Short Estrous Cycles Research Articles

Short Estrous Cycle Post-ovulation in Peri-pubertal Sahiwal and Jersey Crossbred Heifers

This investigation focuses on analysing the follicular dynamics exhibited during peri-pubertal period in Sahiwal and Jersey crossbred heifers. The aim of the study was to assess first ovulation in the heifers following puberty (N=20; 10 for each breed). Heifers were subjected to alternate day trans-rectal ultrasonography (TRUS) when the diameter of dominant follicle surpassed 9 mm diameter. Transrectal ultrasonography (TRUS) was performed to observe and assess first ovulation in heifers. The size of the first pre-ovulatory follicle in Sahiwal and Jersey Crossbred heifer in peri-pubertal stage was 10.52±0.13 and 10.15±0.51 mm, respectively and the corpus luteum attained its maximum size of 13.89 and 11.26 mm, was significantly different (p<0.01) at day 8.6±0.4 and 8.2±0.48 in Sahiwal and Jersey crossbred heifers, respectively. The regression of corpus luteum (CL) adjudged by the Colour Doppler initiated on 10.6±0.4 and 11.0±0.63 day for Sahiwal and Jersey crossbred heifers, respectively. Some other follicular dynamics parameters i.e. day of wave onset, number of follicles recruited, inter-wave duration along with maximum diameter of dominant follicle, day of maximum diameter, growth rate, length of growth and static phase, duration of static phase and onset of atresia was recorded, however, no significant difference (p>0.05) was recorded between breeds. On an interesting note, the next estrous cycle for heifers did not lead to ovulation despite having follicular size more than10 mm in both the breeds.
 Conclusion: In peroration, peri-pubertal Sahiwal and Jersey crossbred heifers had notably precocious luteal regression after first ovulation, without subsequent ovulation in next estrous cycle.

Short-term treatment with deslorelin implants to improve the bucks’ ability to stimulate cyclic activity during the late non-breeding season

• Treatment with deslorelin during 5 d induced an increase in testosterone in bucks. • Testosterone concentration increased in all bucks joined with anestrous does. • Response of does to male effect with treated or untreated bucks was similar. The sudden introduction of males to anestrous females stimulates synchronous ovulations. The effectiveness of males to induce this response is androgen dependent. The aim of the present study was to compare the reproductive response of anestrous does to the introduction of teaser bucks treated with or without deslorelin implants, which continuously release a GnRH agonist. While 5 bucks were acutely treated with a single subcutaneous implant containing 7.4 mg of deslorelin (Suprelorin, Virbac) (group Des), other 5 bucks remained as controls (group Con). Each buck was placed with one group of 8 adult females. Deslorelin implants were inserted on Day -6 and from Day 0 to Day 9, bucks were joined with females from 07:00 to 08:00 and from 19:00 to 20:00 every day. Testosterone concentration was measured from blood samples collected twice a day (12 h apart, am/pm) on Days -11, -10, -9 and from Day -6 to Day -1, and collected immediately after buck stimulation from Day 0 to Day 9. Does that came into estrus and that showed short estrous cycles was registered from Day 0 to Day 9. Transrectal ultrasound examination for recording cyclicity on basis of presence of corpus luteum was done between Days 22 and 27, whereas ultrasonographic pregnancy diagnosis was carried out on Day 49. Testosterone concentration was greater in Des than Con bucks before joining them with females (36.0 ± 7.6 nmol/L vs 15.0 ± 6.8 nmol/L; P = 0.04), but the difference disappeared when all the experiment was analyzed together. Non significant differences were observed in reproductive response of does stimulated by treated or control males. Therefore, we concluded that both treated and control bucks were fully capable of inducing reproductive activity in anestrous does.

