Reproductive cycles in Tarsius bancanus

The reproductive condition of three pairs of Bornean tarsiers (Tarsius bancanus) was documented for 16 months. Each pair was housed separately under a constant photoperiod (L:D = 11.5:12.5) similar to that in their native habitat. Reproductive cycles of females were monitored visually for 6 months and were then monitored with vaginal smears and measurements of external genitalia for an additional 10 months. Progressive proliferation and cornification of vaginal epithelial cells during proestrus and estrus was accompanied by an enlargement of the external genitalia. Cycle lengths averaged 24.0 ± 3.2 days. The external genitalia were swollen each cycle for a period of 6–9 days. Copulations occurred on the 1st day of estrus, which lasted 1–3 days. No menstruation was observed. There was no evidence of seasonality of estrous cycles with this photoperiod. Testicular measurements of males showed no overt seasonal changes. There was variation in testicular size, and one male copulated at a range of testicular sizes. The data indicate that T. bancanus has estrous cycles similar to those of prosimian primates and some New World monkeys and that these cycles occur throughout the year under constant photoperiodic conditions.     

Reproductive endocrine responses to photoperiod and exogenous gonadotropins in the pallas' cat (Otocolobus manul)

Fecal samples were collected for 14–26 months from three male and six female Pallas' cats (Otocolobus manul) to examine gonadal steroidogenic activity in response to changes in photoperiod and treatment with exogenous gonadotropins. Females exhibited a seasonal anestrus from May–December, excreting consistently low concentrations of fecal estrogens (overall mean, 50.2±8.5 ng/g). During the breeding season (January–April), baseline fecal estrogen concentrations were higher, averaging 128.4±18.9 ng/g, with peak concentrations ranging from 455.8–909.6 ng/g. Interpeak intervals in estrogen excretion ranged between 7 and 21 days, with an average estrous cycle length of 14.3±1.7 days. Two females became pregnant after natural mating, with overall luteal progestogen concentrations averaging ～40 μg/g throughout gestation. Fecal estrogens increased in mid‐gestation, peaking just before birth. Induction of follicular development with eCG (100–300 IU, i.m.) resulted in an increase in fecal estrogens (peak range, 263.1–1198.1 ng/g), followed by a postovulatory increase in fecal progestogens (overall mean, 41.1±11.9 μg/g) after hCG (75–150 IU, i.m.). Despite apparently normal ovarian responses, none of the females conceived after artificial insemination (AI). The gonadotropin‐induced nonpregnant luteal phase lasted 49.8±5.3 days (range, 30–60 days), whereas gestation lasted ～70 days. In the male Pallas' cat, fecal androgens were elevated from November–April (overall mean, 352.3±30.3 ng/g) compared with nadir concentrations during the rest of the year (82.1±3.3 ng/g). Entrainment of seasonality to photoperiod was demonstrated by stimulation of gonadal steroidogenic activity in cats exposed to increasing artificial light during natural (nonbreeding season) and artificially induced short‐day photoperiods. In summary, reproduction in Pallas' cats is highly seasonal and photoperiod‐dependent. Females exhibit elevated baseline and peak fecal estrogen concentrations for 3–4 months during late winter/early spring. Testicular steroidogenic activity precedes the rise in female estrogen excretion by about 2 months, presumably to ensure maximal sperm production during the breeding season. Zoo Biol 21:347–364, 2002. Published 2002 Wiley‐Liss, Inc.     

