Mating of captive thirteen-lined ground squirrels and the annual timing of estrus

Thirteen-lined ground squirrels (Spermophilus tridecemlineatus) have a single annual mating season in Michigan, beginning shortly after their spring emergence from hibernation. Captive females were studied during a 3-year period to determine relations among time of removal from the coldroom, vaginal estrus, and mating behavior. Following a 7-month period females spent in a coldroom, vaginal lavages were taken daily to monitor changes in estrous condition. Females removed from the coldroom about when free-living animals emerge from hibernation were in vaginal estrus within 24-48 hr and had an initial period of persistent estrus (ca. 3 weeks), followed by briefer (less than 1 week) and more sporadic estrous periods. Females left in the coldroom 3 weeks longer than normal had significantly briefer initial periods of vaginal estrus after being removed from the coldroom. Similarly, virgin Yearlings and virgin 2-Year-Olds had significantly briefer initial periods of estrus than nonvirgin Adults (greater than or equal to 2 years old). In 1985, eight of eight females paired with males mated within the first week after removal from the coldroom and subsequently produced litters. Mated females remained in vaginal diestrus from within a few days of mating until after parturition. In contrast, unmated females remained in prolonged vaginal estrus during this period. Females first paired with males 3 weeks after being taken from the coldroom failed to mate. In 1986, five of six females first paired with males 2 weeks after being removed from the coldroom similarly failed to mate. However, five of six females did mate that were removed from the coldroom 10 days after those in the previously described group and paired with a male 4 days after removal. This first report of reliable mating behavior in captive thirteen-lined ground squirrels should facilitate subsequent analysis of reproductive patterns in this species.     

Estrus and estrogen changes in mated and unmated free-living European ground squirrels

The course of behavioral and vaginal estrus and patterns of circulating estrogens were followed in free-living European ground squirrels (Spermophilus citellus) after their emergence from hibernation. Normally mating females were compared to a second group in an area where males had been removed from the population before female emergence. Both groups showed vaginal estrus, but the patterns differed. Mating shortened vaginal estrus to a 3-day period compared to 8 days in unmated females. The extent (cell number) of cell cornification during estrus and the cellular components (percentage distribution) of metestrus did not differ between the two groups. Females in the area without males had significantly higher estrogen levels during estrus and metestrus compared to those in the control area. European ground squirrels were found to be monestrous, as none of the unmated females reentered estrus after metor diestrus was detected. The prolongation of vaginal estrus in unmated females can be viewed as either a physiological inevitability or an adaptation to low mate availability. The extension is still relatively short compared to other sciurid species and perhaps a product of constraints producing a strict time frame for reproduction.     

Reproductive effort during gestation and lactation by Richardson's ground squirrels

Summary Reproductive effort by yearling and older female Richardson's ground squirrels was studied over a 4-year period in southern Alberta by obtaining serial weight records from marked individuals to compare the mother's mass at critical points in the annual cycle (emergence from hibernation, estrus, parturition, and litter emergence) with her litter's mass at birth and weaning. Yearlings weighed only 80% of older adults at emergence from hibernation, but they mated at the same time as older females, attained adult mass coincident with pregnancy, and weaned litters that were not significantly smaller in size or mass than those of older females. Age and maternal mass were weak predictors of litter size and litter mass. Of the net increase in mass of the combined mother-litter unit during gestation, over half (60% of 139 g for yearlings; 52% of 127 g for older females) was attributable to an increase in the mother's own mass, whereas during lactation almost all of the net increase (93% of 545 g for yearlings; 96% of 567 g for older females) was attributable to an increase in the litter's mass. On a daily basis, deposition of mass in the litter was 6 times greater during lactation than gestation. On average, neonates weighed 2.3% (6.5 g) of maternal mass at birth and 23.1% (81 g) at emergence from the natal burrow; offspring masses at birth and at emergence were significantly negatively correlated with litter size. On average, litters weighed 16.3% (48 g) of maternal mass at birth and 157.5% (578 g) at emergence from the natal burrow. Compared with other hibernating sciurids, Richardson's ground squirrels have a similar offspring mass relative to maternal mass both at birth and at emergence from the natal burrow. However, because of the large litter size (typically 6–8), absolute reproductive effort, measured either as litter mass at birth or at natal emergence, is large for the body size of the species.     

