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.

Natural and gonadotropin-induced ovarian activity in tigers (Panthera tigris) assessed by fecal steroid analyses.

Fecal samples were collected from female tigers (n = 17) to compare endocrine patterns associated with natural ovarian activity with those after chorionic gonadotropin ovulation induction and artificial insemination (AI). Baseline fecal estradiol concentrations were 65.77 +/- 3.61 ng/g with estrual peaks of 167.39 +/- 9.92 ng/g and an anovulatory cycle length of 17.96 +/- 0.70 days. Peak fecal estradiol was higher when females were housed with a male for breeding (262.30 +/- 41.43 vs. 165.30 +/- 3.67 ng/g; P < 0.05). The majority of animals showed some seasonal differences in fecal estradiol however, patterns were inconsistent. Fecal progestagens increased only after breeding confirming tigers are primarily induced ovulators. The non-pregnant luteal phase was 34.50 +/- 1.85 days in duration. In pregnant tigers, fecal progestagens remained elevated for 108 days until parturition and the diagnosis of pregnancy was possible based on the elevated fecal progestagens after 35 days of gestation. Tigers were administered equine chorionic gonadotropin (eCG) to stimulate follicular growth and human chorionic gonadotropin (hCG) to induce ovulation prior to AI [200 IU eCG/100 IU hCG (n = 5); 400 IU eCG/200 IU hCG (n = 2); 500 IU eCG/100 IU hCG (n = 2); 1000 IU eCG/750 IU hCG (n = 11); 1000 IU eCG/1000 IU hCG (n = 4)]. None of the tigers subjected to AI became pregnant (n = 9). Fecal endocrine patterns in gonadotropin-stimulated tigers were considerably different from those observed in naturally bred tigers. In particular, fecal estradiol concentrations were higher than those observed during natural estrus and remained elevated for longer periods of time in tigers administered the higher doses of gonadotropins typically used in conjunction with AI in this species. These abnormal endocrine patterns may help explain the poor success rate of AI in this species.

Influence of oral melatonin on natural and gonadotropin-induced ovarian function in the domestic cat.

Ovarian hyperstimulation after exogenous gonadotropin stimulation is believed to be a cause of poor success after artificial insemination (AI) in felids. The objectives of this study were to assess the effect of oral melatonin on endogenous ovarian activity in the domestic cat and subsequent eCG/hCG-induced ovarian activity. Serum melatonin concentrations peaked approximately 1h after a single oral dose of 30 mg melatonin and remained elevated above endogenous day-time concentrations for >8h. The calculated circulating half-life (mean +/- S.E.M) of oral melatonin was 45.4+/-3.5 min, and the elimination rate constant (k(10)) was 55.2+/-4.2 min(-1). Oral melatonin (30 mg per day) administered 3h before lights-off effectively and reversibly suppressed estrous elevations in fecal estrogens after 25 days of treatment. There was a progressive decrease in baseline estrogen concentrations from inter-estrous concentrations after 25 days of treatment to below inter-estrous concentrations after 35 days of treatment. Oral melatonin treatment (30 mg per day for 30 days) prior to eCG/hCG administration only marginally reduced ancillary follicle development and had no significant effect on the quantity or quality of embryos produced by AI. Thus, oral melatonin effectively inhibited endogenous ovarian activity and had no adverse impact on embryo quality after AI in the domestic cat; however, this treatment was only marginally effective in minimizing eCG/hCG-induced ovarian hyperstimulation.

Liquid storage of Asian elephant (Elephas maximus) sperm at 4 degrees C.

