Regression Of Ovarian Follicles Research Articles

Dinámica folicular durante el ciclo estral natural en búfalas (Bubalus bubalis)

El objetivo del estudio fue monitorear la dinámica folicular del ciclo estral natural de hembras bufalinas en Colombia. Se evaluaron los patrones de crecimiento y regresión de folículos ováricos de 11 búfalas durante dos ciclos estrales. Se realizaron exámenes ecográficos interdiarios de los ovarios para establecer patrones de ondas foliculares, número de ondas, día de emergencia, número de folículos reclutados, y características del folículo dominante (FD) y del cuerpo lúteo (CL). Las concentraciones de progesterona (P4) se determinaron por radioinmunoensayo. Se evaluaron 17 ciclos normales (2, 11 y 4 ciclos con una, dos y tres ondas foliculares, respectivamente). El intervalo inter-ovulatorio fue de 12.5 ± 2.7, 20.5 ± 1.2 y 28.8 ± 1.9 días para los ciclos con 1, 2 y 3 ondas foliculares, respectivamente. Las ondas foliculares emergieron los días 0 ± 2.3 en ciclos de una onda, los días 2.3 ± 1.0 y 10.5 ± 1.0 en ciclos de dos ondas y los días 1.25 ± 1.6, 8.0 ± 1.9 y 20.8 ± 1.6 (promedio ± e.e.) en ciclos de tres ondas. El diámetro máximo (cm) alcanzado por el FD fue de 1.2 ± 0.4 en ciclos de una onda, de 1.02 ± 0.2 y 1.3 ± 0.3 en ciclos de dos ondas, y de 1.2 ± 0.3, 1.3 ± 0.3 y 1.2 ± 0.3 en ciclos de tres ondas. La concentración de P4 en el día de máximo diámetro del CL en promedio fue de 7.2 ± 6.6 ng/ml. Se concluye que la dinámica folicular de la búfala colombiana se caracteriza por presentar patrones de una, dos y tres ondas foliculares, con predominio de ciclos de dos ondas.

استئناف النشاط المبيضي بعد الولادة في الأبقار الماشية = Resumption of Ovarian Activity in Shami Cows Postpartum

Forty one Shami cows available in Dier-Al-Hajar Station, having 1-5 lactations were used to monitor ovarian activity postpartum (pp), determine the times of the 1st ovulation and estrus, the diameters of dominant follicles and length of ovarian cycle till day 65 pp. Transrectal Ultrasound Echo System (7.5 MHz probe) was used to monitor the daily development and regression of ovarian follicles during the study. Results indicated that the frequency of the first ovulation pp was 19.5, 36.6, 24.4 and 7.3% for cows ovulating the 1st, 2nd, 3rd and 4th dominant follicles, respectively, and there is no ovulation in 12.2% during this study. The first ovulation was determined after 34.6±1.9 day pp, while estrus detected on day 49.1±2.3 pp. There were no effects of parities (primiparous and multiparous), season and suckling on the time of 1st ovulation pp. However, the 1st estrus occurred earlier in primiparous than in multiparous cows and in winter compared to other seasons. The frequency of short (8-13 days), intermediate (17-24 days) and long ovarian cycle (cycles without estrus detected) (25-31days) was 27.8, 58.3 and 13.9%, respectively, with an average length equals to 18.8±1.1 days. It was concluded that Shami cows resumed their ovarian activity quickly pp, this refers to the ability of insemination and fertilization within 2-3 months pp if there is the appropriate of environmental and management.

Prevalence and pathology of oviduct impaction in commercial white leghorn layer chicken in Namakkal region of India