Sexual maturation in male Belding's ground squirrels: influence of body weight

The relation between body weight and sexual maturation was examined in a hibernator, Belding's ground squirrel, by manipulating the availability of food to weaned juvenile males. Following body weight manipulation in the summer, testicular growth, serum testosterone, and spermatogenesis were monitored during the subsequent year, which included 7 mo when males were in the coldroom (ca. 8 degrees C), followed by 5 mo in the laboratory (ca. 20 degrees C). Juveniles (less than 1 yr old) maintained on a restricted diet entered the coldroom at normal body weights for their age class in nature and had immature gonads throughout the year, which is characteristic of this group in the field. In contrast, juveniles given abundant food during the summer entered the coldroom at body weights typical for free-living yearlings and exhibited mature gonads shortly after males were removed from the cold (high relative testis weights, high serum testosterone levels, and all stages of spermatogenesis). The high level of gonadal activity in overfed males was confined to a period of a few weeks in the spring, which coincided with the time when mating occurs in nature. The ability of male Belding's ground squirrels to accumulate body weight prior to hibernation seems important to sexual maturation in this seasonally breeding rodent.     

Determinants of reproductive success in female Columbian ground squirrels

Summary We studied the reproductive success of female Columbian ground squirrels (Spermophilus columbianus) in southwestern Alberta for nine years. We defined reproductive success as the number of offspring surviving their first hibernation, classified as yearlings. The number of weaned juveniles explained one third of the variance in number of yearlings at emergence from their first hibernation the following spring, and much of the variance in individual reproductive success originated after weaning. Weight of adult females at emergence from hibernation was correlated with annual reproductive success. The mother's survival beyond weaning and the subsequent winter's snow accumulation had positive effects on annual reproductive success, whereas population density and summer temperature had negative effects. We found no effects on annual reproductive success of date of litter emergence, weight at emergence as a yearling, presence or absence of adult kin, distance from the natal site, location within the study area, winter temperature or summer precipitation. Age of first breeding did not affect lifetime reproductive success, which ranged from 0 to 19 yearlings produced over a lifetime. The greatest source of variation in lifetime reproductive success for females surviving to breeding age was offspring survival, followed by reproductive lifespan.     

Intraspecific differences in the pattern of hibernation in the ground squirrelSpermophilus beldingi

Summary Intraspecific differences in the patterns of heterothermy were found in captive Belding's ground squirrels that hibernated undisturbed at ambient temperatures of 5°C, 10°C, and 15°C. The timing of all entrances into and arousals from hibernation was determined from records of copper-constantan thermocouples that were mounted on the floor of each animal's nest box and connected to continuously recording potentiometers. In the absence of food, large adult males terminated hibernation spontaneously in the spring. In contrast, females and small non-breeding males (yearlings) did not stop hibernating but instead they shortened their bouts of torpor in the spring so that they aroused every three or four days. This interval of frequent arousals, termed the emergence period, lastel until the squirrels became emaciated, and it was only in the 2 or 3 weeks preceeding death (starvation period) that arousal frequency once again decreased towards midwinter values (Fig. 3). These animals terminated hibernation when fed during the emergence or starvation periods, but they were able to resume torpor if that feeding lasted less than a week.Termination of hibernation and reproductive development in males were related to the size of the animals, not their age. Males two years and older which did not deposit normal quantities of fat were like yearlings in that they had open-ended hibernation seasons and showed little testicular enlargement. Likewise, juvenile males that grew to near adult size in their first summer spontaneously terminated hibernation and had well developed testes like most older individuals. In addition, both the frequency and duration of arousals in the emergence period were related, in part, to the extent of the animals' fat reserves, such that large squirrels spent more time at high body temperatures than small individuals (Figs. 5, 6). This trend was most pronounced at high ambient temperatures.These intraspecific differences in hibernation physiology are consistent with the sex and agerelated differences in the timing of emergence above ground in nature. The increase in the time spent euthermic in the spring isinterpreted as an adaptation for increasing the opportunities for environmental assessment. The intraspecific differences in the extent of this euthermia appear to be associated with differences in the balance between the energy supplies available to an animal and its need to accelerate the use of that energy (i.e., arouse) in order to achieve an early and accurately-time emergence from the hibernaculum.     