The Asian elephant (Elephas maximus) population in the wild has been in decline for several decades and breeding in captivity has not been self-sustaining. The use of artificial insemination (AI) can help overcome many of the difficulties associated with breeding elephants in captivity; however, the ability to store semen for extended periods of time is critical to the successful application of AI to elephants. The objective of the present study was to assess the effects of four different semen extenders and the presence of egg yolk on the viability and motility of Asian elephant semen stored at 4 degrees C. High quality ejaculates (n=4) were collected from two Asian elephant bulls by rectal massage. Aliquots of each ejaculate were extended in four different diluents (Beltsville thawing solution (BTS); Tris-citric acid (TCA)/fructose-based; Beltsville F5 (BF5); dextrose-supplemented phosphate-buffered saline (PBS)) with or without egg yolk then cooled and stored at 4 degrees C. The percentages of viable (viability) and motile (motility) sperm were evaluated at 8, 24 and 48 h following collection. The addition of egg yolk significantly reduced the percentage loss in viability from initial collection to 48 h compared to extenders without egg yolk (17.0 +/- 8.2 versus 32.6 +/- 8.9 decline in percent viable sperm in the population, respectively; P<0.05). Extender and egg yolk affected (P<0.005) total motility and percent progressively motile sperm at all evaluation times during incubation. TCA + egg yolk maintained higher (P<0.05) levels of progressive motility compared to other extenders supplemented with egg yolk. These results indicate that Asian elephant semen extended in TCA diluent supplemented with egg yolk can maintain at least 50% viability and motility when stored at 4 degrees C for 48 h.

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.

Ovarian function in the Nile hippopotamus and the effects of Depo-Provera administration.

The preliminary results of an investigation into the reproductive endocrinology of the hippopotamus (Hippopotamus amphibius) and the effects of the progestin Depo-Provera on ovarian function are presented. Faecal progestagen analysis indicated that hippos have an oestrous cycle of 29.2 +/- 0.9 days and faecal progestagen concentrations of 323.6 +/- 31.4 ng g(-1) during the luteal phase. Concentrations were higher (765.9 +/- 162.4 ng g(-1); P < 0.05) during pregnancy than during the luteal phase and remained high until parturition. A lactational anoestrus was usually, but not always, observed during nursing. The onset of puberty was observed in three animals and started at 2.5-3.5 years of age. After Depo-Provera treatment, increases in faecal progestagens indicative of ovulation were observed and were not significantly different from luteal concentrations observed before treatment (236.3 +/- 24.4 versus 340.1 +/- 47.9 ng g(-1), respectively); however, the duration of the luteal phase was shorter (P < 0.05) than before treatment (11.3 +/- 1.0 versus 18.9 +/- 1.0 days, respectively). Females returned to normal cyclicity at day 100.7 +/- 15.3 (range 70-116 days) after administration and one female conceived on day 100 after administration.

Seasonal analysis of semen characteristics, serum testosterone and fecal androgens in the ocelot (Leopardus pardalis), margay (L. wiedii) and tigrina (L. tigrinus).

Captive adult male ocelots (Leopardus pardalis, n = 3), margays (L. wiedii, n = 3) and tigrinas (L. tigrinus, n = 4) in two locations in southern Brazil were studied for 14 consecutive months to evaluate the effect of season on testicular function. Reproductive evaluations, including testicular measurements, electroejaculation and blood collection were conducted monthly. Fecal samples were collected weekly for androgen metabolite analysis to assess testicular steroidogenic activity. Ocelots had the highest number of motile spermatozoa in the ejaculate (114.7+/-15.8 x 10(6); P < 0.05), the highest percentage of morphologically normal spermatozoa (82.4+/-1.2%; P < 0.05) and the highest concentration of fecal androgens (1.71 vs. 0.14 microg/g; P < 0.05). Margays and tigrinas had lower numbers of motile spermatozoa (23.4+/-2.8 x 10(6), 74.2+/-8.9 x 10(6), respectively), lower percentages of morphologically normal spermatozoa (57.4+/-2.8, 59.2+/-3.5%, respectively), and lower fecal androgen concentrations (0.15+/-0.01, 0.23+/-0.01 microg/g, respectively). Serum testosterone concentrations were similar among the three species. Fecal androgen concentrations were not affected by season, with the exception of the ocelot where concentrations were higher (P < 0.05) in the summer. Ejaculates were collected throughout the year; however, peaks in average sperm production were observed during the summer for all species. In summary, this study has identified several species differences in male testicular traits among ocelots, margays and tigrinas. Results of longitudinal reproductive assessments suggest males of each species are capable of breeding throughout the year.

