Electro-oophorogram: A preliminary study of the electric activity of the ovary

The electric activity of the ovary was studied in 13 female mongrel dogs aiming at characterizing a normal electro-oophorogram (EOOG). Two monopolar silver-silver chloride electrodes were sutured under anesthesia to the ovary of the bitches which were in the anestrus phase of the estrous cycle. A daily recording session of 60 min was performed for 10 days. Furthermore, the effect of ovarian vessels' clamping, of oophorectomy and of ovarian insult by irradiation on the electric activity, was studied. Electric waves were recorded from the two electrodes. Each wave consisted of a negative followed by a positive deflection with a mean amplitude of 52.6 +/- 10.7 microV and frequency of 9.2 +/- 1.6 cycles per second. The waves showed the same amplitude and frequency from the two electrodes and were reproducible when the test was repeated in the same animal. Fast activity spikes were not encountered. Temporary clamping of the ovarian vessels caused diminution of the normal ovarian electric activity which returned to the preclamping state after clamp release. A 'silent' EOOG was obtained after oophorectomy. Two EOOG patterns were recorded from the irradiated ovary: silent and dysrhythmic. To conclude, an EOOG could be characterized for the bitches in the anestrus phase which is a quiescent phase of the estrous cycle. Further studies are required to record the EOOG in the other phases of the estrous cycle and in the various pathologic conditions of the ovary.

[Sonographic presentation of the physiologic ovarian function in the anovulatory and pseudopregnant cycle of the cat]

Continuous sonographic examinations of the physiological ovarian structures were performed in four anovulatory and 14 pseudopregnant cycles. The animals were examined in standing position from the right and left flank using a mechanical 13 MHz sector scanner with integrated stand off pad. The intervals were two or three days during anoestrous and luteal phases and one day during follicular phases. The follicles could be identified from a minimum size of 1.0 mm and reached maximum mean diameters of 3.3 mm within at most eight days. The period of follicular regression was eight days in the anovulatory cycles. In the pseudopregnant cycles ovulation could be sonographically verified by the disappearance of follicles of 3 or more mm in diameter within 24 hours. Immediately thereafter the ovary had a more or less homogeneous appearance. Luteal development gave different sonographic findings. In general anechoic structures of 1 mm in diameter were recognizable within three days after ovulation, coming up to 5.3 mm within five days. Compact corpora lutea were easily identified as nearly homogeneous structures, that bulged over the ovarian surface. Corpora lutea, that were embedded in the ovary could not be detected without doubt.

[Metabolism-reproduction interactions in domestic animals]

In farm animals as in human, reproduction is affected by changes in the level of energetic balance. The main factors that link metabolism and reproduction, like insulin, IGFs, glucose, FFA, leptin and NPY, act on hypothalamo-pituitary axis as well as on gonads by directly altering gametogenesis.

Ovarian follicular dynamics during anoestrus in ewes

The aim of the present study was to document ovarian antral follicle dynamics throughout seasonal anoestrus in sheep. Daily transrectal ultrasonography was performed during four 17 day scanning periods from March to July in Western White-faced crossbred ewes. Blood samples were collected each day with ultrasonographic scanning for measurement of serum concentrations of FSH, oestradiol and progesterone. Blood samples were also taken every 15 min for 6 h, mid-way through each period of ultrasonographic examination, to determine the patterns of secretion of gonadotrophic hormones. Hormonal data were then related to observed changes in follicular populations and the patterns of antral ovarian follicle turnover. Ultrasonography showed that the ovaries of anoestrous ewes remained active and that the largest ovarian antral follicles grew to a periovulatory size (> or = 5 mm in diameter) at all stages of anoestrus. The total number of all ovarian follicles > or = 3 mm in diameter was lower during early anoestrus compared with at mid-anoestrus because of a significantly smaller number of small (3 mm) and medium (4 mm) ovarian follicles. The largest ovarian follicles (attaining > or = 5 mm in diameter before regression) exhibited a wave-like pattern of growth; an average of three waves of follicular development were recorded in sheep during each of the four 17 day scanning periods in anoestrus, with follicular waves emerging approximately every 5 days. This rhythmic pattern of follicular emergence was found to be associated with the occurrence of fluctuations in serum FSH concentrations. The growth rate of the largest follicles of the wave increased significantly from early to late anoestrus in sheep. In addition, ovarian follicles not growing beyond 3 mm in diameter showed organized patterns of growth and regression; their numbers tended to be lower (P = 0.09) at 3 days before and on the day of follicular wave emergence. Some ewes were seen to maintain synthesis of progesterone throughout anoestrus. This submaximal progesterone secretion tended to occur at irregular intervals and was not coupled with changes in concentrations or patterns of gonadotrophin release, ovulations or detectable morphological luteinization of ovarian antral follicles. It was concluded that the growth of ovarian antral follicles to an ovulatory size was maintained throughout anoestrus in ewes, with a transient shift in the number of small and medium-sized follicles during mid-anoestrus, and that the periodic emergence of waves of large follicles (> or = 5 mm in diameter) occurred in synchrony with an endogenous rhythm of FSH secretion.