PSX-6 The appropriate phase of follicle size and progesterone concentration could control ovulation of ruminant animal

Abstract Ovarian follicular development was monitored daily by transrectal ultrasonographic examination in 20 female goats for 2 successive estrous cycles (40 cycles). These animals exhibited ovulatory cycles with a mean length of 20.8 ± 1.1 days. The mean number of follicles ovulated was 2.3 ± 0.9 and their diameter before ovulation was 6.9 ± 1.1 mm. Among 40 estrous cycles examined, 9 (23 %) displayed 1 latent follicular wave and the remaining 31 (77 %) cycles displayed 2 latent follicular waves. Three and 4 days after the second spontaneous ovulation (day 0 = ovulation), when diameter of dominant follicles of the first latent wave exceeded 5.5 mm, 20 goats were treated with a luteolytic dose of prostaglandin F2a (PGF2a) and randomly assigned to one of three groups. This treatment immediately decreased plasma levels of progesterone and increased those of estradiol, resulting in ovulation 2 or 3 days later. One group of goats (n = 5) treated with PGF2a at the first latent follicular wave and was mated with fertile male goat, resulting in 4 pregnancies. For the second group of goats (n = 5), 4 successive short estrous cycles were induced. A total of 35 short ovulatory cycles were induced at a mean interval of 6.5 ± 1.2 days with a range of 4–9 days. Five of goats were allowed to mate following 4 consecutive short ovulatory cycles; normal oestrous behavior was observed at each estrus. The goats were successfully mated, became pregnant and delivered kids of normal body weight and length. The remaining goats (n = 6), in addition to PGF2a treatment, received exogenous progesterone supplement which allowed latent follicular development to occur, but prevented ovulation until the effect of progesterone supplement subsided. Thus, it was concluded that appropriate phase of follicle size and progesterone concentration could control ovulation of ruminant animal.

Effects of live yeast dietary supplementation on hormonal profile, ovarian follicular dynamics, and reproductive performance in dairy cows exposed to high ambient temperature

Two experiments were conducted to investigate the effects of dietary supplementation with live yeast culture on hormonal profile, ovarian follicular dynamics and reproductive performance of lactating dairy cows exposed to high ambient temperature. In Expt. 1, Holstein cows were fed a diet with (n = 6) or without (n = 6) 4 g yeast/h/d from 21 d before expected calving date until 8 weeks postpartum. Concentrations of glucose, insulin, insulin like growth factor-I (IGF-I), estradiol-17β (E−17β) and progesterone (P4) were determined in plasma, and transrectal ultrasonography was used to monitor ovarian follicular dynamics. In Expt. 2, 150 Holstein cows (75/dietary group) received same diets as Expt. 1 with the exception that diets were fed from d 1 to d 70 postpartum. The effect of dietary treatments on reproductive performance was examined. In Expt. 1, plasma IGF concentrations during dietary treatment were higher (P = 0.05) in cows fed diets supplemented with yeast. On d 60 postpartum, average plasma concentrations of glucose (48.3 vs. 41.0 mg/dL) and insulin (0.90 vs. 0.23 μU/mL), were also greater in cows fed diets supplemented with yeast compared to that in cow fed diets without supplementation. Similarly, plasma concentrations of E−17β at estrus (P = 0.016) and P4 on d 10 of the estrous cycle (P = 0.021) were greater in yeast-supplemented cows. Moreover, yeast supplementation resulted on average in an estrous cycle 2.6 d shorter (P = 0.05) and in the development of larger ovulatory follicles (18.4 vs. 17.2 mm in diameter; P < 0.01). In Expt. 2, days open were fewer and the proportion of pregnant cows at 120 and 150 d postpartum were greater (P < 0.01) in cows fed diets supplemented with yeast compared to those receiving diets without yeast. In summary, cows fed diets supplemented with yeast had greater plasma IGF-I, E−17β and P4 concentrations, larger ovulatory follicles, shorter estrous cycles, and improved reproductive performance. Therefore, live yeast dietary supplementation could enhance lactating dairy cow's fertility during heat stress through improvement in hormonal profile and development of larger ovulatory follicles.

