Folliculogenesis during the transitional period and early ovulatory season in mares

Individual follicles were monitored by ultrasonography in 15 mares during the transitional period preceding the first ovulation of the year and in 9 mares during the first interovulatory interval. During the transitional period, 7 mares developed 1-3 anovulatory follicular waves characterized by a dominant follicle (maximum diameter greater than or equal to 38 mm) that had growing, static, and regressing phases. The emergence of a subsequent wave (anovulatory or ovulatory) did not occur until the dominant follicle of the previous wave was in the static phase. After the emergence of the subsequent wave, the previous dominant follicle regressed. The mean (+/- s.d.) length of the interval between successive waves was 10.8 +/- 2.2 days. Before the emergence of waves (identified by a dominant follicle), follicular activity seemed erratic and follicles did not reach greater than 35 mm. During the interovulatory interval, 6 mares developed 2 waves (an anovulatory wave and a subsequent ovulatory wave) and 3 mares developed only 1 detected wave (the ovulatory wave). The ovulatory follicle at the end of the transitional period reached 20 mm earlier (Day - 15), grew slower (2.6 +/- 0.1 mm/day; mean +/- s.e.m.) but reached a larger diameter on Day - 1 (50.5 +/- 1.1 mm) than for the ovulatory follicle at the end of the interovulatory interval (Day - 10, 3.6 +/- 0.2 mm/day, 44.4 +/- 1.0 mm, respectively; P less than 0.05 for each end point). The interval from cessation of growth of the largest subordinate follicle to the occurrence of ovulation was longer (P less than 0.05) for end of the transitional period (9.5 +/- 0.7 days) than for the end of the interovulatory interval (6.8 +/- 0.6 days). Results demonstrated the occurrence of rhythmic follicular waves during some transitional periods and the occurrence of 2 waves during some of the first oestrous cycles of the year.     

Is slow follicular growth the cause of silent estrus in water buffaloes?

The present experiment was conducted to study the growth profile of the ovulatory follicle in relation to the expression of estrus following administration of PGF(2alpha) to subestrus buffaloes. After detection of a mature corpus luteum by examination per rectum, confirmed by ultrasound scanning, subestrus buffaloes (n=20) were treated (Day 0) with single dose of Dinoprost tromethamin (25 mg, i.m.). Blood samples were collected at 0, 24 and 48 h after treatment for estimation of plasma progesterone concentration. Growth profile of the ovulatory follicle was monitored daily through ultrasound scanning starting from Day 0 until ovulation and the regression profile of CL was monitored at 0, 24 and 48 h of treatment. Estrus was detected by exposure to a fertile buffalo bull three times a day until expression of overt estrus or ovulation. Behavioral estrus was recorded in 14 animals and 6 animals ovulated silently. Sixteen animals including six animals with silent estrus ovulated from the dominant follicle present at treatment (Group A) and remaining four animals ovulated from the dominant follicle of succeeding follicular wave (Group B). The intervals from treatment to estrus (6.5+/-0.25 versus 3.2+/-0.27 days, P<0.001) and treatment to ovulation (7.5+/-0.25 versus 5.4+/-0.46 days, P<0.005) were significantly longer in animals of Group B compared with animals of Group A. Significant differences were observed in growth profile of the ovulatory follicle between animals of Groups A and B with respect to size of the follicle on Day 0 (9.8+/-0.7 versus 5.3+/-0.45 mm, P<0.001), daily growth rate (0.97+/-0.07 versus 1.6+/-0.2 mm/day, P<0.01) and increase in diameter (4.1+/-0.6 versus 7.8+/-0.7 mm, P<0.01). The animals with silent estrus (subgroup A-2) had significantly smaller diameter of the ovulatory follicle on Day 0 (7.7+/-0.4 versus 11.0+/-0.7 mm, P<0.005), its daily growth rate was significantly slower (0.7+/-0.02 versus 1.1+/-0.1 mm/day, P<0.01) and they recorded significantly longer interval from treatment to ovulation (7.3+/-0.56 versus 4.2+/-0.27 days, P<0.001) compared with the animals that showed overt estrus (subgroup A-1). The corpus luteum area (CL area) and plasma progesterone (P(4)) concentration declined continuously from 0 to 48 h after PGF(2alpha) treatment in the animals of both the Groups A and B. Non-significant differences were observed in mean CL area and plasma P(4) concentration at 0, 24 and 48 h post-treatment between animals of Groups A and B and also between animals of subgroups A-1 and A-2. The small size and the slow growth rate of the ovulatory follicle were identified as the possible cause of silent estrus in subestrus buffaloes after PGF(2alpha) treatment.     