Effect of acute food deprivation on lactational infertility in rats is reduced by leptin administration

The goals of these experiments were to determine whether lactational anestrus would be prolonged by a 48-h fast at days 13 and 14 postpartum (pp) and, if so, to determine whether this effect could be reversed by treatment with the Ob protein leptin. We found that food deprivation on days 13 and 14 pp prolonged lactational infertility by 7 days and that the nutritional experience of both the dam and her litter contributed to this effect. Leptin administration (2.5 mg . kg-1 . day-1) during food deprivation was sufficient to reduce the length of lactational infertility compared with vehicle-treated food-deprived rats (P < 0.05). Similar leptin treatment in ad libitum-fed animals reduced food intake (P < 0.05) and litter growth (P < 0.05) but had no statistically significant effect on maternal weight gain or length of lactational infertility. Food-deprived lactating animals had lower circulating leptin levels than ad libitum-fed lactating animals on day 15 pp (P < 0.05), as determined by RIA. Levels in nonlactating rats were higher than in either lactating group (P < 0.05).

Seasonal patterns of luteal cyclicity in young red deer (Cervus elaphus) and sambar deer (Cervus unicolor)

Seasonal onset of pubertal ovulation and incidence of luteal cyclicity was assessed from plasma progesterone profiles over 15 months for tame red deer (n = 7) and sambar deer (n = 7) hinds. Seasonal responses to photoperiod were determined from plasma prolactin profiles. All red deer attained puberty at 17-18 months of age in May-June and expressed 3-6 luteal cycles of length 20.0+/-10.4 days (mean+/-s.e.m.) over 52-102 days. Six sambar deer attained puberty at 7-19 months of age, between August and December. Duration of luteal cyclicity was variable. While one animal remained continuously cyclic for 13 months, most entered anoestrus between November and February. The mean length of the luteal cycle was 17.2+/-0.3 days. While red deer exhibited strongly seasonal patterns of prolactin secretion, sambar deer showed no such seasonal trends. The data collectively indicate that young sambar hinds at temperate latitudes exhibit loosely defined patterns of reproductive seasonality that are 4-6 months out of phase with those of red deer, although some individuals may be non-seasonal. Failure to express seasonal patterns of prolactin secretion indicates that sambar deer may not perceive photoperiodic cues to the same extent as do red deer.

Length of postpartum anestrus in goats in subtropical Mexico: effect of season of parturition and duration of nursing

The aim of this study was to determine whether season of birth and length of nursing affected the duration of postpartum anestrus in Creole female goats maintained on a constant plane of nutrition in subtropical Mexico. Three experiments were conducted in the Laguna region in the State of Coahuila, Mexico (26 degrees N). In the first experiment, 34 goats gave birth in January; in the second, 31 females gave birth in May; and in the third, 22 goats kidded in October. At parturition, females were allocated to 1 of 3 groups based on body weight and date of parturition: kids were weaned at 2, 30 or 90 d according to their group. After weaning, females were milked manually once a day until the end of the study. All animals were kept in a shed and were fed alfalfa ad libitum and given 200 g of concentrate daily. Starting 1 wk after parturition, estrous behavior was detected twice daily using an apron-bearing male, and blood samples were obtained twice weekly to determine ovarian activity from the plasma progesterone levels. A strong effect of month of parturition was found on the duration of postpartum anestrus (P < 0.0001), which was longer in females kidding in January (about 200 d) than in those kidding in May (about 100 d) or October (about 50 d). A tendency for an interaction between season of parturition and length of nursing was observed in the length of anovulation (P < 0.07): for parturition in October, anestrus was longer when kids were weaned after 90 d than after 2 or 30 d (P < 0.01). Season of parturition also affected dates of reinitiation of ovulatory and estrous activity (P < 0.001). Proportions of normal, short and long cycles and of associations between estrous and ovulations were not influenced by season of parturition or the age of weaning. These data demonstrate that in subtropical latitudes, season of parturition can dramatically influence the duration of postpartum anestrus independently of the availability of food.

Melatonin treatment of embryo donor and recipient ewes during anestrus affects their endocrine status, but not ovulation rate, embryo survival or pregnancy