Effect of Season of Calving and Mastitis on Reproductive Performance of Baladi and Crossbred Cows (Baladi X Friesian) under the Environmental Conditions of Aswan Governorate in South Egypt

The current work was carried out on two hundred of Baladi and crossbred (Baladi x Friesian) cows to estimate effect of season of calving and mastitis on the reproductive performance under the environmental conditions of Aswan governorate in south Egypt. The cows follow up after one month post-partum and the California Mastitis Test was performed for all experimental cows by (California Mastitis Test). According to season of calving the cows were divided into two groups. The first group that calved during the cold season and the second group calved during the hot season. The cows Baladi and crossbred cows that calved during the cold and hot seasons were divided into two groups according to suffering of mastitis healthy cows and cows with mastitis (sub-clinical mastitis). The results demonstrated that the interval from calving to first service was longer (75.56± 12.3, 82.63±7.51days) (P <0.05) in cows that calved during the hot season than cows that calved during the cold season ( 65.71± 14.27, 74.58± 8.94 days) in healthy Baladi and crossbred cows respectively. The interval from calving to the first service was longer in Baladi cows that suffer from mastitis (78.96± 15.08, 84.95±8.4 days) compared with healthy cows (65.71± 14.27, 75.56± 12.3days) during the two seasons cold and hot respectively. The interval from calving to the first service was longer in crossbred cows that suffer from mastitis (85.89± 6.81, 87.09±7.11 days) compared with healthy cows (74.58± 8.94, 82.63±7.51 days) during the two season cold and hot respectively. The interval from calving to conception was greater in cows that calved in the hot season (96.93±10.66, 101.26±13.65days) (P <0.05) than cold season (90.38±11.44, 93.16±11.37days) in healthy Baladi and crossbred cows respectively. The interval from calving to conception was higher in cows with mastitis than healthy cows in Baladi and crossbred cows in two seasons. Number of services pre conception were greater in Baladi and crossbred cows that suffer from mastitis (2.1±0.62, 2.05±0.22 and 2.08± 0.63, 2.13± 0.67 services) compared with healthy cows (1.95± 0.58, 1.89±0.42 and 2.0± 0.63 , 1.92± 0.67 services) during the two season cold and hot respectively. Conception rate in Baladi and crossbred cows that suffer from mastitis was lower (37.9, 15.0, 15.8and 16.1%) compared with healthy cows (66.7, 36.7, 66.7and 42.1%) during the two season cold and hot respectively. The percentage of mastitis cases were more frequent in cows during the cold season (58, 76%) compared to hot season (40, 62%) in Baladi and crossbred cows respectively. The rates of short estrous cycles were higher in cows with mastitis during the hot season (42.9, 38.5%) than cold season (33.3, 25%) in Baladi and crossbred cows respectively. The present study clarified that there is a negative effect of hot season and mastitis on the reproductive performance of Baladi and crossbred cows under the environmental conditions of south Egypt. Thus, the present study recommended must preparing effective defense programs in order to decreasing proportion of infection by mastitis for betterment the reproductive performance of Baladi and crossbred cows especially during the hot season of Aswan governorate

Seasonal Changes of Some Reproductive Traits in Farafra Ewes under Egyptian Environmental Condition

AbstractThirty Egyptian Farafra ewes were used to study the effect of seasonal variations on reproductive cycleand ovarian activity. Estrus was detected twice daily throughout the year. Percentages of ewes showingestrus monthly, number of estrous cycle/ewe/season, estrous cycle length and heat duration weremeasured throughout different seasons of the year. Changes in ovarian activity were examined usingLaparoscopy technique. Percentage of ovulated ewes, ovulation rate and number of large and smallfollicles were recorded over different seasons. The obtained results revealed that the highest activecycles were observed in autumn and summer (87.1 and 84%), while the lowest was observed in spring(64.3%). Percentages of ewes that exhibited normal estrous cycle length during winter, spring; summerand autumn were 73.3, 47.0, 64.0, and 44.5%, respectively. While, the percentage of the short estrouscycle length was high in autumn (37.0%). During spring, summer and winter, the percentages of thelong cycle length were 25.0, 20.0 and 20.0 %, respectively. The percentages of ewes showed normalheat duration during autumn was 63.0%, summer (56.0%) and spring (46.4%), while the percentage ofewes exhibited short heat duration were in spring (53.6%) and winter (50%). During autumn, ewesrecorded the longest (p 3 mm3) in diameterwere significantly higher (P<0.05) in winter. Plasma progesterone concentration was always the lowestat the onset of estrous, increased gradually to a maximum level in day 8 and remained until day 14 (lutealphase), then declined in day 16 in winter, spring and summer and at day 18 in autumn. In conclusion,subtropical Farafra ewes were almost cyclic throughout the year. Reproductive performance of Farafraewes still need more studies to reveal the strength and potential of this breed.