Follicular and FSH dynamics in ewes with a history of high and low ovulation rates

Daily transrectal ultrasound scanning and twice-daily blood sampling were used to monitor the temporal relationships between FSH concentrations and follicle development during complete interovulatory intervals for ewes in which the ovulation rate in each of the 2 previous years was high or low (> or = 3 and < or = 2 ovulations, respectively). Follicles that reached > or = 5 mm were used to define a follicular wave and were tracked retrospectively to 3 mm (emergence). The hypothesis that FSH surges (identified with a computer program) and follicular waves (retrospectively determined based on ultrasound scanning) are temporally associated was supported in both groups by the emergence of an anovulatory or ovulatory follicular wave near the peak of an FSH surge. Further support for the hypothesis was a significant increase in FSH concentrations before and a significant decrease after follicular-wave emergence in both groups independent of the identification of FSH surges. Ewes with a history of high ovulation rates had smaller follicles (anovulatory and ovulatory) and more ovulations, but the 2 groups were similar in the number of ovulatory follicular waves and associated FSH surges, number and characteristics of the FSH surges, and mean FSH concentrations per interovulatory interval. Surges of FSH were periodic (every 3 or 4 d) regardless of the ovulation-rate group or follicle response. In ewes with a low ovulation rate, the nonovulatory FSH surges were most frequently associated with emergence of detected anovulatory follicular waves. In ewes with a high ovulation rate, more FSH surges were not associated with a detected follicular wave, as defined, presumably because the largest follicle did not reach 5 mm. The results indicated that the factors resulting in a high ovulation rate were not exerted through circulatory patterns or concentrations of FSH but involved a shorter growth phase and smaller maximal diameter of follicles.     

Interrelationships of estradiol, inhibin, and gonadotropins during follicle deviation in pony mares

The changes in circulating concentrations of FSH, LH, estradiol, and total inhibin associated with the beginning of follicle diameter deviation were compared among the last anovulatory follicular wave of the year and the first and second ovulatory waves in pony mares ( n=7 ). Follicle diameters and circulating hormone concentrations for each wave were normalized to the observed beginning of deviation (Day 0). Follicle deviation was demonstrated during the anovulatory wave as well as during the ovulatory waves, and the diameter of the future dominant follicle at the beginning of deviation was similar for the three waves (overall mean: 23.7+/-0.6 mm). Circulating estradiol concentrations did not increase during the last anovulatory wave but increased similarly for the two ovulatory waves, beginning near the onset of deviation. There were no differences among waves in concentrations of inhibin encompassing deviation. The FSH concentrations for the wave-stimulating FSH surge did not differ significantly among the three waves; combined for the three waves, concentrations decreased between Days -3 and 7. Circulating LH did not increase during the last anovulatory wave but increased during the first and second ovulatory waves beginning on Days 6 and -2, respectively. Results indicated that the increase in circulating estradiol at the beginning of deviation was not required for suppression of the wave-stimulating FSH surge and the initiation of deviation, based on an estradiol increase in association with deviation during the ovulatory waves but not during the anovulatory wave. Concentrations of inhibin were similar among waves and, therefore on a temporal basis, the similar suppression of FSH was attributable to inhibin. The later increase in LH before the first ovulation was not attributable to estradiol, based on the similarity between the two ovulatory waves in the increasing estradiol concentrations.     

Temporal associations among ovarian events in cattle during oestrous cycles with two and three follicular waves

For 18 two-wave interovulatory intervals in heifers, the follicular waves were first detected on Days -0.2 +/- 0.1 and 9.6 +/- 0.2, and for 4 three-wave intervals on Days -0.5 +/- 0.3, 9.0 +/- 0.0 and 16.0 +/- 1.1 (ovulation is Day 0). The day-to-day mean diameter profile of the dominant follicle of the 1st wave and the day of emergence of the 2nd wave were not significantly different between 2-wave and 3-wave intervals. There were no indications, therefore, that events occurring during the first half of the interovulatory interval were associated with the later emergence of a 3rd wave. The dominant ovulatory follicle differed significantly (P less than 0.05 at least) between 2-wave and 3-wave intervals in day of emergence (Day 9.6 +/- 0.2 and 16.0 +/- 1.1), length of interval from emergence of follicle to ovulation (10.9 +/- 0.4 and 6.8 +/- 0.6 days), and diameter on day before ovulation (16.5 +/- 0.4 and 13.9 +/- 0.4 mm). The mean length of 2-wave interovulatory intervals (20.4 +/- 0.3 days) was shorter (P less than 0.01) than for 3-wave intervals (22.8 +/- 0.6 days). The mean day of luteal regression for 2-wave and 3-wave intervals was 16.5 +/- 0.4 and 19.2 +/- 0.5 (P less than 0.01). For all intervals, luteal regression occurred after emergence of the ovulatory wave, and the next wave did not emerge until near the day of ovulation at the onset of the subsequent interovulatory interval. In conclusion, the emergence of a 3rd wave was associated with a longer luteal phase, and the viable dominant follicle present at the time of luteolysis became the ovulatory follicle.     