Shifts in gonadotropin and steroid levels that precede anestrus in female golden hamsters exposed to a short photoperiod

Female golden hamsters exposed to short photoperiods become anestrous and exhibit daily surges of gonadotropins and progesterone. Since little is known about the transition between the cycling and anovulatory states, the following experiments were done to determine whether there are hormonal changes that precede cessation of estrous cyclicity. Females killed on the morning of estrus, up to the tenth estrous cycle in short days, showed no hormonal or ovarian morphologic evidence of changes in reproductive function. When assessed on the afternoon of estrus, however, serum levels of luteinizing hormone and progesterone increased significantly before vaginal and ovarian cyclicity ceased. Females sampled in both the morning and afternoon at increasing durations since their last vaginal estrus revealed that maximal daily surges of both gonadotropins and progesterone were not consistently manifested until the vaginal cycle had been absent for 2 weeks. By then, estrogen levels and uterine weights were low and ovaries showed hypertrophied interstitia and arrested follicular growth. We have demonstrated that there are hormonal changes in females before the loss of the vaginal cycle and onset of major daily hormonal surges. Our results suggest that alterations in feedback relationships between steroid hormones and gonadotropins may precede photoperiod-induced anestrus.     

Reproductive Decisions in Female European Ground Squirrels: Factors Affecting Reproductive Output and Maternal Investment

Physiological and behavioural parameters associated with reproductive effort and success were investigated in female European ground squirrels Spermophilus citellus . The proportion of reproductive (lactating) females in the study population was over 90% and was not related to age. Timing of oestrus and ovulation was found to be affected by the female's emergence date and condition. Females with low emergence mass showed delayed oestrus. Differences in ovulation dates were shown to affect reproductive output in terms of litter size and sex ratio. Early litters were larger and male biased. X-ray techniques were used to determine intrauterine litter size in individual females. The results indicated that litter size and sex ratio were fixed prenatally. Lactation costs were reflected in the intensity of mass loss and duration of lactation. Mass loss varied with litter size, in that females with large litters showed a more rapid loss than others. The second parental investment parameter, lactation duration, varied among individual females and was dependent on the timing of reproduction and litter size (except yearlings). Early born litters, which were, in most cases, larger than later ones, were nursed longer. Prolonged lactation periods affected female condition in that they started prehibernation fattening later and entered hibernation with a lower mass than individuals that had shorter lactation periods. Yearling females probably could not afford the energetic costs of long lactation, independent of their offspring number. These results indicated that females with higher reproductive output and higher investment were unable to compensate these costs before hibernation. Consequences for these individuals could therefore be lower over-winter survival or a delayed oestrus in the following season.     

Vaginal oestrus during the reproductive and non-reproductive period in European ground squirrels

Most hibernating animals are thought to be monoestrous because reproductive activity is subject to strong time constraints. In previous studies, female European ground squirrels (Spermophilus citellus) turned out to have elevated oestradiol levels during late lactation and after weaning, indicating ovarian activity during summer. Therefore, we monitored vaginal cytology, endocrine changes, and vulval development in semi-free-living female European ground squirrels throughout one active season. Vaginal oestrus, defined by the predominance of cornified cells in smear samples, was found during the mating period shortly after vernal emergence. This phase was followed by metoestrus, characterised by the appearance of leukocytes, and a subsequent anoestrous phase. During weaning or postlactation, a second vaginal oestrus was documented in all experimental females, again followed by a metoestrous and an anoestrous phase lasting until hibernation. In line with the second vaginal oestrus, plasma oestradiol concentrations peaked during postlactation. Progesterone levels were elevated from gestation to postlactation, and titres were marginally higher during vaginal oestrus in summer than in spring. Vulval swelling was more pronounced during the first than the second vaginal oestrus. The second oestrous cycle was non-reproductive, as males were sexually inactive with regressed testes during summer. We assume that the second oestrous cycle and the accompanying endocrine changes have beneficial effects on prehibernatory fattening and reproductive performance in the subsequent season. This might allow females to become oestrous immediately after emergence from hibernation in spring.     