Ovarian and behavioral cyclicity of the laboratory maintained cat

This study examined the sexual behavior-ovarian activity relationship of the laboratory cat maintained under consistent environmental conditions. Mean (±SEM) lengths of estrus for nonovulating, mated ovulating, and human chorionic gonadotrophin (HCG)-induced ovulating queens were 5.8 ± 0.17, 6.5 ± 0.75, and 10.0 ± 0.65 days, respectively. The duration of estrus was significantly (P < 0.01) longer in HCG-treated queens in comparison to the nonovulating or mated ovulating groups. No differences were observed in the number of behavioral estrous periods detected monthly. Duration of estrus was affected by season with significantly shorter periods of estrus observed in June (P < 0.05), September (P < 0.05), October (P < 0.05), and November (P < 0.01) compared to the March, April, May, August, or December averages. Length of estrous cycle (from Day 1 of estrus to Day 1 of next estrus) was variable (range: 6–120 days); however, 49.8% of the estrous cycles were 12 to 21 days in length. Although the ovaries of queens displaying sexual receptivity always contained developing or mature foilicles, ovaries of cats showing no estrous behavior also showed patterns of follicular development and regression at 14- to 19-day intervals. These results suggest that the estrous cycle of the laboratory maintained cat varies from 2 to 3 weeks in duration and that reproductive behavioral patterns alone are not always an accurate indication of ovarian activity or duration of the reproductive cycle.     

What photoperiodic signal is provided by a continuous-release melatonin implant?

The purpose of this study was to evaluate whether the insertion of a continuous-release melatonin implant into ewes provides a short-day photoperiodic signal or acts as a functional pinealectomy (provides no specific photoperiodic signal but renders ewes incapable of responding to changes in photoperiod). Ewes primed with 60 long days (18L:6D) during the spring were moved to intermediate day length (13L:11D) for 66 days and then given one of five treatments: 1) short-day control, second drop in photoperiod to 8L:16D; 2) intermediate-photoperiod control, kept on 13L:11D; 3) pinealectomy and kept on 13L:11D; 4) melatonin implant and kept on 13L:11D; 5) melatonin implant and moved to 8L:16D. Mean number of estrous cycles per group and total duration of reproductive activity were determined. Ewes in all groups began to exhibit estrous cycles after the initial reduction in photoperiod. The number of estrous cycles and duration of reproductive activity differed among groups. The number of estrous cycles and duration of reproductive activity was extended in ewes receiving the second drop in photoperiod compared to that of the intermediate-photoperiod controls. Pinealectomized ewes had a number of estrous cycles and duration of reproductive activity similar to those of ewes maintained on the intermediate photoperiod. Melatonin implants increased the number of estrous cycles and prolonged reproductive activity in ewes maintained on the intermediate photoperiod; melatonin implants did not prevent the extension of reproductive activity in ewes receiving the second photoperiodic drop to the short daylength.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurons of the lateral preoptic area/rostral anterior hypothalamic area are required for photoperiodic inhibition of estrous cyclicity in sheep

Photoperiod determines the timing of reproductive activity in many species, yet the neural pathways whereby day length is transduced to a signal influencing gonadotropin-releasing hormone (GnRH) release are not fully understood. Physical lesions of the lateral preoptic area (lPOA)/rostral anterior hypothalamic area (rAHA) in female sheep extend the period of estrous cyclicity during inhibitory photoperiods. In the present study we sought to determine whether destroying only neurons and not fibers of passage in this area would lead to similar resistance to photosuppression. Additionally, neural tract-tracing was used to map connectivity between the lPOA/rAHA and other hypothalamic areas implicated in photoperiodic regulation of reproduction. Progesterone secretion was monitored in six sheep to determine estrous cycles for 90 days during a short-day (permissive) photoperiod. Three sheep then received bilateral injections of the excitotoxic glutamate analog, n-methyl-aspartic acid, directed toward the lPOA/rAHA, whereas three others served as controls. All were then exposed to a long-day (suppressive) photoperiod for 120 days. Control sheep ceased cycling at 40 ± 10 days (mean ± SEM), whereas lesioned sheep continued cycling through the end of the study. The results of the tract-tracing study revealed both afferent and efferent projections to the medial POA, retrochiasmatic area, arcuate nucleus, and premammillary region. Furthermore, close proximal associations with GnRH neurons from efferent projections were observed. We conclude that neurons located within the lPOA/rAHA are important for timing cessation of estrous cycles during photosuppression and that this area communicates directly with GnRH neurons and other hypothalamic areas involved in the photoperiodic regulation of reproduction.     

