Effects of a progestagen on buck-induced short ovarian cycles in the creole meat goat

Two experiments were conducted to determine the effects of progestagens on the buck-induced ovarian cycle in anovular female Creole goats. In the first experiment, 25 anovular females served as a control group and 23 anovular females received a fluorogestone acetate (FGA)-impregnated sponge (45 mg) which was removed at the time males were introduced in the two groups. In the second experiment 10 anovular females served as the control group, and another 10 anovular females received an injection of FGA (5.2 mg) at the time males were introduced. Ovarian activity was traced by laparoscopy (Exp. 1) or progesterone levels (Exp. 2); oestrus and litter size were recorded, and fertility was calculated. In Exp. 2 blood samples were taken every 4 h to study the buck-induced preovulatory luteinizing hormone (LH) surge, and twice daily for progesterone plasma levels.FGA pretreatment did not modify the percentage of females ovulating in either experiment. The percentage of females showing oestrus at first ovulation in Exp. 1 was enhanced by treatment (55% vs 100%), and in both experiments FGA pretreatment restored the normal lifespan of corpora lutea compared to untreated females (96% vs 14%). FGA injection delayed the onset of oestrus and the preovulatory LH surge by 20 h, but did not modify either duration of oestrus or duration of the LH surge.Fertility of control females was low at first ovulation compared to FGA-treated females (10% vs 85%); but fertilization occurred at the subsequent ovulations in most of the control females.It is concluded that progestagen pretreatment is an efficient technique to control buck-induced short ovarian cycles. The exact role of the progestagen, through a delay of LH surge or a direct effect on follicles, remains unknown.     

Stimulation of seasonally anovular merino ewes by rams. I. Time from introduction of the rams to the preovulatory LH surge and ovulation

Two experiments were performed on seasonally anovular Merino ewes to determine the intervals between time of introduction of rams, the preovulatory surge of LH and the first ovulation. Ovulation was determined by laparoscopy and LH was measured by solid phase radioimmunoassay. In Experiment 1 the interval between the introduction of rams and the beginning of the LH surge was 27 ± 4 h (mean ± S.E., range 6–52 h), and in Experiment 2 probit analysis shows that 50% of teased ewes ovulated within 41 h of being exposed to rams.     

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.     

Influence of male endocrine condition on the choice of social contact in pair-living Mongolian gerbils (Meriones unguiculatus)

In two previous studies influence of gonadal hormones on male—female interaction has been investigated. Interaction between pair-living cagemates and non-cagemates was compared. In the first study the animals met in direct paired encounters, and in the second study the tested animals had the choice of wiremesh-restricted contact with the cagemate or a non-cagemate. The present choice test involves direct contact with the animal chosen in a series of consecutive trials. The two incentive animals were again non-cagemate and the cagemate of the experimental animal. The males tested were intact or castrated. The females were tested in induced oestrus. The females tested with intact males showes a higher choice of the cagemate. This was also the case in castrated males. Intact males and females tested with castrated males showed no significant difference in their choice. Differences in the results and testing conditions of the present and the previous choice test allowing restricted contact are discussed.     

Length of progesterone exposure needed to resolve large follicle anovular condition in dairy cows

