Evidence of ovulation in goats (Capra hircus ) with short estrous cycle and its occurrence in the tropics

The influence of season and exposure to buck on the length of the estrous cycle were determined in 32 normally cycling native goats of different ages and parity. The estrous cycle durations were classified as short, medium and long. Ten goats (31%) exhibited medium length estrous cycles; 22 animals (69%) exhibited a combination of short, medium and long estrous cycles. Of the 155 estrous cycles studied, 15% were short, 72% were medium and 13% were long. Short estrous cycles were significantly shorter (P < 0.01) in estrus duration than medium or long estrous cycles. Significant differences (P < 0.05) for estrous cycle length and estrus duration were found between does but not within does. The presence of a buck for 8 to 16 h showed no significant effect on the length of the estrous cycle or on estrus duration, but a 24-h exposure period to a buck yielded shorter estrous cycles and estrus duration than found in the unexposed control group. Estrous cycles were significantly shorter (P < 0.01) in October, when rainfall is 57.9% of the annual total, and significantly longer (P < 0.01) in February, when rainfall is low at 0.2% of the annual total. A negative linear relationship (r = -0.87) was observed between estrous cycle and rainfall. Twenty-eight (90.3 %) of the short estrous cycles were ovulatory. The short cycles had a relatively lower ovulation rate than medium and long estrous cycles. The results indicate that the short estrous cycle in goats is associated with ovulation, and its occurrence in the tropics is related to rainfall.     

Luteal function of induced corpora lutea in the bitch

Nineteen anestrous bitches with a mean of 22 kg body weight and ranging from 2 to 4 years of age were induced to exhibit estrus and ovulate using PMSG and HCG. Twelve days after the first day of estrus, bitches were assigned to four treatment groups. Group (A) consisted of six bitches, Group (B) of five bitches and Groups (C) and (D) of four bitches each. At this time, bitches in Groups (A), (B) and (C) were laparotomized and those assigned to Groups (A) and (B) were bilaterally hysterectomized leaving the cervix and oviducts intact. Although bitches in Group (C) were laparotomized, they were not hysterectomized. Group (D) bitches were not subjected to any surgical procedures. Homologous uterine extract was prepared from each bitch in Group (A) and administered intramuscularly beginning on day 25 (day 0 = first day of estrus) and continued every other day for 61 days post-estrus. Bitches in Group (B) were similarly injected with equal volumes of 0.9% saline. Blood samples, obtained prior to laparotomy and every other day for 85 days thereafter, were assayed for plasma progesterone concentrations using radioimmunoassay. One bitch in each of Groups (A) and (D) did not form luteal tissue following treatment with PMSG and HCG although both bitches exhibited estrus following treatment. All other bitches showed an increase in progesterone levels (4 to 19 ng/ml) between the first day of estrus and 10 days post-estrus. Thereafter, progesterone levels progressively declined in all groups with levels below 1 ng/ml between 38 to 40 days post-estrus. Results of this study suggested that CL formed in the bitch following PMSG and HCG treatment have a reduced function compared to non-induced CL of a normal, non-fertile estrous cycle. Such premature CL regression appears to be independent of the presence or absence of the uterus.     

Estrus induction in the bitch using a combination diethylstilbestrol and FSH-P

The purpose of the study was to induce estrus and ovulation in normal bitches using a combination of diethylstilbestrol (DES) and follicle stimulating hormone of porcine pituitary origin (FSH-P). Thirteen mature mongrel female dogs were divided into two groups, the first group was treated for estrus induction during late anestrus and the second group during mid-anestrus. The dogs were monitored by teasing, vaginal cytology, and hormonal assay during the induced (n = 13) and the previous spontaneous estrous cycle (n = 9). Six of eight and three of five bitches came into standing estrus in the first and second group, respectively. Of the bitches that came into estrus, three conceived in the first group and one in the second. The average induced litter size was 7.0 versus 7.5 for the colony. Based on vaginal cytology the induced proestrus and estrus lasted 1.7 (0 to 3) and 12.9 (4 to 24) d, respectively, while the spontaneous proestrus and estrus lasted 5.8 (0-17) and 12.8 (9-15) d, respectively. Progesterone profiles were similar between the induced and spontaneous estrous cycles, although the progesterone peak was higher during the spontaneous cycle. The preovulatory luteinizing hormone (LH) surge was observed in only one induced estrous cycle. Modest results were obtained with this therapy. However, the litter sizes were normal and the induced cycles were very similar to the physiologic ones. No side effects were seen with the oral form of DES.     

