections by the male peaked above baseline levels on the day of an LH surge, and up to 9 days before, in both cycling females and, thus, might be a useful behavioral index of estrus. The male also carried out more genital inspections, flehmen, and trunk touches to the back leg toward ovulatory cycling than noncycling females. Overall, our results indicated that: 1) a single subadult African elephant male could discriminate two females in the ovulatory phase of their cycle (i.e., during the 3 weeks preceding ovulation) from the mid luteal phase; 2) the male also discriminated two cycling females in the ovulatory and anovulatory follicular phases from two noncycling females; 3) two females in the ovulatory phase of the cycle displayed a greater variety of tactile‐contact behavior toward the male compared to the other cycle phases. Zoo Biol 0:1–19, 2005. © 2005 Wiley‐Liss, Inc.     

Oestrous state dynamics in chemical communication by captive female Asian elephants

In many mammals, reproductive status is revealed through chemical cues in urine. The reproductive status of receivers may influence their interest in such signals. For social mammals that live in matrilineal groups, females may benefit by detecting the reproductive condition of herdmates. Responses to urine during oestrous cycles of senders and receivers are potential indicators of signal functions. We examined the chemosensory responses, first by four captive female Asian elephants,Elephas maximus , over their oestrous cycles to familiar follicular and luteal phase urine and second by 14 different female Asian elephants to unfamiliar conspecific follicular and luteal phase urine. We asked whether females could distinguish the reproductive state of another female as measured by their differential response to luteal- and follicular-phase urine. We further examined the influence of the receiver's reproductive status on response levels. Females responded more with specific tactolfactory trunk behaviours to follicular- than to luteal-phase urine, but only when the receiving female was in her follicular phase. Like their male conspecifics, Asian elephant females can detect changes in the reproductive state of conspecifics. The functional significance of this ability has yet to be determined but may be related more to the resource holding power of females in follicular phase than to a means for females to synchronize oestrous cycles. Such female-female communication may have important effects on social group dynamics. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Ovarian function in the elephant: luteinizing hormone and progesterone cycles in African and Asian elephants

Serum samples were collected weekly for 3 yr from two female African elephants, for 18 mo from two other female African elephants, and for 2 yr from two female Asian elephants. Animals were not sedated at the time of blood collection. Ovarian cycles, characterized by changes in progesterone and immunoreactive luteinizing hormone (ILH) concentrations, averaged 15.9 +/- 0.6 wk (N = 25) for African females and 14.7 +/- 0.5 wk for Asian females (N = 10). The length of the active luteal phase averaged 10.0 +/- 0.3 wk for African elephants (range 8-14 wk) and 10.6 +/- 0.6 wk for Asian females (range 9-13 wk). Interluteal phases were 5.9 +/- 0.6 wk for African females and 4.2 +/- 0.5 wk for Asian females. One African female (Maliaca) had two extended interluteal phases, both occurring between the months of February and May. Excluding these two periods, there were no differences in the length of the ovarian cycle or the length of the luteal phase between species of elephant. Serum progesterone in both species ranged from less than 50 pg/ml to 933 pg/ml. Average progesterone concentrations during the luteal phase were significantly lower in African elephants compared with Asian elephants (328 +/- 13, N = 30 cycles vs. 456 +/- 23, N = 14 cycles; p less than 0.001). ILH ranged from nondetectable to 11.6 ng/ml. These data suggest that the length of the ovarian cycle in the African elephant is about 16 wk and confirm that the length of the ovarian cycle in the Asian elephant is about 15 wk.     

Non-invasive assessment of the reproductive cycle in free-ranging female African elephants (Loxodonta africana) treated with a gonadotropin-releasing hormone (GnRH) vaccine for inducing anoestrus

