Studies of the oestrous cycle, oestrus and pregnancy in the koala (Phascolarctos cinereus)

As an integral part of the development of an artificial insemination programme in the captive koala, female reproductive physiology and behaviour were studied. The oestrous cycle in non-mated and mated koalas was characterized by means of behavioural oestrus, morphology of external genitalia and changes in the peripheral plasma concentrations of oestradiol and progestogen. The mean (+/- SEM) duration of the non-mated oestrous cycle and duration of oestrus in 12 koalas was 32.9 +/- 1.1 (n = 22) and 10.3 +/- 0.9 (n = 24) days, respectively. Although the commencement of oestrous behaviour was associated with increasing or high concentrations of oestradiol, there were no consistent changes in the morphology or appearance of the clitoris, pericloacal region, pouch or mammary teats that could be used to characterize the non-mated cycle. As progestogen concentrations remained at basal values throughout the interoestrous period, non-mated cycles were considered non-luteal and presumed anovulatory. After mating of the 12 koalas, six females gave birth with a mean (+/- SEM) gestation of 34.8 +/- 0.3 days, whereas the remaining six non-parturient females returned to oestrus 49.5 +/- 1. 0 days later. After mating, oestrous behaviour ceased and the progestogen profile showed a significant increase in both pregnant and non-parturient females, indicating that a luteal phase had been induced by the physical act of mating. Progestogen concentrations throughout the luteal phase of the pregnant females were significantly higher than those of non-parturient females. Parturition was associated with a decreasing concentration of progestogen, which was increased above that of basal concentrations until 7 days post partum.     

Successful artificial insemination in the koala (Phascolarctos cinereus) using extended and extended-chilled semen collected by electroejaculation

Artificial insemination in the koala using chilled, electroejaculated semen provides for a marked improvement in the reproductive and genetic management of captive koala colonies in Australia and internationally, and makes available the option of using semen collected from wild populations to expand restricted gene pools. Dilution of koala semen for artificial insemination is complicated because koalas are induced ovulators, and it is thought that ovulating factors are present in the semen, so that semen extension for preservation purposes might be anticipated to result in a failure to induce ovulation. The first two experiments of this study were designed to determine whether artificial insemination using undiluted, extended, and extended-chilled semen collected by electroejaculation was capable of inducing a luteal phase and/or the production of pouch young. In Experiment 1, 1 ml undiluted electroejaculated semen, 2 ml diluted (1:1) semen, and 1 ml diluted (1:1) semen resulted in seven of nine, six of nine, and six of nine koalas showing a luteal phase, respectively; four pouch young were produced in each treatment. A second artificial insemination experiment was conducted in which 2 ml diluted (1:1) semen was administered in three groups of nine koalas. The first group received semen that had been collected and diluted immediately without chilling, the second group was deposited with semen stored chilled for 24 h, and the final group received semen that had been chilled for 72 h. In the first group, five females had a luteal phase, but none became pregnant. In group 2, two of the five females that had a luteal phase gave birth, whereas in group 3, four of the six females that had a luteal phase produced pouch young. In addition, experiment 3 was conducted to determine whether it was possible to produce pouch young by naturally mating koalas that were in the latter stages of their behavioral estrus; this information is important to the logistics of transporting koala semen for artificial insemination by establishing the maximum time frame in which females might be expected to shed a fertile oocyte. Of the 12 females mated on Day 8 of estrus, 6 gave birth, whereas only 3 of the 10 females naturally mated on Day 10 of estrus produced pouch young. The majority of females (21 of 22) in experiment 3 showed evidence of a luteal phase. Together, these experiments have shown that it is possible to use undiluted, extended, or extended-chilled semen to produce koala offspring up to Day 8 of estrus at conception rates similar to those achieved following natural mating. These findings represent a significant advancement in the use of reproductive technology in marsupials and provide the basis for the shipment of koala semen over long distances. The pouch young produced in this study represent the first marsupials born following artificial insemination of extended-chilled semen and bring the total number of koalas produced by artificial insemination to 31.     