Complex interrelationships among CL,preovulatory follicle,number of follicular waves,and right or left ovaries in heifers

The diameter of the dominant follicle (DF) of wave 1 was studied on Days 9 to 17 (Day 0 = ovulation) in a survey of the ipsilateral and contralateral relationships between the location of the DF and CL, and number of follicular waves per interovulatory interval (IOI). For contralateral relationships, regardless of number of waves the diameter of the DF of wave 1 decreased (P < 0.03) between Days 11 and 13 when referenced to the follicle–CL relationship of wave 1 and decreased (P < 0.008) between Days 9 and 11 when referenced to the preovulatory follicle (PF)–CL relationship. For wave 2 in two-wave IOIs, the CL ovary of ipsilateral relationships had more (P < 0.05) follicles that reached at least 6 mm than the non-CL ovary. In three-wave IOIs, frequency of IOIs with the DF in the CL ovary was greater (P < 0.02) for wave 2 than for wave 3. In wave 3, the preovulatory and the largest subordinate follicles were located more frequently (P < 0.005) in the contralateral ovary. Ovulation in two-wave IOIs occurred more frequently (P < 0.0009) from the right ovary. In three-wave IOIs with a contralateral relationship ovulation occurred more frequently (P < 0.003) from the left ovary; a negative intraovarian effect of the CL on location of the PF may account for more ovulations from the left ovary and a reported greater frequency of the contralateral relationship. The hypothesis was supported that the ipsilateral versus contralateral relationship between the PF and CL is affected by the DF–CL relationship during the previous follicular waves and by the number and identity of waves per IOI.     

Effect of oestradiol benzoate given after prostaglandin at two stages of follicle wave development on oestrus synchronisation,the LH surge and ovulation in heifers

Oestrus synchronization following prostaglandin-induced luteolysis is variable and dependent on follicle wave status in cattle. Oestradiol benzoate (ODB) has been used following prostaglandin to reduce the interval to oestrus and ovulation, but the effect of follicle wave status at the time of ODB administration is not clear. The aim of this study was to characterize the endocrine and follicular responses following ODB after luteolysis at different stages of the follicle wave. Prostaglandin was administered at either emergence or dominance of the second follicle wave. Twenty-four hours later animals received either 0.5mg ODB in oil or a control oil injection. Follicular development was monitored daily by ultrasonography, oestrous behavior was determined and blood samples were collected. In animals treated with ODB at emergence, there was a reduction (P<0.05) in the maximum diameter of the ovulatory follicle (11.7+/-1.2 mm versus 13.1+/-0.1 mm) and in the interval from prostaglandin to oestrus (52.0+/-2.3 h versus 88.0+/-9.6h), to the LH surge (53.3+/-3.5 h versus 89.1+/-6.5 h) and to ovulation (96+/-0.0 h versus 129.6+/-9.6h), compared with controls. In animals treated with ODB at dominance, there was a reduction (P<0.05) in the interval from prostaglandin to the LH surge (54.0+/-3.1 h versus 70.9+/-4.8 h), but not in the interval from prostaglandin to oestrus (53.3+/-2.7 h versus 65.7+/-4.5 h; P=0.11), to ovulation (96.0+/-0.0 h versus 110.4+/-4.8 h; P=0.12) or the maximum diameter of the ovulatory follicle (12.7+/-0.3 mm versus 13.6+/-0.4 mm; P=0.12), compared with controls. Treatment did not affect (P>0.05) the length of the subsequent oestrous cycle or corpus luteum size. In conclusion, the use of ODB advanced, but did not alter the temporal relationships among oestrus, the LH surge and ovulation, regardless of stage of follicle development at treatment.     

Effects of lactational and reproductive status on ovarian follicular waves in llamas (Lama glama)

The effects of lactational status and reproductive status on patterns of follicle growth and regression were studied in 41 llamas. Animals were examined daily by transrectal ultrasonography for at least 30 days. The presence or absence of a corpus luteum and the diameter of the largest and second largest follicle in each ovary were recorded. Llamas were categorized as lactating (N = 16) or non-lactating (N = 25) and randomly allotted to the following groups (reproductive status): (1) unmated (anovulatory group, N = 14), (2) mated by a vasectomized male (ovulatory non-pregnant group, N = 12), (3) mated by an intact male and confirmed pregnant (pregnant group, N = 15). Ovulation occurred on the 2nd day after mating with a vasectomized or intact male in 26/27 (96%) ovulating llamas. Interval from mating to ovulation (2.0 +/- 0.1 days) and growth rate of the preovulatory follicle (0.8 +/- 0.2 mm/day) were not affected by lactational status or the type of mating (vasectomized vs intact male). Waves of follicular activity were indicated by periodic increases in the number of follicles detected and an associated emergence of a dominant follicle that grew to greater than or equal to 7 mm. There was an inverse relationship (r = -0.2; P = 0.002) between the number of follicles detected and the diameter of the largest follicle. Successive dominant follicles emerged at intervals of 19.8 +/- 0.7 days in unmated and vasectomy-mated llamas and 14.8 +/- 0.6 days in pregnant llamas (P = 0.001). Lactation was associated with an interwave interval that was shortened by 2.5 +/- 0.05 days averaged over all groups (P = 0.03). Maximum diameter of anovulatory dominant follicles ranged from 9 to 16 mm and was greater (P less than 0.05) for non-pregnant llamas (anovulatory group, 12.1 +/- 0.4 mm; ovulatory group, 11.5 +/- 0.2 mm) than for pregnant llamas (9.7 +/- 0.2 mm). In addition, lactation was associated with smaller (P less than 0.05) maximum diameter of dominant follicles averaged over all reproductive statuses (10.4 +/- 0.2 vs 11.7 +/- 0.3 mm). The corpus luteum was maintained for a mean of 10 days after ovulation in non-pregnant llamas and to the end of the observational period in pregnant llamas. The presence (ovulatory non-pregnant group) and persistence (pregnant group) of a corpus luteum was associated with a depression in the number of follicles detected and reduced prominence of dominant follicles (anovulatory group greater than ovulatory non-pregnant group greater than pregnant group).(ABSTRACT TRUNCATED AT 400 WORDS)     