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

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

Reproductive photorefractoriness in rams and accompanying changes in the patterns of melatonin and prolactin secretion

Exposure of rams to alternating 16-week cycles of long and short days (16L:8D and 8L:16D) results in periods of testicular regression followed by testicular redevelopment, and there is an inverse relationship between the blood levels of prolactin and testis activity. In this study, two groups of rams were held under long or short day lengths for a period of 94 weeks. When held under either long or short days for more than 16 weeks, the animals showed spontaneous changes in gonadal activity and in the secretion of prolactin, both of which were no longer correlated with the prevailing photoperiod, i.e., they became photorefractory. The photorefractoriness was characterized by cyclical changes in testis function which were independent of day length. The period of these spontaneous cycles was similar during both treatment regimens (long days: 40.9 +/- 1.5 weeks; short days: 38.1 +/- 0.33 weeks), suggesting the presence of an endogenous pacemaker for the reproductive system. The changes in blood prolactin levels during photorefractoriness were no longer correlated with testis activity, and though cyclical, the period lengths differed under the two regimens (long days: 31.8 +/- 1.4 weeks; short days: 48.6 +/- 0.3 weeks). The rates of change in testis function and prolactin secretion were slower during the refractory state than during the photosensitive state. Upon switching the rams to a different photoperiod after the 94 weeks of exposure to fixed day lengths, the rams showed relatively rapid testicular and prolactin responses. Photoperiodic information appears to be relayed to the endocrine system through the daily pattern of melatonin secretion by the pineal. We measured the daily blood levels of melatonin on several occasions during phases of photosensitivity and photorefractoriness in the same group of rams. During the first 21 weeks under both lighting treatments, the rams showed synchronized daily patterns in their blood levels of melatonin, with elevated levels occurring mainly during the daily period of darkness. Similar synchronized daily rhythms were also seen when the rams were switched to a different photoperiod following 94 weeks of exposure to either long or short days. Between Weeks 21 and 94, the daily rhythms of melatonin did not occur consistently in all rams; often, the patterns differed markedly between individual rams held under the same day length and peak levels of melatonin were not always confined to periods of darkness.(ABSTRACT TRUNCATED AT 400 WORDS)     

Influences of the adrenal gland and photoperiod on the hamster oestrus cycle

The influence of the adrenal gland and photoperiod on the adult female hamster estrous cycle was investigated. Hamsters were exposed to 14 hours of light per day and estrous cycles were monitored. Normal cycles were characterized by a copious discharge every 4th day. Hamsters were then adrenalectomized, adrenalectomized and blinded, or blinded only. Adrenalectomized/blinded hamsters were given a .2% sodium saccharine-1%(w/v) sodium chloride solution to drink which promotes long-term survival in most adrenalectomized hamsters. With blinding alone, it took from 18 to 62 days for cessation of estrous cycles. Cycles ceased in a mean of 36.2 days in blinded/adrenalectomized hamsters. After adrenalectomy only, 3 hamsters continued to show 4-day estrous cycles for at least 9 weeks in response to the long days. 6 adrenalectomized animals died due to adrenal insufficiency but displayed several 4-day estrous cycles. It is suggested that in the hamster, adrenal hormones are nonessential for the long-term expression of estrous cyclicity. However, further research is needed to determine whether adrenal hormones are capable of modulating photoperiodic time measurement or ovarian regression.     

Cervical patency during non-ovulatory and ovulatory estrus cycles in domestic cats