Ovarian response to hCG treatment during the oestrous cycle in heifers

The aims of this study were to investigate whether treatment with a single ovulatory dose of hCG, between the day of oestrus and the end of the luteal phase, could induce extra ovulations in heifers and whether the presence of an existing corpus luteum (CL) affected the response. Heifers (N = 32) were injected with 1500 i.u. hCG or saline on a given day of the oestrous cycle. Treatments were repeated during subsequent cycles to provide a total of 71 observations, 57 of which followed an injection of hCG, given between Day 0 (oestrus) and Day 16, and 14 of which followed saline injections as controls. Ovulatory responses were noted by laparoscopy 2 days after hCG treatment. No heifers injected with saline produced additional CL. Of the hCG-treated cycles, 23 resulted in the formation of an additional CL, and this was significantly affected by the stage of the oestrous cycle when hCG was given; a greater response was observed during the early (Days 4-7) and late (Days 14-16) stages of the luteal phase than at the mid-luteal phase of the oestrous cycle. Two heifers were also treated with hCG on Days 17 or 18 of the oestrous cycle, but before oestrus; both had induced CL. There were no significant differences between the left-right orientation of the existing CL or the hCG-induced CL. These results demonstrate that the large, luteal-phase follicle of the cow is capable of ovulating in response to hCG and that the induced CL is not affected by the presence of an existing CL.     

Stimulus requirements for pregnancy initiation in the golden hamster (Mesocricetus auratus) change with time of mating during the receptive period

When maintained under a 14L:10D photoperiod, the duration of behavioural receptivity in female golden hamsters was about 18-21 h depending on age and/or parity. The effectiveness of mating stimuli in initiating pregnancy was shown to be a function of when in the receptive period (early, middle, late) that mating occurred. During the 9-h period before ovulation, 5 ejaculatory series were sufficient to produce a nearly 100% pregnancy rate and maximum litter size. During the ovulation period, however, high pregnancy rates were achieved only when mating continued to satiety (12-15 ejaculatory series plus 10-24 long intromissions). Late in the receptive period even mating to satiety failed to result in a pregnancy. In general, pregnancy rates were significantly higher for young virgin than for older multiparous females when mating occurred during or after the ovulation period. The reduced fecundity of females mating during or after ovulation was due to insufficient vaginocervical stimulation to induce functional luteal activity and not to lack of spermatozoa. Females mating late in the receptive period did not show a cessation of oestrous cycles which characteristically follows the induction of a luteal phase. Greater amounts of vaginocervical stimulation during this time increased the number of females which delivered litters but had no significant effect on litter size. These results suggest that levels of male copulatory behaviour considered 'excessive' when mating occurs early in the receptive period are essential for pregnancy initiation when mating occurs later.     

Non-invasive monitoring of male and female numbat (Myrmecobius fasciatus: Myrmecobiidae) reproductive activity

The reproductive endocrinology of the highly endangered numbat (Myrmecobius fasciatus) is described for the first time. Patterns of faecal steroid secretion (progesterone [PM], oestradiol-17β [E2] and testosterone [TM] metabolites) were examined within a captive numbat population over 1 year and revealed a highly synchronized seasonal pattern of reproduction. TM secretion increased progressively from September to November, peaked in December and then decreased in February. All females displayed luteal phases (1-3), between late-November to late-March, in association with pregnant (Pr, n=4), non-productive mated oestrous cycles (NMEC, n=8) and non-mated oestrous cycles (NEC, n=6). The mean oestrous cycle length was 30.2±1.1d (n=11) and was comprised of a mean follicular (n=11) and luteal (n=18) phase length of 16.2±1.6d and 14.0±0.8d, respectively. No variation in mean luteal phase length or PM concentration according to cycle type (Pr, NMEC, NEC) or cycle number (1st, 2nd or 3rd cycle) was detected. Longitudinal profiling of PM secretion confirmed that the female numbat is seasonally polyoestrous and that the luteal phase occurs spontaneously. Changes in the secretion of E2 provided little instructive information on oestrous cycle activity. Mating success was 31%, with age and subject having no effect on mating success. Timing of introduction, of male to female, appeared to impact mating success, with paired animals introduced for a shorter time frame (≤14d) prior to the first observed mating successfully producing young. Collectively, results of the present study confirm that PM and TM can be reliably used to index numbat reproductive activity.     