圈养马麝(Moschus sifanicus)发情交配节律的比较研究

在1997～2000年间,甘肃兴隆山麝场的圈养马麝发情交配的时间节律保持相对年间恒定,1996年麝场进行了大规模的圈群间动物调整,导致该年的马麝圈群进入发情较迟,发情持续时间也较其他年份长。总体上,圈养马麝的发情持续时间达3个月,而66％的的发情交配发生于1个月内（从11月21日～12月21日）,发情季节（75％的发情完成累计时间）长36天。雌性圈养马麝发情的时间格局受圈养环境的季节性因子影响。饲养人员的饲养风格及各个饲养区内雌性马麝的社会行为的调节效应,各饲养区动物的发情时间格局有显著差异。年龄可影响马麝的发情交配,5．5岁龄以上的马麝发情定时更早。上一年度的繁殖成功与否和当年动物发情迟早无显著相关。野捕圈养麝群和其F1代圈群间的发情时间格局无显著差异。有较多发情周期的个体并不比发情周期仅1～2次的个体更早进入发情。     

Estrus induction in Beagle bitches with the GnRH-agonist implant containing 4.7 mg Deslorelin

Estrogens, gonadotrophins, dopamine agonists, gonadotrophin releasing hormone (GnRH) and its agonists have been used for estrus induction in bitches. A long acting GnRH agonist implant (4.7 mg Deslorelin; Suprelorin®, Virbac) with a continuous hormone release has been developed for suppression of sexual function in male dogs. In this study we administered the Deslorelin implant placed subcutaneously on the medial side of the leg to induce estrus in 11 anestrous Beagle bitches (group A). 6 Beagle bitches (group B) with a spontaneous estrous cycle were used as controls. The progress of pre-estrus and estrus was documented by behaviour, vaginoscopy, vaginal cytology and progesterone concentration. In group A a bloody vaginal discharge was detected on average 4.8 (range 3-10) d after application of the implant. At this moment implants were removed under local anaesthesia. Pre-estrus lasted for an average of 4.5 d (range 1-12). All bitches showed estrous signs and ovulated. The ovulation took place on day 8.2 (range 4-15) after start of pre-estrus. In group B pre-estrus lasted for 7.5 d (range 6-9), and the mean day of ovulation was day 11 (range 9-13). As a consequence of ovulation, progesterone serum concentrations exceeded 10 ng/ml during or after the time of ovulation in all bitches. All bitches were bred to fertile Beagle stud dogs or inseminated with fresh semen intravaginally. Between days nine and 19 after ovulation all bitches underwent ovariohysterectomy. The uterine horns were flushed and flushes were examined for ova or embryos. The pregnancy rate in group A was 63.6% and in group B 66.7%. Despite the significantly shorter period of pre-estrus a fertile estrus could be induced in 7 out of 11 treated bitches. Induction of a fertile estrus can be achieved with a GnRH-implant—already registered for the use in male dogs—placed subcutaneously on the medial side of the leg.     

