The estrous cycle in the dog: a review

Clinical, morphologic and hormonal changes throughout the estrous cycle in the dog are discussed in relation to the well established stages in this species — proestrus, estrus, metestrus and anestrus. Although most efforts in the past have been devoted to the period of reproduction, events throughout the remaining months of the cycle are presented to characterize the dog as a monocyclic animal in contrast to polycyclic species.     

The estrous cycle and induction of estrus in the australian feral sow (Sus scrofa)

In the first of 2 experiments, the estrous cycles of 11 Australian feral sows were studied. In 9 of the 11 sows the cycle was characterized by cyclic occurrences of low (0 to 2 ng/ml) and high (24.2 to 47.2 ng/ml) levels of progesterone. The low levels were associated, in all sows but one, with the standing response, lasting from 1 to 4 days, to a feral boar. Concomitant cyclic changes in vulval swelling and consistency of the vaginal mucus were also observed. Using intervals between the standing estrous response or the marked changes in the secretion of progesterone, the mean length of the cycle was calculated as 19.8 and 20.0 d, respectively. Two of the sows did not exhibit cyclic changes in any of the parameters measured, and on no occasion did either stand for service. In the second experiment, it was shown that estrus can be reliably induced in feral sows by either 1 of 2 methods: first, sows were induced to abort by prostaglandin injection. They were then administered gonadotrophin 48 to 72 h post abortion, and came into estrus 4 to 5 days later. Second, estrus was suppressed by feeding sows altrenogest, and was induced again about 9 days following altrenogest withdrawal.     

Endocrine events during the periestrous period and the subsequent estrous cycle in ewes after estrus synchronization

The aim of the present study was to investigate the endocrinology of the periestrus period and that of the subsequent estrous cycle in ewes synchronized during the breeding season. Animals were treated for 14 days with either MAP intravaginal sponges or subcutaneous progesterone implants, followed by administration of 500 IU PMSG at the time of withdrawal. The time to estrus occurrence following progestagen withdrawal differed significantly between groups (45.3+/-2.7h for the MAP and 21.5+/-1.2h for the implant group, P<0.001). Estradiol levels around estrus did not differ between groups, but a significant difference was detected for the interval from peak estradiol to estrus, with a shorter interval for the implant group (26.7+/-0.7 and 2.7+/-0.9h, P<0.001). Progesterone implants shortened the interval from removal to LH surge, compared to the MAP group (31.2+/-4.4 and 56.5+/-3.6h, respectively, P<0.05). An earlier response was also observed for the interval from estradiol peak to LH peak in the implant group (12.1+/-3.3 and 37+/-2h, respectively, P<0.005), but no difference was observed for the interval from estrus to LH surge. Progesterone levels, particularly during the Days 6 to 10 of the subsequent estrous cycle were significantly higher (P<0.05) in the implant group. It is concluded that the kind of progesterone treatment may affect the time of estrus and the LH peak as well as the progesterone levels of the subsequent cycle.     

Manipulation and control of the estrous cycle in pasture-based dairy cows

Treatments designed to synchronize luteolysis, preovulatory follicular development, and ovulation, and resynchronize estrus after a first AI have improved responses to synchronization treatments. Protocols based only on the use of PGF result in variable onset of estrus. Concentrations of progesterone prior to administering PGF have affected submission rates and fertility while administration of estradiol benzoate (EB) after inducing luteolysis has improved the synchrony of estrus and ovulation in some studies. In pasture-based dairy cows, GnRH-based protocols have generally resulted in one-third of both anestrous and cycling cows conceiving following synchronization of ovulation and timed AI. Protocols which use intravaginal progesterone releasing inserts (IVP4) are effective in inducing estrus in over 90% of treated dairy cows. Resynchronization of estrus after reinsertion of an IVP4 also improves the synchrony of returns to estrus, but pregnancy rates to the first AI have been reduced in some studies, and submission rates at a resynchronized estrus are less than at the first synchronized estrus. Administration of EB can be used to synchronize follicle wave emergence in resynchronized cows with intervals to new wave emergence comparable to that in cows synchronized for a first AI, but plasma concentrations of progesterone following treatment may be reduced. Synchronization of estrus and ovulation can be enhanced by administration of EB or GnRH during proestrus, but dose, timing and stage of follicular development at the time of treatment can affect outcomes.     