Postpartum hormone and energy profiles and their influence on the resumption of ovarian cyclicity in Curraleiro Pé-Duro cows

The objective of this study was to evaluate hormone and energy profiles in the postpartum period and to correlate these profiles with the resumption of ovarian cyclicity, as well as characterizing the postpartum short estrous cycle of Curraleiro Pé-Duro cows. Twelve Curraleiro Pé-Duro cows were examined via rectal palpation and ultrasound at 10 days postpartum, and subsequently examined daily to evaluate the resumption of ovarian cyclicity as well as every five days in order to evaluate uterine involution. Upon analysis of the data, it was possible to observe the formation of two distinct groups, one of which was comprised of those animals which returned to cyclicity within 60 days postpartum and another comprised of those animals which returned to cyclicity more than 105 days postpartum. Therefore, animals were divided into two groups; precocious, designated Ov Group, and delayed, designated NOv Group, wherein the cut-off time for all tests was 60 days postpartum. Statistically significant differences (P < 0.01) between the groups occurred only regarding the day of 1st ovulation, which in the Ov Group averaged 51.4 ± 9.3 days and in the NOv Group averaged 138.3 ± 19.8 days postpartum. The other postpartum short estrous cycle variables assessed did not show statistically significant differences (P > 0.05) between the groups. NEFA, BHBA and thyroxine concentration levels did not differ (P > 0.05) between the groups in any of the statistical analyses. However, in the analysis comparing growth curves, triglycerides levels were higher for the Ov Group (P = 0.04) and cholesterol levels were higher for the NOv Group (P = 0.02). In this experiment, a small influence of a negative energy balance between the groups was observed, suggesting that these animals can present significant genetic variability due to natural selection, as evidenced by the formation of groups of animals with precocious and delayed reproductive characteristics.

Luzindole accelerates the aging of estrous function of female rats

In this paper, we investigated the dynamics of aging of the estrous function of female rats kept in the conditions of standard vivarium lighting and receiving luzindol - the blocker of melatonin receptors. Every three months, daily, for two weeks, vaginal smears were taken from the animals and cytological examination of the vaginal contents was conducted. Despite different mechanisms of the development of melatonin system failure (a decreased production of melatonin and a blockade of melatonin receptors), the effects of the influence on the ovulatory function are similar. In case of the blockade of melatonin receptors, the appearance of premature signs of aging of the reproductive function in rats was observed. It was manifested by an increased duration of ovulatory cycle; a decrease in the number of regular cycles; the emergence of irregular cycles; a decrease in the number of short estrous cycles and an increase of long cycles; the early development of persistent estrus.

Resumption of cyclic ovarian activity in postpartum ewes: a review

The reproduction rate is considered a crucial factor that affects the ability of producers to meet the growing demand for ovines meat, and optimizing this factor will maximize the production rate and increase the efficiency of livestock. A reduction in the length of the postpartum anestrus period results in a shorter interval between lambing and conception and enables more lambs to be produced throughout the life of a ewe. This review discusses the current knowledge of several factors associated with the resumption of cyclic ovarian function in postpartum ewes and how the suckling management of ewes may affect this process. Factors that influence the resumption of cyclic ovarian activity include uterine involution, follicular development, occurrence of silent ovulation and short estrous cycles, breed, reproductive seasonality, nutrition and lactation. Controlled suckling and early weaning are management practices that may be used to obtain three lambings in a 24-month period. In the majority of the studies the interval between lambing and first estrus was reduced when a controlled suckling management strategy was used, therefore the controlled suckling appears to be the best alternative because it has produced good results and is easy to implement. Currently, however, this practice is still not widely used.