Milk progesterone profiles in crossbred Brown Swiss x Nellore cattle following natural service

Ovarian activity and estrous behaviour were monitored through milk progesterone determinations and twice daily visual observations in 70 crossbred Brown Swiss x Nellore cows following natural service. Whole milk samples were collected on the day of estrus (Day 1), Day 11, and every 5 d thereafter until the next estrus or pregnancy confirmation. Seventy percent of the cows behaved as expected, i.e. they showed a 19-to 25-d interval between estrus and the next ovulation, or they became pregnant. Estrous cycles of regular length (18 to 24 d) were found in 54% of the cases. Prolonged luteal phases (interval from estrus to next ovulation > 28 d) were found in 15.7% of cows. Short estrous cycles (interestrous interval < 18 d) were found in 7.1% of the cases. Periods of acyclicity (basal progesterone levels for periods >/= 15 d) were found in 5.8% of the cases, and one cow exhibited estrus while pregnant and had a high progesterone concentration. Cows with a prolonged luteal phase and those with a short estrous cycle had an interval between ovulations of 35.0 +/- 6.7 d (x +/- SD) and 9.6 +/- 3.1 d, respectively. Signs of estrus were not detected in 33.3% of the ovulations confirmed by progesterone determinations. Low conception rates, failures in estrus detection and a high frequency of abnormal postbreeding luteal phases were found.     

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.     

Ovarian activity during normal and abnormal length estrous cycles in the goat

Ovarian and behavioral cyclicity were studied during 3-5 estrous cycles in a group of 10 multiparous, Nubian does. Changes in ovarian morphology throughout the estrous cycle were identified and photographed laparoscopically. Forty-eight estrous cycles were observed during the study and of these, 21 were abnormally short in duration (mean +/- SEM, 6.5 +/- 0.5 days). Mean duration of the estrous cycle for the 27 normal length cycles was 21.5 +/- 0.8 days. Eighteen/21 (86%) of the short cycles and 6/27 (22%) of the normal cycles were initiated during early breeding season (between September 1st and October 15th). There were no differences (P greater than 0.05) in the duration of estrus for the short (mean, 2.9 +/- 0.3 days) and normal (mean, 2.8 +/- 0.8 days) cycle groups. A total of 6/11 (55%) of the short duration cycles examined laparoscopically appeared to be anovulatory, but ovulation was observed in all normal cycles examined. The number of corpora lutea (CL) observed during normal length and short estrous cycles was 3.1 +/- 0.2 and 2.2 +/- 0.2, respectively (P less than 0.01). The cumulative percentage of does that showed morphological evidence of ovulation by the first, second and fifth day after the onset of estrus was 30%, 60% and 100%, respectively. Based on distinct differences in morphology and development, 2 types of CL were identified. The maximum visible diameter of Type I and Type II CL was 9.4 +/- 0.6 mm and 5.1 +/- 0.5 mm, respectively. These data document ovarian morphology throughout the normal and abnormal duration estrous cycle of the goat and indicate that 1) short estrous cycles observed early in the breeding season are associated with prematurely regressing CL or anovulation and 2) the ovary produces 2 morphologically distinct types of CL which differ not only in size and appearance, but also potentially in postovulatory function and longevity.     

Domestic queens under natural temperate photoperiod do not manifest seasonal anestrus

Domestic cat seasonality between the tropics and the arctic zones is scarcely described and results are inconsistent. The aim of this study was to describe domestic feline seasonal patterns under a natural temperate photoperiod. A total of 372 estrous cycles were studied in 34 post pubertal cats during 900 days. The queens were housed in a cat colony (31°25' South Latitude, 64°11' West Longitude), acclimated under natural photoperiod and daily observed for reproductive behavior. Vaginal cytology was conducted three times a week. For each cat the number of estrous cycles and days in estrus per month for each year were recorded. The months of the year were grouped in four periods of 3 months each according to day length and photoperiod. Comparisons of estrous days among periods were performed by ANOVA for repeated measures. All the cats had estrous cycles throughout the year without intervals of anestrus. Mean number of estrous days differed among the periods (P<0.01), those of long day length and ascending photoperiod being greater (12.5±0.6) to those of descending photoperiod either with long (8.9±0.7) or short (9.3±0.7) days. When the two periods with ascending day lengths were merged and compared to the two periods with descending day lengths merged, the number of estrous days were greater when day length ascended (P<0.01). Nearly 60% of the estrous cycles occurred during the periods of ascending day length. It is concluded, that domestic cats under natural temperate photoperiod have estrous cycles throughout the year showing peak activity the months with increasing photoperiod.     