The cervix functions as a barrier to spermatozoa. Vaginal artificial insemination in cats is, therefore, likely to be successful only at the period of estrus when the cervix is open. This study aimed to define the period of cervical patency in cats in both non-ovulatory and ovulatory estrus cycles. A total of 15 reproductive cycles were studied in six cats during the estrous stage. Cervical patency was monitored with the cats under sedation, by infusing 2 mL of Iohexol contrast medium via a 3.5 French tomcat catheter into the cranial vagina during estrus. Day one of estrus was defined as the first day the cats showed estrous behavior. Non-ovulatory cycles were characterized by a serum progesterone concentration on days 11-15 that was below 5 nmol/L and a normal interestrus interval of 7-14 days. Ovulatory cycles were characterized by a serum progesterone concentration on days 11-15 that was above 5 nmol/L and an interestrus interval that exceeded 30 days. The cervix was considered to be open when the contrast medium was seen to enter the uterus, and to be closed when the contrast medium remained in the vagina. Blood samples were collected at each examination and were assayed for estradiol-17beta and progesterone concentrations. The cervix was open on the first day of standing estrus at a mean estradiol-17beta serum concentration of 87.4+/-21.8 pmol/L (range 14 to >or=180 pmol/L) and closed at an estradiol concentration of 47.1+/-12.4 pmol/L (range 4 to >or=180 pmol/L). In the ovulatory cycles the cervix was closed at a progesterone concentration of 9.8+/-4.4 nmol/L (range 0.6-28.4 nmol/L). There was no difference in the duration of cervical patency in non-ovulatory and ovulatory cycles (5.5+/-1.2 days and 5.2+/-0.5 days, respectively) (p>0.05). The higher overall mean concentrations of estradiol-17beta seen in the ovulatory cycles than in the non-ovulatory cycles, indicate that a high level of estradiol is necessary for induction of ovulation. Ovulation in 60% of unmated females in this study indicates that the techniques used for evaluation of cyclus stage and cervical opening have the potential to induce ovulation in the cat. This study demonstrates that cervical patency is not influenced by the occurrence of ovulation, but is due to individual variations between cats.     

Effects of Calf Removal at Parturition on Postpartum Ovarian Activity in Zebu (Bos indicus) Cows in the Humid Tropics

To assess endocrine and morphological responses of ovaries to total weaning at parturition, 6 Zebu (Bos indicus) cows 5 years or older were investigated. Following parturition, blood samples were collected daily during the first month and twice weekly thereafter until day 60 to determine concentrations of progesterone (P4) and prostaglandin F2α metabolite. It took between 25 to 32 days to complete uterine involution.The prostaglandin metabolite remained elevated for a mean period of 14.2 days (range, 4-21) postpartum. Five of the animals resumed cyclicity with a short estrous cycle starting between days 7 to 34 and lasting between 7 and 14 days. No estrous behavior was recorded prior to the short estrous cycles, but subsequent normal-length estrous cycles were all preceded by signs of estrus. In the 1 animal that resumed cyclicity with an estrous cycle of normal length on day 37 (length 20 days), the cycle was preceded by estrous behavior. Progesterone concentrations reached a mean maximum of 4.8 nmol liter−1 during the short estrous cycles, and prostaglandin metabolite concentrations peaked while P4 concentrations were decreasing. P4 concentrations reached a mean maximum of 12.2 nmol liter−1 during the estrous cycles of normal length. The interval from parturition to the first estrous cycle of normal length varied between 16 and 48 days, and the length of the cycle was 18 to 22 days. Starting 2 days postpartum, ovaries from 5 of the cows were scanned by ultrasonography every second day until day 30 postpartum. Medium-sized follicles were detected between days 4 to 7 postpartum in 4 of the scanned cows that later had short estrous cycles. The time between parturition and the appearance of the first dominant follicle was 7.6 days (range 6-10 days). The interval between parturition and the appearance of the first ovulatory-sized follicle was 10.2 days (range 8-13 days). In 3 of the scanned cows this ovulatory-sized follicle ovulated. We conclude that cyclic ovarian activity in Zebu cows can start early in the postpartum period in the absence of offspring, and that short luteal phases, not preceded by estrous behavior, may play an important role in establishing normal postpartum ovarian activity.     

Suprachiasmatic nucleus and photic entrainment of circannual rhythms in ground squirrels.

