Anovulatory Period Research Articles

Extending the Postpartum Anovulatory Period in Dairy Cattle with Estradiol Cypionate

Estradiol cypionate (ECP), a long-acting estrogen, has been used therapeutically in early postpartum (PP) dairy cows. In experiment 1, effects of ECP on circulating reproductive hormones, cyclicity, and ovarian function in early PP dairy cows were investigated. Lactating Holsteins received 10mg of ECP (ECP; n = 17) or placebo (CON; n = 16) on d 7 PP. Serum and ultrasound data were acquired from 5 to 90 d of lactation. Compared to CON, ECP cows had greater serum estradiol for 10 d and lower serum FSH for 15 d posttreatment. After ECP, the appearance of follicles ≥10mm and time to first ovulation were delayed. Nevertheless, by 90 d PP, normal estrous cycles were found in only 50% of CON versus 88% of ECP cows. Primiparous, but not multiparous, cows receiving ECP had higher milk yields. Experiment 2 investigated effects of ECP on reproduction and milk production on a commercial dairy. Cows were blocked by parity and randomized to three treatments: 0 (n = 85), 4 (n = 85), or 10 (n = 86) mg of ECP on d 5 to 8 PP. Data included cycling status (two ultrasound examinations at 30 to 33 d PP and 7 d later), individual reproduction records, and daily milk yields from 10 to 90 d PP. In primiparous cows, ECP had no significant effects on ovulatory status or milk yields. By 40 d PP, a greater percentage of multiparous cows receiving 10mg of ECP remained anovulatory compared with those receiving 0 or 4mg. Milk yields were highest for multiparous cows receiving 4mg of ECP, intermediate for the 10-mg dose, and lowest for controls. Lower conception was observed in multiparous cows receiving 4mg of ECP. In summary, ECP delayed time to first ovulation particularly in multiparous cows, an effect associated with observed inhibition of circulating FSH. Milk yield responses to ECP were inconsistent within parity groups across the two experiments.

The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period1

An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS went reproductively quiescent. Plasma leptin concentrations varied widely before the onset of restriction, even though all mares were in good body condition. During the experiment, leptin concentrations gradually decreased (P < 0.0001) over time in both groups, but were higher (P < 0.009) in mares with high vs low BCS after 6 wk of restriction, regardless of initial concentration. No differences (P > 0.1) between groups were detected for plasma concentrations of LH, FSH, TSH, GH, glucose, or insulin in samples collected weekly; in contrast, plasma prolactin concentrations were higher (P < 0.02) in mares with high BCS, but also decreased over time (P < 0.008). Plasma IGF-I concentrations tended (P = 0.1) to be greater in mares with high vs low BCS. The prolactin response to sulpiride injection on January 7 did not differ (P > 0.1) between groups. During 12 h of frequent blood sampling on January 12, LH concentrations were higher (P < 0.0001), whereas GH concentrations (P < 0.0001) and response to secretagogue (EP51389; P < 0.03) were lower in mares with high BCS. On January 19, the LH response to GnRH was higher (P < 0.02) in mares with high BCS; the prolactin response to TRH also was higher (P < 0.01) in mares with high BCS. In conclusion, nutrient restriction resulting in low BCS in mares resulted in a profound seasonal anovulatory period that was accompanied by lower leptin, IGF-I, and prolactin concentrations. All but one mare with high BCS continued to cycle throughout the winter or had significant follicular activity on the ovaries. Although leptin concentrations on average are very low in mares with low BCS and higher in well-fed mares, there is a wide variation in concentrations among well-fed mares, indicating that some other factor(s) may determine leptin concentrations under conditions of high BCS.