Luteal competency during the resumption of ovarian cyclicity in postpartum Brahman cows

Twenty pluriparous, spring-calving Brahman cows were used to determine luteal competency, as measured by serum progesterone concentrations, during the first and the second postpartum estrous cycles. Prior to and after calving, all cows were maintained in good body condition on Coastal bermudagrass pasture (IFN 1-00-703). The calves were allowed to suckle ad libitum, and sterile marker bulls were maintained with the cow herd as an aid in estrus detection throughout the trial. Cow weight and body condition score were recorded within 24 hours after calving and again at the first behavioral estrus observed. From day 1 through day 14 (day 0 = estrus) of both the first and the second postpartum estrous cycles, blood samples were collected from each cow, processed to yield serum and analyzed by radioimmunoassay for progesterone concentrations. There was a higher incidence of abnormal estrous cycles following the first postpartum estrus (35%) than following the second (5%) postpartum estrus (P<0.05). The abnormal first estrous cycles were characterized by either a short luteal phase (four cows) or by standing estrus behavior without luteal tissue formation (three cows). When serum progesterone concentrations were compared for all cows during the first estrous cycle with those during the second estrous cycle, there was less progesterone released during the cycle (P<0.05) and lower peak progesterone concentrations (P<0.10) during the first estrous cycle. However, if the abnormal cows were excluded from the analyses, there was no difference (P>0.10) in either progesterone concentrations through the 14 days measured or in peak progesterone concentrations between the first and the second postpartum estrous cycles. It can be concluded from this study that the higher incidence of abnormal luteal function following the first postpartum estrus may contribute to the decreased conception rates observed when cows are bred at their first postpartum estrus.     

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.     

Environmental factors influencing the seasonality of estrus in chimpanzees

Although the energetics of the estrous cycle in primates is not well understood, evidence suggests that energy and nutrient acquisition influence ovulation and the timing of conception. Energy for estrus has to compete with energy allocated for cellular maintenance, thermoregulation, movement for food, and predation avoidance. While some chimpanzee (Pan troglodytes) populations do not have a seasonal birth period, evidence suggests that there is seasonality in the number of estrous females. Similarly, the onset of postpartum cycles has been reported to be seasonal. We used 33 months of data from the Taï National Park, Côte dIvoire, to examine how the number of estrous females in a given month was influenced by the abundance and distribution of food, diet, rainfall and temperature. In a second analysis, we examined if there was a seasonal effect on first estrous swellings in adolescent females and postpartum adult females. Results demonstrated that the number of females in estrous in a given month was positively related to food abundance and percent foraging time spent eating insects, and negatively related to mean rainfall in the two preceding months and the mean high temperature. The timing of first estrous swellings of postpartum females and prepartum young females was positively related to the food abundance, and negatively related to mean high temperature. These results showed that environmental conditions can seasonally limit the energetically demanding estrus cycle. The presence of estrous females increases gregariousness in chimpanzee communities, and this study identified environmental factors that affect estrus directly and hence social grouping indirectly.     

Low doses of bromocriptine shorten the interestrous interval in the bitch without lowering plasma prolactin concentration

In order to investigate the effect of different doses of bromocriptine on plasma prolactin concentration and the interestrous interval, beagle bitches were treated twice daily with 5 microg (5-group), 20 microg (20-group), or 50 microg (50-group) bromocriptine per kg body weight orally, starting 28 days after ovulation. In the 5-group, the difference between the mean plasma prolactin concentration before and that during bromocriptine treatment was not significant. In contrast, mean plasma prolactin concentration decreased significantly after the start of bromocriptine treatment in the 20- and 50-groups. The mean interestrous interval was significantly shorter in all three groups than in untreated bitches in the same colony. The mean interestrous interval in the 20-group and that in the 50-group were similar, but both were significantly shorter than that in the 5-group. The results of this study indicate that bromocriptine shortens the interestrous interval in the bitch even when the dose is so low that it does not lower plasma prolactin concentration. Induction of estrus in the bitch by bromocriptine therefore involves a mechanism other than via the lowering of plasma prolactin concentration. Furthermore, this study shows that the extent of shortening of the interestrous interval by bromocriptine is dose dependent.     