Hypothalamic unresponsiveness to an estradiol surge appears to be an underlying cause of large follicle anovular condition (follicular cysts), but progesterone exposure for 7 days resolves this condition. In this study, dairy cows with induced (Experiment 1) or naturally occurring (Experiment 2) follicular cysts were treated for different times with progesterone. In Experiment 1, 16 of 26 cows (62%) were induced into anovulation by causing a GnRH/LH surge when no ovulatory follicle was on the ovary. Anovular cows (n = 16) were assigned to one of four treatment groups ( 0, 1, 3, or 7 days of progesterone treatment) using an intravaginal, progesterone-releasing implant (CIDR). All anovular cows had low circulating progesterone concentrations before controlled internal drug releasing (CIDR) and greater concentrations that reached steady state (1.3 +/- 0.1 ng/mL progesterone) by 3 h after CIDR insertion. Circulating progesterone decreased to basal concentrations by 4 h after CIDR removal. Cows were treated with 5mg estradiol benzoate (EB) 12 h after CIDR removal. None (n = 4) of the control cows (0 day) had an LH surge after EB. All of the 3 days (5/5) and 7 days (4/4) CIDR-treated cows had an LH surge following EB, but only one of the 1 day (1/3) CIDR-treated cows. Magnitude of the LH peak was similar in the 3 and 7 days cows. All cows treated for 7 days ovulated (4/4), whereas, ovulation occurred in only 3/5, 1/3, and 0/4 of the cows treated for 3, 1, and 0 day, respectively. The two cows in the 3 days group that did not ovulate had a normal LH surge, but these two cows had a smaller maximal follicle size than cows that ovulated. In Experiment 2, naturally anovular lactating dairy cows (24 of 248) were identified using weekly ultrasonography. All anovular cows grew follicles to >12 mm, with 54% (13 of 24) having follicles larger than ovular size (15-24 mm) and 33% (8 of 24) having follicles that would be considered cystic (>25 mm). Anovular cows were randomly assigned to CIDR treatment for 0, 1, or 3 days. All (7/7) of 3 days, 33% (3/9) of 1 day, and 25% (2/8) of control (0 day) cows ovulated by 1 week after CIDR removal. Thus, 3 days but not 1 day of progesterone exposure appears to be sufficient to reinitiate estradiol responsiveness of the hypothalamus.     

Ovarian estradiol modulates the stimulatory effect of ovulation-inducing factor (OIF) on pituitary LH secretion in llamas

This study was designed to: 1) characterize the effect of ovulation-inducing factor (OIF) on pituitary LH secretion in ovariectomized (OVX) llamas; and 2) determine the effect of OIF on LH secretion in OVX llamas pretreated with estradiol-17β (E-17β) or estradiol benzoate (EB). In Experiment 1, intact and OVX llamas (n = 5 or 6 per group) were assigned to a two by two factorial design: 1) Intact llamas treated with 1 mL of phosphate buffered saline (PBS); 2) Intact llamas treated with 1 mg of purified OIF; 3) OVX llamas treated with 1 mL of PBS; or 4) OVX llamas treated with 1 mg of purified OIF. In Experiment 2, intact and OVX llamas (n = 5 or 6 per group) were randomly assigned to the following groups: 1) Intact llamas treated with 1 mg of purified OIF; 2) OVX llamas treated with 1.0 mL of PBS; 3) OVX llamas treated with 1.0 mg of purified OIF; 4) OVX llamas primed with E-17β, followed by 1.0 mg of purified OIF. Experiment 3 was similar as described for Experiment 2, except that priming was done with EB. In Experiment 1, animal category by treatment and animal category by treatment by time interactions tended (P = 0.08) to affect LH concentration. The effect of OIF on LH released was partly restored (P < 0.05), to the values observed for the intact OIF-treated females, when OVX llamas were primed with E-17β or BE (Experiments 2 and 3). We concluded that peripheral estradiol concentrations in llamas partially modulates the effect of OIF on pituitary LH secretion; however, other ovarian factor(s) could also participate in this modulatory action.     

Influence of gonadal hormones on the behaviour of pair-living Mongolian gerbils (Meriones Unguiculatus) towards the cagemate versus a non-cagemate in a social choice test

Laboratory, semi-natural and field observations indicate that the Mongolian gerbil may naturally live in pairs or family groups. Endocrine influence on behaviour towards cagemates and non-cagemates was investigated. The males tested were intact or castrated. The hormonal condition of the females was controlled by gonadectomy and oestrogen and progesterone replacement treatment. The duration and number of visits to the incentive animals were recorded in a choice test, which allowed restricted contact between the experimental and incentive animals. Anoestrous females approached the intact cagemates more than the non-cagemates, while the intact males approached the non-cagemates more often. A comparison of the female behaviour under the different female endocrine conditions tested showed that females significantly increased their response in oestrus towards the strange intact males but not towards their cagemates. Experimental intact males analogously increased their response towards the strange oestrus female but not towards the cagemate. In tests which involved castrated males either as experimentals or incentives, no behavioural change was seen relative to the endocrine condition of the female. The hormonal effects seen were thus connected with the social relationship, as the hormone-induced changes were seen only in behaviour towards a strange animal.     