ABSTRACT: BACKGROUND: In southern Africa, various options to manage elephant populations are being considered. Immunocontraception is considered to be the most ethically acceptable and logistically feasible method for control of smaller and confined populations. In this regard, the use of gonadotropin-releasing hormone (GnRH) vaccine has not been investigated in female elephants, although it has been reported to be safe and effective in several domestic and wildlife species. The aims of this study were to monitor the oestrous cycles of free-ranging African elephant cows using faecal progestagen metabolites and to evaluate the efficacy of a GnRH vaccine to induce anoestrus in treated cows. METHODS: Between May 2009 - June 2010, luteal activity of 12 elephant cows was monitored non-invasively using an enzyme immunoassay detecting faecal 5alpha-reduced pregnanes (faecal progestagen metabolites, FPM) on a private game reserve in South Africa. No bulls of breeding age were present on the reserve prior to and for the duration of the study. After a 3-month control period, 8 randomly-selected females were treated twice with 600 micrograms of GnRH vaccine (Improvac[REGISTERED SIGN], Pfizer Animal Health, Sandton, South Africa) 5-7 weeks apart. Four of these females had been treated previously with the porcine zona pellucida (pZP) vaccine for four years (2004-2007). RESULTS: All 12 monitored females (8 treated and 4 controls) showed signs of luteal activity as evidenced by FPM concentrations exceeding individual baseline values more than once. A total of 16 oestrous cycles could be identified in 8 cows with four of these within the 13 to 17 weeks range previously reported for captive African elephants. According to the FPM concentrations the GnRH vaccine was unable to induce anoestrus in the treated cows. Overall FPM levels in samples collected during the wet season (mean 4.03 micrograms/gram dry faeces) were significantly higher (P<0.002) than the dry season (mean 2.59 micrograms/gram dry faeces). CONCLUSIONS: The GnRH vaccination protocol failed to induce anoestrus in the treated female elephants. These results indicate that irregular oestrous cycles occur amongst free-ranging elephants and are not restricted to elephants in captivity. The relationship between ecological conditions and endocrine activity were confirmed. Free-ranging female elephants were observed to not cycle continuously throughout the year in the absence of adult bulls.     

Role of the double luteinizing hormone peak, luteinizing follicles, and the secretion of inhibin for dominant follicle selection in Asian elephants (Elephas maximus)

Elephants express two luteinizing hormone (LH) peaks timed 3 wk apart during the follicular phase. This is in marked contrast with the classic mammalian estrous cycle model with its single, ovulation-inducing LH peak. It is not clear why ovulation and a rise in progesterone only occur after the second LH peak in elephants. However, by combining ovarian ultrasound and hormone measurements in five Asian elephants (Elephas maximus), we have found a novel strategy for dominant follicle selection and luteal tissue accumulation. Two distinct waves of follicles develop during the follicular phase, each of which is terminated by an LH peak. At the first (anovulatory) LH surge, the largest follicles measure between 10 and 19.0 mm. At 7 ± 2.4 days before the second (ovulatory) LH surge, luteinization of these large follicles occurs. Simultaneously with luteinized follicle (LUF) formation, immunoreactive (ir) inhibin concentrations rise and stay elevated for 41.8 ± 5.8 days after ovulation and the subsequent rise in progesterone. We have found a significant relationship between LUF diameter and serum ir-inhibin level (r(2) = 0.82, P < 0.001). The results indicate that circulating ir-inhibin concentrations are derived from the luteinized granulosa cells of LUFs. Therefore, it appears that the development of LUFs is a precondition for inhibin secretion, which in turn impacts the selection of the ovulatory follicle. Only now, a single dominant follicle may deviate from the second follicular wave and ovulate after the second LH peak. Thus, elephants have evolved a different strategy for corpus luteum formation and selection of the ovulatory follicle as compared with other mammals.     

Estrous state influences on investigative,aggressive, and tail flicking behavior in captive female Asian elephants

Females of species that live in matrilineal hierarchies may compete for temporally limited resources, yet maintain social harmony to facilitate cohesion. The relative degree of aggressive and nonaggressive interactions may depend on the reproductive condition of sender and receiver. Individuals can benefit by clearly signaling and detecting reproductive condition. Asian elephants (Elephas maximus) live in social matrilineal herds. Females have long estrous cycles (14–16 weeks) composed of luteal (8–12 weeks) and follicular (4–8 weeks) phases. In this study, we observed the behavior of four captive Asian elephant females during multiple estrous cycles over 2 years. We evaluated whether investigative, aggressive, and tail flicking behaviors were related to reproductive condition. Investigative trunk tip contacts showed no distinct pattern by senders, but were more prevalent toward female elephants that were in their follicular compared with their luteal phase. The genital area was the most frequently contacted region and may release reproductively related chemosignals. Aggression did not differ significantly with estrus; however, rates of aggression were elevated when senders were approaching ovulation and receivers were in the luteal phase. Females in the follicular phase may honestly advertise their condition. Contacts by conspecifics may serve to assess condition and reduce aggression. A behavior termed “tail flicking” was performed mainly during the mid‐follicular phase when estrogen and luteinizing hormone levels are known to spike. Tail flicking may disperse chemical signals in urine or mucus as well as act as a tonic signal that could provide a means of anticipating forthcoming ovulation by elephants and also for human observers and caretakers. Zoo Biol 27:167–180, 2008. © 2008 Wiley‐Liss, Inc.     