Aim : The avian oviduct is a tubular organ responsible for fertilization, secretion of the components surrounding the yolk and transport of egg in the reproductive tract. Disorders of oviduct may have a great bearing on production potential and incur a heavy loss. A study was undertaken to assess the prevalence and pathological changes of impacted oviduct in commercial white leghorn layer chicken in Namakkal region of India for a period of four years from 2006 to 2009. : A total of 5145 carcasses of white leghorn layers, above 20 weeks age from 255 flocks were examined for various oviduct abnormalities. Heart blood, liver and oviduct swabs collected upon necropsy from 45 layer chicken from six flocks with oviduct impaction were screened for bacterial agents. Pooled tissue (trachea, lung, spleen, caecal tonsil, kidney and oviduct) samples from impacted oviduct cases were screened for viral agents. Serum samples collected from affected flocks were screened for Newcastle disease virus (NDV), infectious bronchitis virus (IBV) and egg drop syndrome - 76 (EDS-76) virus by haemagglutination inhibition (HI) and (Mg) and (Ms) by ELISA. Flock details and pathological changes were recorded in affected flocks to assess the prevalence and impact of oviduct impaction on commercial layer chicken. : The results of the present investigation indicated that the oviduct impaction was responsible for 0.87% of the reproductive tract abnormalities in commercial layers between 21 and 80 wk of age. Egg production drop, morbidity and mortality recorded in the affected flocks were varied from 3 to 8, 0.4 to 1.2 and 0.2 to 0.5 % respectively. The oviduct impaction was commonly noticed above 40 wk old layers and predominantly during colder months. Serum samples collected from three flocks with oviduct impaction were found positive for Mg and Ms infection in ELISA test. was isolated as a pure culture in 29 birds and concurrent with other bacterial agents in 16 birds. Serotyping of isolates revealed that O , O and O were the predominant types. Necropsy examination of carcasses with impacted oviduct showed emaciation, peritonitis, regression of ovarian follicles and distension of oviduct commonly in the infundibulum and magnum region. The exudate was either large mass with concentric layering on cut section or numerous caesous masses with varying size and shape often mixed with creamy or serosangunious fluid. Histopathological examination of oviduct revealed the presence of lymphoid foci in the epithelial layer with marked atrophy and degeneration of mucosal folds. : Impacted oviduct constituted 0.87 % of oviduct abnormality in commercial layer chicken with an overall mortality of 0.5 %. The findings of this study showed that the oviduct impaction might be caused by in concurrence with spp.

Ovarian follicular dynamics during the interovulatory interval in Najdi goats

The pattern of growth and regression of ovarian follicles was characterized during the estrus cycle in 5 Najdi goats by daily ultrasonographic examination of the ovaries. Follicles ≥2 mm was measured and their relative locations within the ovary were determined to follow the sequential development of each individual follicle. Results indicated the presence of either four (n = 2 estrus cycles) or five (n = 3 estrus cycles) waves of follicular growth during the interovulatory interval. Each wave was characterized by the development of at least 1 large follicle (dominant) and a variable number of small follicles (subordinate). The mean number of follicular waves in Najdi goats is 4.6 ± 0.55, the days of wave emergence were on -0.8 ± 1.06, 3.2 ± 0.4, 7.0 ± 0.6, 12.3 ± 1.72 and 13.0 ± 1.63, for the first to fifth follicular waves, retrospectively. In goats with four or five follicular waves the dominant follicle in forth or fifth wave was ovulatory follicle. The mean number of ovulations in Najdi goats is 1.8 ± 0.4. Means of values were analyzed by repeated measures test using general linear model (GLM). Key words: Goats, estrous, follicles, ultrasonography.

Is one-wave follicular growth during the estrous cycle a usual phenomenon in water buffaloes ( Bubalus bubalis)?

The pattern of growth and regression of ovarian follicles was monitored once daily for one complete estrous cycle in eight individual water buffaloes by ultrasonographic scanning of the ovaries for an entire interovulatory interval of normal cycle length. One-wave follicular growth was observed in five animals and two-wave follicular growth in three buffaloes during the estrous cycle. The first follicular wave of a two-wave cycle emerged significantly earlier ( P < 0.05) than the emergence of the solitary wave of a one-wave cycle. One- and two-wave cycles differed significantly ( P < 0.05) with respect to the mean interovulatory interval (21.0 ± 0.54 days versus 22.7 ± 0.33 days) and the mean interestrus interval (20.8 ± 0.58 days versus 22.3 ± 0.66 days). The overall linear growth rate of the ovulatory follicle was significantly greater ( P < 0.01) in a two-wave cycle compared to that of a one-wave cycle (1.17 ± 0.33 mm/day versus 0.32 ± 0.01 mm/day). In a one-wave pattern, the growth profile of the solitary dominant follicle was atypical, showing three distinct phases, i.e. growth phase, regression phase and regrowth phase culminating in ovulation. The level of plasma progesterone steadily increased from day 0 of estrous cycle, attained peak level on day 14 and declined thereafter. A slower growth rate of the dominant follicle was observed in the presence of higher plasma progesterone concentration. The present study shows that one-wave follicular growth is a normal phenomenon in suckled water buffaloes.

Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares

Ten mares were studied from February (winter anoestrus) to their second ovulation in the breeding season to investigate the relationship between resumption of ovarian cyclicity in the spring and circulating concentrations of FSH, inhibin A and inhibin isoforms containing pro- and -alphaC immunoreactivity. An additional four mares were studied during one oestrous cycle. Growth and regression of ovarian follicles were monitored by transrectal ultrasonography. The frequency of blood sampling varied from three times a week to once a day, depending on the follicular activity present. Concentrations of FSH, oestradiol, inhibin A and pro- and -alphaC isoforms were low during deep winter anoestrus when minimal follicular activity was present in the ovaries. During spring transition, an increase in FSH concentration preceded the emergence of each follicular wave. Concentrations of inhibins were significantly higher (P < 0.05) during growth of anovulatory follicles in spring transition than during winter anoestrus. Plasma concentrations of oestradiol and inhibin A were significantly higher (P < 0.001, P < 0.05, respectively) during the growth of preovulatory follicles than during the growth of transitional anovulatory follicles, but concentrations of inhibin pro-alphaC isoforms did not differ between the two types of follicle. During the oestrous cycle, there was a significant inverse relationship (P < 0.001) between concentrations of FSH and the inhibins. Plasma inhibin pro-alphaC isoforms, but not inhibin A, reached a peak on the day of ovulation. The results strongly indicate that FSH regulates growth of spring anovulatory and preovulatory follicles. Inhibins are likely to contribute to negative feedback on the release of FSH from the pituitary gland both during the transitional period and the breeding season in mares.

Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares

Ten mares were studied from February (winter anoestrus) to their second ovulation in the breeding season to investigate the relationship between resumption of ovarian cyclicity in the spring and circulating concentrations of FSH, inhibin A and inhibin isoforms containing pro- and -alphaC immunoreactivity. An additional four mares were studied during one oestrous cycle. Growth and regression of ovarian follicles were monitored by transrectal ultrasonography. The frequency of blood sampling varied from three times a week to once a day, depending on the follicular activity present. Concentrations of FSH, oestradiol, inhibin A and pro- and -alphaC isoforms were low during deep winter anoestrus when minimal follicular activity was present in the ovaries. During spring transition, an increase in FSH concentration preceded the emergence of each follicular wave. Concentrations of inhibins were significantly higher (P < 0.05) during growth of anovulatory follicles in spring transition than during winter anoestrus. Plasma concentrations of oestradiol and inhibin A were significantly higher (P < 0.001, P < 0.05, respectively) during the growth of preovulatory follicles than during the growth of transitional anovulatory follicles, but concentrations of inhibin pro-alphaC isoforms did not differ between the two types of follicle. During the oestrous cycle, there was a significant inverse relationship (P < 0.001) between concentrations of FSH and the inhibins. Plasma inhibin pro-alphaC isoforms, but not inhibin A, reached a peak on the day of ovulation. The results strongly indicate that FSH regulates growth of spring anovulatory and preovulatory follicles. Inhibins are likely to contribute to negative feedback on the release of FSH from the pituitary gland both during the transitional period and the breeding season in mares.

Effects of Controlled Heat Stress on Ovarian Function of Dairy Cattle. 2. Heifers

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of dairy heifers. Estrus was synchronized in Holstein heifers (estrus = d 0), and heifers then were randomly assigned to either heat stress (n = 10; 33°C, 60% relative humidity) or thermoneutral (n = 11; 21°C, 60% relative humidity) treatment. For heat-stressed heifers, ambient temperature was increased from thermoneutrality to heat stress (33°C) between d 9 and 14 (2.4°C/d increase) after the synchronized estrus and remained between 31 and 33.5°C until d 22. From d 11 to 21, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography, and blood was collected daily for serum progesterone and estradiol analyses. The second wave dominant follicle was larger for the heifers in the thermoneutral environment than for heat-stressed heifers, and ovulation of the second wave dominant follicle occurred in 9 of 11 thermoneutral heifers. For 6 of 10 heat-stressed heifers, the second wave dominant follicle regressed and was replaced by an ovulatory third wave dominant follicle. Smaller follicular size in heat stressed heifers was associated with decreased serum estradiol concentrations between d 11 and 21. Serum concentrations of progesterone during the luteal phase were similar, but luteolysis was delayed in heat-stressed heifers compared with onset in heifers in the thermoneutral treatment. Conclusions were that heat stress inhibited the growth and function of the dominant follicle so that most of the heat-stressed heifers had three follicular waves and a delay in corpus luteum regression.