The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period

To determine whether plasma leptin concentrations and glucose tolerance are affected by changes in energy balance, nine healthy Shetland ponies were fed at 140% followed by 75% of their maintenance requirements for 13 days in each of the two periods. Bodyweight was recorded every three days. Blood samples were taken every two days and analysed for leptin and cortisol. An oral glucose tolerance test was performed on day 7 of each period. Serial blood samples were analysed for glucose and insulin.Although bodyweight was not affected, plasma leptin concentrations increased (P < 0.001) initially during overfeeding, but returned to previous values after 7 days. During underfeeding, plasma leptin concentrations decreased (P < 0.001). Underfeeding was associated with a higher AUC for plasma glucose (P = 0.02) and plasma insulin (P = 0.05) resulting in a decreased glucose tolerance (AUC glucose/AUC insulin; P = 0.008), probably due to a plasma cortisol increase caused by the reduced feed intake. It is concluded that changes in energy balance, without altering bodyweight, can influence plasma leptin concentrations in ponies.

The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period.

An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS went reproductively quiescent. Plasma leptin concentrations varied widely before the onset of restriction, even though all mares were in good body condition. During the experiment, leptin concentrations gradually decreased (P < 0.0001) over time in both groups, but were higher (P < 0.009) in mares with high vs low BCS after 6 wk of restriction, regardless of initial concentration. No differences (P > 0.1) between groups were detected for plasma concentrations of LH, FSH, TSH, GH, glucose, or insulin in samples collected weekly; in contrast, plasma prolactin concentrations were higher (P < 0.02) in mares with high BCS, but also decreased over time (P < 0.008). Plasma IGF-I concentrations tended (P = 0.1) to be greater in mares with high vs low BCS. The prolactin response to sulpiride injection on January 7 did not differ (P > 0.1) between groups. During 12 h of frequent blood sampling on January 12, LH concentrations were higher (P < 0.0001), whereas GH concentrations (P < 0.0001) and response to secretagogue (EP51389; P < 0.03) were lower in mares with high BCS. On January 19, the LH response to GnRH was higher (P < 0.02) in mares with high BCS; the prolactin response to TRH also was higher (P < 0.01) in mares with high BCS. In conclusion, nutrient restriction resulting in low BCS in mares resulted in a profound seasonal anovulatory period that was accompanied by lower leptin, IGF-I, and prolactin concentrations. All but one mare with high BCS continued to cycle throughout the winter or had significant follicular activity on the ovaries. Although leptin concentrations on average are very low in mares with low BCS and higher in well-fed mares, there is a wide variation in concentrations among well-fed mares, indicating that some other factor(s) may determine leptin concentrations under conditions of high BCS.

The timing of the onset of puberty, extension of the breeding season, and length of postpartum anestrus in the female mouflon (Ovis gmelini musimon).

The timing of the onset of puberty, duration of seasonal ovulatory activity, and length of postpartum anestrus were studied by means of blood plasma progesterone concentrations in a flock of European female mouflons (Ovis gmelini musimon) maintained in captivity under natural photoperiod (40 degrees 25'N). Concentrations of progesterone in the peripheral blood were determined by radioimmunoassay in samples collected from the jugular vein twice a week. First ovulations in the breeding season were highly synchronized and occurred in mid-October. In contrast, the cessation of ovulatory cycles showed significant variation among females and extended from February to May, depending on age, with 2-yr-old animals exhibiting the longest anovulatory period (P < 0.01). When lambing occurred within the breeding season (February-April), 12 out of 26 animals had their first ovulation 25 +/- 1.8 days after parturition. The 14 late-lambing females had the first postpartum ovulation delayed until the next breeding season. March/April-born mouflon lambs that reached a minimum threshold body weight (23.8 +/- 0.6 kg) in their first breeding season reached puberty at 8 mo of age. In those with slower growth rates, however, the prepubertal period was extended throughout the first breeding and nonbreeding seasons, reaching puberty during the breeding season of the following year at 19 mo of age and 27 +/- 0.3 kg body weight. Further, attainment of puberty in ewe lambs born in June/July was also delayed until the breeding season of the following year, when animals had reached a threshold body weight at 17 mo of age.

Suppressed production of transforming growth factor-beta(2)mRNA in endometrium of women with polycystic ovary syndrome.

Production of transforming growth factor-beta(2)mRNA in the endometrium of women with polycystic ovary syndrome decreased compared to normal and this decrease directly depends on the duration of anovulatory period (from 3 weeks to 4 months). Low production of transforming growth factor-beta(2)mRNA probably contributes to the development of endometrial hyperplasia in women with polycystic ovary syndrome.