Reproductive steroid hormones and ovarian activity in felids of the Leopardus genus.

Reproductive endocrine patterns were characterized in female ocelots (Leopardus pardalis; n = 3), tigrinas (Leopardus tigrinus; n = 2), and margays (Leopardus wiedii; n = 2) housed in captivity in southern Brazil. Females were maintained as singletons and exposed to natural fluctuations in photoperiod. Cyclic changes in ovarian steroids were monitored by analyzing estrogen and progestogen metabolites in fecal samples collected five times weekly for 14 to 18 months. Based on intervals between fecal estrogen peaks, mean (+/- SEM) duration of the estrous cycle was 18.4 +/- 1.6 days for the ocelots (range, 7-31 days; n = 75 cycles), 16.7 +/- 1.3 days for the tigrinas (range, 11-27 days; n = 23 cycles), and 17.6 +/- 1.5 days for the margays (range, 11-25 days; n = 32 cycles). Fecal progestogen analyses combined with two laparoscopic observations of the ovaries confirmed that ocelots and tigrinas did not ovulate spontaneously. In contrast, non-mating-induced luteal phases of 40.1 +/- 6.3 days in duration (range, 30-60 days) were observed frequently in both margays. There was no evidence of gonadal seasonality in margays in either follicular or luteal activity. In ocelots, cyclic changes in estrogen excretion were observed during each month of the year; however, only one female cycled continuously. In the other two ocelots, periods of acyclicity of several months' duration were observed. It was not possible to conclude whether tigrinas were aseasonal because estrous cyclicity was observed in only one of two individuals. In the female that cycled, a 3-month period of acyclicity was observed in the late fall/early winter. These data demonstrate similarities among three felid species of the genus Leopardus, including evidence they are polyestrous but experience unexplained periods of ovarian inactivity. Only the margays differed by exhibiting occasional spontaneous, non-mating-induced ovulations. Historically, these species have not bred well in captivity. However, it is hoped that understanding the biological similarities and differences among them could lead to improved management strategies that may one day result in increased reproductive success. Zoo Biol 20:103-116, 2001. Copyright 2001 Wiley-Liss, Inc.

Understanding the basic reproductive biology of wild felids by monitoring of faecal steroids.

The ability to track gonadal activity is essential for understanding the fundamentals of reproduction. Faecal steroid metabolite monitoring is a well established tool for evaluating reproductive processes in diverse mammalian species, including felids. Domestic cats were used as a model and injection of radiolabelled oestradiol, progesterone, testosterone and cortisol revealed that > 85% of metabolites were excreted in faeces with a time lag of 12-24 h. Steroids were extracted by boiling faecal material (wet or dry) in 90% aqueous ethanol followed by immunoassay with group-specific antibodies that crossreact with excreted metabolites. This approach was used to illustrate the diversity of oestrous cycle characteristics, gonadal responses to photoperiod and ovulatory sensitivity within the felid taxon. Longitudinal analyses demonstrated that faecal oestradiol increases with observed oestrus, and that the duration of the oestrous cycle varies among felid species. Seasonality in gonadal activity was observed in some species (for example clouded leopard, Pallas' cat), whereas other species (for example margay, cheetah, oncilla) are cyclic all year round. Although cats are considered induced ovulators, non-mating and spontaneous ovulation occurred in some species (for example domestic cat, clouded leopard, lion, leopard, margay) with varying frequency. There was also evidence that suppressed ovarian activity and oestrus occurred in group-housed cats (for example cheetahs). As assisted reproductive techniques, such as artificial insemination, are becoming increasingly important for managing zoo species, steroid metabolite monitoring has been especially useful for examining the efficacy of associated hormonal therapies. Exogenous gonadotrophins used to induce ovulation often caused ovarian hyperstimulation, which resulted in a maternal endocrine environment that differed from that of naturally mated cats. Finally, there is evidence that the adrenal status of animals managed under different husbandry conditions can be assessed non-invasively, thereby enhancing our understanding of how social and environmental factors affect animal well-being and reproductive fitness. In summary, understanding the basic endocrinology of endangered felids generates knowledge that can be used to improve management strategies. Because of its enormous utility and non-invasive nature, faecal hormone monitoring is one of the most powerful tools available in zoo research today.