The efficacy of photoperiod as a zeitgeber for entrainment of circannual body weight and estrous rhythms was tested in female golden-mantled ground squirrels maintained for 3 or more years in either a simulated natural photoperiod (SNP) or a fixed LD 14:10 photoperiod (FP). The role of the retinohypothalamic tract--suprachiasmatic nucleus (RHT-SCN) projection in photic entrainment was assessed in animals that sustained destruction of the SCN (SCNX). Circannual rhythms were lengthened by the SNP as compared to the FP. Mean periods (tau's) for neurologically intact animals in the third year of testing were 49.6 +/- 0.3 weeks and 43.1 +/- 1.2 weeks (p less than 0.001) for the SNP and FP groups, respectively; furthermore, 56% and 7% of animals in these groups had tau's not significantly different from 365 days (p less than 0.005), and within-group variability was lower for SNP than for FP squirrels (p less than 0.01). SCNX squirrels differed from animals with the SCN intact (SCNC), as evidenced by higher within-group variability (p less than 0.001); only 29% of SCNX squirrels had tau's not different from 365 days (p less than 0.03 compared to the SCNC group). The coupling between estrous and body weight rhythms that was evident in SCN-intact SNP and FP squirrels was disrupted in SCNX animals. The RHT-SCN pathway is implicated in entrainment and in maintenance of normal phase relations among the several circannual rhythms. In a second experiment, female squirrels were maintained for 2.5 years in an accelerated SNP that compressed two normal annual photocycles into each calendar year. Of 12 squirrels, 3 had tau's that did not differ significantly from 6 months; 6 had tau's equivalent to 12 months; and 3 had tau's significantly different from both 6 months and 12 months. The data suggest that photoperiod is a major zeitgeber for entrainment of golden-mantled ground squirrels circannual rhythms.     

Concentrations of 13, 14-dihydro-15-keto-prostaglandin F(2)alpha, estradiol-17beta and progesterone during the peripubertal period in heifers

Twenty prepubertal Holstein heifers were utilized to assess plasma 13, 14-dihydro-15-keto-prostaglandin F(2)alpha (PGFM), serum progesterone (P(4)) and estradiol-17beta (E(2)) concentrations as well as the E(2):P(4) ratio during the onset of puberty in cattle. All animals were maintained as a group along with a sterile marker bull to assist in the detection of estrus. Upon detection of the first estrus (Day=O), daily blood samples were collected from a jugular vein until the heifers had completed 3 estrous cycles. The average body weight and age at first estrus were 247.6+/-4.8 kg and 304.0+/-7.5 days, respectively. Frequency of abnormal length estrous cycles was greater (P<0.02) during the first (40%) and second (35%) cycles than during the third estrous cycle (0%). All heifers had normal cycle lengths (18 to 24 days) by the third estrous cycle. Serum P(4) was greater during the third cycle (P<0.05) from Day 10 to Day 4 before the next estrus compared with the same period of the first estrous cycle. Serum E(2) did not peak until the day of estrus in the first cycle, whereas E(2) reached a maximal level 2 days before estrus in the third estrous cycle. Serum E(2) was higher (P<0.0001) 2 days before estrus in the third cycle than in the first estrous cycle. Plasma PGFM reached maximum concentrations 3 days before estrus in the third cycle compared with 1 day before estrus at the end of first estrous cycle. As estrus approached during the third cycle, PGFM rose 1 day before E(2) rose and P(4) declined, while the rise in PGFM and E(2) occurred simultaneously, with P(4) declining at the end of the first estrous cycle. During diestrus, the E(2):P(4) ratio was lower (P<0.07) in the third cycle than in the first, but it was higher (P<0.04) at estrus and 1 day before in the third estrous cycle. These data reveal a high incidence of abnormal length estrous cycles during the first two estrous cycles of the peripubertal period, and demonstrate anomalies in uterine and ovarian endocrine activity during the peripubertal period in cattle.     