Sexual motivation suppresses paternal behaviour of male gerbils during their mates' postpartum oestrus

Adult male Mongolian gerbils, Meriones unguiculatus, avoid contact with their young on the day that the young are born. However, on succeeding days, fathers spend nearly as much time in contact with their offspring as do mothers. We undertook a series of studies to investigate the causes of the day-to-day change in male parental behaviour. In experiment 1, we tested males' response to pups before, after and on the day of their mates' parturition, and found that males were more parental both before and after the day of birth of their young than on that day. In experiment 2, we compared the parental behaviour of males paired either with intact or with ovariectomized dams (which do not come into postpartum oestrus) and found that males that were mated to intact females were less attentive to pups on the day of their birth than were the males mated to ovariectomized females. In experiment 3, we compared the parental responses of castrated and intact males to newborn pups and found that castrated males were more parental than intact males. In experiment 4, we compared the parental responses of males that were exposed to postpartum oestrous females but prevented from mating for 24 h. Extending the period of male sexual arousal to 24 h inhibited paternal responsiveness to neonates for 24 h. We interpret these results as being consistent with the hypothesis that on the day of birth of a litter, a male's parental behaviour is inhibited by the motivation to mate during his partner's postpartum oestrus.     

Delayed puberty in lambs chronically treated with oestradiol

Intact female lambs were chronically treated with low levels of oestradiol by Silastic implant from 20 weeks of age. Reproductive cycles were initiated in only 33% of these lambs (3 of 9) compared to 80% of untreated females (11 of 14) by 45 weeks when the study was terminated. Moreover, in the 3 oestradiol-treated lambs which began cycles, the age at first oestrus was delayed 3 weeks (37 +/- 1 weeks of age vs 34 +/- 1 weeks of age for untreated controls). Retardation of the pubertal process was not due to absence of the pubertal rise in circulating LH. At about 32 weeks of age, chronic oestradiol treatment was no longer able to suppress tonic LH secretion and serum LH increased in intact, oestradiol-treated lambs. These results indicate that a maturational decrease in responsiveness to oestradiol inhibition of tonic LH secretion can be demonstrated in the intact female, as in the ovariectomized female. However, chronic oestradiol suppression of prepubertal LH secretion also delays onset of reproductive cycles. This finding raises the possibility that low tonic LH secretion, presumably in the form of slow pulses, is necessary for development or maintenance of ovarian function before puberty. In the absence of LH during the last part of sexual maturation, the ability of the ovary to respond to the high frequency LH pulses during the pubertal gonadotrophin rise may be delayed.     

Increased plasma LH levels in seasonally anovular merino ewes following the introduction of rams

Seven seasonally anovular Merino ewes, isolated from rams, were bled every 10 min for 12 h. Rams were introduced the following day, after a further 2 h of sampling every 10 min, and samples were taken for the following 10 h. Three days after the introduction of rams, the ewes underwent laparoscopy, and four had ovulated.Radioimmunoassay of plasma samples revealed pulsatile rhythms in the concentration of LH, with the frequency of pulses varying between ewes, from about once hourly to once every 10 h. Upon the introduction of rams, LH secretion increased within 10 min in six ewes, of which four ovulated within 3 days. There is apparently a relationship between the pattern of LH secretion after introducing the rams, and the ovulatory response that can be expected.     