Thirty-two Border Leicester x Scottish Blackface ewes that lambed in March were individually penned with their lambs from April 16th and given daily an oral dose of 3 mg melatonin at 1500 h (Group M). A further 32 acted as controls (Group C). Within each group half were used as embryo donors (Group D) following superovulation and half received embryos (Group R) following an induced estrus. Prior to weaning on 21 May ewes received ad libitum a complete diet providing 9 megajoules (MJ) of metabolizable energy and 125 g/kg crude protein. Thereafter each received 1.6 kg of the diet daily. In early June each ewe received an intravaginal device (300 mg progesterone) inserted for 12 d. Donors were superovulated with 4 i.m. injections of porcine FSH 12 h apart, commencing 24 h before progesterone withdrawal. Ovulation in recipients was induced with 800 IU PMSG injected i.m. at progesterone removal. Donor ewes were inseminated 52 h after progesterone withdrawal. Embryos were collected 4 d later and transferred to recipients. Melatonin suppressed plasma prolactin (P < 0.001) and advanced estrus (P < 0.05) and timing of the LH peak (P < 0.05). These events also occurred earlier in donors than in recipients (P < 0.01). Mean (+/- SEM) ovulation rates for melatonin-treated and control donors were 5.5 +/- 0.71 and 4.7 +/- 0.66, respectively (NS). Corresponding recipient values were 3.3 +/- 0.40 and 3.4 +/- 0.39 (NS). Mean (+/- SEM) embryo yields were 2.9 +/- 0.64 and 2.6 +/- 0.73 for melatonin-treated (n = 15) and control (n = 16) donors, respectively, and for the 12 ewes per treatment that supplied embryos, corresponding numbers classified as viable were 2.7 +/- 0.47 and 2.3 +/- 0.61 (NS). Following transfer, 57% of embryos developed to lambs when both donor and recipient received melatonin, 86% when only the donor received melatonin, 91% when only the recipient received melatonin, and 67% when neither received melatonin (NS). Thus, embryo survival following transfer was not improved by treating recipients with melatonin. Gestation length and lamb birthweights were unaffected by melatonin. Unlike nonpregnant control ewes, melatonin-treated recipients that failed to remain pregnant sustained estrous cyclicity following embryo transfer.

The effects of perphenazine and bromocriptine on follicular dynamics and endocrine profiles in anestrous pony mares

Nineteen anestrous pony mares were used in a project designed to determine the effects of altered prolactin concentrations on follicular dynamics and endocrine profiles during spring transition. The dopamine antagonist, perphenazine, was administered daily to mares (0.375 mg/kg body weight) in Group A (n = 6), while Group B mares (n = 7) received 0.08 mg/kg metabolic weight (kg75) dopamine agonist, 2-bromo-ergocriptine, intramuscularly twice daily. Mares in Group C (n = 6) received 0.08 mg/kg75, i.m., saline twice daily. Treatment began January 20, 1994, and continued until ovulation occurred. Mares were teased 3 times weakly with an intact stallion. The ovaries of the ponies were palpated and imaged weekly using an ultrasonic B-mode unit with a 5 Mhz intrarectal transducer until they either exhibited estrual behavior and had at least a 20-mm follicle, or had at least a 25-mm follicle with no signs of estrus. At this time, ovaries were palpated and imaged 4 times weekly. Blood samples were obtained immediately prior to ultrasonic imaging for measurement of prolactin, FSH and estradiol-17 beta. Perphenazine treatment advanced the spring transitional period and subsequent ovulation by approximately 30 d. Group A exhibited the onset of estrual behavior earlier (P < 0.01) than control mares. In addition, Group A mares developed large follicles (> 30 mm) earlier (P < 0.01) than Group B mares, with least square means for Groups A and B of 47.0 +/- 8.8 vs 88.1 +/- 8.2 d, respectively. Control mares developed 30-mm follicles intermediate to Groups A and B at 67.3 +/- 8.8 d. Bromocriptine decreased (P < 0.05) plasma prolactin levels throughout the study, while perphenazine had no significant overall effect. However, perphenazine treatment did increase (P < 0.05) mean plasma prolactin concentrations from Day 31 to 60 of treatment. There were no differences in mean plasma FSH or estradiol-17 beta between treatment groups. We concluded that daily perphenazine treatment hastened the growth of follicles and subsequent ovulation while bromocriptine treatment appeared to delay the growth of preovulatory size follicles without affecting the time of ovulation.

Biostimulatory effects of estrous cows and bulls on resumption of ovarian activity in postpartum anestrous Zebu (Bos indicus) cows in the humid tropics

Suckled postpartum Zebu (Bos indicus) cows were exposed either to estrous females alone or together with bulls to determine if this regimen would stimulate the resumption of ovarian activity. The study was carried out on 60 Zebu cows. The animals were allocated at parturition to 1 of 3 treatment groups. Group FB cows (n = 14) were exposed to progestogen treated females (approximately 3 cows per progestogen treated cow) and a bull for 42 d. Group F cows (n = 31) were exposed to progestogen treated females and after 21 d a bull was introduced and remained with the group until the end of the experiment 21 d later. Estrus was induced with Syncro Mate B treatment and the cows were in estrus when introduced into Groups FB and F. Group N cows (n = 15) were introduced to a bull 21 d after the treatments had begun in Groups FB and F, and the bull remained with these cows until the end of the study. On average, resumption of ovarian activity occurred in 57% (8/14), 19% (6/31) and 7% (1/15) of the cows in Group FB, F and N, respectively, within 21 d after the start of treatments. The difference was significant between Group FB and Groups F and N (P < 0.05). During the second part of the experiment, in which the bull was introduced to Groups F and N, an additional 32% (10/31) of the cows in Group F and 33% (5/15) in Group N resumed ovarian activity. No cows in Group FB resumed ovarian activity during this period. There were significant differences in body condition between cows that resumed ovarian activity and those that remained in anestrus (P < 0.05). We conclude that biostimulation effectively enhanced resumption of ovarian activity in anestrous suckled Zebu cows. This technique offers a potentially useful and practical way to improve reproductive efficiency in anestrous Zebu cattle in the tropics.