Parameters of Mating Effort and Success in Male European Ground Squirrels,Spermophilus citellus

Behavioural and physiological changes during the reproductive period were documented in male European ground squirrels including: initiated conflict, scent marking, locomotion and range size, as well as testis size, scrotal pigmentation, testosterone levels and changes in body mass. Spring emergence dates in adult males varied but preceded those of females. Gonadal maturation was complete in adult males at emergence. Most yearlings did not mature and emerged with females. After a quiescent premating phase, male range, range overlap, conflict rates and locomotion increased at female emergence. The synchrony of females, their small ranges and short latencies to ovulation produced a highly male-biased operational sex ratio (OSR) and potential for scramble competition polygyny. In contrast to other ground squirrel species, each female apparently mated with only a single male. Scramble competition did appear to occur, in that males tried to contact as many females as often as possible before copulation. Females placed high temporal prerequisites on males. Costs of scrambling were documented by body mass loss during mating, which covaried with the number of ‘acquired’ females. Testicular regression occurred earlier, and fattening, moult and onset of next hibernation were delayed in successful males. The determinant factor in these costs was found to be mass loss intensity during the main mating period. Surprisingly, this factor was best related to feeding changes and not to locomotion or aggression. Time budget constraints perhaps imposed by the female, with compounding influences of exercise and stress effects of conflict, then negatively affected ensuing seasonal activities. The individual changes may adversely affect individual survivability and/or future reproductive success.     

Sexual differences in over-winter torpor patterns of Richardson's ground squirrels in natural hibernacula

Summary Over-winter torpor patterns of Richardson's ground squirrels hibernating in southern Alberta were monitored with temperature-sensitive radiocollars to determine if these patterns differed between males and females in a manner related to the greater costs of mating effort by males than females. The hibernation season (from immergence to emergence) was composed of three periods: post-immergence euthermy, heterothermy, and pre-emergence euthermy. The hibernation season was shorter for juveniles than adults both among males (< 150 versus 234 days) and females (185 versus 231 days), a reflection of the later immergence into hibernation by juveniles. However, regardless of the absolute duration of hibernation, heterothermy accounted for a smaller proportion of the hibernation season of males (93±5%) than females (98±1%) and, within the heterothermal period, males had shorter torpor bouts and longer inter-torpor arousals. Overall, males spent a smaller proportion of the hibernation season in torpor (85±6%) than females (92±1%). This sexual difference was largely attributable to the longer duration of preemergence euthermy for males than females. Males terminated torpor in January and February, when hibernacula were at their coldest, then remained euthermic for 8.8 days (range 0.5–25.0 days) before emergence. In contrast, females terminated torpor in March, when hibernaculum temperatures were increasing, then remained euthermic for only 1.1 days (range 0.5–2.0 days) before emergence. Males lost less mass per euthermic day during hibernation than females (7.0 versus 9.3 g/day). Males and females hibernated at similar depths (56 cm), but males had larger chambers than females (18 versus 16 cm³/g). Many males, but no females, cached seeds in the hibernaculum. Males met the costs of thermogenesis and euthermy from a combination of fat reserves and food caches, whereas females relied solely on fat. Access to food caches permitted males to terminate torpor several weeks in advance of emergence, during which time they recouped mass and developed sperm in preparation for the forthcoming mating season.     

Four years of induction/synchronization of estrus in dairy goats: effect on the evolution of eCG binding rate in relation with the parameters of reproduction

Ninety-eight Alpine goats of two herds were followed over 4 years in a program of annual artificial insemination after estrus induction/synchronization, including progestagen administration (vaginal sponge) followed by prostaglandin analog and equine chorionic gonadotrophin (eCG) 48 h before sponge removal. Goats were sampled every 4 hours from the 16th to the 56th following sponge removal, for determination of LH surge and tested for estrus by the presence of a buck. Seven days after AI, endoscopic examination of the ovaries was performed to determine the number of corpus lutea. Pregnancy diagnosis was performed at day 21-22 post AI by determination of plasma progesterone and at day 40-45 by ultrasonography. Parturition, number and sex of kids were recorded. All the goats were sampled before and after each treatment, for anti-eCG antibodies screening. Statistical analysis of the results clearly established a significant effect of the treatments on anti-eCG antibodies. Time of estrus and LH surge were significantly different between herd. The antibodies significantly delayed the time of coming out of estrus as well as the time of LH surge. Two antagonistic effects were evidenced: first, the delayed of time of estrus and time of LH surge in relation with the immune reaction to eCG; secondly, the ahead of time of estrus and time of LH surge during the years of treatment, identical to both herd. The antibodies negatively influenced the percentage of ovulating females as well as kidding rate. Finally, no effect of antibodies on prolificacy was found.     