Comparative histopathology of the estrous or menstrual cycle in laboratory animals.

Accurate analysis of female reproductive toxicity requires a thorough understanding the differences in and specifics of estrous or menstrual cycles between laboratory animals. There are some species differences such as the time of sex maturation, the length of the estrous or menstrual cycle, the length of the luteal phase, the number of dominant follicles or corpora lutea, the size of follicles, processes of luteinization, and hormonal changes during the estrous or menstrual cycle. Rodents have a short estrous cycle, and their ovarian cycling features are the same in both ovaries, which contain a large number of follicles and corpora lutea. The dog estrous cycle is much longer than those of other laboratory animals, and it includes a long anestrus phase. The duration of the menstrual cycle of monkeys is roughly 30 days, and their ovarian cycling features are different between the left and right ovaries. In both rodents and dogs, the theca cells invade the early luteum, mixing with granulosa cells during luteinization. However in monkeys, the theca layer dose not mix with the granulosa cells as it invaginates only slightly into the early luteum. In addition, we found that high progesterone levels after ovulation are sustained for a much shorter duration in rodents than in dogs and monkeys due to the comparatively rapid passage of the rodent luteal phase. Based on these species differences, animal species for use in ovarian toxicology studies need to be selected appropriately.

Maintenance or regression of the corpus luteum during multiple decisive periods of bovinepregnancy

In ruminants, there are specific times during the estrous cycle or pregnancy when the corpus luteum (CL) may undergo regression. This review has attempted to summarize the physiological and cellular mechanisms involved in CL regression or maintenance during four distinct periods. The first period is near day 7 when animals that are ovulating after a period of low circulating progesterone (P4), such as first pubertal ovulation or first postpartum ovulation, are at risk of having a premature increase in Prostaglandin F2α (PGF) secreted from the uterus resulting in early CL regression and a short estrous cycle. The second period is when normal luteolysis occurs at day 18-25 of the cycle or when the CL is rescued by interferon-tau secreted by the elongating embryo. The uterine mechanisms that determine the timing of this luteolysis or the prevention of luteolysis have been generally defined. Induction and activation of endometrial E2 receptors result in induction of endometrial oxytocin receptors that can now be activated by normal pulses of oxytocin. Of particular importance is the observation that the primary mechanisms are only activated through local (ipsilateral) and not a systemic route due to transfer of PGF from the uterine vein to the ovarian artery. In addition at the CL level, studies are providing definition to the cellular and molecular mechanisms that are activated in response to uterine PGF pulses or pregnancy. The third period that is discussed occurs in the second month of pregnancy (day 28-60) when undefined mechanisms result in CL maintenance of an ipsilateral CL but regression of a contralateral (opposite side from pregnancy) CL. The final period that is discussed is regression of the CL just prior to parturition. Although, cortisol from the fetus appears to be the primary initiator of luteolysis, PGF seems to be the final signal that causes regression of the CL. Thus, in all four periods, regression of the CL is likely to be caused by the direct actions of PGF that is secreted from the uterus. The uterine mechanisms that result in secretion of PGF seem to be normally inhibited during the early luteal phase, making short luteal phases not a normal event, and are altered during early pregnancy (day 18-25) resulting in prevention of luteolysis. During much of pregnancy, the mechanisms that cause PGF secretion from the uterus in response to oxytocin are intact but luteolysis does not normally occur, perhaps due to lack of efficient utero-ovarian transfer of PGF.

LH secretion around induced ovulation during early and late diestrus and its effect on the appearance of short estrous cycles in cyclic dairy heifers