Hormonal and ovarian responses to a 5-day progesterone treatment in anoestrous dairy cows in the third week post-partum

Primiparous cows with low body condition at calving have an extended anovulatory period. Induction of ovulation and oestrus is possible with progesterone treatment but the response to this treatment differs between Friesian and Jersey breeds. The objective of this study was to describe changes in pulsatile LH secretion and the synchrony of developing ovarian follicles that occur during a progesterone treatment period of 5 days in primiparous anovulatory cows. The experimental model compared the progesterone treatment with spontaneous post-partum changes as well as a breed comparison in a factorial design. Thirty-six cows (Jersey n=19 and Friesian n=17) were managed to calve with a low body condition score (BCS<4.5). Daily changes in ovarian follicle size were observed with transrectal ultrasonography in each cow from 8 days post-partum. Thirty of these cows were diagnosed to be anovulatory at 12–18 days post-partum (day 0) and allocated to a treatment ( n=16) or a control group ( n=14), balanced for breed. Each treated cow had a progesterone-releasing controlled internal drug-releasing (CIDR) device inserted vaginally for 5 days while control cows were left untreated. Changes in plasma LH concentrations were measured with intensive blood sampling over 8 h on days −1, 1, and 4. Blood samples were also collected daily (06:00 h) for determination of plasma progesterone as well as oestradiol concentrations on days 6 and 8. Treatment with progesterone was associated with a transient initial decrease (day 1) in both LH pulse frequency and mean LH concentrations after device insertion, but both had returned to pre-treatment levels by day 4. Jersey cows had a greater pulse frequency, but there was no breed difference in mean LH concentrations. Patterns of ovarian follicle growth were affected by progesterone treatment with an increase in diameter of the dominant follicle (DF) identified after treatment initiation. This followed an earlier emergence of a new DF after device insertion. Follicular response to progesterone was dependent on the diameter of the DF present at treatment initiation. Those follicles ≥9 mm were replaced by a new DF during treatment such that the DF observed at the time of device removal was large (≥9 mm) and growing in 13/16 cases. Progesterone was not effective for the induction of an LH surge, ovulation and oestrus in anovulatory cows with a low BCS. However, treatment was associated with synchronous development of a DF so that it was large and growing at the end of the treatment period in most cases. This synchronous development may be due to the transient suppression of LH and the presence of an LH-dependent DF.

Does anovulation induced by oral contraceptives favor pregnancy during the following two menstrual cycles?

Objective: To compare IVF and pregnancy outcomes before and after anovulation induced by oral contraceptives. Design: Observational clinical study. Setting: Infertility clinic. Patient(s): Forty women with two intact ovaries (32 of 40 couples with male factor infertility and 8 with unknown causes of infertility) underwent 190 IVF treatment cycles (55 natural cycles and 135 clomiphene citrate–stimulated cycles). Intervention(s): If the women failed to conceive after 2–4 IVF treatment cycles, oral contraceptives were used to induce anovulation for 1 month before IVF was performed in two consecutive cycles. Main Outcome Measure(s): Rates of oocyte retrieval, fertilization, cleavage, preembryo formation, pregnancy, and implantation were compared before and after a period of anovulation. Result(s): The pregnancy rate per cycle of the first and second cycle combined (23%) and that of the second cycle alone (30%) after a period of anovulation were significantly higher than that observed before a period of anovulation (9%). Conclusion(s): Anovulation induced by oral contraceptives, showing bilateral ovarian quiescence, enhances pregnancy rates in the following two menstrual cycles of IVF treatment.