Selective control of the estrous cycle of the dog through suppression of estrus and reduction of the length of anestrus

The objective of this study was to determine the effectiveness of testosterone in suppressing estrus in the bitch, and of cabergoline in shortening the length of the subsequent anestrous period. In Experiment 1, 12 diestrual Beagle bitches were randomly divided into two groups when plasma progesterone (P(4)) concentration was <1 ng/ml (Day 0). Starting on Day 0, bitches in Group 1 (n=6) were treated with testosterone cypionate every 14 days for a total of 239 days, and bitches in Group 2 served as untreated controls. On Day 274, bitches in both groups were treated with cabergoline for 40 days and blood samples were obtained on Days 274, 276 and 279 for determination of plasma prolactin (PRL) concentrations using RIA. All bitches were observed for proestrual bleeding during treatment with cabergoline. In Experiment 2, 12 Greyhound bitches previously treated with testosterone within the last 6 months were randomly divided into two groups. At the initiation of this experiment, P(4) concentration was determined to verify that all bitches had a concentration of <1 ng/ml (Day 0). Starting on Day 0, bitches in Group 1 (n=6) were treated with cabergoline for 36 days, and bitches in Group 2 (n=6) served as untreated controls. Blood samples were obtained on Days 0, 2 and 5 to determine PRL concentrations. All bitches were observed for proestrual bleeding during treatment with cabergoline. In Experiment 1, one bitch (Group 1) exhibited estrus after treatment with testosterone (1mg/kg body weight) for 43 days, and one bitch (Group 1) exhibited estrus after treatment with testosterone (2mg/kg body weight) for 113 days. None of the other four bitches in Group 1 exhibited estrus during the period of testosterone treatment (239 days). All bitches in Group 2 (control) exhibited estrus during the 239 days of the study. In addition, five of the six testosterone-treated bitches showed signs of proestrual bleeding within an average of 12.6 days (range of 5-25 days) after treatment with cabergoline; and, four of the six nontestosterone bitches showed signs of proestrual bleeding within an average of 28 days (range of 6-46 days). Prolactin concentrations in bitches in both Groups 1 and 2 significantly decreased after treatment with cabergoline. In Experiment 2, one of the six bitches showed signs of proestrual bleeding within 15 days after treatment with cabergoline. From the results of this study, it was concluded that exogenous testosterone was moderately effective (66%) in suppressing estrus in Beagle bitches, and cabergoline was effective in shortening the length of the anestrous period of Beagle bitches whose estrous cycle was previously suppressed with exogenous testosterone, but less effective in shortening the length of the anestrous period in Greyhound bitches previously treated with testosterone to suppress estrus.     

Progesterone profiles around the time of insemination do not show clear differences between of pregnant and not pregnant dairy cows

In this study, features of progesterone profiles were examined in relation to the outcome of insemination. Three groups of estrous cycles were analyzed: resulting in pregnancy, not resulting in pregnancy and resulting in lost pregnancy. The aim of the study was to identify a complex of progesterone profile features associated with successful insemination. The features used were (1) from the estrous cycle preceding the artificial insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone, luteal phase peak, pre-estrus maximum rate of decline in progesterone and the length of follicular and luteal phase and (2) from the estrous cycle following insemination: estrus progesterone concentration, post-estrus maximum rate of increase in progesterone and days from estrus to post-estrus maximum rate of increase in progesterone. A discriminant analysis did not reveal clear differences between the groups. However, the analysis correctly classified 75% of true pregnant cows. Conversely, only 60% of not pregnant animals were classified as such by the discriminate analysis. Individual analysis of progesterone profile features in pregnant and not pregnant groups of estrous cycles showed that a shorter follicular phase preceding insemination is associated with proper timing of post-ovulatory luteinisation and therefore is more likely to result in pregnancy.     