Chorionic gonadotropin administration in domestic cats causes an abnormal endocrine environment that disrupts oviductal embryo transport.

Fecal steroid analysis was used to investigate relationships between endocrine parameters and embryo characteristics in domestic cats subjected to chorionic gonadotropin stimulation and artificial insemination (AI). In Study 1, normal endocrine patterns were assessed in 12 cycling domestic queens. Fecal estradiol (E) patterns established an anovulatory cycle length of 18.3 +/- 0.4 d with estrus lasting 6.3 +/- 0.3 d. Eight females (67%) exhibited at least one spontaneous ovulation based on sustained increases in fecal progestagens (P). In Study 2, queens were mated during natural estrus (NE, n = 5) or subjected to exogenous i.m. gonadotropin stimulation, 100 IU eCG followed by 75 IU hCG 80 h later, (GS, n = 5). Compared with NE queens, fecal E concentrations were higher (P < 0.05) and remained elevated longer after ovulation induction with hCG. In Study 3, gonadotropin-stimulated queens (n = 7) were artificially inseminated and ovariohysterectomized 160 h after hCG. Ancillary follicles and/or corpora lutea were observed in 5 of 6 (83%) ovulating queens. Both fecal E and number of unovulated follicles observed at ovariohysterectomy were negatively correlated with the percentage of embryos recovered from the uterus (r = -0.91 and r = -0.87, respectively; P < 0.05). In summary, exogenous gonadotropin administration causes an abnormal endocrine environment in domestic cats, likely due to ancillary follicle development. The sustained elevations in estradiol appear to impair oviductal transport of embryos, possibly leading to the reduced fertility typically observed in cats subjected to gonadotropin stimulation and AI.

Hormone secretion in the asian elephant (Elephas maximus): characterization of ovulatory and anovulatory luteinizing hormone surges.

In the elephant, two distinct LH surges occur 3 wk apart during the nonluteal phase of the estrous cycle, but only the second surge (ovLH) induces ovulation. The function of the first, anovulatory surge (anLH) is unknown, nor is it clear what regulates the timing of these two surges. To further study this observation in the Asian elephant, serum concentrations of LH, FSH, progesterone, inhibin, estradiol, and prolactin were quantified throughout the estrous cycle to establish temporal hormonal relationships. To examine long-term dynamics of hormone secretion, analyses were conducted in weekly blood samples collected from 3 Asian elephants for up to 3 yr. To determine whether differences existed in secretory patterns between the anLH and ovLH surges, daily blood samples were analyzed from 21 nonluteal-phase periods from 7 Asian elephants. During the nonluteal phase, serum LH was elevated for 1-2 days during anLH and ovLH surges with no differences in peak concentration between the two surges. The anLH surge occurred 19.9+/-1.2 days after the end of the luteal phase and was followed by the ovLH surge 20.8+/-0.5 days later. Serum FSH concentrations were highest at the beginning of the nonluteal phase and gradually declined to nadir concentrations within 4 days of the ovLH surge. FSH remained low until after the ovLH surge and then increased during the luteal phase. Serum inhibin concentrations were negatively correlated with FSH during the nonluteal phase (r = -0.53). Concentrations of estradiol and prolactin fluctuated throughout the estrous cycle with no discernible patterns evident. In sum, there were no clear differences in associated hormone secretory patterns between the anLH and ovLH surge. However, elevated FSH at the beginning of the nonluteal phase may be important for follicle recruitment, with the first anLH surge acting to complete the follicle selection process before ovulation.