Estrus induction in white rhinoceros (Ceratotherium simum)

The estrous cycle length in the white rhinoceros (Ceratotherium simum) is either 4 or 10 wk. The cause(s) for this variation as well as the poor fertility rate in captivity remains under debate in this species. Most captive adult white rhinoceros undergo long anovulatory periods without luteal activity which are considered a major reason for their low reproductive rate. In this study, the synthetic progestin chlormadinone acetate (CMA) was tested in combination with hCG or the GnRH analogue deslorelin for its efficiency to induce ovulation in fourteen females without luteal activity and in three, regular cycling females. HCG (N = 12), injectable GnRH analogue (N = 8) and GnRH analogue implants (N = 15) were given to induce ovulation after CMA treatment. Treatment success was determined using both transrectal ultrasonography and progesterone metabolite EIA analysis. A preovulatory sized follicle (3.5 ± 0.1 cm) or a corpus luteum (5.1 ± 0.7) was present on the ovary one day after induction in 93.1% of the treatments. Despite this high rate of ovarian response, ovulation rate differed between the study groups. The ovulation rate for hCG, injectable GnRH analogue and GnRH analogue implants was 66.7%, 62.5% and 93.3%, respectively. Ovulation rate in cyclic females treated with GnRH implants was 100% (6/6) compared with 89% (8/9) in females without luteal activity receiving the same treatment. The length of the estrous cycle when induced with hCG was 4 wk (85.7%). The estrous cycle when induced with GnRH analogue was predominantly 10 wk long. Two females without luteal activity treated with GnRH became pregnant. In conclusion, CMA in combination with GnRH analogue implants was highly effective to induce ovulation in white rhinoceroses and thus can contribute to efforts aimed at increasing natural mating and reproductive rates in the captive white rhinoceros population.     

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.     

Social influences on oestrous cycle length and plasma progesterone concentrations in the female lesser mouse lemur (Microcebus murinus)

Plasma progesterone concentrations were recorded during one breeding season in 19 lesser mouse lemur females living in different social conditions. The oestrous cycle length and the progesterone profile mainly depended on the social environment of the female. For totally isolated females, the oestrous cycle lasted 38 +/- 5.7 days and included a 25-30-days spontaneous luteal phase with a progesterone peak about 100 ng/ml between the 20th and 25th days after oestrus, and a prolonged preovulatory period of 10-15 days which could be considered equivalent to the follicular phase of a menstrual cycle. When females were able to communicate through olfactory, visual and auditory signals, the oestrous cycle was significantly lengthened (53.7 +/- 5.9 days). When females had tactile contacts, the oestrous cycle was further lengthened (62.7 +/- 0.8 days). This lengthening of the oestrous cycle was related to an extension of the luteal phase associated with a decrease in progesterone concentrations during this period. In females maintained with one male (paired) or with males and females (heterosexually grouped), large individual variations were shown in cycle lengths or in progesterone concentrations. In these females, cycle lengths and progesterone concentrations were inversely correlated to plasma cortisol concentrations.     

Evidence for a coitally induced 'mnemonic' involved in luteal function in the vole (Microtus agrestis).

The development of luteal function in the vole is dependent on a neuroendocrine reflex which is initially activated by mating. Bromocriptine was used to destroy the CL initially induced by mating and fresh CL were induced by hormone treatment. The fate of such newly formed CL suggested that the luteotrophic effect of mating continued for about 10 days after mating, despite the destruction of the original mating-induced CL. The luteotrophic effect of mating therefore seems to be 'remembered'. A study of the fate of hormonally induced CL in females in which pregnancy had been blocked by exposure to a strange male suggested that the strange male may cause pregnancy failure by inhibiting or suppressing the luteotrophic 'mnemonic' activated by the stud mating.     