Reproductive seasonality in the female scimitar‐horned oryx (Oryx dammah)

AbstractFaecal oestrogen and progestin analyses were used to assess ovarian activity in non‐pregnant scimitar‐horned oryx (Oryx dammah) during a 13‐month interval. Mean (± SE) luteal phase, interluteal phase and oestrous cycle duration were 18.8 (± 0.5), 5.1 (± 0.2) and 23.8 (± 1.3) days, respectively. All females exhibited a synchronized anovulatory period that ranged from 36–95 days during spring. Short ovarian cycles (10.6 (± 0.8) days) were observed intermittently throughout the year and before the spontaneous resumption of oestrous cyclicity. Periovulatory peaks in oestrogen concentrations were detected for 42.5% (31/73) of ovarian cycles. A parallel analysis of reproductive data from the North American studbook (1985–1994) revealed that captive‐held scimitar‐horned oryx gave birth throughout the year. Sex ratio at birth was male‐biased (54.4%), and 19.1% of all calves failed to survive to 6 months of age (220 out of 1149 births). Only 0.7% of births resulted in twins. Median interbirth interval was 277 days, and 75% of these intervals were less than 332 days. Interbirth interval was extended (P &lt; 0.05) if parturition occurred from January through May. In summary, the scimitar‐horned oryx is a seasonally polyoestrous species that experiences a distinct anovulatory period during spring in north‐east America.

Reproductive seasonality in the female scimitar-horned oryx (Oryx dammah)

Faecal oestrogen and progestin analyses were used to assess ovarian activity in non-pregnant scimitar-horned oryx (Oryx dammah) during a 13-month interval. Mean (± SE) luteal phase, interluteal phase and oestrous cycle duration were 18.8 (± 0.5), 5.1 (± 0.2) and 23.8 (± 1.3) days, respectively. All females exhibited a synchronized anovulatory period that ranged from 36–95 days during spring. Short ovarian cycles (10.6 (± 0.8) days) were observed intermittently throughout the year and before the spontaneous resumption of oestrous cyclicity. Periovulatory peaks in oestrogen concentrations were detected for 42.5% (31/73) of ovarian cycles. A parallel analysis of reproductive data from the North American studbook (1985–1994) revealed that captive-held scimitar-horned oryx gave birth throughout the year. Sex ratio at birth was male-biased (54.4%), and 19.1% of all calves failed to survive to 6 months of age (220 out of 1149 births). Only 0.7% of births resulted in twins. Median interbirth interval was 277 days, and 75% of these intervals were less than 332 days. Interbirth interval was extended (P < 0.05) if parturition occurred from January through May. In summary, the scimitar-horned oryx is a seasonally polyoestrous species that experiences a distinct anovulatory period during spring in north-east America.

The Wisdom of the Body Revisited.

Being selected a Cannon lecturer by the American Physiological Society is a singular honor under any circumstances, but a particularly poignant one for me because of my origins in Cannon’s old Department at the Harvard Medical School. In fact, when I began my career there as an instructor 45 years

Effects of body condition at calving, post-partum nutrition and calf access on the interval from calving to first ovulation in beef cows: Ovarian folliculogenesis and gonadotrophin secretion

The interval from calving to first ovulation is a major factor affecting reproductive and productive efficiency in beef cows. While this interval is affected by pre- and post-partum nutrition, the maternal-offspring bond is generally considered to be the major cause of delayed ovulation in beef cows. The endocrine and physiological mechanisms by which these factors either singularly or interactively control the duration of the post-partum anovulatory period are not well established, although they most likely involve the regulation of pulsatile LH release. The present study sought to examine the interactive effects of pre- and post-partum nutrition on LH secretion and follicle wave dynamics following acute calf isolation and once-a-day suckling (restricted access), after emergence of the fourth follicular wave post partum.

Annual energy intake and the metabolic and reproductive performance of beef cows differing in body size and milk potential