Ovarian dynamics, serum estradiol and progesterone concentrations during the interovulatory interval in goats

Ovarian changes determined by daily transrectal ultrasonic scanning, and its correlation with serum progesterone (P4) and estradiol (E2) concentrations were studied in seven cyclic Saanen goats. Estrous cycles were synchronized with 2 injections of a PGF2 alpha analogue 9 d apart. All follicles > or = 2 mm in diameter and CL were measured each day. One goat showed a longer interestrous interval, associated with development of a cystic-luteinized structure. The mean interovulatory interval for the other 6 goats was 20.8 +/- 0.4 d. The incidence of goats with 4, 3, and 2 follicular waves was 3, 1 and 2 respectively; follicular waves emerged on Days 0.5 +/- 0.6, 7.2 +/- 0.7, 10.7 +/- 0.5 and 13.7 +/- 0.8 for Wave 1, 2, 3 and the Ovulatory wave, respectively. The largest follicle of Wave 2 was smaller (4.9 +/- 0.1 mm) than the largest follicles of Wave 3 (6.2 +/- 0.1 mm; P < or = 0.01) and of the Ovulatory wave (7.0 +/- 0.5 mm; P < or = 0.01), and tended to be smaller than the largest follicle of Wave 1 (6.3 +/- 0.6 mm; P < or = 0.09). Interval between emergence of Wave 1 and Wave 2 was longer than interval between emergence of Wave 2 and Wave 3 (7.3 +/- 0.9 d vs 4.0 +/- 0.4 d; P < or = 0.01), and between Wave 3 and the Ovulatory wave (3.8 +/- 1.1 d; P < or = 0.05). Two days before ovulation, the diameter of the ovulatory follicle was larger (P < or = 0.01) than the first subordinate follicle. Serum E2 concentrations increased from the day of ovulation (2.7 +/- 0.3 pg/mL) to Day 2 (7.6 +/- 0.9 pg/mL; P < or = 0.01), associated with the early-mid growing phase of the largest follicle of Wave 1, and then decreased to basal levels on Day 5 (P < or = 0.01) and peaked again (16.5 +/- 2.4 pg/mL) 2 d before ovulation. The CL were detected ultrasonically on Day 3 post ovulation and attained a mean maximum diameter of 13.5 +/- 0.8 mm between Days 8 and 14. The following characteristics were observed: 1) ovarian follicular development in goats is wave-like; 2) increased P4 concentrations may be promoting follicular wave turnover; 3) it is suggested that the presence of follicular dominance and the production of E2 are different among waves. While in Wave 1 and in the Ovulatory wave, follicular dominance is present and production of E2 is consistent, no changes in serum E2 concentrations were found in other stages of the interovulatory interval. In the intervening waves, no indicators of follicular dominance could be firmly documented.     

Developmental pattern of small antral follicles in the bovine ovary

The study was designed to characterize the developmental pattern of 1- to 3-mm follicles and to determine the stage at which the future dominant follicle first attains a size advantage among its cohorts. In experiment 1, heifers (n = 18) were examined every 24 h by transrectal ultrasonography for one interovulatory interval (IOI). In experiment 2, cows (n = 9) were examined every 6 h from 5 to 13 days after ovulation to monitor precisely the diameter changes of individual follicles >/=1 mm during emergence of wave 2. Results revealed a change over days (P < 0.05) in the number of 1- to 3-mm follicles, with a maximum (P < 0.05) 1 or 2 days before wave emergence (conventionally defined as the time when the dominant follicle is first detected at 4 mm), followed 3-4 days later by a maximum (P < 0.05) in the number of >/=4-mm follicles. The profiles of small (1-3 mm) and large (>/=4-mm) follicles were inversely proportional (r = -0.79; P = 0.01). The profile of the number of 1- to 3-mm follicles during wave emergence was similar (P = 0.63) between waves in two-wave IOI, but differed (P < 0.01) among waves in three-wave IOI as a result of a greater number of follicles in the ovulatory wave (P < 0.04). As well, the number of follicles in the ovulatory wave tended to be greater (P < 0.06) in three-wave IOI than in two-wave IOI. The future dominant follicle was first identified at a diameter of 1 mm and emerged 6-12 h earlier than the first subordinate follicle (P < 0.01). After detection of the dominant follicle at 1 mm (0 h), its diameter differed from that of the first and second subordinate follicles at 24 h (P = 0.04) and 12 h (P = 0.01), when the dominant follicle was 2.4 +/- 0.17 mm and 1.7 +/- 0.14 mm, respectively. The growth rate of the dominant follicle differed from that of the first and second subordinate follicles at 120 h (P = 0.03) and 108 h (P = 0.02), when the dominant follicle was 9.5 +/- 0.30 mm and 8.8 +/- 0.49 mm, respectively. Emergence of the future dominant (r = 0.71), first (r = 0.73), and second (r = 0.76) subordinate follicles was temporally associated (P < 0.01) with a rise in circulating concentrations of FSH. Transient, nocturnal elevations in plasma FSH concentration were followed within 6 h by an increase in the growth rate of 1- to 3-mm follicles. We conclude that 1) 1- to 3-mm follicles develop in a wave-like manner in association with surges in plasma concentrations of FSH, 2) 1- to 3-mm follicles are exquisitely responsive to transient elevations in FSH, and 3) selection of the dominant follicle is manifest earlier than previously documented and is characterized by a hierarchical progression over a period encompassing the entire FSH surge (5 days).     