Follicular dynamics during postpartum anestrus and the first estrous cycle in suckled or non-suckled Brahman (Bos indicus) cows

Brahman (Bos indicus) cows, were selected at 28+/-10 days after calving and analyzed by real time rectal ultrasonography three times a week, in order to evaluate and compare follicular and corpus luteum development during postpartum (PP) anestrus and the first PP estrous cycle under sylvopastoril conditions. Suckling (S, n=11) or non-suckling (NS, n=5) cows were evaluated in a zone of tropical dry forest (450m of altitude, mean temperature=27 degrees C, annual rainfall=1000mm). Estrous detection was performed twice daily by direct observation. Progesterone was quantified using RIA. From 28+/-10 days postcalving to resumption of estrous cycles, there were no differences (P>0.05) between NS and S cows for diameter of the dominant or first subordinate follicle, follicular growth rate, or interdominance interval. Silent ovulation, corpus luteum formation and subsequent progesterone concentrations ranging from 0.3 to 9. 7ng/ml, were found in both groups. The first calving to ovulation and calving to standing estrus intervals were shorter (P<0.01) in NS (34.8+/-5.81 and 41.2+/-9.03 days) than in S (65+/-4.82 and 81+/-6. 21 days) cows. Follicular development and progesterone concentrations during the first PP estrous cycle did not differ (P>0. 05) between NS and S cows. These results suggest that Brahman cows could have an early PP resumption of follicular recruitment if fed under sylvopastoril system conditions. However, non-suckled cows did have an earlier standing estrus and ovulation than did suckled cows.     

Characterization and distribution of gonadotrophs in the pars distalis and pars tuberalis of the equine pituitary gland during the estrous cycle and seasonal anestrus

Little is known about the neuroendocrine control of fertility in the horse. In this species, unusual features characterize the normal estrous cycle such as a prolonged preovulatory LH surge during the follicular phase and a distinctive FSH surge during the midluteal phase. This study investigated the distribution and hormonal identity of gonadotrophs in the pars distalis (PD) and pars tuberalis (PT) of the equine pituitary gland as possible morphological bases for the referred unusual endocrine characteristics. In addition, the proportion of gonadotrophs in relation to other pituitary cell types during both the estrous cycle and anestrus were investigated. Pituitary glands were collected from sexually active (n = 5) and seasonally anestrous (n = 5) mares in November, and single or double immunofluorescent staining was carried out on 6-microm sections using monoclonal antibodies to the LHbeta or FSHbeta subunits and a polyclonal antibody to ovine LHbeta. Gonadotrophs were densely distributed around the pars intermedia in the PD and in the caudal ventral region of the PT. In addition to isolated cells, clusters of gonadotrophs were found surrounding the capillaries. No significant differences were detected in the number of gonadotrophs between sexually active and anestrous mares in either the PD or PT. In the PD, gonadotrophs represented 22.7 +/- 5. 8% and 19.1 +/- 2.1% of the total cell density in sexually active and anestrous animals, respectively (P: > 0.05). However, in the PT, gonadotrophs accounted for a higher proportion of the total cell population in sexually active (6 +/- 0.1%) than in anestrous (1.2 +/- 0.05%) mares (P: < 0.02). Double immunofluorescence revealed that the majority of gonadotrophs were bihormonal (i.e., positive for LH and FSH); however, in the sexually active mare, a larger proportion of gonadotrophs (22.5 +/- 3.6%) were monohormonal for either LH or FSH, when compared to anestrous animals (9.7 +/- 1.2%; P: < 0.02). Based on these findings we conclude that: 1) although the relative distribution of gonadotrophs is similar to those reported for other species, a significantly larger proportion of gonadotroph cells is present in the equine pituitary gland; 2) gonadotroph density does not appear to differ between sexually active and anestrous mares in the PD; 3) a larger proportion of gonadotrophs is apparent in the PT of sexually active animals; and 4) although a large incidence of bihormonal gonadotrophs is present in the horse, specific LH or FSH cells differentiate predominantly during the sexually active phase.     