Coital stimuli controlling luteinizing hormone secretion and ovulation in the female ferret

A series of experiments focused on the masculine coital behaviors controlling pituitary luteinizing hormone (LH) secretion and reflex ovulation in the estrous female ferret. An initial experiment investigated which coital stimuli from the male are required to induce ovulation. It was found that corpus luteum formation, which served as an index of ovulation, occurred in estrous female ferrets only if the male achieved a penile intromission. Neck gripping, mounting, and pelvic thrusting behavior without intromission by the male failed to induce ovulation. A second experiment investigated the timing and magnitude of the coitus-induced LH surge associated with ovulation. Blood was obtained via jugular catheters from estrous females in various mating situations. Plasma LH concentrations were measured by a heterologous radioimmunoassay that was validated for use in the ferret. A significant surge in plasma LH occurred only when an intromission was achieved by the stud male. Plasma LH was significantly elevated 2.0 h after the introduction of the male, peak values were reached 6.0 h later, and this elevation lasted on average 5.7 hours (5/5 females). No LH rise occurred in 2/2 female ferrets in which only neck gripping, mounting, and pelvic thrusting, but no intromission, were allowed to occur. The ferret mating pattern and the resultant LH response differ from those seen in three other induced ovulators (cat, vole, and rabbit) in which the male's intromission latency and duration are much shorter than in the ferret, and in which a distinctive peak in plasma LH often occurs within 1 h after mating.     

Induction of oestrus in the camel (Camelus dromedarius) during seasonal anoestrus

Injection of 7000 i.u. PMSG induced oestrus in 7 camels during the last part of seasonal anoestrus. Mature follicles developed and a CL was formed after fertile mating. However, pregnancy was not maintained by Day 60 in the 3 females detected as pregnant by rectal palpation and increased progesterone concentrations at Day 50. A single male camel mated with 4 of the females 2-16 days after the PMSG injection, and 2 or 3 matings occurred. The failure of pregnancy after induction of oestrus and mating during seasonal anoestrus was probably due to inadequate luteal function.     

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.      

Effect on oestrus and ovulation of exposing creole goats to the male at three times of the year

The characteristics of the oestrous and ovarian cycles of local goats were studied over 2 years, on 96 females in March, 60 in July and 100 in November. After 3 weeks of separation between sexes, the females with inactive ovaries were identified and harnessed males were introduced. Detection of oestrus was undertaken daily and the date and rate of ovulation were checked at laparoscopies. The proportion of females with non-cyclic ovaries before the mating period varied according to the season and whether the females were nulliparous or suckling. Among the females with inactive ovaries before the mating period, 97% ovulated 2 . 8 days after the introduction of males; 68% of these initial ovulations were accompanied by oestrus and 76% resulted in short luteal phases (5 . 3 days) followed by a second ovulation accompanied by oestrus 89% of the time. The proportions of initial ovulations with oestrus and of initial ovulations followed by a short luteal phase were in linear relationship with the proportion of females with non-cyclic ovaries before the mating period. For the females with cyclic ovaries before the mating period, the distribution of first oestrus during the 8 days after the introduction of males was significantly different from the expected uniform distribution. A possible luteolytic action of teasing was suspected. The fertility of females in all groups was high (greater than 79%). Litter size was not different for non-cyclic and for cyclic females.     

Dynamics of male residence and female oestrus during a breeding season of blue monkeys in the Kakamega Forest, Kenya

Blue monkeys (Cercopithecus mitis stuhlmanni) are seasonal breeders with a dynamic mating system in which typical one‐male social units are regularly disrupted and replaced by multi‐male ones. The number of males in the group is correlated with the number of oestrous females. We used observations of male presence and female oestrus on individual days during a 6‐month period to assess whether the presence of multiple males in a group stimulates female oestrus or whether oestrous females attract multiple males to the group. We confirmed prior observations with our finding that the number of males in a group was significantly correlated (r_s = 0.435, P < 0.0001) with the number of oestrous females across 126 observation days. A transition matrix did not show an obvious relationship between day‐to‐day changes in the numbers of oestrous females and males. However, cross‐correlation analysis provided stronger support for the idea that the number of oestrous females attracts males to a group than for the idea that the influx of strange males stimulates oestrus in female blue monkeys. Autocorrelation analysis showed that while female oestrus appeared to show a high degree of synchrony, as expected in a seasonal breeder, there was no evidence that the number of males accompanying a group of females influenced the likelihood of other males joining or leaving the group. Overall, our results confirm that female oestrous behaviour stimulates changes in male residence patterns. However, other observations suggest that changes in male residence may also stimulate female oestrus in some circumstances.     