AbstractThe metabolic status and reproductive performance of four pure breeds of beef cow (small size and low milk potential, Aberdeen Angus; small size and high milk potential, Welsh Black; large size and low milk potential, Charolais; and large size and high milk potential, Simmental) were monitored during their first two parities. Heifers from each breed were allocated to one of two levels of annual energy intake relative to metabolic body weight (M075) (mean daily intakes equivalent to 705 and 820 kj/kg M0·75) in a factorial design. In the 1st year 64 heifers (eight per treatment) which had calved as a consequence of first or second service were selected for the experiment. In the 2nd year 40 of these animals (five per treatment) which held to first or second service remained on experiment. Animals were housed all year round and given diets designed to represent energy intakes while grazing during the summer and conserved feeding during the winter. Pregnancy was established in late July of each year using a combination of oestrous synchronization and artificial insemination. Blood samples were collected at monthly intervals from weaning in November until calving in May; three times weekly from calving until oestrous synchronization (11 weeks later); and fortnightly thereafter until weaning.For the annual levels of dietary energy intake offered, two breeds (Welsh Black and Charolais) exhibited relatively high growth rates and had the longest post-partum anovulatory periods; and Charolais cows also had the poorest conception rates of all breeds. Relatively lean cows at calving (body condition score &lt; 2·5 units) were sensitive, in terms of the duration of the anovulatory period, to live-weight loss during the early post-partum period, particularly when blood glucose levels were low, whereas relatively fat cows at calving (body condition score &gt; 2·5 units) were not. The data suggest: (i) that mechanisms controlling the anabolic processes governing maternal growth are antagonistic towards those that control reproduction; and (ii) the catabolism of lean tissue rather than fat tissue during the early post-partum period is also antagonistic towards the mechanisms that govern reproductive function in cows.

The effect of dietary protein on reproduction in the mare. IV. Serum progestagen, FSH, LH and melatonin concentrations during the anovulatory, transitional and ovulatory periods in the non-pregnant mare.

The effect of total protein intake and protein quality on the serum concentrations of certain reproductive hormones during the anovulatory, transitional and ovulatory periods were studied in 36 Anglo-Arab mares. High-quality protein stimulated FSH and LH production during the late transitional period. Serum progestagen and melatonin concentrations were unaffected by the quality of protein nutrition during the anovulatory period. Mares receiving high-quality protein exhibited a 10-14-day cyclical pattern of FSH release approximately 4-6 weeks earlier than the mares fed the lower-quality protein diet, and also ovulated 3-4 weeks earlier than the mares on the lower-quality protein diet. Progesterone concentrations during the 1st oestrous cycle after the anovulatory period were unaffected by protein quality in the diet.

The effect of body condition, feed level and temporary calf separation on the post-partum anoestrous period and LH and FSH levels in beef cows

Compared with other species of farm livestock the reproductive performance of beef cows is poor. Mating and calving periods are frequently extended to avoid having a large proportion of barren Cows. vs. For example the ‘average’ MLC recorded herd has a calving period of over 4months. This makes management of beef cow herds difficult and has a deleterious effect on biological efficiency and profitability.One of the major limitations to improvement of reproductive efficiency in beef cattle is the extended post-partum anoestrus. Beef cows have longer post-partum anoestrous periods than dairy cows. In one study of three different herds (Peters and Riley, 1982) the mean length of the anovulatory period ranged from 24 to 88 days.

Ability of androgenized goat wethers and does to induce estrus in goats under extensive conditions during anestrus and breeding seasons

Two hundred and ten Criollo crossbred goats under extensive conditions were randomly allotted to treatments to measure effects of exposure to intact bucks (♂), androgenized wethers (W) or androgenized does (♀), during the breeding season (November), on estrus response. Castrated bucks were androgenized by injecting 60 mg of testosterone propionate every 3 days for 20 days and every 4 days during the teasing period. Does were given 300 mg of testosterone during 2 consecutive days, additional 300 mg on Day 5 and 60 mg every 4 days. After 13 days of stimulus, induction of estrus did not vary among teasers (87.1, 94.3 and 84.0% for ♂, W and ♀, respectively) but time to onset of estrus was significantly shorter ( P < 0.01) for goats exposed to ♂ (4.6 ± 0.40 days) compared with goats exposed to W (6.9 ± 0.39 days) and ♀ (8.1 ± 0.46 days). In another experiment conducted during the non-breeding season (April) a total of 150 goats were divided into two groups and exposed either to ♂ or W. After 37 days of teasing the proportion of does exhibiting behavioral estrus was half of that observed during the breeding season. There was no significant effect of teasers on estrus response (46.7 and 51.7% for ♂ and W, respectively) but the time to onset of estrus was shorter for ♂ (27.3 ± 0.66) compared with W (30.7 ± 1.26). Results of a third experiment showed that pregnancy rate (76.5% vs 24.7%) and prolificacy (1.61 ± 0.04 vs 1.25 ± 0.08) was affected ( P < 0.01) by month of breeding (January vs April). Results demonstrate that androgenized wethers and testosterone-treated does can be used successfully to induce estrus during the breeding season of goats, but that, under these conditions, only half of the does respond to this teasing during the non-breeding season, which leads to poor reproductive performance when goats were exposed to bucks during the non-responsive anovulatory period.