Partner preference of intact and ovariectomized female gray short-tailed opossums (Monodelphis domestica)

Intact, ovariectomized and ovariectomized estradiol (E)-treated female gray short-tailed opossums were placed in a test situation in which they could choose between an intact and a castrated male. Intact females chose to visit intact males first and visited them more frequently and spent more time with intact than with castrated males. Ovariectomized (OVX) females did not show this preference for visiting intact males over castrates. When compared to OVX females with blank implants, OVX females with E implants spent less time with castrated males. Like intact females, OVX and OVX-E-treated females preferred to stay in close proximity to but not actually in the cage of intact rather than castrated males. To our knowledge, this is the first experimental study of partner preference and its relationship to hormonal condition in a female marsupial.     

Effect of prenatal stress and gonadal hormone condition on depressive behaviors of female and male rats

Whether prenatal stress (PNS) and gonadal hormones may influence depressive behavior of rats in the forced swim test was investigated. In Experiment I, adult diestrous female rats had increased immobility, which is indicative of depression, but did not show any significant difference in the duration of struggling compared to intact adult males. In Experiment 2, the behavior of adult intact, castrated, or castrated dihydrotestosterone (DHT)- or estrogen (E2)-replaced offspring of dams that were restrained under lights for 45 min on gestational day 18 (PNS) or were not subjected to gestational stress (non-PNS, control condition) were compared. There were no effects of PNS, but DHT and E2 produced anti-depressant effects on behavior of male rats. Castration decreased struggling and increased immobility compared to intact rats. DHT or E2 replacement was able to partially reinstate struggling and immobility behavior but not to levels of intact males. In Experiment 3, behavior of PNS or control rats that were in proestrus or were ovariectomized and DHT, E2, or vehicle-replaced were compared. Ovariectomy decreased struggling and increased immobility compared to that of proestrous rats. E2 or DHT to control females increased anti-depressant struggling behavior compared to ovariectomized control or PNS rats administered vehicle, which demonstrated greater duration of struggling than did E2-primed, PNS rats. E2 or DHT administration decreased immobility of PNS and control females. These findings suggest that E2 and DHT have some anti-depressant effects but that modest PNS may alter E2's ability to alleviate some depressive behavior in female, but not male rats.     

A positive feedback effect of oestradiol on LH release in the male marmoset monkey, Callithrix jacchus.

Subcutaneous injections of oestradiol benzoate in oil, resulting in a sustained elevation of circulating oestradiol levels, induced an initial suppression of LH secretion, followed by a positive discharge of LH in castrated male and female and in intact male marmosets. Oestrogen-induced LH release (producing maximum LH concentrations 24 h after the injection) was observed in 75% of castrated males and females. A positive discharge of LH occurred in 50% of intact males 28-36 h after oestrogen administration.     

Oestrous cycle dynamics in peri-pubertal and mature Javanese thin-tail sheep

Duration of oestrus, time of ovulation and hormone profiles for progesterone and LH in prepubertal, pubertal and mature Javanese thin-tail sheep were studied at synchronized oestrus following progestagen-PMSG treatment and at the first natural oestrus after synchronization.The ewe lambs responded to progestagen-PMSG treatment by showing earlier onset of oestrus and an earlier and higher peak of LH concentration than mature ewes. For pre-pubertal, pubertal and mature ewes the mean LH peaks were 49.9, 43.9 and 37.9 ng/ml (P>0.05) at mean intervals of 7.5, 8.4 and 16.5 h (P < 0.05), respectively, after onset of oestrus. Duration of oestrus was 41.2 h in pubertal lambs and averaged 37.5 h in the other two groups (P>0.05). Except in one mature ewe, ovulation occurred between 24 and 36 h after onset of oestrus and the majority ovulated at around the end of oestrus. The corpora lutea developed normally, as indicated by plasma-progesterone changes. The patterns of plasma-progesterone changes were similar in all three groups, though the concentrations were lower in the ewe lambs.At the first natural oestrus after synchronization, mature ewes showed longer (P>0.05) oestrus (31.5 vs. 24.3 h), longer time interval from onset of oestrus to the LH peak (16.0 vs. 12.0 h) and from the LH peak to ovulation (21.0 vs. 19.6 h) than peri-pubertal lambs. Six of eight pre-pubertal lambs did not ovulate at their first natural oestrus, resulting in a conception rate of 11% for that group, while in pubertal lambs and mature ewes conception rates were 70% and 100%, respectively.     