Follicular dynamics in Serrana goats

Twenty-two Serrana goats were studied through two successive estrous cycles in order to characterize their follicular dynamics during the breeding season. The ovaries of the goats were scanned daily by real-time ultrasonography and all follicles >or=3mm were measured and classified. The data were classified by the number of follicular waves per goat to test the hypothesis that temporal and morphological differences between the last follicular wave of an ovary, irrespective of ovulation, will affect the selection of the next ovulatory wave. The mean interovulatory interval was 20.7+/-1.0 days (mean+/-S.D.). Three to five waves per estrous cycle were observed and 61.3% (19/31) of cycles had four waves. In estrous cycles with four waves, the day of onset of the first, second, third and fourth wave was 1.4+/-1.0, 6.9+/-1.4, 11.6+/-1.8 and 16.8+/-1.6, respectively. No differences (P>0.05) were found between the day of onset of the first and second waves for estrous cycles with three, four or five waves. However, the day of onset of the third and fourth waves occurred later when the number of waves per estrous cycle increased (P<0.001). The duration of the interwave interval (time between the day of onset of two consecutive waves) was longer when the second wave was ovulatory. The length of the growth phase (2.4+/-0.9 days) and size (5.9+/-0.7 mm) of the dominant follicle in the second wave were lower (P<0.01) than for the first wave (3.3+/-1.2 days and 6.6+/-0.9 mm, respectively) and the fifth wave (4.1+/-1.2 days and 7.5+/-1.0mm, respectively). Within pairs of ovaries, the onset of the last wave occurred later (P<0.05) and was less variable in ovulatory ovaries (day 16.8+/-1.4, n=20) than in anovulatory ovaries (day 15.1+/-3.7, n=20). The length of the growing phase was longer (P<0.001) in the last waves of ovulatory ovaries (3.1+/-0.9 days) than in the last waves of anovulatory ovaries (1.7+/-0.8 days). These results support the hypothesis that the day of onset of the ovulatory wave is related to or, at least, conditioned by the luteolysis and the decrease in plasma progesterone. In summary, the estrous cycle of Serrana goats is characterized by sequential follicular wave growth with a great variability in their onset and duration, with the exception of the ovulatory wave. The temporal and morphological differences observed in the last wave of estrous cycle provide strong evidence for the role of progesterone in their regulation.     

Comparison of the effect of natural mating, LH, and GnRH on interval to ovulation and luteal function in llamas

Gonadotropins and GnRH have been used to electively induce ovulation in llamas and alpacas, but critical evaluation of the natural interval to ovulation after mating has not been performed nor has a direct comparison of the effects of natural mating versus hormone treatments on this interval and subsequent luteal development. The objectives of this study were to compare the effects of hormonal treatments and natural mating on ovulation induction, interval to ovulation, and luteal development in llamas. The ovaries of llamas were examined by transrectal ultrasonography once daily. Llamas with a large follicle were assigned randomly to be: (1) mated with an intact male (mated; n=10); (2) given 5 mg of LH im (LH; n=11); or (3) 50 microg of GnRH im (GnRH; n=10). Ultrasound examinations were performed every 4h from treatment (day 0) to ovulation and thereafter once daily for 15 consecutive days to monitor CL growth and regression (n=5 per group). Plasma progesterone concentrations were measured at days 0, 3, 6, 9, and 12 after treatment to evaluate CL function. The size of the largest preovulatory follicle at the time of treatment did not differ among groups (11+/-0.6, 10.5+/-0.8, 11.8+/-0.9 mm, for mated, LH, and GnRH groups, respectively; P=0.6). No differences were detected among groups (mated, LH, and GnRH) in ovulation rate (80%, 91%, 80%, respectively; P=0.6), or interval from treatment to ovulation (30.0+/-0.5, 29.3+/-0.6, 29.3+/-0.7h, respectively; P=0.9). Similarly, no differences were detected among groups (mated, LH, and GnRH) in maximum CL diameter (14.2+/-0.3, 13.2+/-0.5, and 13.0+/-0.7 mm, respectively; P=0.5), the day of maximum CL diameter (7.6+/-0.2, 7.6+/-0.2, and 7.4+/-0.4 mm, respectively; P=0.6), or the day on which the CL began to regress (12.3+/-0.3 [non-pregnant, n=3], 11.8+/-0.6, 12.2+/-0.4, respectively; P=0.4). The diameter of the CL and plasma progesterone concentrations changed over days (P<0.0001) but the profiles did not differ among groups. In summary, ovulation rate, interval to ovulation, and luteal development were similar among llamas that were mated naturally or treated with LH or GnRH. We conclude that both hormonal preparations are equally reliable for inducing ovulation and suitable for synchronization for artificial insemination or embryo transfer program.     