Ovulatory cycles and anovulatory periods in the addax (Addax nasomaculatus)

Changes in serum oestradiol and progesterone were measured to study their dynamics during ovulatory cycles in six female addax, an endangered antelope. Blood was collected three times per week, during chute restraint, for 3 months (November to February) before introduction of a male, and continued until pregnancy was diagnosed with ultrasound. Serum was analysed by enzymeimmunoassay. Mean luteal phase, interluteal phase, and cycle durations were 22.7 +/- 2.0, 8.78 +/- 0.5 and 32.3 +/- 1.7 days, respectively. Ultrasonography revealed coiled uterine horns and maximum follicle and corpus luteum diameters of 15 and 27 mm, respectively. Each female experienced an anovulatory period, during which oestradiol continued to fluctuate, but progesterone remained below 2 ng ml-1. These periods ranged from 39 to 131 days and were not synchronous; ovulatory cycles resumed spontaneously in all females. All four females placed with a male conceived. Because addax give birth all year round, they are not considered seasonal breeders. The sporadic periods of anovulation that occurred during the winter months of this study suggest a possible seasonal effect. However, systematic sampling has not been conducted during summer and early autumn and will be necessary to address this question.

The Effect of Energy Balance on Ovarian Activity in a Herd of Norwegian Cattle

The study involved 34 primiparous cows fed ad libitum grass silage and fixed amounts of concentrate per cow and stage of lactation. It revealed that number of days from calving to maximum progesterone concentration in first luteal phase was negatively related to (p < 0.05) energy balance summarized over weeks 3-12 post-partum. One standard deviation improvement of the summarized energy balance relative to the mean reduced the length of the anovulatory period by 12 days. Similarly, an improved energy balance enhanced progesterone secretion during the oestrus cycle and early pregnancy, as measured by 3 variables; 1) maximum progesterone concentration in first luteal phase, 2) cumulative progesterone secretion bounded by the maximum concentrations in first and in third luteal phase and 3) cumulative progesterone secretion in the first month of pregnancy. All results were supported by the estimated regression coefficients of the 4 ovarian activity variables on summarized non-estrified fatty acids and acetoacetate variables.

Patterns of follicular development during periods of anovulation in pasture-fed dairy cows after calving

The ovaries of 17 Friesian cows aged two to seven years were examined daily by transrectal ultrasound from one week after calving. The position and size of all follicles more than 2 mm in diameter were recorded. A large (more than 9 mm in diameter) follicle was present on at least one ovary by six to 17 days after calving, and in two of the cows it ovulated; the remaining cows had from two to nine large follicles before they ovulated. The mean ( sem) interval from calving to the first ovulation was 43 ·4 (5·3) (range 13 to 93) days, after 4·2 (0·6) waves of follicles.

The dexamethasone induced suppression of androgen secretions suppressed estrous behavior in pony mares during the winter

For 23-days, 12 intact pony mares were administered daily injections of dexamethasone (6 mares) or sesame oil (6 mares) during the winter anovulatory period. Blood samples were collected daily (beginning the first day of treatment) for 42 days and assayed for progesterone, testosterone, androstenedione, estradiol, and LH. Four of the six sesame oil treated mares exhibited estrous behavior whereas none of the dexamethasone treated mares exhibited estrous behavior (P<.05). Plasma LH, progesterone, and estradiol concentrations were unchanged by the dexamethasone treatment but testosterone concentrations were suppressed (P<.05) and androstenedione concentrations tended (P<.10) to be suppressed by dexamethasone treatment. Therefore, in the presence of suppressed endogenous androgens, estrous behavior during the winter anovulatory season was eliminated.