Luteinizing hormone release and reproductive traits in anestrous, estrus-cycling, and ovariectomized cattle after tyrosine supplementation

The role of rumen-protected L-tyrosine as a nutritional signal altering LH release and other reproductive traits in cattle was studied. In Exp. 1, 28 suckled crossbred cows were assigned randomly to five treatments (0 or 40 g of tyrosine daily in feed for 3 d followed by a single i.v. injection of 200 micrograms of GnRH or 1 mg/kg of naloxone on d 26 +/- 1 postpartum; no tyrosine plus an injection of saline was the control). Peak LH after GnRH was greater (P < .001) in GnRH-treated cows regardless of tyrosine supplementation. Compared to cows receiving saline, days to first postpartum ovulation were reduced (P < .05) by naloxone, tyrosine, and GnRH. In Exp. 2, 47 suckled crossbred cows were assigned randomly to six treatments (0, 20, or 40 g of tyrosine daily for 3 d before GnRH or saline was injected i.m. on d 23 +/- 1 postpartum). Injection of GnRH increased (P < .001) LH. An interaction (P = .08) of tyrosine and GnRH tended to reduce days to first postpartum ovulation. In Exp. 3, tyrosine (40 g) administered once daily for 3 d to ovariectomized cows (six cows per treatment) had no effect on any characteristic of LH before or after estradiol-17 beta. In Exp. 4, suckled cows (n = 136) were allotted randomly to two treatments (0 or 30 g of tyrosine daily for 3 d before a PGF2 alpha-synchronized estrus). Tyrosine increased (P = .05) the percentage of cows in estrus after PGF2 alpha but reduced (P = .05) AI conception rate. These results fail to support the thesis that tyrosine alters LH release in cattle. Supplemental tyrosine increased expression of estrus in suckled cows after PGF2 alpha and tended to reduce intervals to first postpartum ovulation.

Ultrasonographic monitoring of antral follicle development in red deer (Cervus elaphus)

Ovarian follicular dynamics were monitored in 12 surgically modified red deer hinds (ovaries adhered to vaginal wall) by transvaginal real-time ultrasonography during the luteal cycle, anoestrus and induction of superovulation. All 12 hinds showed evidence of regular luteal (plasma progesterone) cyclicity during the breeding season, although luteal tissue was not observed on the ultrasonograms. During the normal luteal cycle (14-22 days) total numbers of follicles > 3 mm did not vary significantly by day (range of means: 1.8-3.4; P > 0.05). A single large (> or = 6 mm) follicle was usually present on all days except immediately after ovulation (day 0). However, the appearance of new follicles (> or = 3 mm) was not random, and was greatest on day 1 and day 14 (P < 0.05). Tracking of individual follicles revealed irregular waves of emergence and disappearance of the largest follicle, with either one (n = 1), two (n = 3) or three (n = 5) waves observed across nine luteal cycles. New follicles (> or = 3 mm) emerged after regression or ovulation of a large follicle, suggesting a dominance effect. There were no significant differences in the overall mean numbers of follicles during early, mid- and late anoestrus (September, November and April, respectively) but follicle turnover was more rapid during mid-anoestrus as evidenced by a significantly greater number of new small (> 3 mm) follicles (P < 0.001). Administration of superovulatory doses of ovine FSH during the breeding season resulted in a marked increase in the appearance of new follicles within 48 h of initiation of the injection regimen. By termination at 96 h, the time of progesterone withdrawal, the mean number of follicles > 3 mm was significantly higher than for control hinds (9.8 versus 3.0; P < 0.0001). While most follicles ovulated progressively 2-7 days later, about 40% persisted beyond this period. The study demonstrated the presence of discrete patterns of antral follicle growth and regression during the breeding and non-breeding seasons, with the luteal cycle characterized by a variable number (1-3) of dominant follicle waves. Anoestrus represents a period of dynamic changes in follicular turnover.