The pattern of reproduction in female Columbian black-tailed deer, Odocoileus hemionus columbianus.

Ovarian cycles and the pattern of reproduction in female black-tailed deer in British Columbia were ascertained largely through examination of the ovaries from 444 females. Cyclic development and degeneration of single follicles of ovulatory size occurred several weeks before first ovulation. As the breeding season approached, a second or third large follicle developed in each cycle but in 48% of adult females the follicles were at different stages of maturation. Those failing to rupture at first ovulation luteinized 1 to 2 days thereafter. The first ovulation of the season, in November, never resulted in a lasting pregnancy even though some ova were penetrated by spermatozoa and began to cleave. First ovulation was apparently 'silent' in five of seven females for their ova lacked spermatozoa. Of sixty-one pregnant females, fifty-nine conceived at second ovulation; the other two conceived at subsequent ovulations more widely spaced than the 8- to 9-day interval between first and second ovulations. The synchrony of ovulatory cycles among adult females was such that half of them ovulated for the second time in a span of 7 or 8 days. Primary CL that formed after first ovulation grew to an average maximum volume of only about 45 mm3, whereas those originating at second ovulation grew to twice that size within 5 to 8 days. First generation CL shrank from 35 mm3 to 10 mm3 within 2 days. They disappeared within 18 months but corpora albicantia persisted for the life of the female. The possible ecological significance of the reproductive pattern is discussed.     

Ultrasonographic study of the effects of the corpus luteum on antral follicular development in unilaterally ovulating western white-faced ewes

The objective of this study was to examine the local effects of the corpus luteum (CL) on ovarian antral follicle development by looking at follicle populations and dynamics in ovaries with or without CL, in unilaterally ovulating ewes, using a retrospective analysis of daily ultrasonographic records. The present report summarises the data from the first luteal phase of the breeding season (August-October; n = 4), a luteal phase in the mid-breeding season (November-December; n = 5), the last luteal phase of the breeding season (January-March; n = 5), and the luteal phase after GnRH-induced ovulations in mid-anoestrus (May-June; n = 4) of western white-faced ewes. Mean daily numbers of 3mm follicles that did not grow any larger were significantly reduced in the CL-containing ovaries of ewes at all periods of study except for the transition to anoestrus. With all scanning periods combined, daily numbers of 3mm follicles not growing further increased (P<0.05) between day 6 and 15 after ovulation in the CL-containing ovaries. Based on mean data for the whole periods of observation, the non-CL-bearing ovaries of ewes in the transition to anoestrus had fewer (P<0.05) follicles growing from 3 to > or =5mm in size before regression compared with the mid-breeding season and mid-anoestrus. The lifespan of follicles reaching > or =5mm in diameter was shorter (P < 0.05) in the CL- compared with non-CL-containing ovaries of anoestrous ewes induced to ovulate with GnRH ((6.5+/- 1.3) and (9.0+/- 1.0) days, respectively). Circulating concentrations of progesterone were lower during both transitional periods (into and out of anoestrus) and mid-anoestrus than during the mid-breeding season (P < 0.001), and were less during anoestrus than during both transitional periods (P < 0.05). It was concluded that CL/luteal structures locally suppressed the growth of ovarian antral follicles to the 3mm size-range except during the transition to anoestrus, but that there was no inhibitory effect of the CL on the growth of ovarian follicles to larger diameters. The presence of CL/luteal structures did not affect the length of the lifespan of follicles reaching > or =5mm in diameter nor the number of ovulations per ovary in cyclic ewes, but shortened large follicle lifespan in anoestrous ewes. Variations in peripheral concentrations of progesterone across the breeding season and between the breeding season and anoestrus did not alter the lifespan of large antral follicles. In the transition to anoestrus and during mid-anoestrus, the presence of the CL in an ovary appeared to maintain follicle development to ovulatory sizes and to increase the rate of turnover of large antral follicles, respectively.     

Reduction in size of the ovulatory follicle reduces subsequent luteal size and pregnancy rate