Effects of hCG on folliculogenesis and fecundity in mink (Mustela vision Schreb)

The endogenous hormonal response obtained after reproductive organs are challenged by exogenous hormones is increasingly being used to predict presence of functional reserves and to apply this information to improve efficiency of managed breeding programs. With that in mind, the aim of the present study was to investigate the effect of a single treatment with hCG on folliculogenesis and fertility in standard 7-month-old mink females. The extent of stimulation following treatment was determined by examining patterns of vaginal smears. Characteristics of each cycle stage were: estrus, preponderance of cornified epithelial cells; proestrus, polygonal, elongate epithelial cells; anestrus, parabasal, intermediate and leucocyte cells. Smears exhibiting a mixed population of cells were categorized as being in transition between adjacent stages anestrus–proestrus or proestrus–estrus. The initial evaluations were done on Day 6 after hCG treatment. Histomorphometric examination of ovaries and uteri was done during seasonal anestrus (November) and in the breeding season (March). Vaginal cytology patterns were correlated with changes in folliculogenesis. A mean of 1.3 mature (Graafian) follicles were counted during estrus, while the mean number seen during anestrus, anestrus–proestrus and proestrus, were 0.4, 0.3 and 1.0, respectively. During the breeding season, in females that were not treated, the numbers of growing follicles decreased and maturing follicles increased, whereas females that came in estrus after treatment with hCG in November had increased numbers of both growing and maturing follicles. Fertility after breeding in hCG-treated females was increased by 9.2% (P<0.05) as compared to untreated females. Females showing the highest fertility rise (27%) were predominantly in the group that showed estrus after hCG treatment. We conclude that monitoring the response of the mink reproductive system to hCG stimulation in November may be a useful tool for identifying females of high fertility in the spring.     

Evidence of non-hibernation in Cantabrian brown bears

Evidence of non-hibernation in brown bears Ursus arctos Linnaeus, 1758 on the Iberian Peninsula has existed since the Middle Ages. We systematically monitored brown bears in the Cantabrian Mountains (Northern Spain) by recording tracks and sightings from 1998 to 2007 to document hibernation behaviour. Our results indicate that females with yearlings and solitary yearlings were more active in winter than bears over two years old. Intensive snow tracking and direct observations of five family groups indicated that they travelled, fed and defecated in winter, which are activities not compatible with the physiological state of hibernation. Also, based on tracking data, the maximum period between two consecutive locations of active family groups in winter was less than that needed by bears to emerge from a state of hibernation (6 days). We conclude that the family groups which we monitored in winter did not hibernate.     

The postpartum buffalo. II. Acyclicity and anestrus

Prolonged postpartum acyclicity (absence of ovarian cyclic activity) and anestrum (absence of overt estrous signs) are major sources of economic loss to buffalo breeders. Studies on the epidemiology of these two problems are highly recommended to achieve successful control. Review of the available literature on controlled studies in dairy buffaloes revealed that first ovulation as detected by rectal palpation and progesterone analysis occurred between 28-71 and 24-55 days, respectively, after calving. Postpartum estrus in the same studies occurred between 44 and 87 days. Reports concerned with data compiled from breeding records of research stations, breeding farms and small holders where estrus is a subjective measure, gave much longer periods. Also data from Egypt, India and Pakistan indicate that only 34-49% of buffaloes showed estrus during the first 90 days after calving and 31-42% remained anestrus for more than 150 days. In swamp buffaloes both postpartum ovulation and estrus are more delayed than in dairy buffaloes. The role of suckling, nutrition, body condition score at calving, milk yield, parity, season of calving and other minor factors were discussed. First postpartum ovulation is frequently followed by one or more short estrous cycles (<18 days). Long anovulatory and anestrous periods due to prolonged inter-luteal phase were reported to occur after short cycles. Also long anestrous periods due to cessation of cyclic activity (true anestrus) for 3 or more weeks and prolonged luteal activity for 28 days or more were described to occur in about 25 and 8-11% of the buffaloes, respectively, after the first or second ovulation. These cycle irregularities certainly impose difficulties on estrus detection programs in postpartum buffaloes. Four main forms of anestrus i.e. true anestrus (inactive ovaries and small and medium sized anovulatory follicles), subestrus, prolonged luteal activity and ovarian cysts in addition to pregnancy are reviewed in this article. Differentiation between true anestrus and subestrus is particularly important in buffaloes because of their weak estrous signs. However, the accuracy of a single rectal palpation of the ovaries is limited with an overestimation of the frequency of true anestrus due to misdiagnosis of the corpus luteum. The possible causes are discussed.     