Estrus and luteal function in suckled beef cows that were anestrous when treated with an intravaginal device containing progesterone with or without a subsequent injection of estradiol benzoate

The objectives in this study were to determine whether treatment with progesterone (P4) via an intravaginal device would induce estrus and development of corpora lutea (CL) with typical life spans and whether treatment with estradiol benzoate (EB) following device removal would enhance the responses. At treatment initiation (d 0), suckled beef cows (n = 362) that were anestrous received one of the following: 1) an intravaginal device containing P4 for 7 d plus an injection of 1 mg of EB 24 to 30 h after device removal (P4+EB), 2) an intravaginal device containing P4 for 7 d (P4), 3) a sham device for 7 d plus an injection of 1 mg of EB 24 to 30 h after device removal (EB), or 4) a sham device for 7 d (control). Progesterone treatment increased the proportion of cows that formed CL with a typical lifespan (P < .001) and exhibited behavioral estrus (P < .05). Treatment with EB in combination with P4 increased (P < .001) the proportion of cows that exhibited estrus. Treatment with P4 alone had no effect, but the combination of P4 and EB increased (P < .01) the proportion of cows that formed short-lived or typical lifespan CL by the end of the experiment compared with untreated cows. In summary, treatment with P4 increased the incidence of estrus and the proportion of cows that formed CL with a typical lifespan. Treatment with P4 resulted in resumption of luteal function in suckled beef cows that were anestrous, with most cows developing CL with a typical lifespan, whereas EB enhanced the expression of estrus.

A critical period for thyroid hormone action on seasonal changes in reproductive neuroendocrine function in the ewe

Thyroid hormones are obligatory for the annually recurring termination of reproductive activity in a spectrum of seasonal breeders, including sheep. Previous studies involving thyroidectomy and T4 replacement have led to the hypothesis that, in the ewe, thyroid hormones are necessary only during a limited interval late in the breeding season for the neuroendocrine processes that cause the transition to anestrus. The present series of experiments tested this hypothesis by assessing the influence of thyroidectomy, with or without T4 replacement for specific durations and at different times of the year, on the transition to anestrus. Seasonal alterations in reproductive neuroendocrine activity were monitored by changes in serum LH concentration in ovariectomized ewes bearing s.c. SILASTIC brand silicon tubing implants containing estradiol. Thyroidectomy in mid-December, just before the putative period of thyroid hormone action, prevented the development of the neuroendocrine anestrous season (fall in LH in this animal model). T4 replacement for 90 days beginning in late December (i.e., during the postulated period of thyroid hormone action) overcame the blockade of anestrus, causing LH to fall in ewes thyroidectomized several months previously. The minimal effective duration of exposure to thyroid hormones required for the transition to anestrus was estimated to be 60-90 days. Further, exposure to T4 for 60-90 days beginning in late December was found to be the only time of the year that thyroid hormones were required to maintain seasonal changes in reproductive neuroendocrine activity. Finally, replacement of T4 for 90 days at a different time of year (beginning in August) failed to provoke development of neuroendocrine anestrus in thyroidectomized ewes. These results support the hypothesis that thyroid hormones are necessary only during a limited interval late in the breeding season to promote seasonal reproductive suppression in the ewe. Further, the reproductive neuroendocrine axis is not equally responsive to thyroid hormone at all times of the year. This suggests there is a critical period of responsiveness during which thyroid hormones must be present for anestrus to develop.

Influence of postpartum weight and body condition change on duration of anestrus by undernourished suckled beef heifers

Two experiments were conducted to determine the relationship between change in weight and body condition on postpartum interval of thin first-calf beef heifers. Twenty-nine (Exp. I) and 36 (Exp. II) Angus and Angus-sired crossbred heifers were limit-fed to reduce their condition score (BCS) to 4 (scale of 1 to 9) at calving. After calving, heifers were assigned to one of four daily ME intakes (range of 198 to 305 kcal ME/kg BW.75) designed to create a range of BCS changes. Each unit change in BCS was associated (R2 = .72; P < .0001) with a 33-kg weight change. Mean postpartum interval (PPI) from calving to initiation of luteal activity was 121 +/- 6.0 d. As dietary energy density increased, PPI decreased (P < .01). Condition score at calving (CCS) accounted for a greater proportion of the variation (R2 = .37) associated with PPI than did condition score change from calving to d 90 postpartum (CSCH90; R2 = .27) or weight change from calving to d 90 postpartum (WTCH90; R2 = .17). The "best fit" equation (R2 = .56) for predicting PPI included CCS and CSCH90: PPI = 244.5 - 28.28(CCS) - 23.07(CSCH90) + 6.36(CSCH90(2)). Maximum reduction in PPI occurred when heifers gained 1.8 units of BCS during the first 90 d of lactation. Gaining BCS at a faster rate was of no additional benefit.

Ovarian follicular dynamics in ewes during the transition from anoestrus to the breeding season