We hypothesized that reducing the size of the ovulatory follicle using aspiration and GnRH would reduce the size of the resulting CL, reduce circulating progesterone concentrations, and alter conception rates. Lactating dairy cows (n=52) had synchronized ovulation and AI by treating with GnRH and PGF2alpha as follows: Day -9, GnRH (100 microg); Day -2, PGF2alpha (25 mg); Day 0, GnRH (100 microg); Day 1, AI. Treated cows (aspirated group; n=29) had all follicles > 4 mm in diameter aspirated on Days -5 or -6 in order to start a new follicular wave. Control cows (nonaspirated group: n=23) had no follicle aspiration. The size of follicles and CL were monitored by ultrasonography. The synchronized ovulation rate (ovulation rate to second GnRH injection: 42/52=80.8%) and double ovulation rate of synchronized cows (6/42=14.3%) did not differ (P > 0.05) between groups. Aspiration reduced the size of the ovulatory follicle (P < 0.0001; 11.5 +/- 0.2 vs 14.5 +/- 0.4 mm), and serum estradiol concentrations at second GnRH treatment (P < 0.0002; 2.5 +/- 0.4 vs 5.7 +/- 0.6 pg/mL). The volume of CL was less (P < 0.05) for aspirated than nonaspirated cows on Day 7 (2,862 +/- 228 vs 5,363 +/- 342 mm3) or Day 14 (4,652 +/- 283 vs 6,526 +/- 373 mm3). Similarly, serum progesterone concentrations were less on Day 7 (P < 0.05) and Day 14 (P < 0.10) for aspirated cows. Pregnancy rate per AI for synchronized cows was lower (P < 0.05) for aspirated (3/21=14.3%) than nonaspirated (10/21=47.6%) cows. In conclusion, ovulation of smaller follicles produced lowered fertility possibly because development of smaller CL decreased circulating progesterone concentrations.     

Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesis

The existence of short ovulatory cycles (5-day duration) after the first male-induced ovulations in anovulatory ewes and goats, associated or not with the appearance of oestrous behaviour, is the origin of the two-peak abnormal distribution of parturitions after the "male effect". We propose here a working hypothesis to explain the presence of these short cycles. The male-effect is efficient during anoestrus, when follicles contain granulosa cells of lower quality than during the breeding season. They generate corpora lutea (CL) with a lower proportion of large luteal cells compared to small cells, which secrete less progesterone, compared to what is observed in the breeding season cycle. This is probably not sufficient to block prostaglandin synthesis in the endometrial cells of the uterus at the time when the responsiveness to prostaglandins of the new-formed CL is initiated and, in parallel, to centrally reduce LH pulsatility. This LH pulsatility stimulates a new wave of follicles secreting oestradiol which, in turn, stimulates prostaglandin synthesis and provokes luteolysis and new ovulation(s). The occurrence of a new follicular wave on days 3-4 of the first male-induced cycle and the initiation of the responsiveness to prostaglandins of the CL from day 3 of the oestrous cycle are probably the key elements which ensure such regularity in the duration of the short cycles. Exogenous progesterone injection suppresses short cycles, probably not by delaying ovulation time, but rather by blocking prostaglandin synthesis, thus impairing luteolysis. The existence, or not, of oestrous behaviour associated to these ovulatory events mainly varies with species: ewes, compared to does, require a more intense endogenous progesterone priming; only ovulations preceded by normal cycles are associated with oestrous behaviour. Thus, the precise and delicate mechanism underlying the existence of short ovulatory and oestrous cycles induced by the male effect appears to be dependent on the various levels of the hypothalamo-pituitary-ovario-uterine axis.     

Effect of GnRH treatment during the anovulatory season on multiple ovulation rate and on follicular development during the ensuing pregnancy in mares

Seasonally anovulatory mares were injected, i.m., twice daily with a GnRH analogue (GnRH-A), and hCG was given when the largest follicle reached 35 mm in diameter. In Exp. 1, treatment was initiated on 23 December when the largest follicle per mare was less than or equal to 17 mm. An ovulatory response (ovulation within 21 days) occurred in 17 of 30 (57%) GnRH-A-treated mares on a mean of 15.8 days. The shortest interval to ovulation in control mares (N = 10) was 57 days. The diameter of the largest follicle first increased significantly 6 days after start of treatment. In Exp. 2, treatment was begun on 15 January and mares were categorized according to the largest follicle at start of treatment. The proportion of mares ovulating within 21 days increased significantly according to initial diameter of largest follicle (less than or equal to 15 mm, 9/25 mares ovulated; 15-19 mm, 13/21; 20-24 mm, 20/24; greater than 25 mm, 3/3). The multiple ovulation rate was greater (P less than 0.01) for treated mares (27/86 mares had multiple ovulations) than for control mares (2/35). Treated mares in which the largest follicle at start of treatment was greater than or equal to 25 mm had a higher (P less than 0.01) multiple ovulation rate (9/14) than did mares in which the largest follicle was less than 25 mm (18/72). The pregnancy rate for single ovulators was not different between control mares (26/30 pregnant mares) and treated mares (43/54).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of estradiol valerate on ovarian follicle dynamics and superovulatory response in progestin-treated cattle