Interrelationship of serum testosterone, dominance and ovarian cyclicity status in female African elephants

The African elephant population in North American zoos is not self-sustaining, in part due to the prevalence of ovarian acyclicity. While little is known about the cause of this condition, earlier research has shown that females without cyclic corpus luteum (CL) function rank higher in the dominance hierarchy than females with cyclic CL function. The goal of this study was to measure longitudinal serum testosterone concentrations in captive female African elephants to determine if there is a relationship among serum testosterone concentrations, social dominance rank and ovarian cyclicity status. Weekly blood samples from 49 female African elephants (24 having and 25 not having cyclic CL function at 22 facilities) were collected over a 12-month period and analyzed for serum testosterone using an enzymeimmunoassay. A progesterone radioimmunoassay was used to quantify serum progestagen concentrations and categorize ovarian cyclicity status. The dominance hierarchy of individual elephants within each herd was assessed by a written temperament survey, which identified 19 dominant, 15 middle and 15 subordinate females. No clear patterns of serum testosterone secretion were observed in females with and without cyclic CL function. Furthermore, no significant relationships were found among serum testosterone concentrations, dominance rank, and ovarian cyclicity status. These data suggest that increased circulating testosterone concentrations are not associated with greater rates of ovarian acyclicity or dominance status in captive female African elephants.     

The use of low-frequency vocalizations in African elephant(Loxodonta africana) reproductive strategies

Fertility-advertisement calls in females are predicted to occur in nonmonogamous species where males and females are widely separated in space. In African elephants, low-frequency vocalizations have thus been suggested as a reproductive strategy used by fertile females to attract mates. This study examined the use of low-frequency vocalizations with respect to different phases of the estrous cycle in African elephants by simultaneously monitoring vocalizations, behavior, and hormonal profiles. Subjects were one male and six female African elephants housed at Disney's Animal Kingdom. No acoustically distinct vocalizations were restricted to the ovulatory follicular phase. However, overall rate of low-frequency vocalization as well as the rate of one acoustically distinct vocalization changed over the estrous cycle, with highest rates of calling related to the first period of follicular growth, or anovulatory follicular phase. Elevated rates of vocalization thus were not restricted to behavioral estrus and occurred much earlier in the estrous cycle than in most species that produce fertility-advertisement calls. Both herd composition and elephant identity also affected rates of vocalization. Vocalizations therefore may not be reliable signals of actual fertility. However, the increase in vocalizations in advance of estrus may attract males to the herd prior to ovulation, facilitating both male-male competition and female choice. Once present in the herd, males may then switch strategies to use more reliable chemical and visual cues to detect ovulating females.     

Monitoring ovarian cycles and pregnancy in brown brocket deer (Mazama gouazoubira) by measurement of fecal progesterone metabolites

In the present study, pregnancy and the estrous cycle were monitored in captive brown brocket deer (Mazama gouazoubira) by measuring fecal progestagens with a commercial enzyme immunoassay (EIA), along with behavioral data. Fecal samples were collected twice a week during pregnancy and daily during the estrous cycle and post-partum period. It was possible to distinguish between inter-luteal and luteal phases of the estrous cycle. Behavioral estrus corresponded with low concentrations of fecal progestagens. Samples from two consecutive cycles were available from five hinds, and the mean estrous cycle (n=10) was 26.9+/-1.7 d (mean+/-S.E.M.). However, when two extreme cycles (34 and 37 d) were deleted, the mean estrous cycle was 24.7+/-1.2 d. Three animals became pregnant (gestation ranged from 208 to 215 d). After fertile breeding, progestagen concentration in these hinds remained among luteal phase concentrations throughout pregnancy, with the exception of a few peaks. Within 4 d post-partum, two hinds reached interluteal phase values, while one hind maintained luteal concentrations for at least 1 week.     