Waves of follicle development during the estrous cycle in sheep

The pattern of ovarian follicle development in maiden cyclic lambs was characterized using the definition of a follicle wave as the changes in the number of follicles among the days of the estrous cycle, as originally defined in cattle by Rajakoski in 1960. We also examined the steroid content relationships among follicles on Days 5 (Wave 1) and 14 (Waves 2 and 3) of the estrous cycle. In Experiment 1, the ovaries of 20 cyclic lambs (40 to 45 kg) were examined daily using transrectal ultrasonography for 1 or 2 estrous cycles (n = 31 cycles). The number of small (2 and 3 mm in diameter), medium (4 and 5 mm) and large (> or = 6 mm) follicles were aligned with the beginning and end of the average length estrous cycle and then compared among days. Identified follicles were defined as those that grew to > or = 4 mm and remained at > or = 3 mm for > or = 3 d. The number of identified follicles emerging (retrospectively identified at 2 or 3 mm) per ewe per day was also aligned with the average length estrous cycle. In Experiment 2, ewe lambs were ovariectomized on Day 5 (n = 6) or 14 (n = 5) of the estrous cycle, then follicle diameters and follicular fluid concentrations of estradiol and progesterone were compared among follicles. Data were analyzed by repeated measures ANOVA and compared among days using Fisher's LSD. In Experiment 1, either 2 (n = 10 cycles), 3 (n = 20 cycles) or 4 (n = 1 cycle) periods of emergence of identified follicles occurred during individual cycles, with estrous cycle lengths of 15.6 +/- 1.6, 16.1 +/- 1.1 and 17 d respectively. In animals with 2 or 3 periods of emergence of identified follicles, the total number of small, medium and large follicles differed (P < 0.05) among days of the estrous cycle showing a wave-like pattern. In Experiment 2, a single follicle collected on each of Days 5 and 14 of the cycle (6.2 +/- 0.2 and 3.9 +/- 0.2 mm in diameter) had a higher (P < 0.05) concentration of follicular fluid estradiol (36.2 +/- 4.4 and 50.9 +/- 21.6 ng/mL) than other follicles collected on the same day (next largest follicle: 4.3 +/- 0.3 and 3.5 +/- 0.4 mm; 4.3 +/- 0.9 and 18.2 +/- 6.7 ng/mL estradiol). The results showed that 1) there was a synchronous emergence of follicles associated with fluctuations in the number and size of follicles during the estrous cycle; 2) within a wave there was a hierarchy among follicles for diameter and steroid content; 3) ovarian follicle growth in ewe lambs occurred in 2 or 3 organized waves during the estrous cycle.     

PHOTOPERIODIC ADAPTATION IN DESERT POPULATIONS OF XANTHIUM STRUMARIUM

Reproductive adaptation to photoperiod is diverse among desert populations of Xanthium. Chihuahuan Desert populations require dark periods of 9.5–10.5 hr for reproduction, and Sonoran Desert populations require 9–10.5 hr. Many Chihuahuan populations from western Texas two weeks from sowing need only 10 cycles of 11-hr nights to produce 100% flowering, but Sonoran populations from western Mexico four weeks from sowing need 18 cycles or more. Some Sonoran plants produce buds only at a cooler temperature program, 24–15 C, but Chihuahuan plants produce them more readily under the warmer program, 30–24 C. Chihuahuan plants that were germinated under 11-hr nights and four different temperature programs were induced to flower in each condition. Differences in photoperiod and ripeness-to-flower (maturity) responses were also demonstrated under natural day lengths in central Texas. Although desert populations occurring at approximately the same latitude in either the Chihuahuan or Sonoran Desert are exposed to similar day lengths, each population may be adapted to different photoperiod cues that maximize its utilization of the local growing conditions.     