Effect of hCG administration on day 7 of the estrous cycle on follicular dynamics and cycle length in cows

The use of hCG in cattle at breeding or at different times after breeding has been associated with extension in estrous cycle length among cows that do not become pregnant. The objective of this study was to determine whether the increase in estrous cycle length observed in hCG-treated cows that fail to become pregnant is due to changes in ovarian follicular dynamics. Twelve nonbred lactating cows were randomly assigned either to receive hCG on Day 7 of the cycle (Day 0 = day of estrus, n = 6) or to serve as controls (n = 6). Ultrasound scanning was conducted daily from Day 0 until the onset of the next ovulation to monitor follicular and corpus luteum (CL) dynamics. Blood samples were collected for progesterone analysis at each ultrasound session. Ovulation of the Day 7 follicle occurred in all 6 hCG-treated cows. The time of emergence of the second-wave of follicular growth was advanced in hCG-treated cows but was not statistically different (P > 0.05) from that of the control cows (10.8 +/- 0.3 vs 12.7 +/- 1.4 d). The mean diameter of the second-wave dominant follicle from Days 15 to 18 was not different (P > 0.05) between the treatment groups. However, the second-wave dominant follicle had a slower growth rate (0.8 vs 1.3 mm/d) among cows treated with hCG compared with that of the controls. The second-wave dominant follicle was the ovulatory follicle in 5 control cows, but only in 3 hCG-treated cows. The dominant follicle from the third wave ovulated in 1 control and in 3 hCG-treated cows. The lifespan of the spontaneous CL and the time to low progesterone levels (< 1 ng/ml) were not different between the control and hCG-treated cows. These results suggest an altered follicular dynamic but no extension in estrous cycle length when hCG is administered on Day 7 of the cycle in postpartum cows.     

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early ( Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early ( Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).     

Effect of stage of the estrous cycle on interval to estrus after PGF(2alpha) in beef cattle

Effect of stage of the estrous cycle at the time of prostaglandin F(2alpha) (PGF(2alpha)) injection on subsequent reproductive events in beef females was studied in four trials involving 194 animals. Cycling animals were given two injections of 25 mg PGF(2alpha) 11 days apart or, in some cases, the interval was altered to allow the second injection to fall on a specific day of the cycle. Day of estrous cycle at time of the second injection was determined by estrous detection. Interval from the second PGF(2alpha) injection to the onset of estrus (interval to estrus) was shorter (P<.01) in heifers than in cows. Both cows and heifers injected on days 5 to 9 (early cycle) had a shorter (P<.01) interval to estrus (estrus = day 0) than did those injected on days 10 to 15 (late cycle). Conception rate was lower (P<.05) for early-cycle heifers than for late-cycle heifers inseminated by appointment at 80 hours. There was no significant difference in conception rate of early-or late-cycle heifers or cows inseminated according to estrous detection or early- or late-cycle cows inseminated at 80 hours. Progesterone concentrations in blood samples collected in heifers at 4-hour intervals after the second PGF(2alpha) injection on either day 7 or day 14 declined linearly (P<.05) through 36 hours. Day of the estrous cycle at PGF(2alpha) injection had no effect on rate of progesterone decline, even though heifers injected on day 7 had a shorter (P<.05) interval to estrus. All animals whose cycle length was not affected by the second PGF(2alpha) injection were treated on days 5 through 8 of the cycle, indicating that PGF(2alpha) was less effective in regressing the corpus luteum between days 4 and 9 of the cycle than later in the cycle.     

Endocrine control of estrous cycle in mithun (Bos frontalis)

The objective of the present study was to establish the profiles of luteinising hormone (LH), follicle stimulating hormone (FSH), estradiol 17beta (E2) and progesterone (P4) secretion and their interrelationships during the natural estrous cycle of mithun (Bos frontalis). Daily blood samples were collected from second or third postpartum estrous cycles for determination of plasma concentrations of LH, FSH, E2 and P4. Concentration of P4 was found to be lowest on the day of estrus. It increased following estrus, attained the highest concentration on day 11 and decreased thereafter. Concentrations of LH and FSH varied significantly (p<0.01) during the first and last 6 days of the cycle and their variations were found to be synchronised. Both LH and FSH attained a biphasic peak during the estrous cycle. This biphasic peak lasted on from day -5 to day 3 of the cycle. The variations in maximum LH and FSH concentrations of both the phases did not differ significantly. During the entire estrous cycle, the E2 concentrations attained either one peak or two peaks. The first peak, approximately on day 4 before estrus was common in all animals. One additional peak was found on the day of estrus in 45% animals. A significant (p<0.01) negative relationship was found between P4 and, LH and FSH during the first and last 6 days of cycle. But a significant (p相似文献   