Increasing ovulation rate and lambing rate in sheep by treatment with a steroid enzyme inhibitor

Treatment of ewes with a 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) inhibitor (Epostane) resulted in a significant increase in both ovulation rate and in the mean number of lambs per ewe lambing. The progestagen sponge plus 3 beta-HSD inhibitor treatment also caused a significant increase in oestrous cycle duration of approximately 1.5 days. Treatment of ewes with the 3 beta-HSD inhibitor caused a significant decrease in peripheral progesterone concentrations, which were reduced even further when 3 beta-HSD inhibitor treatment was given to ewes after insertion of a progestagen sponge. However, mean oestradiol concentrations were significantly higher in the two treatment groups, both at the end of the luteal phase and during the follicular phase of the oestrous cycle. These results demonstrate that ovulation rate and the production of lambs per ewe lambing can be significantly increased by 3 beta-HSD inhibitor treatment.     

Effect of sex hormones on neuromuscular control patterns during landing.

The purpose of the study was to investigate the effects of sex hormones across menstrual cycle phases on lower extremity neuromuscular control patterns during the landing phase of a drop jump. A repeated-measures design was utilized to examine sex hormone effects in 26 recreationally active eumenorrheic women. Varus/valgus knee angle and EMG activity from six lower extremity muscles were recorded during three drop jumps from a 50 cm platform in each phase of the menstrual cycle. Blood assays verified sex hormone levels and cycle phase. The semitendinosus muscle exhibited onset delays (p0.006) relative to ground contact during the luteal phase, and demonstrated a significant (p0.05) difference between early and late follicular phases. Muscle timing differences between the gluteus maximus and semitendinosus were decreased (p0.05) in the luteal compared to early follicular phases. These results suggest a different co-contractive behavior between the gluteus maximus and semitendinosus, signifying a shift in neuromuscular control patterns. It appears that female recreational athletes utilize a different neuromuscular control pattern for performing a drop jump sequence when estrogen levels are high (luteal phase) compared to when they are low (early follicular phase).     

Assessment of ovarian activity in captive goral (Naemorhedus griseus) using noninvasive fecal steroid monitoring

To date, there is no information on gonadal steroidogenic activity of female goral (Naemorhedus griseus), a threatened species of Thailand. Captive goral populations have been established to produce animals for ex situ conservation and reintroduction, but as yet none are self-sustaining. The objectives of the present study were to (1) determine the influence of season on ovarian steriodogenic function; and (2) examine the relationship between gonadal hormone excretion and sexual behaviors throughout the year. Fecal samples were collected 5 to 7 days/wk for 15 months from 8 adult females housed at Omkoi Wildlife Breeding Center in Thailand and analyzed for ovarian steroid metabolites using validated enzyme immunoassays. Observations of sexual behaviors and mating were conducted each morning for 30 min/session. Based on fecal estrogen and progestagen metabolite concentrations, the overall estrous cycle length was about 21 days, with a 2- to 3-day follicular phase and an 18- to 20-day luteal phase. Sexual behaviors, most notably tail-up, increased for 2 to 3 days during the time estrogens were elevated during mating. Fecal progestagens were elevated during luteal phases and increased further during gestation, which lasted approximately 7 months. The lactation period was 5 months, and females were anestrus for 2 to 5 of those months, with the exception of one that cycled continuously throughout. Two females conceived around 2 months postpartum and so were pregnant during lactation. Birth records over the past 21 years indicated young are born throughout the year. This combined with the hormonal data suggests that female gorals are not strongly seasonal, at least in captivity, although there was considerable variation among females in estrogen and progestagen patterns. In conclusion, fecal steroid metabolite monitoring is an effective means of assessing ovarian function in this species and will be a useful tool for breeding management and planned development of assisted reproductive techniques such as artificial insemination and embryo transfer.     