Reproductive activity in captive female cheetahs (Acinonyx jubatus) assessed by faecal steroids.

Faecal oestradiol and progestogen metabolite excretion was monitored in adult, female cheetahs (Acinonyx jubatus) (n = 26) for 1-24 months. Increased faecal oestradiol excretion was associated with mating or equine chorionic gonadotrophin (eCG) administration for artificial insemination, whereas increased progestogen metabolites were observed during natural and human chorionic gonadotrophin (hCG)-induced pregnant and nonpregnant luteal phases. On the basis of oestradiol excretory patterns, duration of the oestrous cycle (mean +/- SEM) was 13.6 +/- 1.2 days with high oestradiol concentrations lasting for 4.1 +/- 0.8 days. In non-gonadotrophin-treated cheetahs, 75% showed evidence of oestrous cyclicity; however, none evaluated for 1 year or longer were continuously cyclic. Rather, cyclicity was interrupted by periods of anoestrus, often exceeding several months in duration. These inactive ovarian periods were unrelated to season and were not synchronous among females. Mean duration of gestation (breeding to parturition) was 94.2 +/- 0.5 days, whereas duration of faecal progestogen metabolite excretion during the nonpregnant luteal phase was 51.2 +/- 3.5 days. On the basis of progestogen metabolite evaluations, spontaneous ovulation (non-mating induced) occurred only once in two females (2 of 184 oestrous cycles; 1.1%). Peak eCG-stimulated, preovulatory oestradiol concentrations were similar to those associated with natural oestrus, whereas progestogen metabolite profiles after hCG resembled those during pregnant and nonpregnant luteal phases after natural mating. In summary, results confirm that the cheetah is polyoestrus and ovulation is almost always induced. However, new evidence suggests that many females inexplicably experience periods of anoestrus unrelated to season, while 25% of the cheetahs examined expressed no ovarian activity during the study period.

Natural versus chorionic gonadotropin-induced ovarian responses in the clouded leopard (Neofelis nebulosa) assessed by fecal steroid analysis.

The clouded leopard (Neofelis nebulosa) is an endangered species difficult to propagate in captivity because of sexual incompatibility between paired individuals. Fecal estradiol (E2) and progesterone (P4) metabolites were quantified in 14 females to noninvasively monitor seasonal reproductive patterns and compare ovarian responses to natural mating vs. exogenous gonadotropins. Increased E2 excretion was associated with behavioral estrus or eCG treatment, whereas elevated P4 metabolites were observed during natural and hCG-induced pregnant and nonpregnant luteal phases. On the basis of fecal E2 profiles, duration of the estrous cycle was 24 +/- 2 days, with estrus lasting 6 +/- 1 days. Mean gestation length was 89 +/- 2 days, whereas duration of the nonpregnant luteal phase was 47 +/- 2 days. Females experienced a seasonal anestrus during the late summer and early fall. One female demonstrated a lactational anestrus after the birth of three cubs. On nine occasions, clouded leopards ovulated spontaneously (based on elevated fecal P4 metabolite concentrations) in the absence of mating. Patterns of eCG-stimulated E2 excretion were similar to those associated with natural estrus and were unaffected by eCG dosage (25, 50, or 100 IU). In contrast, post-hCG P4 metabolite profiles varied considerably, with responses including anovulation, attenuated luteal P4 metabolite production, and hyperstimulated luteal function. In some females, compromised luteal function after ovulation induction appeared to be due to the presence of mature CL from previous spontaneous (without copulation) ovulations at the time of gonadotropin treatment. Duration of post-hCG P4 metabolite excretion was reduced approximately 40% in these individuals compared to females with no evidence of active luteal activity. In sum, these are the first data describing the ovarian cycle of this endangered species. The information is important because it is based on the longitudinal assessment of multiple females using a completely atraumatic approach, thereby eliminating the potential confounding impact of stress. Data indicate that spontaneous ovulations and the presence of active luteal tissue on the ovary can profoundly affect ovarian responses to exogenous gonadotropin therapy. Therefore, fecal steroid monitoring can serve as a useful adjunct to developing assisted reproduction techniques, especially the hormonal induction of ovulation for planned artificial insemination.