The aim of this study was to investigate the effect of the stage of the estrus cycle (early vs. late diestrus) on the LH secretion after induced ovulation and on the incidence of short estrous cycles in dairy heifers. Cyclic heifers were presynchronized with dexcloprostenol and divided into Groups D7 (n = 6) and D14 (n = 6). On Day 7 (D7) or Day 14 (D14) after ovulation (Day 0), all animals were treated with dexcloprostenol followed by 0.1 mg of gonadorelin (GnRH) 24 hours later. Blood samples were taken daily for progesterone (P4) analysis and for LH analysis every 10 minutes for 3 hours on Days 1, 3, and 5 and every 30 minutes for 6 hours starting just before GnRH administration. In a control group, Group C (n = 7), estrus was synchronized with an intravaginal progesterone-releasing device (CIDR) inserted for 9 days. Blood for P4 analysis was taken daily for 16 days and for LH analysis every 30 minutes for 31 hours starting 30 hours after CIDR removal (unmanipulated LH peak) and every 10 minutes for 3 hours on Days 1, 3, and 5 after ovulation. In all groups, ovarian structures and ovulation were detected via daily transrectal ultrasound examination around first and second ovulation. In D7, all cycles (6/6) were shorter than normal (range 7–9 days). In D14, 2 of the 6 animals had a short cycle (both 7 days) whereas 4 had a cycle of normal length. All cycles were of normal length in C. Animals in D7 and D14 were divided according to their cycle length into short (SC) and normal (NC) cycle groups. The mean size of the ovulatory follicle during the 3 days before ovulation was significantly different between D7 and D14 and on 3 days and 1 day before ovulation between SC and NC. Secretion of LH during the 6 hours after GnRH administration did not differ between D7 and D14, or SC and NC. The mean basal LH secretion in D7 and D14 on Days 1, 3, and 5 was significantly different. No difference on those days was noted between SC and NC. In conclusion, when ovulation is induced with GnRH 24 hours after giving dexcloprostenol, short estrous cycles can occur during both early and late diestrus. The preovulatory LH surge did not differ between D7 and D14, or SC and NC. Also, basal LH secretion on Days 1, 3, and 5 was similar in SC and NC, and lower basal LH concentration coincided with higher P4 concentration.

LEVEL OF ESTRADIOL 17-β SERUM AND OVARIAN FOLLICULARE DYNAMICS IN SHORT ESTROUS CYCLE OF BALI CATTLE

The aims of the research were to confirm the short estrous cycles and determine the blood level ofestradiol 17-β and ovarian follicukar dynamics in these cases. The research was conducted using sevenBali cattle, approximately 2 years of age, kept in healthy condition with normal estrous cycles.Observation of estrus symptoms was performed daily. Ovarian follicles was examined and measuredusing ultrasonography started at the estrus day. Blood samples were collected from jugular vein, bloodsample collection and ultrasonographical examination of the ovaries were performed daily in the sametime. Serum level of estradiol 17-β was performed using EIA. The short cycle estrus were observed in 4Bali cattle (n=7) among natural estrous cycle. They have only one wave ovarian follicular developmentwhereas the maximal size of ovarian follicles ovulation likes the normal cycle The duration of shortestrous cycle was 7-10 days with normal usual estrus behavior. The peak of blood serum level was107.77 ± 55.94 pg/ml when the diameter dominant follicle of short estrous cycle was reached 10.5 ±0.38 mm. It can be concluded that the short estrous cycles may occur in Bali cattle after puberty amongnormal cycles.

Endometrial expression of progesterone, estrogen, and oxytocin receptors and of 20α-hydroxysteroid dehydrogenase and cyclooxygenase II 2 and 5 days after ovulation in induced short and normal estrous cycles in dairy cows

The aim of this study was to investigate causes of the short estrous cycles that occur frequently in dairy cows after estrus synchronization using PGF2α and GnRH. Expression of oxytocin receptor (OR), progesterone receptor (PR), and estrogen receptor (ER); of cyclo-oxygenase II (COX-II) and 20α-hydroxysteroid dehydrogenase (20α-HSD); and of peripheral blood estradiol-17ß and progesterone (P4) concentrations were analyzed in estrous cycles of normal length and in induced short estrous cycles. On Day 8 (ovulation = Day 0), presynchronized dairy cows (n = 14) were given 0.15 mg of dexcloprostenol and 0.1 mg of gonadorelin 24 hours later. Animals were bled once daily for P4 and estradiol-17ß analyses, and endometrial biopsy specimens were taken on Days 2 and 5 for PR, ER, OR, 20α-HSD, and COX-II determinations with immunohistochemistry and/or real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). Ovulations and ovarian structures were monitored with transrectal ultrasound daily until the next ovulation. After excluding one case of incomplete luteal regression, short estrous cycles occurred in 8 of 13 cases (length from 8 to 12 days). No differences were established in endometrial ER, PR, or COX-II expression between the normal and short cycle groups in the semi-quantitative immunohistochemistry analysis. In qRT-PCR analysis, no differences were found in relative gene expression of endometrial ER, PR, OR, 20α-HSD, or COX-II between normal and short cycles. Despite evidence from previous studies that short estrous cycles are induced by premature prostaglandin release, differences in these receptors or in enzyme expression do not explain the release.