Concentrations of progesterone,testosterone and estradiol-17β in the serum during the estrous cycle of Asian elephants (Elephas maximus)

The levels of progesterone, testosterone and estradiol-17β in serum samples from two female Asian elephants were measured for the period of 32 months from February 1987 to September 1989. Serum samples were collected weekly from unanesthetized elephants. Each elephant showed eight ovarian cycles in 32 months. Ovarian cycles, characterized by changes in concentrations of serum progesterone, averaged 16.8 ± 0.6 (mean ± SEM. n = 14) weeks in length. The changes in concentrations of testosterone in the serum showed a similar pattern to those of progesterone with a striking increase noted during the luteal phase. The highest levels of serum estradiol-17β were noted when progesterone levels showed low basal values. These results suggest that estradiol-17β may be an index of follicular maturation during the estrous cycle in Asian elephants, and that the ovaries of Asian elephants may produce testosterone in the luteal phase.     

Modeling population viability of captive elephants in Myanmar (Burma): implications for wild populations

Captive Asian elephants Elephas maximus , used as work animals, constitute up to 22–30% of remaining Asian elephants. Myanmar has the largest captive population worldwide (∼6000), maintained at this level for over a century. We used published demographic data to assess the viability of this captive population. We tested how this population can be self-sustained, how many elephants must be supplemented from the wild to maintain it, and what consequences live capture may have for Myanmar's wild population. Our results demonstrate that the current captive population is not self-sustaining because mortality is too high and birth rates are too low. Our models also suggest ∼100 elephants year⁻¹ have been captured in the wild to supplement the captive population. Such supplementation cannot be supported by a wild population of fewer than 4000 elephants. Given the most recent expert estimate of ∼2000 wild elephants remaining in Myanmar, a harvest of 100 elephants year⁻¹ could result in extinction of the wild population in 31 years. Continued live capture threatens the survival of wild and captive populations and must stop. In addition, captive breeding should be increased. These measures are essential to slow the decline and extinction of all of Myanmar's elephants.     

The menstrual cycle and its effect on behaviour in the Talapoin monkey (Miopithecus talapoin)

The menstrual cycles of 14 captive Talapoin monkeys ( Miopithecus talapoin ) were studied by making serial observations on the vaginal smears and sexual skin swellings for up to 15 months. Twelve of these females menstruated and the mean duration of their cycle was32–9 days (95% confidence limits 28.0-37.7). The corresponding value for the seven most regular females was 33.0 days (29.1-36.8). There were rhythmic changes in the vaginal smears and sexual skin during the menstrual cycle. Maximum cornification of the smears and maximum sexual skin swelling were observed at midcycle; the sexual skin deflated and the smear became less cornified during the luteal phase. The follicular phase—i.e. from menstruation to maximum skin swelling lasted 20.4 days with a wide distribution, in contrast to the mean duration of the luteal phase (13.7 days) which showed a pronounced peak at 14 days. The menstrual cycle of the talapoin thus resembles those of certain other Old World monkeys that exhibit perineal sexual skin swelling.
Sexual behaviour of the male and female was maximal near the female's midcycle and minimal during the luteal phase, with intermediate values in the follicular phase. The males were most aggressive towards other females of the group when one female was at midcycle; there were no consistent changes in aggression between the male and the female herself. The number of times one animal looks at another (a characteristic behaviour pattern in talapoins) was measured and occurred most often at midcycle, but other preliminary observations indicated a more pronounced correlation between this behaviour pattern and an animal's position in the hierarchy.     

社群压力对圈养雌性亚洲象动情的影响

亚洲象是中国一级濒危保护动物,改善圈养亚洲象的繁殖状况是亚洲象保护工作的重要内容之一。本研究旨在通过分析社群压力对圈养雌性亚洲象应激和动情状况的影响,从而探究圈养雌性亚洲象长期不动情的原因。通过放射性免疫法检测雌性亚洲象尿液中皮质醇、孕酮和雌二醇水平以及粪便中皮质醇和雌二醇水平,以雌激素水平反映亚洲象的动情状况,以皮质醇水平反映亚洲象的应激状态,以争斗行为和友好行为的发生情况反映圈养群体的社群压力。研究发现：(1)处于优势地位的个体表现出更多的斗争行为,处于从属地位的个体受到更多的攻击行为;(2)优势个体的皮质醇水平显著高于处于从属地位个体的皮质醇水平;(3)优势个体的雌二醇和孕酮具有小幅周期性波动,而从属个体的雌二醇和孕酮水平没有表现出明显的波动。从本研究结果可以看出圈养亚洲象群体中优势个体对从属个体的行为抑制可能是导致从属个体雌激素水平低,长期不能参与繁殖的原因。