Importance of intense male sexual behavior for inducing the preovulatory LH surge and ovulation in seasonally anovulatory female goats

The present study was carried out to determine whether the presence of photostimulated sedated male goats could stimulate the LH preovulatory surge and ovulation in seasonal anestrous goats. Sexually experienced male goats were treated with artificial long days (16 hours light per day) from 1 November to 15 January to stimulate their sexual activity in March and April, corresponding to the natural sexual rest. A female group of goats (n = 20) was exposed to non-sedated males who displayed an intense sexual behavior and provided strong odor (non-sedated group). Another female group of goats (n = 20) was exposed to the photo-stimulated male goats, but these males were sedated with Xylazine 2% to prevent the expression of sexual behavior (sedated group). The sedated males also provided a strong odor. Females of both groups had full physical and visual contact with non-sedated or sedated males. In both groups, the males remained with females during 4 days. The LH preovulatory surge of 10 female goats per group was measured by determination of LH plasma concentrations in samples taken every 3 hours. In addition, in all goats, (n = 20 by group), ovulation was determined by measuring plasma concentrations of progesterone. The proportion of female goats showing a preovulatory LH surge was higher in goats exposed to non-sedated (10/10) than in those exposed to sedated bucks (0/10; P < 0.0001). Similarly, most of does in contact with non-sedated males ovulated (19/20), but none of those in contact with sedated males did so (0/20; P < 0.0001). We conclude that the expression of an intense sexual behavior by male goats is necessary to induce LH preovulatory surge and ovulation in seasonally anovulatory goats.     

A definition of the breeding season of Pool Dorset ewes

The seasonality of oestrus and ovulation of 62 Poll Dorset ewes was examined over a period of 16 months commencing October, 1981. Laparoscopic observations showed that the majority of these ewes were anovular during the South Australian spring and early summer (September to December). The number of ewes with corpora lutea (93.6%) and the mean ovulation rate (1.62) reached a peak in June. Oestrus was stimulated in anovular ewes in late spring by the introduction of vasectomised rams. The mean ovulation rate at the teased ovulation was 1.68, although teased ewes did not exhibit oestrus at this ovulation.     

Corpus luteum function in ewes stimulated by rams

In late February Dorset rams were introduced (day = 0) to 40 mature Romney ewes that were observed by laparoscopy to be anovular. The ovaries of 20 of these ewes were examined by laparoscopy every second day while the remaining 20 ewes served as unoperated controls. Jugular blood samples were taken daily and plasma progesterone concentrations assayed to provide information on the functional status of any corpora lutea (CL) arising from ovulations stimulated by introduction of the rams. Eighty-five percent (-17/20) of the ewes that were repeatedly laparoscoped had ovulated within 4 days of ram introduction and premature regression of the CL had occurred between days 4 and 8 in 8 ewes and days 6 to 10 in 2 ewes. A second ovulation was observed after or during the premature regression of the first CL and this subsequent CL was maintained for the normal duration. The prematurely regressing CL produced a small peak in progesterone concentration on days 4 to 5 but the concentrations declined on days 6 to 7. In the unoperated ewes 50% (-10/20) appeared, from the progesterone profiles, to have ovulated by day 4 and half of these appeared to have premature CL regression. The interval from introduction of the ram to first oestrus was 23 days in ewes with premature regression of the CL and 19 days in ewes ovulating within 4 days but having no premature regression. From the results it was concluded that the premature regression of the CL is the cause of the delayed interval from ram introduction to first oestrus in Romney ewes and is a major factor contributing to the two peaks of oestrous activity observed after ram introduction.     