Three experiments evaluated the effects of estradiol valerate (EV) on ovarian follicular and CL dynamics, intervals to estrus and ovulation, and superovulatory response in cattle. Experiment 1 compared the efficacy of two norgestomet ear implants (Crestar and Syncro-Mate B; SMB) for 9 d (with PGF at implant removal), combined with either 5 mg estradiol-17beta and 100 mg progesterone (EP) or 5 mg EV and 3mg norgestomet (EN) im at the time of implant insertion on CL diameter and follicular wave dynamics. Ovaries were monitored by ultrasonography. There was no effect of norgestomet implant. Diameter of the CL decreased following EN treatment (P < 0.01). Mean (+/- S.D.) day of follicular wave emergence (FWE) was earlier (P < 0.0001) and less variable (P < 0.0001) in EP- (3.6 +/- 0.5 d) than in EN- (5.7 +/- 1.5 d) treated heifers. Intervals from implant removal to estrus (P < 0.001) and ovulation (P < 0.01) were shorter in EN- (45.7 +/- 11.7 and 74.3 +/- 12.6 h, respectively) than in EP- (56.4 +/- 14.1 and 83.3 +/- 17.0 h, respectively) treated heifers. Experiment 2 compared the efficacy of EP versus EN in synchronizing FWE for superovulation in SMB-implanted cows. At random stages of the estrous cycle, Holstein cows (n = 78) received two SMB implants (Day 0) and were randomly assigned to receive EN on Day 0 or EP on Day 1. Folltropin-V treatments were initiated on the evening of Day 5, with PGF in the morning and evening of Day 8, when SMB were removed. Cows were inseminated after the onset of estrus and embryos were recovered 7 d later. Non-lactating cows had more CL (16.7 +/- 11.3 versus 8.3 +/- 4.9) and total ova/embryos (14.7 +/- 9.5 versus 7.9 +/- 4.6) than lactating cows (P < 0.05). EP-treated cows tended (P = 0.09) to yield more transferable embryos (5.6 +/- 5.2) than EN-treated cows (4.0 +/- 3.7). Experiment 3 compared the effect of dose of EV on ovarian follicle and CL growth profiles and synchrony of estrus and ovulation in CIDR-treated beef cows (n = 43). At random stages of the estrous cycle (Day 0), cows received a CIDR and no further treatment (Control), or an injection of 1, 2, or 5 mg im of EV. On Day 7, CIDR were removed and cows received PGF. Follicular wave emergence occurred within 7 d in 7/10 Control cows and 31/32 EV-treated cows (P < 0.05). In responding cows, interval from treatment to FWE was longer (P < 0.05) in those treated with 5 mg EV (4.8 +/- 1.2 d) than in those treated with 1 mg (3.2 +/- 0.9 d) or 2 mg (3.4 +/- 0.8 d) EV, while Control cows were intermediate (3.8 +/- 2.0 d). Diameter of the dominant follicle was smaller (P < 0.05) at CIDR removal and tended (P = 0.08) to be smaller just prior to ovulation in the 5 mg EV group (8.5 +/- 2.2 and 13.2 +/- 0.6 mm, respectively) than in the Control (11.8 +/- 4.6 and 15.5 +/- 2.9 mm, respectively) or 1mg EV (11.7 +/- 2.5 and 15.1 +/- 2.2 mm, respectively) groups, with the 2mg EV group (10.7 +/- 1.5 and 14.3 +/- 1.7 mm, respectively) intermediate. Diameter of the dominant follicle at CIDR removal was less variable (P < 0.01) in the 2 and 5mg EV groups than in the Control group, and intermediate in the 1mg EV group. In summary, treatment with 5mg EV resulted in a longer and more variable interval to follicular wave emergence than treatment with 5mg estradiol-17beta, which affected preovulatory dominant follicle size following progestin removal, and may have also affected superstimulatory response in Holstein cows. Additionally, 5 mg EV appeared to induce luteolysis in heifers, reducing the interval to ovulation following norgestomet removal. Conversely, intervals to, and synchrony of, follicular wave emergence, estrus and ovulation following treatment with 1 or 2 mg EV suggested that reduced doses of EV may be more useful for the synchronization of follicular wave emergence in progestogen-treated cattle.     

Ovarian and endocrine responses to prostaglandin F2alpha (PGF2alpha) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F(2alpha) (PGF(2alpha)) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF(2alpha) (15 mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF(2alpha) treatment (2.3+/-0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7+/-0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF(2alpha) injection (3.0+/-0.6 ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF(2alpha) treatment (2.0+/-0.3 ovulations/ewe; P>0.05). The mean interval from PGF(2alpha) to emergence of the next follicular wave (1.0+/-0.4 and 4.0+/-0.0 d, respectively; P<0.001) and the interval from PGF(2alpha) treatment to the next FSH peak (0 and 3.5+/-0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7+/-0.2, and six ewes ovulated both before and after the onset of estrus (3.0+/-0.5 ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1+/-0.3 or 5.5+/-0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF(2alpha) at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF(2alpha)-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.     

Induction of multiple ovulations during the ovulatory season in mares

The efficacy of an equine pituitary extract for induction of multiple ovulations during the ovulatory season was studied in 112 horse mares in four experiments. Combined for all experiments, 70% of the mares (78 112 ) had multiple ovulations for an average of 3.0 ovulations per mare. The interval between first and last ovulation was decreased (P<0.01) when human chorionic gonadotropin (hCG) was included in the treatment regimen (0.0 +/- 0.0 versus 1.6 +/- 0.4 days). Ovulation rate was lower (P<0.01) when extract treatment was initiated at day 19 (1.3 +/- 0.2) than when initiated at day 15 post-ovulation (2.9 +/- 0.5). Initiation of extract treatment at day 11 was as effective as initiation at day 15, with or without an injection of prostaglandin F(2alpha) on the first day of extract treatment. Increasing the dose of extract from 750 to 1500 or 2250 units per day did not significantly increase the ovulatory response.