Reproductive characteristics of the female laboratory rat

The laboratory rat is widely used in research studies as a model of mammalian health and disease. This review provides the basic facts about female rat reproduction and highlights the reproductive characteristics which make the rat a preferred animal model for research on reproduction. Rats have short estrous cycle, lasting four to five days. The estrous cycle consists of four stages known as proestrus, estrus, metestrus and diestrus. Phases of the estrous cycle can be detected by observing behavioral changes or examining vaginal cytology. Detection of sperm in vaginal smear is an excellent predictor of pregnancy in rats. Implantation is initiated on day 5 and completed by day 7 of pregnancy. Gestation takes 21 to 23 days from copulation to parturition. Short estrous cycle and gestation period make the rat an ideal animal model for research on reproduction. Key words: Rat, estrous cycle, pregnancy detection, fertilization, embryonic development, implantation, gestation, weaning.

Induced Endometriosis in Nonhuman Primates1

Induced Endometriosis in Nonhuman Primates1

Presynchronizing PGF2α and GnRH injections before timed artificial insemination CO-Synch + CIDR program (2013)

Fixed-time artificial insemination is an effective management tool that reduces the labor associated with more conventional artificial insemination programs requiring detection of estrus. The 7-day CO-Synch + controlled internal drug release (CIDR) insert protocol has been shown to effectively initiate estrus and ovulation in cycling and non-cycling suckled beef cows, producing pregnancy rates at or greater than 50% in beef cows. The gonadotropin-releasing hormone (GnRH) injection that begins the CO-Synch + CIDR program initiates ovulation in a large proportion of cows, particularly anestrous cows. The CIDR, which releases progesterone intravaginally, prevents short estrous cycles that usually follow the first postpartum ovulation in beef cows. Our hypothesis was that inducing estrus with a prostaglandin injection followed 3 days later with a GnRH injection, 7 days before applying the 7-day CO-Synch + CIDR protocol, might increase the percentage of cycling cows that would exhibit synchronous follicular waves after the onset of the CO-Synch + CIDR protocol. We also hypothesized that the additional GnRH injection would increase the percentage of anestrous cows that would ovulate, thereby increasing pregnancy outcomes.

The Cheetah (Acinonyx jubatus) Is Distinctively Sensitive to Short-Term Progestin Exposure.