Comparative aspects of steroid hormone metabolism and ovarian activity in felids, measured noninvasively in feces.

Noninvasive fecal assays were used to study steroid metabolism and ovarian activity in several felid species. Using the domestic cat (Felis catus) as model, the excretory products of injected [14C]estradiol (E2) and [14C]progesterone (P4) were determined. Within 2 days, 97.0 +/- 0.6% and 96.7 +/- 0.5% of recovered E2 and P4 radioactivity, respectively, was found in feces. E2 was excreted as unconjugated estradiol and estrone (40%) and as a non-enzyme-hydrolyzable conjugate (60%). P4 was excreted primarily as non-enzyme-hydrolyzable, conjugated metabolites (78%) and as unconjugated pregnenolone epimers. A simple method for extracting fecal steroid metabolites optimized extraction efficiencies of the E2 and P4 excretion products (90.1 +/- 0.8% and 87.2 +/- 1.4%, respectively). Analysis of HPLC fractions of extracted fecal samples from the radiolabel-injected domestic cats revealed that E2 immunoreactivity coincided primarily with the unconjugated metabolized [14C]E2 peak, whereas progestogen immunoreactivity coincided with a single conjugated epimer and multiple unconjugated pregnenolone epimers. After HPLC separation, similar immunoreactive E2 and P4 metabolite profiles were observed in the leopard cat (F. bengalensis), cheetah (Acinonyx jubatus), clouded leopard (Neofelis nebulosa), and snow leopard (Panthera uncia). Longitudinal analyses demonstrated that changes in fecal E2 and P4 metabolite concentrations reflected natural or artificially induced ovarian activity. For example, severalfold increases in E2 excretion were associated with overt estrus or exogenous gonadotropin treatment, and elevated fecal P4 metabolite concentrations occurred during pregnant and nonpregnant (pseudopregnant) luteal phases. Although overall concentrations were similar, the duration of elevated fecal P4 metabolites during pseudopregnancy was approximately half that observed during pregnancy. In summary, steroid metabolism mechanisms appear to be conserved among these physically diverse, taxonomically related species. Results indicate that this hormone-monitoring approach will be extremely useful for elucidating the hormonal regulatory mechanism associated with the reproductive cycle, pregnancy, and parturition of intractable and endangered felid species.

Measurements of faecal oestradiol and progesterone in non-pregnant and pregnant domestic and exotic cats.

Faecal samples collected for variable periods from 12 animals and five species of cats were assayed for progesterone and oestradiol content by application of standard radioimmunoassays to aliquots (50 microliters) of methanol extracts (4 ml) of a mixture of 0.5 g sample, 0.5 ml water and 1 g aluminium oxide, following partitioning of the total extract with petroleum ether (3 ml), further dilution of assay aliquots and drying. Recoveries averaged 100 and 72% for oestradiol and progesterone, respectively. Results included increases in progesterone during luteal phases or pregnancies to 7688 ng g-1 (tiger, Panthera tigris), 2594 ng g-1 (lion, P. leo), 3000 ng g-1 (cheetah, Acinonyx jubatus) and 4915 ng g-1 (caracal, Felis caracal). Faecal oestradiol peaks near oestrus included 246 ng g-1 (tiger), 175 ng g-1 (lion) 190 ng g-1 (cheetah), 23 ng g-1 (caracal) and 190 ng g-1 (domestic cat, F. catus).