Behavioural aspects of the raccoon mating system: determinants of consortship success

We monitored raccoons Procyon lotor, in southern Texas during the 1990-1992 mating seasons to describe mating behaviour and identify factors affecting consortship success. During most of this study, raccoons were spatially aggregated, with female home ranges congregated around permanent water sources and larger home ranges of male groups encompassing each female group. Consortship success varied among males and ranged from zero to six females per male within a mating season. Individual females consorted with one to four different males during an oestrous period; however, most (62%) females consorted with only one male during their oestrus. Dominance through overt conflict appeared to influence male consortship success. During two mating seasons, one male from each group consorted with females on more days than all other males combined. Body weight of males was positively correlated with number of consortship days. As synchrony of oestrus increased, variance in number of consortship days among males decreased, and access to oestrous females increased for subordinate males. Wounding among males increased during the mating season, and was more frequent for males than for females. The mating system, as determined by consortship behaviour, appeared to shift between polygyny and promiscuity, and possibly varied annually as a result of the timing of oestrous cycles. Copyright 1999 The Association for the Study of Animal Behaviour.     

Faecal progesterone metabolites and behavioural observations for the non-invasive assessment of oestrous cycles in the common wombat (Vombatus ursinus) and the southern hairy-nosed wombat (Lasiorhinus latifrons)

Wombats belong to Australia's unique marsupial species. Two of the three remaining species, the common wombat (Vombatus ursinus) and the southern hairy-nosed wombat (Lasiorhinus latifrons) are abundant. The third species, the northern hairy-nosed wombat (Lasiorhinus krefftii) has only about 115 individuals left in the wild. This study aimed to gain further insight into the basic reproductive biology of wombat species and evaluate the value of faecal progesterone metabolites and behavioural patterns as a means for non-invasive monitoring of the oestrous cycle in common and the southern hairy-nosed wombats. In an initial study, three different faecal steroid assays showed that 20alpha-OH-pregnanes were the main progesterone metabolites. These metabolites were examined in captive female common wombats (n = 5) and southern hairy-nosed wombats (n = 2). In one female common wombat 11.7 days with a follicular phase of 25.6 +/- 6.3 days and a luteal phase of 28.2 +/- 12.7 days. The data for faecal pregnanes obtained in the southern and in one male common wombat oestrous related behavioural data were obtained. Individual cycling females exhibited a significant relationship between plasma progesterone and faecal pregnanes. In the common wombat, the values for faecal pregnanes showed an oestrous cycle length of 55.1 +/- hairy-nosed wombat during the breeding season gave an oestrous cycle length of 41.1 +/- 12.8 days with a follicular phase of 27.9 +/- 12.3 days and a short luteal phase of 13.3 +/- 1.1 days. The behavioural data show that the faecal sniffing behaviour of the male, tended to increase around the time that oestrous was found. In conclusion, monitoring of 20alpha-OH-pregnanes in wombat faeces could be a useful methodology to monitor reproductive cycles in the wombat, and can possibly be applied to monitor the endangered northern hairy-nosed wombat.     

Pregnancy, lactation and the oestrous cycle of the pouched mouse, Saccostomus campestris

The anatomy and histology of pouched mouse ovaries were studied during the oestrous cycle, pregnancy and lactation along with the relationship between the ovarian structures and circulating concentrations of progesterone. The structure of the ovaries resembled that of most rodents. Follicular development indicated that ovulation takes place on the night between pro-oestrus and oestrus, i.e. at the time when mating normally occurs. Corpora lutea were accumulating in cyclic females, while successively disappearing during pregnancy, leaving only the set formed after conception. After parturition luteal regression was rapid. Theca interna, included in the corpora lutea, formed glandular stromal tissue after regression of the luteal tissue formed from granulosa cells. The progesterone profile of non-pregnant females indicated a short but functional luteal phase (peak at metoestrus) during the cycle. During pregnancy three peaks of progesterone stood out: (1) when implantation starts, (2) when older sets of corpora lutea showed rejuvenation and placental signs were found in the vaginal smears, and (3) 3 days before expected parturition when luteal development (as judged by histology) reached a peak. The placenta may participate in but not 'take over' the progesterone production during later stages of pregnancy. Very low concentrations of peripheral progesterone during lactation and a very low level of follicular development at that time support an earlier suggestion of a lactational anoestrus in pouched mice.     