Reproductive parameters of clouded leopards (Neofelis nebulosa)

Reproductive data compiled from the International Clouded Leopard Studbook revealed that 75% of all litters were born to females between one and five years of age. Sixty-three percent of the males had sired litters by four years of age with reproduction declining after six years of age. Sixteen zoological institutions surveyed worldwide contributed estrous cycle data from 28 clouded leopards. Sexual maturity (age at first estrus) for these females ranged from 17 to 28 months of age with a mean estrous cycle length of 29.9 ± 13.8 days. The mean length of estrus was six days. Gestation length ranged from 85 to 121 days (X? = 93.4 ± 6.3). There was a significantly higher incidence of estrus in fall and winter compared with spring and summer over latitudes ranging from 36°–45° and 51°–55° (P < .005). Mating occurred in all months except June and October, and cubs were produced in all months except December. The highest frequency of mating occurred during the month of December corresponding with a birth peak in March.     

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.     

Reproductive hormone concentrations during estrus,pregnancy, and pseudopregnancy in the Labrador bitch

Serum luteinizing hormone (LH), estrone, estradiol-17β, and progesterone were measured during the estrous cycle, pregnancy and parturition in seven adult pregnant Labrador bitches and during the estrous cycle and one gestation length equivalent in six adult pseudopregnant bitches. Although the duration of proestrus was similar in both groups, the duration of estrus was longer in the bitches that subsequently became pregnant. Mean serum LH concentrations were similar in both groups during most of the study. However, during Weeks 6 to 9 after the preovulatory LH peak, serum LH concentration was higher in both pseudopregnant and pregnant groups of animals and declined to basal levels thereafter. Mean serum estrone concentrations in the pregnant animals were higher than those of pseudopregnant animals and remained elevated throughout gestation, followed by a decline at whelping. Serum estradiol-17β levels were higher during the 4 wkimmediately following ovulation in the pseudopregnant group compared with those observed in pregnant animals. Serum progesterone concentrations generally remained higher during pseudopregnancy compared with those of the pregnant animals during gestation.In conclusion, a major difference between pregnant and pseudopregnant bitches is a pregnancy-specific elevation in estrone levels. The placenta may be a likely source of estrone during pregnancy.     

The effects of zearalenone on reproduction in swine. I. The relationship between ingested zearalenone dose and anestrus in non-pregnant, sexually mature gilts

Ninety-nine sexually mature, non-pregnant gilts were checked for estrus daily with a mature boar and then allocated at estrus (D O) to receive 2 kg/d of a diet containing 0, 1, 5 or 10 ppm purified zearalenone between D 5 and 20 of the estrous cycle during two seasons of the year (winter and summer). None of the gilts exhibited any visual signs of "hyperestrogenism" and there was no effect of season on interestrous interval (P > 0.05). A significant effect of zearalenone dose on inter-estrous interval was detected (P < 0.001). Gilts receiving 0 or 1 ppm had similar inter-estrous intervals (21.0 +/- 0.3 and 21.5 +/- 0.8 d, respectively) whereas gilts receiving 5 and 10 ppm had extended cycles (29.2 +/- 2.9 and 32.7 +/- 3.3 d, respectively). Plasma progesterone concentrations at D 19 to 21 were higher in gilts with extended cycles (P < 0.001) and corpora lutea (CL) were present at laparotomy. Some 86% of these retained CL underwent spontaneous regression resulting in the onset of estrus within the next 30 d. Fecal zearalenone concentrations rose during ingestion of contaminated diets and declined to pretreatment values within 2 d (1 ppm) to 8 d (10 ppm) of the cessation of treatment. These data show that feeding zearalenone at concentrations of 5 to 10 ppm from D 5 to 20 of the estrous cycle causes luteal maintenance and extended inter-estrous intervals. Spontaneous regression of these CL usually occurs within 30 d after zearalenone is removed from the diet. Fecal zearalenone analysis does not appear to be an effective method for determining prior exposure to zearalenone when carried out more than a few days following the last ingestion of zearalenone.