Sexual characteristics of female dogs during successive phases of the ovarian cycle

Five female beagles were examined periodically throughout their second biannual cycle of proestrus, estrus, metestrus, and anestrus for fluctuations in several physiological and behavioral charateristics. Physiological measures included plasma levels of estradiol and progesterone as well as the vulvar swelling and vaginal bleeding that begin with proestrus and continue in estrus. Behavioral tests revealed changes in female receptivity, attractivity, and proceptivity. Estradiol increased prior to the onset of proestrus and declined during estrus. Progesterone levels were low during most of proestrus, increased from the beginning to the end of estrus, and remained elevated during the first month or more of metestrus. While they were in proestrous females were not receptive but they and their vaginal secretions were highly attractive to males. Attractivity remained high throughout estrus and declined abruptly in the next 24 hr. Receptivity increased over the first 3 days of estrus and continued at a high level until the last 3 days during which it decreased slightly, and then dropped nearly to zero within the next 24 hr. “Sexual reflexes” of the vulva, tail, and hindquarters followed the same course of changes described for attractivity. Proceptive behavior, including seeking proximity to caged males and display of solicitation responses during mating tests was characteristic of females during proestrus and estrus but uncommon or absent in other phases of the cycle. It is hypothesized that in the natural cycle, attractivity and proceptivity develop during proestrus as a consequence of rapidly increasing secretion of estrogen. The onset of receptivity is due to synergistic action of estrogen and progesterone. Estrogen secreted during proestrus primes the system, and progesterone secreted just before and during estrus activates it. Termination of receptivity is thought to be due to the marked decline in estrogen, to inhibition by high concentrations of progesterone, or to a combination of these factors.     

The effects of pheromonal stimuli on estrus and peripheral plasma estradiol in female gray short-tailed opossums (Monodelphis domestica)

Exposure to male pheromones is associated with the activation of vaginal estrus in gray short-tailed opossums. The effects of such exposure on peripheral plasma estradiol-17 beta (E) levels in this marsupial species were examined in this study. Mean E levels of 27.8 pg/ml +/- 4.4 in diestrous females living in a room containing only females were similar to those seen in other marsupials. Direct naso/oral exposure to pheromonal cues provided by males resulted in vaginal estrus in 75% of these females within 4 11 days. None of the females exposed to clean cages came into vaginal estrus. Animals that were in estrus at the time of blood sampling or came into estrus over the experimental period had significantly higher E levels (58.1 +/- 12.6 pg/ml) than females in the pheromone-exposed and control groups that did not come into estrus (23.3 +/- 8.2 pg/ml). These findings are discussed with respect to other marsupial and eutherian species.     

Seasonal variation of cardiovascular function in the marmot, Marmota flaviventris

Monthly measurements of heart rate, mean arterial pressure, and cardiac output were made on active and hibernating marmots from the time of emergence from hibernation through the next hibernation period. From these measurements cardiac index, stroke index, and total peripheral resistance were calculated on the basis of estimated lean body mass. Heart rate was low after emergence (132 +/- 9.5 beats (B)/min), peaked in August (160 +/- 9.3 B/min), and then fell slightly in September and October. During hibernation heart rate fell to 9 +/- 1.1 B/min. Mean arterial pressure, which was low in early spring (101 +/- 6.9 mm Hg), rose to a peak value in June (131 +/- 7.7 mm Hg) and remained essentially unchanged until hibernation when it fell to 52 +/- 4.0 mm Hg. Cardiac index (61 +/- 4.9 ml/kg min) in March rose to a peak in May (83 +/- 8.5 ml/kg min) and fell linearly until October. There was an additional drop in cardiac index during hibernation (7.6 +/- 0.9 ml/kg min). Total peripheral resistance increased linearly from the time of emergence until October. Most of this change was due to the decrease in cardiac index. Stroke index showed no significant changes in the prehibernation period, but increased by 55% during hibernation. Maintenance of arterial pressure in the months preceding hibernation in the face of diminishing cardiac index indicate that alterations in vasomotor tone or shifts in patterns of blood flow occurred prior to the hibernation period.     