Daily transrectal ovarian ultrasonography was performed in ten ewes for 5 consecutive days, once in early July, once in late July (anoestrus) and then continuously until from mid-August until ewes had completed one ovulatory cycle. During anoestrus the size range and numbers of ovarian antral follicles were similar to those seen during the breeding season. However, numbers of small antral follicles (2-3 mm in diameter) decreased during late anoestrus, and maximum follicle diameter increased just before the short period of progesterone secretion preceding the first observed ovulation. The ovarian antral follicles that ovulated first and second in the breeding season grew from 2 mm in diameter to 5.7 +/- 0.3 mm and 6.2 +/- 0.3 mm diameter over 4.7 +/- 0.3 days and 4.6 +/- 0.3 days, respectively, and the interovulatory interval was 16.6 +/- 0.2 days. During the first ovulatory cycle, follicles emerged to grow from the 2 mm size class on 11 of the 17 days, but peaks of emergence were seen on days 2 and 11. The first observed ovulation was preceded by a transient increase in serum concentrations of progesterone (6 days duration), with a peak concentration of 1.30 +/- 0.22 nmol l-1. With ultrasonography, no evidence of ovulation was seen before the increase in progesterone secretion and no luteal structures was detected during the small increase in progesterone secretion; however, luteal structures are normally detected by ultrasonography only from 3 to 5 days after ovulation. An LH surge similar to a preovulatory LH surge preceded the first increase in progesterone secretion in five ewes. Oestrus occurred consistently with ovulation only at the second observed ovulation of the breeding season, after a normal luteal phase. LH pulse frequency and mean and basal serum concentrations of LH all increased in late anoestrus, but no major trends in serum concentrations of FSH and oestradiol were seen during this period. It was concluded that at the end of anoestrus there is not major change in ovarian antral follicle dynamics. At this time, increased LH secretion was seen as was a reduction in numbers of small antral follicles and a greater maximum diameter of follicles. A surge release of LH resulted in a short-lived secretion of progesterone, the source of which was unclear; this was followed by the first observed ovulation and the first ovulatory cycle of the breeding season. Oestrus occurred consistently only at the second observed ovulation of the season and the peak concentration of progesterone at each period of progesterone secretion increased to at least the second ovulatory cycle.

Circulating insulin-like growth factor I, insulin-like growth factor binding proteins, growth hormone, and resumption of estrus in postpartum cows subjected to dietary energy restriction

The objective of this study was to determine whether serum concentrations of growth hormone (GH), IGF-I, IGF binding proteins (IGFBP), and glucose at wk 2 and 10 postpartum were associated with the ability of postpartum beef cows to resume cycling when maintained on a limited nutrient environment. Cows (n = 29) were individually fed either 130 or 170 kcal ME x BW-75 x d-1 during nonlactation and 170 or 210 kcal ME x BW-75 x d-1 during lactation for an average of 4.1 yr before sample collection. The proportion of cows that resumed estrus within 20 wk after parturition was less (P < .05) at the lower feeding rate (5 of 14) than at the higher feeding rate (11 of 15). Concentrations of IGF-I increased from wk 2 to 10 in cows that resumed cycling but not in cows that remained anestrous and were less (P < .05) at wk 2 and 10 in cows that remained anestrous compared to cows that resumed cycling. Circulating amounts of IGFBP-2 at wk 2 were greater (P < .05) and IGFBP-3 concentrations were lower (P < .05) in cows that remained anestrous compared to cows that resumed cycling. Cows on the lower feeding rate that did not cycle had lower body condition scores and greater concentrations of GH compared (P < .05) to other cows. At the higher feeding rate, body condition score and concentrations of GH did not differ between cows that did or did not resume cycling. Circulating concentrations of IGF-I and IGFBP-2 and -3 at wk 2 postpartum were indicators of the capacity of energy-restricted cattle to resume cycling after parturition.

[Endocrine function of the testicle in the Mexican crossbred ram at different times of the year and its opioidergic control during anoestrus]

This work was carried out with the objective of studying the endocrine function of the testes in the Mexican Crossbred Ram (Suffolk x Hampshire) during the different seasons of the year in a latitude of 19 degrees 13' N. Also studied was the opioidergic control of this gland during anoestrus. For this purpose 8 rams were used, from which 3 ml of jugular blood were obtained three times a week to study the seasonal fluctuations in plasma testosterone. The experiment was carried out from May 1993 until June 1994. The androgen was determined by radioimmunoassay. To study the opioidergic control of androgen secretion during seasonal anoestrous (May-June) four of the rams were selected at random and treated with 0.5 mg naloxone at 12 h intervals during 3 continuous weeks. It was observed that blood testosterone was lowest during long days, and concentration was highest during the breeding season. Chronic naloxone medication during anoestrus resulted in a significant increase in blood testosterone (P < 0.001), an effect that was evident after the first week of treatment. When naloxone administration was discontinued, blood testosterone levels returned to basal. With this experiment it was demonstrated that an opioid antagonist such as naloxone administered in low doses, is capable of altering plasma testosterone concentration in the anoestrus ram, giving further support to endogenous opioids as important modulators of reproduction in seasonal breeders such as sheep.