Effect of dexamethasone on the estrous cycle length in Black Bengal goats (Capra hircus )

In an experiment to examine the relationships between adrenals and reproductive cycle, 10 mg dexamethasone (a synthetic glucocorticoid) were injected intramuscularly twice daily for 10 d to four Black Bengal goats, beginning on Day 11 of the synchronized estrous cycle. The extended length of the sexual cycle was monitored by the clinical signs of anestrus. Laparotomy was performed to examine the status of the ovary of an 8, 9, 10 and 8 d extended cycle, respectively. The length of the next cycle was normal. Endogenous cortisol values were suppressed for 11, 13, 20 and 24 d, respectively. It is thought that dexamethasone caused prolonged luteal function either by the suppression of prostaglandin F(2)alpha synthesis or by the suppression of pituitary stimulation of follicular growth.     

Induction of pseudopregnancy using artificial VCS: importance of lordosis intensity and prestimulus estrous cycle length

In cycling female rats, vaginocervical stimulation (VCS) received naturally during mating or by artificial mechanical stimulation induces neuroendocrine and behavioral responses that are critical for reproduction, including bi-circadian prolactin surges which result in pregnancy or an 8-14-day diestrous period called pseudopregnancy (PSP). Following mating, the incidence of PSP is higher when females receive high (10) as opposed to low (3-5) numbers of intromissions. Therefore, a threshold level of VCS must be exceeded before hypothalamic changes required for PSP can occur. This study characterized the threshold curve for PSP induction for artificial VCS (VCS-a). Proestrous females were given 1, 2, 3, 4, or 8 VCS-a applied with a glass rod using 200 g of force for 2 s, with an 8-min interval between stimulations. The lordosis response (LR) to the stimulus was measured on a scale of increasing intensity from 0 to 3, and the occurrence of PSP was measured by daily vaginal lavage. In contrast to previous findings, VCS-a induced robust lordosis responses without concurrent flank and perineal stimulation. The frequency of PSP induction did not increase in females as a function of amounts of VCS-a. However, the occurrence of PSP was strongly tied to the maximum lordosis response (LR(max)) observed. PSP was observed only among multiply stimulated females that showed the highest LR(max) (3.0) to at least one of the stimulations. Multiply stimulated females that showed a LR(max) < 3.0 or females that received only one VCS-a never became PSP. PSP and a stronger LR(max) were more likely to occur in females that had 5-day compared to 4-day prestimulus estrous cycle lengths. We conclude that central mechanisms important for VCS-induced PSP and lordosis may be potentiated by estradiol's actions in estrogen-concentrating forebrain areas.     

Effect of injected bovine interferon-alpha I1 on estrous cycle length and pregnancy success in sheep

In Exp. 1 twice daily i.m. injections of 2 mg recombinant bovine IFN-alpha I1 (rboIFN-alpha I1) (N = 24) or placebo (N = 25) were administered to ewes from Day 12 to Day 16 during a normal oestrous cycle. Treatment did not increase (P greater than 0.10) oestrous cycle length (20.7 +/- 1.2 versus 18.5 +/- 1.4 days). In Exp. 2, ewes were injected twice daily with 2 mg IFN (N = 34) or placebo (N = 36) from Days 11 to 18 after natural mating. The rboIFN-alpha I1 significantly (P = 0.05) improved pregnancy rate (79% versus 58%) as determined by a failure of ewes to return to oestrus within 50 days. The number of ewes that lambed was greatest in the rboIFN-alpha I1-treatment group (71% versus 50%; P = 0.07), and no teratogenic effects were observed in the young born to IFN-treated ewes. The study was repeated a second year with a more fecund group of ewes (Exp. 3). More (P = 0.08) ewes injected with rboIFN-alpha I1 (58/65) than placebo-treated ewes (48/61) were judged pregnant by ultrasound. Again more ewes lambed (55 versus 45) and more lambs were born (98 versus 80) from the rboIFN-alpha I1-treated group. Combining the data from both studies revealed a significant (P = 0.01) effect of treatment. The amount of antiviral activity in jugular vein blood of ewes injected with rboIFN-alpha I1 (2 mg) was determined over time in Exp. 4. Activity rose to a maximum (approximately 450 IRU/ml) within 1-2 h and declined by over 75% in 24 h. Single injections of 1, 2 and 5 mg in buffer or 2 mg emulsified in sesame oil all gave similar profiles of antiviral activity in jugular blood over a 48-h period. In Exp. 5, antiviral activity was measured in uterine vein, ovarian artery and jugular vein serum of untreated pregnant (N = 7) and non-pregnant (N = 11) ewes at Day 15 after mating. Activity was detected in the uterine vein (58 +/- 19 IRU/ml) of all pregnant ewes. The observations in Exps 1-5 are consistent with a role for conceptus-derived IFN-alpha in maternal recognition of pregnancy and suggest that supplemental IFN-alpha might be useful in improving pregnancy success in sheep.     