The estrous cycle of the cheetah, an induced ovulator, occurs about every 14 days. Therefore, the ovary of this species almost is constantly experiencing folliculogenesis and producing surges or waves of estrogen activity. Elevated estrogen compromises the effectiveness of exogenous gonadotropins used to time assisted breeding. Approximately 35% of female cheetahs fail to respond to exogenous gonadotropins, and oocyte quality is compromised when such stimulation commences during an endogenous follicular phase. Given the general sensitivity of felids to progesterone and the comparatively short reproductive cycle of the cheetah, we hypothesized that even a brief exposure (7 days) to a low-dose oral progestin (Altrenogest) would suppress ovarian activity. Cheetah females (age range, 5-11 y) were given either 0.1 mg/kg (n=3, low dose) or 0.4 mg/kg (n=3, high dose) Altrenogest for 7 days. Fecal samples were collected (4-5/wk/female) for 41 to 44 days before, 7 days during and 33 to 36 days after Altrenogest treatment. Baseline fecal estradiol concentrations were calculated for each female using an iterative process, excluding values that exceeded the mean + 1.5 SD. An estradiol peak was the highest value within a group of samples > 1.5 x baseline. An estrous cycle was defined as the interval between two consecutive estradiol peaks = 4 days apart. Data were analyzed by GLM procedures and expressed as LSmeans ± SEM. Females receiving the low Altrenogest dose experienced a longer (P < 0.05) duration from the end of progestin exposure to the next post-treatment estradiol peak (13.3 ± 2.8 days) compared to those receiving the high dose (2.0 ± 2.8 days). For the 5 weeks after treatment, cheetahs receiving the higher Altrenogest dose also had an increased (P < 0.05) frequency of estrous cycles as measured by number of estradiol peaks (5.7 ± 0.7 cycles) compared to those receiving the lower dose (2.3 ± 0.7 cycles over the same time period). Thus, a short administration of oral progestin quickly down-regulated ovarian activity, probably because the induced-ovulating cheetah with naturally short estrous cycles rarely is exposed to progestagens and, therefore, is highly sensitive. The higher Altrenogest dose appeared to stimulate folliculogenesis, perhaps related to a strong endogenous FSH rebound post-progestin withdrawal. These findings have practical application as a simple, short-term approach for suppressing ovarian activity in anticipation of generating a more consistent gonadotropin induction response for timed artificial insemination or embryo transfer.

Presynchronizing Prostaglandin F2α injection before timed artificial insemination CO-Synch + CIDR program (2012)

Introduction Fixed-time artificial insemination is an effective management tool that reduces the labor associated with more conventional programs that require detection of estrus. The 7-day CO-Synch + controlled internal drug release (CIDR) insert protocol has been shown to effectively initiate estrus and ovulation in cycling and non-cycling suckled beef cows, producing pregnancy rates at or greater than 50% in beef cows. The gonadotropin-releasing hormone (GnRH) injection that begins the CO-Synch + CIDR program initiates ovulation in a large proportion of cows, particularly anestrous cows. The CIDR, which releases progesterone intravaginally, prevents short estrous cycles that usually follow the first postpartum ovulation in beef cows. Our hypothesis was that inducing estrus with a prostaglandin injection 3 days before applying the 7-day CO-Synch + CIDR protocol might increase the percentage of cycling cows that would exhibit synchronous follicular waves after the onset of the CO-Synch + CIDR protocol, thereby increasing pregnancy outcomes.

Effect of eCG on early resumption of ovarian activity in postpartum dairy cows

The purpose of the present study was to hasten the resumption of ovarian activity early postpartum in lactating dairy cows, using equine chorionic gonadotropin (eCG), to enhance follicular growth, followed by hCG, to induce ovulation. Primiparous Holstein dairy cows ( n = 21) were assigned equally into eCG, eCG–hCG and Control groups. Cows in the eCG and eCG–hCG groups received an i.m. injection of eCG (500 IU Folligon ®) on Day 6 postpartum. Cows in the eCG–hCG group were also given an i.m. injection of hCG (500 IU Chorulon ®), once dominant follicle reached the diameter of 13–16 mm following eCG injection. Cows in Control group did not receive any treatment. Daily blood sampling and ultrasound examination were conducted, starting at Day 6 postpartum until confirming the third ovulation. Follicles ≥10 mm in diameter were detected on Day 11.5 ± 1.48, 10.1 ± 0.52 and 11.1 ± 1.36 after calving in Control, eCG and eCG–hCG groups, respectively ( P > 0.05). The first wave dominant follicle ovulated in 71.4% of cows treated with eCG and eCG–hCG. In contrast, none of the first wave dominant follicles ovulated in Control cows. By Day 20 postpartum, all cows in eCG group, 6/7 cows in eCG–hCG group and none of the cows in Control group ovulated ( P < 0.05). Short estrous cycles (≤16 days) were detected in 2/7, 1/7 and 6/7 cows in eCG, eCG–hCG and control groups, respectively ( P < 0.05). In conclusion, injection of eCG on Day 6 postpartum could assist the early resumption of ovarian activity by enhancing ovarian follicle growth and early ovulation in postpartum cows. In this context, subsequent hCG injection may not provide any more beneficial effect.