Comparison of the effects of N-methyl-DL-aspartic acid on gonadotropin and prolactin secretion in anestrous mares and mares exhibiting estrous cycles during anestrus

This study investigated the hypothesis that for a subpopulation of horse mares continuation of estrous cycles during the nonbreeding season may be attributed to continued stimulatory glutamatergic activity on GnRH-secreting neurons. The gonadotropin response to the glutamatergic agonist N-methyl-DL-aspartic acid (NMA) was compared in cycling and anestrous mares during the nonbreeding season. It was anticipated that the gonadotropin response to NMA in cycling mares would be attenuated, compared with that of anestrous mares. The experiment used 16 anestrous mares and 15 mares that cycled during the nonbreeding season. The effect of NMA on prolactin secretion was also evaluated. In addition, the seasonal rhythm of prolactin secretion was compared in anestrous and cycling mares during October-April. In cycling mares, the response to NMA was dependent on the stage of the cycle, and a significantly (p < 0.05) larger proportion responded during the luteal phase (6 of 8), compared with the follicular phase (1 of 7 mares). The proportion of anestrous mares that responded to NMA was similar to that of cycling mares during the luteal phase, but larger than during the follicular phase. In anestrous and cycling mares, NMA suppressed prolactin secretion, and in both groups prolactin secretion decreased during the nonbreeding season. Thus, we conclude that differences in reproductive activity in mares during the nonbreeding season are unlikely to reflect a change in glutamatergic activity.

Estradiol acts locally within the retrochiasmatic area to inhibit pulsatile luteinizing-hormone release in the female sheep during anestrus

In the present study we have identified a site of action of estradiol in the inhibition of LH secretion during anestrus in the ewe. In the first experiment, we studied six sites: the medial preoptic area, the lateral preoptic area, the ventromedial hypothalamus, the ventrolateral hypothalamus, the retrochiasmatic area (RCh), and the periventricular posterior hypothalamus. We compared the changes in parameters of pulsatile LH secretion (interpulse interval, mean nadir, mean amplitude, and mean area under curve) during three 6-h sampling periods: before and 30-36 h and 9 days after intracerebral implantation of crystalline estradiol. Animals that received estradiol in the RCh (n = 5) showed a significantly greater increase in both the intervals between pulses of LH (up 116%, p < 0.03) and the area under the curve (up 180%, p < 0.01) than any of the other groups of 7 animals. In the second experiment, implantation of estradiol in the RCh (n = 6) induced an increase in the intervals between pulses of LH (p < 0.03), whereas receiving an empty implant (n = 6) had no effect, showing that estradiol specifically induced increases in the intervals between pulses. Thus, estradiol appears to act in the RCh where the dopaminergic A15 nucleus, known to inhibit pulsatile LH release, is located.

Food supplementation during lactation shortens anestrus and elevates gonadotropins in rats

Breastfeeding delays the resumption of ovulation in women, a phenomenon particularly important in less developed areas. Although human and animal studies indicate that undernutrition extends the period of lactational anestrus, the effect of improving nutritional status during lactation on this time of infecundability, however, is less clear. To assess the effects of food supplementation on duration of lactational anestrus, Sprague-Dawley rats were assigned to one of three dietary groups: 1) control (C), given unrestricted access to diet AIN-76A; 2) food-restricted (FR), fed 50% of the control intake; and 3) food-supplemented (FS), food-restricted until d 0 of lactation and thereafter given unrestricted access to diet AIN-76A. Time to first detectable proestrus was monitored starting on d 10 of lactation. Nursing behaviors and gonadotropin and prolactin concentrations were measured in both intact and ovariectomized dams on d 10, 15 and 20 of lactation; we report these data only on the ovariectomized group, which represents the more appropriate animal model of human reproductive physiology during lactation. Proestrus returned significantly (P < 0.0001) sooner in both FS (18.1 +/- 2.4 d) and C (18.0 +/- 2.9 d) than in FR (28.8 +/- 2.8 d) intact dams. FS rats had higher luteinizing hormone and follicle stimulating hormone concentrations than FR rats (P < 0.0001 for each). Prolactin concentrations were lower on d 20 than on d 10 of lactation for all groups (P < 0.02), but we found no effect of dietary treatment. FS rats spent more time away from their pups (P < 0.05) and experienced less suckling (P < 0.05) than FR rats on d 15 of lactation. These results indicate that food supplementation of previously underfed rats hastens the return of ovulation and is accompanied by alterations in nursing behaviors.

Some effects of adding p-LH in defined amounts to purified p-FSH to modify FSH/LH ratios during the superovulatory treatment of anestrous ewes