Factors affecting gestation length and estrus cycle characteristics in Spanish donkey breeds reared in southern Spain

This paper investigated gestation length and estrus cycle characteristics in three different Spanish donkey breeds (Andalusian, Zamorano-Leones, and Catalonian) kept on farm conditions in southern Spain, using data for ten consecutive breeding seasons. Gestation length was measured in 58 pregnancies. Ovarian ultrasonography was used to detect the ovulation, in order to ascertain true gestation length (ovulation-parturition). Pregnancy was diagnosed approximately 14-18 d after ovulation and confirmed on approximately day 60. Average gestation length was 362 ±15.3 (SD) d, and no significant differences were observed between the three different breeds. Breeding season had a significant effect (P < 0.01), with longer gestation lengths when jennies were covered during the early period. Breed, age of jenny, year of birth, foal gender, month of breeding, and type of gestation had no significant effect on gestation length.After parturition, foal-heat was detected in 53.8% of the postpartum cycles studied (n = 78), and ovulation occurred on day 13.2 ± 2.7. The duration of foal-heat was 4.7 ±1.7 d, with a pregnancy rate of 40.5%.When subsequent estrus cycles were analyzed, the interovulatory interval (n = 68) and estrus duration (n = 258) were extended to a mean 23.8 ± 3.5 and 5.7 ± 2.2 d, respectively. Both variables were influenced by the year of study (P < 0.03 and P < 0.001), whereas month and season of ovulation (P < 0.005 and P < 0.009, respectively) affected only interovulatory intervals. Estrus duration was significantly longer than that observed at the foal-heat (P < 0.006), and the pregnancy rate was 65.8%.This study provides reference values for true gestation length and estrus cycle characteristics in Spanish jennies. Breeding season affected gestation length in farm conditions. Also, seasonal influence was observed on the length of the estrus cycle (i.e., interovulatory interval), although foal-heat was not affected by environmental factors.     

Validation of a mathematical model of the bovine estrous cycle for cows with different estrous cycle characteristics

A recently developed mechanistic mathematical model of the bovine estrous cycle was parameterized to fit empirical data sets collected during one estrous cycle of 31 individual cows, with the main objective to further validate the model. The a priori criteria for validation were (1) the resulting model can simulate the measured data correctly (i.e. goodness of fit), and (2) this is achieved without needing extreme, probably non-physiological parameter values. We used a least squares optimization procedure to identify parameter configurations for the mathematical model to fit the empirical in vivo measurements of follicle and corpus luteum sizes, and the plasma concentrations of progesterone, estradiol, FSH and LH for each cow. The model was capable of accommodating normal variation in estrous cycle characteristics of individual cows. With the parameter sets estimated for the individual cows, the model behavior changed for 21 cows, with improved fit of the simulated output curves for 18 of these 21 cows. Moreover, the number of follicular waves was predicted correctly for 18 of the 25 two-wave and three-wave cows, without extreme parameter value changes. Estimation of specific parameters confirmed results of previous model simulations indicating that parameters involved in luteolytic signaling are very important for regulation of general estrous cycle characteristics, and are likely responsible for differences in estrous cycle characteristics between cows.