Familiarity and flexible mating strategies of a solitary rodent, Dipodomys ingens

Because mating is a product of individual reproductive strategies that may vary with changing conditions, we predicted variable mating behaviour in an arid-adapted, territorial rodent, the giant kangaroo rat, Dipodomys ingens. We also predicted that familiarity would facilitate nonaggressive courtship and mating in this solitary rodent. Through direct observations in the field, we found that mating varied from exclusive to multiple partners. Where densities were low, and on nights when multiple females were in oestrus, each animal mated with one member of the opposite sex. In conditions where the operational sex ratio was skewed towards multiple males, males footdrummed and competed for females. Males were able to mate with one or two females in adjacent territories, and they successfully competed for these same females throughout the breeding season. Females that mated exclusively with one male had more pups emerge from the burrow compared with females that experienced male competition. Females allowed nearest neighbour males to enter their burrows, and they engaged in more nonaggressive contact with close neighbours than with other males. Paired encounters in the field showed less aggression towards neighbours than strangers. In laboratory tests, females were less aggressive towards and allowed more contact with familiar than unfamiliar males. These results show that D. ingens can alter mating strategies as conditions change. Familiarity is an important factor in nonaggressive interactions between males and females and may be important to mate preferences in females during reproduction. The less aggressive behaviour to neighbours than to strangers (‘dear enemy’ phenomenon) is consistent with other solitary animals that defend multipurpose territories. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Oestrus and LH responses to oestradiol during lactational anoestrus in Chinese Meishan and large white sows.

To investigate endocrine mechanisms associated with the occasional occurrence of fertile oestrus during lactation in the high prolific Chinese Meishan (MS) breed, the incidence of oestrus and changes in plasma luteinizing hormone (LH) levels before and after oestradiol benzoate (OB, 15 micrograms/kg body weight) administration on day 22 was compared in 4 MS and 6 Large White (LW) sows. All sows exhibited oestrus in response to OB. Only 1 sow (MS) ovulated in response to OB, became pregnant and farrowed. Mean plasma LH levels before OB were low (MS: 0.38 +/- 0.06 ng LH/ml, LW: 0.29 +/- 0.04 ng LH/ml, ns). LH levels above 2 ng/ml (surge) occurred in 2/4 MS and 2/6 LW sows at 60 +/- 5 h after OB. The MS sow that ovulated had an LH surge level of 4.5 ng/ml plasma at 40 h after OB. These results indicate minor breed differences in the control of LH secretion during lactational anoestrus.     

Male reproductive condition is the limiting factor of efficiency in the male effect during seasonal anestrus in female goats

Two experiments were conducted to determine whether the failure of males to induce sexual activity in goats during seasonal anestrus is due to unresponsiveness of females to male stimulus or insufficient stimulation from males. In the first study, one group of males (sexually inactive, SI; n = 4) was kept under natural photoperiod while the other (sexually active, SA; n = 4) was subjected to 2.5 mo of long days (16L:8D) and received 2 s.c. implants of melatonin. Two mo later, 2 different flocks of anovulatory goats previously separated from bucks were exposed to either SI (n = 34) or SA (n = 40) bucks. Progesterone assays and estrous behavior were used to determine ovarian and behavioral responses of the females to teasing. Of the goats exposed to SI males, only 2 ovulated, and none showed estrous behavior during the 35 days of the study. In contrast, all females (40 of 40) in contact with SA males ovulated and showed at least one estrous behavior during the first 11 days following male introduction (P < 0.001). Overall, 38 of 40 females stimulated with SA bucks were diagnosed pregnant at Day 35, according to progesterone assay (versus 0 in SI-treated group: P < 0.001). To control for a possible difference of responsiveness between flocks, the experiment was repeated 1 yr later using a single flock of goats divided into 2 groups. Again, over the first 14 days, 1 of 33 goats showed estrous behavior in the SI-treated group versus 27 of 33 in the SA-treated group (P < 0.001). Therefore, treating bucks with long days and melatonin increased their teasing capacity to induce sexual activity in females during anestrus. These results indicate that the absence of response to teasing at this time of the year is not due to female unresponsiveness, but to insufficient stimulation from the male.