Photoperiodic disruption of photorefractoriness in the ewe

The primary objective of this study was to determine the duration of exposure to a long-day or short-day photoperiod required to disrupt photorefractoriness to short-day and long-day photoperiods, respectively. In Experiment 1, 4 groups of Suffolk breed ewes--designated B1, B2, B3, and B4--were placed in photochambers one day before the winter solstice, exposed to a 16L:8D photoperiod for 0, 30, 60, or 90 days, and then exposed to a 10L:14D photoperiod until the time of the summer solstice. Blood samples taken by venipuncture thrice weekly were analyzed for progesterone concentrations. The interval between start of the study and cessation of estrous cycles did not differ significantly between groups (p greater than 0.05). All 6 ewes in Group B1 then remained in anestrus for the duration of the study. Four of the 6 ewes in Group B2, and all ewes in Groups B3 and B4 resumed cycles after exposure to the 10L:14D photoperiod. In Experiment 2, 4 groups of ewes--designated A1, A2, A3, and A4--were placed in photochambers one day before the summer solstice, exposed to a 10L:14D photoperiod for 0, 30, 60, and 90 days, respectively, and then exposed to a 16L:8D photoperiod. Ewes in Group A1 started estrous cycles at a time not significantly different from ewes kept outdoors. However, onset of cycles was significantly advanced (p less than 0.05) in ewes exposed to 10L:14D. After ewes were returned to the 16L:8D photoperiod, estrous cycles were suppressed in 5 of 6 ewes in Group A2 and in all ewes in Groups A3 and A4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Progesterone concentrations during estrous cycle of dairy cows exposed to electric and magnetic fields

Sixteen multiparous nonpregnant lactating Holstein cows (each weighing 662 ± 65 kg in 150.4 ±40 day of lactation) were confined to wooden metabolic cages with 12:12 h light:dark cycle during the experiment. The cows were divided into two sequences of eight cows each and exposed to electric and magnetic fields (EMF) in an exposure chamber. This chamber produced a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 μT at 60 Hz. One sequence was exposed for three estrous cycles of 24 to 27 days. During the first estrous cycle, the electric and magnetic fields were off; during the second estrous cycle, they were on; and during the third estrous cycle, they were off. The second sequence was also exposed for three 24 to 26 days estrous cycles, but the exposure to the fields was reversed (first estrous cycle, on; second estrous cycle, off; third estrous cycle, on). The length of each exposure period (21 to 27 days) varied according to the estrous cycle length. No differences were detected in plasma progesterone concentrations and area under the progesterone curve during estrous cycles between EMF nonexposed and exposed periods (2.28 ±0.17 and 2.25 ± 0.17; and 24.5 ± 1.9 vs. 26.4 ± 1.9 ng/ml, respectively). However, estrous cycle length, determined by the presence of a functional corpus luteum detected by concentrations of progesterone equal to or more than 1 ng/ml plasma, was shorter in nonexposed cows than when they were exposed to EMF (22.0 ± 0.9 vs. 25.3 ± 1.4 days). Bioelectromagnetics 19:438–443, 1998. © 1998 Wiley-Liss, Inc.     

Differential effects of multiple short day lengths on body weights of gonadectomized siberian hamsters

Siberian hamsters (Phodopus sungorus) maintained under simulated natural photoperiods exhibit marked reductions in body weight as day lengths decrease in summer and fall. This experiment assessed whether the component of the seasonal body weight rhythm that is independent of gonadal hormones exhibits a graded dependence on decreasing day lengths or whether the entire program of weight loss is triggered by the crossing of a single critical day length in late summer. Male hamsters born into a photoperiod with 13 h light and 11 h dark (i.e., 13L : 11D) were castrated and transferred to simulated natural photoperiod for early April at 40 degrees N latitude. At the summer solstice (15L : 9D) some hamsters remained on that photoperiod whereas others experienced gradual decreases in day length. Three additional groups were moved to static photoperiods when day lengths had subsequently declined to 13L : 11D, 11L : 13D, or 9L : 15D, respectively. Day lengths decreasing to 13L : 11D were sufficient to suppress body weight but were less inhibitory than further decreases in day length. Hamsters identified as photononresponsive on the basis of daily activity rhythms increased body weight monotonically. These results establish that steroid-independent modulation of body weight depends on photoperiod in a graded fashion.     