Nonlactating Leccese ewes (n = 61) were used during seasonal anestrus to investigate the effects on ovarian response and embryo production of adding defined amounts of p-LH to purified p-FSH as well as decreasing the FSH/LH ratio during treatment. The ewes were synchronized with FGA-impregnated intravaginal pessaries for 9 days and prostaglandin F2 alpha (Cloprostenol) injected on the seventh day. They were divided into six treatment groups in a 3 x 2 factorial design: three amounts of purified p-LH (100, 50 or 25% equivalent to 525, 262 or 131 IU p-LH) x 2 regimen of p-FSH and p-LH administration (constant or decreasing FSH/LH ratio). Each ewe received a total of 525 IU p-FSH at a decreasing dose, twice daily over a 3-day period. Group I (n = 11), Group II (n = 10) and Group III (n = 10) were treated with p-FSH supplemented with p-LH at 100%, 50% and 25%, respectively, of p-FSH dose and a constant FSH/LH ratio throughout the treatment period. Group IV (n = 10), Group V (n = 10) and Group VI (n = 10) were treated with p-FSH supplemented with p-LH at 100%, 50% and 25%, respectively, of p-FSH dose but with a decreasing FSH/LH ratio over the 3 days of the treatment: 1.7-0.86-0.43 for Group IV; 3.4-1.7-0.86 for Group V; 6-3-1.5 for Group VI. Embryos were flushed surgically on Day 6 after estrus. The ovulation rate did not differ among the groups (8-12.8). Superovulation with 100% p-LH and decreasing the FSH/LH ratio (Group IV) resulted in: (i) the highest ova recovery (9.8 +/- 1.7), and this was significantly different (P < 0.05) from the 25% p-LH treated group (Group VI; 5.0 +/- 1.7), (ii) the highest fertilization rate (90.6 +/- 9.2%), with a significant (P < 0.01) difference compared with the constant ratio regimen (Group I; 62.6 +/- 8.3%); (iii) the highest transferable embryo yield (6.4 +/- 1.1), differing significantly (P < 0.01) from Group VI (2.2 +/- 1.1) and Group I (2.7 +/- 1.0). It is concluded that decreasing the amount of p-LH added to purified p-FSH did not improve the superovulatory response of ewes during the anestrous period. Transferable embryo production was significantly improved when ewes were treated with p-LH equivalent to 100% p-FSH, with the FSH/LH ratio decreasing during treatment.

Influence of previous photoperiodic exposure on the reproductive response to a specific photoperiod signal in ewes

Two experiments were carried out to determine whether the reproductive response of ewes to a specific photoperiodic signal depends on the time of year that the signal is given, and, if so, whether this dependence can be attributed to the photoperiodic history of the ewes. The aim of experiment 1 was to expand upon previous findings that the reproductive response to a specific photoperiodic challenge in ewes previously maintained on natural photoperiod varies with time of year. Ewes were transferred at one of three times of year from natural photoperiod to photochambers and were immediately exposed to 35 long days (18L:6D) followed by continuous exposure to short days (8.5L: 15.5D); this treatment is referred to as LD-->SD. The three times of year when long days started corresponded to the beginning of the breeding season, the mid-breeding season, and early anestrus (September 21, December 21, March 21, respectively). In ewes exposed to LD-->SD beginning in September, the breeding season and subsequent anestrous season was not altered. In ewes exposed to LD-->SD beginning in December, the transition to anestrus was advanced (p < 0.05) relative to that in controls maintained in simulated natural photoperiod. Subsequently, half of these ewes resumed reproductive activity within 180 days; this occurred 131 +/- 8 days after transfer to short days. In contrast, all ewes exposed to LD-->SD beginning in March resumed reproductive activity; this began 100 +/- 3 days after transfer to short days (p < 0.05 versus December group). The purpose of experiment 2 was to assess the extent to which the difference in response to a photoperiodic challenge can be attributed to photoperiodic history. Ewes were maintained on short days from the winter solstice interrupted with 35 long days from March 21, June 21, September 21, or December 21. The majority of ewes exhibited an onset of reproductive activity after exposure to LD-->SD at the different times of year, and there was no group difference in latency to onset of reproductive activity. The duration of reproductive activity, however, was longer (p < 0.05) in ewes exposed to LD-->SD beginning in June than in the other groups. Thus we conclude that the seasonal difference in the ability of the photoperiodic challenge of long followed by short days to induce reproductive activity in ewes previously maintained outdoors can be attributed, in large measure, to photoperiodic history. Other factors, such as phase of the endogenous rhythm, however, may influence the duration of reproductive activity resulting from this photoperiodic challenge.

Prolactin administration to seasonally anestrous mares: reproductive, metabolic, and hair-shedding responses

Eight pony mares received 4 mg of recombinant porcine prolactin (rpPRL) daily for 45 d beginning on January 15; eight control mares received vehicle. Reproductive end points and various indicators of metabolism, hair shedding, and thyroid activity were monitored. Prolactin concentrations peaked in mares treated with rpPRL at 94 +/- 19 ng/mL 2 h after injection and were 5.1 +/- 1.7 ng/mL 24 h after injection. Treatment with rpPRL increased (P < .01) hair shedding within 14 d, which peaked at 28 d and then dropped precipitously. Binding of 125I-equine prolactin confirmed that antibodies were present in rpPRL-treated mares by 28 d, thus only data up to that time are included herein. The percentage of mares in estrus after 17 d of treatment was greater (P < .05) for mares treated with rpPRL than for controls, although the average day of estrus onset did not differ (P > .1). The date of first ovulation, determined from plasma progesterone concentrations, was hastened (P < .005) in mares treated with rpPRL (February 6 +/- 3 d) relative to control mares (March 14 +/- 6 d). Concentrations of insulin-like growth factor I and nonesterified fatty acids were not affected (P < .05) over time. There were minor differences between groups in thyroid hormone secretion. Various assessments of glucose and insulin indicated no perturbation (P > .1) due to treatment with rpPRL. We conclude that prolactin mediates the onset of vernal hair shedding in mares and is in some way involved with ovulation.