Influence of reproductive stage at PRID insertion on synchronization of estrus and ovulation in mares

In the present study, we investigated the effects of reproductive status, size of follicles and plasma progesterone concentrations of mares at PRID insertion on the efficacy of the treatment, estrous cycle patterns, plasma concentrations of progesterone and LH. The progesterone-releasing device (PRID) was administered intravaginally to 28 Haflinger mares for 11 days at different reproductive stages: anestrus (n=6), estrus (n=11) and diestrus (n=11). Plasma concentrations of progesterone at insertion (Day 1) of PRID differed among treatment groups (anestrus: 0.2-0.6 ng mL(-1), estrus: 0.2-0.5 and diestrus: 1.6-10.8 ng mL(-1); P<0.001). Total secretion of progesterone (area under curve (AUC)) during treatment period revealed highest values in diestrus (38.2+/-3.1 ng mL(-1)h(-1)) followed by estrus (25.1+/-2.7) and anestrus (21.0+/-0.4 ng mL(-1)h(-1); P<0.05). Progesterone area under curve (AUC) was positively correlated with initial progesterone concentrations (R=0.5; P<0.05), but it did not correlate with the interval from PRID removal to ovulation. Plasma concentrations of LH during treatment period, were significantly lower in anestrous mares (184.6+/-28.6 ng mL(-1)h(-1)) when compared to estrous and diestrous mares (349.7+/-53.3 and 370.5+/-40.3 ng mL(-1)h(-1); P<0.05). Follicular size at PRID insertion had no effects on the intervals from PRID removal to subsequent estrus and ovulation. Follicle diameters at removal of PRID were significantly correlated with the interval from coil removal to estrus (R=-0.55, P<0.05) and ovulation (R=-0.72, P<0.0004) in cyclic mares. In anestrus 0 of 6 (0%) mares, in estrus 5 of 11 (45.5%) and in diestrus 6 of 11 (54.5%) mares ovulated within a defined interval of 1 day before to 1 day after mean interval from PRID removal to ovulation. In cyclic mares, response to treatment was significantly higher when compared to anestrous mares: almost all mares responded with estrus and ovulation independent from the stage of the estrous cycle at the start of treatment. However, accuracy of synchronization was still unsatisfactory. In cyclic mares, the plasma progesterone concentrations at insertion of PRID seem to be more important for the efficacy of the treatment than the assignment to estrous cycle stages.     

Characterization of the estrous cycle in Octodon degus

We characterized the reproductive cycle of Octodon degus to determine whether reproductive maturation is spontaneous in juveniles and if ovarian cyclicity and luteal function are spontaneous in adults. Laboratory-reared prepubertal and adult females were monitored for vaginal patency and increased wheel-running. Sexual receptivity was assessed by pairing adult females with a male 1) continuously, 2) at the time of vaginal patency, or 3) following estradiol treatment. Blood samples were assayed for estradiol and progesterone concentrations on Days 1, 4, 8, and 16 relative to vaginal opening. Ovarian tissues were collected 6 and 16 days after behavioral estrus and 6 days after copulation for histology. In juveniles, the onset of cyclic vaginal patency and increased wheel-running activity was spontaneous, occurred in the absence of proximal male cues, and appeared at regular intervals (17.5 ± 1.4 days). In adults, vaginal patency and increased wheel-running occurred cyclically (21.2 ± 0.6 days) in the absence of proximal male cues, and these traits predicted the time of sexual receptivity. Corpora lutea develop spontaneously and are maintained for 12-14 days. The ovaries had well-developed corpora lutea 6 days after mating and 6 days after estrus without mating. Progesterone concentrations were highest in the second half of the cycle when corpora lutea were present and estradiol concentrations peaked on the day of estrus. Thus, female degus appear to exhibit a spontaneous reproductive cycle consistent with other Hystricognathi rodents. Octodon degus is a novel model with which to examine the mechanisms underlying different reproductive cycles.