Reproductive gonadal steroidogenic activity in the fishing cat (Prionailurus viverrinus) assessed by fecal steroid analyses

Non-invasive fecal steroid analyses were used to characterize gonadal activity in the fishing cat (Prionailurus viverrinus). Estrogen, progestagen and androgen metabolites were quantified in fecal samples collected for 12 months from four males and 10 females housed at seven North American zoological institutions. Male reproductive hormone concentrations did not vary (P>0.05) among season, and estrogen cycles were observed year-round in females and averaged (±SEM) 19.9±1.0 days. Mean peak estrogen concentration during estrus (460.0±72.6ng/g feces) was five-fold higher than baseline (87.3±14.0ng/g feces). Five of seven females (71.4%) housed alone or with another female demonstrated spontaneous luteal activity (apparent ovulation without copulation), with mean progestagen concentration (20.3±4.7μg/g feces), increasing nearly five-fold above baseline (4.1±0.8μg/g feces). The non-pregnant luteal phase averaged 32.9±2.5 days (n=13). One female delivered kittens 70 days after natural mating with fecal progestagen concentrations averaging 51.2±5.2μg/g feces. Two additional females were administered exogenous gonadotropins (150IU eCG; 100IU hCG), which caused hyper-elevated concentrations of fecal estrogen and progestagen (plus ovulation). Results indicate that: (1) male and female fishing cats managed in North American zoos are reproductively active year round; (2) 71.4% of females experienced spontaneous ovulation; and (3) females are responsive to exogenous gonadotropins for ovulation induction, but a regimen that produces a normative ovarian steroidogenic response needs to be identified.     

Characteristics of the estrous cycle of the swamp buffalo under temperate conditions

Estrous cycle, duration of estrus and time of ovulation of eight cyclic buffaloes were examined during a period of one year. Animals were kept under loose-housing conditions and fed according to the Japanese Feeding Standards for dairy cattle. All the animals were observed for the occurrence of estrus twice daily by using a vasectomized bull, and ovarian cycles of each animal were monitored by weekly rectal palpation. Duration of estrus and time of ovulation were determined in 32 estrous periods from eight animals. Animals came in estrus throughout the year. The estrous cycles corresponding to single ovarian cycles ranged from 11 to 38 days with a mode interval of 20 days, averaged 21.5 +/- 4.7 days. Percentage of the cycles within a range of a mean +/- 1 SD (17-26 days) was 79.2 %, whereas that of cycles shorter or longer than the expected range was 9.4 % and 11.4 %, respectively. Estrus took place regardless of the time of day and lasted 9 to 27 hr (19.9 +/- 4.4 hr). Ovulation occurred 6 to 21 hr (13.9 +/- 3.4 hr) after the end of estrus, with a mode interval of 12 hr. There were no significant seasonal variations in the estrus characteristics studied.     

Relationship between gonadal steroid hormones and vulvar bleeding in southern tamandua, Tamandua tetradactyla

This study aimed at demonstrating the profiles of circulating gonadal steroid hormones during the estrous cycle and pregnancy in a southern tamandua (Tamandua tetradactyla). Additionally, this study clarified the relationship between vulvar bleeding and hormonal changes. The concentrations of serum progesterone (P(4)) and estradiol-17β (E(2)) were determined by enzyme immunoassays. Serum P(4) and E(2) concentrations changed cyclically and the estrous cycle length (± SD) based on the E(2) cycles was 44.3 ± 4.5 days. Vulvar bleeding started to be seen at the decreasing of P(4). The cycle length for vulvar bleeding was 43.3 ± 4.2 days. Interval from the first day of bleeding to the peak of E(2) concentration was 23.1 ± 3.1 days. Serum P(4) during pregnancy remained high and E(2) increased 8 weeks after conception and remained high until parturition. The female delivered normally after a 165 day-pregnancy period and reared the offspring well. Approximately 3 weeks after parturition, serum E(2) and P(4) cycles resumed. Visual bleeding may be useful as a real-time indicator for understanding the ovarian cycle of southern tamanduas, and estrus could be expected approximately 3 weeks after the first bleeding.