A physiological increase in LH may influence vascular permeability in the rat testis

Adult male rats were injected with different doses of hCG, or with 2.5 micrograms ovine LH subcutaneously, and other rats were mated with oestrous females. The animals were examined 4 h after treatments. Treatment with hCG resulted in a dose-dependent increase in leucocyte concentration in testicular blood vessels and in the number of blood vessels which could be labelled with intravenously injected carbon particles. Carbon leakage was not observed in control testes. Treatment with a low dose of ovine LH or inducing an endogenous LH peak by mating also resulted in leucocyte accumulation and vascular leakage of carbon in the testis. The magnitude of the response was considerably lower than after high doses of hCG. The physiological relevance of the discrete response observed after physiological LH stimulation is unknown but LH-induced changes in testicular microcirculation could be of interest for the understanding of the physiology and pathophysiology of the testis.     

Do cyclic female goats respond to males with an increase in LH secretion during the breeding season?

The male effect is currently only used during seasonal or lactational anoestrus because the response is thought to be blocked in cyclic females by periods of elevated progesterone. In this study, we tested whether cyclic, female goats would respond to male exposure with an increase in pulsatile LH secretion. During May (breeding season; Southern Hemisphere) the cycles of 16 Australian Cashmere goats were synchronised using intravaginal progesterone pessaries. Pessary insertion was staggered to produce groups in their early luteal (EL; n=8) and late luteal phases (LL; n=8). The LL group was retrospectively subdivided into mid-luteal (ML; n=4) and late luteal (LL; n=4) groups due to differences in oestrous cycle length that emerged during the study. Male exposure stimulated an increase in LH pulse frequency in the EL and LL groups (P<0.01) but not in the ML group (P>0.1). This increase was accompanied by an increase in basal and mean concentrations of LH in the LL group (P<0.05) but not in EL (P<0.1) or ML (P>0.1) group. There was no effect of male exposure on LH pulse amplitude (P>0.1). Progesterone concentrations differed among all groups on the day of male exposure (P<0.05) and declined significantly over the 12-h sampling period in the LL group (P<0.05). Prolactin concentrations declined in the EL group but did not change significantly in the ML or LL group. In conclusion, male exposure induced an increase in pulsatile LH in goats in the early and late luteal phases of the oestrous cycle. The high concentrations of progesterone in females in the mid-luteal phase appeared to block the male effect.     

Secretory dynamics of bioactive and immunoactive LH during the oestrous cycle of the sheep

Blood samples were collected every 15 min for 6 h during the follicular (1 day before oestrus), and early (Days +1 to +3), mid- (Days +4 to +8), and full (Days +9 to +14) luteal phases of the oestrous cycle. Serum concentrations of immunoactive LH were measured by radioimmunoassay. The biological activity of serum LH was determined by an in-vitro bioassay that uses LH-induced testosterone production from mouse interstitial cells as an endpoint. Only ovine and bovine LH and hCG had appreciable activity in this bioassay. The temporal pattern of secretion of bioactive LH paralleled the secretory pattern of immunoactive LH at all stages of the ovine oestrous cycle. However, the secretory pattern itself varied regularly through the oestrous cycle. The frequency of secretory excursions of LH was highest during the follicular phase (6.2 +/- 0.9 pulses/6 h) and was progressively reduced through the luteal phase (1.1 +/- 0.1 pulses/6 h during full luteal phase). Conversely, amplitude of secretory excursions of immunoactive LH was low during the follicular phase (0.79 +/- 0.08 ng/ml) and significantly (P less than 0.05) increased during the mid- and full luteal phases (1.49 +/- 0.10 and 2.37 +/- 0.20 ng/ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)