Effects of Controlled Heat Stress on Ovarian Function of Dairy Cattle. 1. Lactating Cows

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29°C, 60% relative humidity) or thermoneutral (n = 11; 19°C, 60% relative humidity) treatment. For cows undergoing heat stress, ambient temperature (19°C) was increased from d 11 to 13 of the estrous cycle (3.3°C/d increase) and remained at 29°C until d 21. Beginning on d 11, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography. Blood was collected daily by coccygeal venipuncture for measurement of serum concentrations of progesterone and estradiol. The second wave dominant follicle was more likely to ovulate in cows in the thermoneutral treatment than in cows undergoing heat stress (91 vs. 18% ovulation, respectively). Patterns of follicular growth in cows under-going heat stress were associated with decreased serum estradiol from d 11 to 21 and on the day of luteolysis. The average day of luteolysis was delayed by 9 d in heat-stressed cows. Conclusions were that follicular growth and development and luteolytic mechanisms were compromised in heat-stressed cows; as a result, luteolysis was delayed, and second wave dominant follicles did not ovulate.

Estrus synchronization in cattle using estradiol, melengestrol acetate and PGF

In Experiment 1, all cattle were fed MGA (0.5 mg/head/d) for 7 d (designated Days 0 to 6) and given PGF on Day 6. One-half were administered estradiol valerate (EV; 5 mg, im) on Day 0. At Location 1, a higher proportion (P < 0.005) of EV-treated heifers were detected in estrus and bred by AI between Days 7 and 13 than control heifers not receiving EV (27 of 33 versus 15 of 32), but the number of pregnancies (12 vs 10) was not significantly different. Eighty-three of 104 EV-treated and 89 of 106 control cows were inseminated, resulting in 50 and 45 pregnancies, respectively (not significant). At Location 2, cattle were similarly treated and exposed to bulls on Days 7 to 49. Fall pregnancy rate was higher (P < 0.015) for EV-treated than control heifers (44 of 48 vs 33 of 46), but was not significantly different for cows (22 of 26 vs 19 of 23). In Experiment 2, estradiol 17β (E17β; 5 mg, im) and progesterone (100 mg, im) were administered on Day 0 (instead of EV). In a third group (designated the PGF group), cattle were bred on Days 0 to 6, and PGF was administered on Day 6 to those not yet bred. For 213 cows, the percentage pregnant to a synchronized estrus was greater in the PGF group (72%) than in either the control group treated with MGA (49%; P = 0.005) or the group receiving MGA and E17β (54%; P < 0.025). Fall pregnancy rates were 91, 89, and 96% for the 213 cows (not significant) and 89, 93, and 98% for 131 heifers (not significant) in the PGF, MGA and E17β groups, respectively. In cattle without a functional CL, the average diameter of the largest follicle at Day 6 was 1 to 2 mm smaller in the E17β + MGA group than in the MGA group (difference significant only in cows at Location 1). Combined for both locations, the synchronized pregnancy rate in heifers without a functional CL on Day 6 was higher (P < 0.05) in the E17β + MGA group than in the MGA group (11 of 21, 52% versus 4 of 20, 20%). Estrogen treatment caused regression of ovarian follicles with emergence of a new follicular wave. Including estrogen in an estrus synchronization program utilizing MGA and PGF significantly increased fall pregnancy rate in heifers (at 1 location) and the synchronized pregnancy rate of heifers without a functional CL at the time of PGF treatment (combined for both locations).

Ovarian follicular dynamics in water buffalo

The pattern of growth and regression of ovarian follicles was characterized during 7 complete estrous cycles in 5 water buffalo by daily ultrasonographic examinations of the ovaries. Follicles ≥ 4 mm were measured and their relative locations within the ovary were determined to follow the sequential development of each individual follicle. Results indicated the presence of either one (n = 3 estrous cycles) or two (n = 4 estrous cycles) waves of follicular growth per cycle. Each wave was characterized by the development of 1 large (dominant) follicle and a variable number of smaller (nondominant) follicles. In the single follicular wave pattern, the wave started on Day 1.3 ± 0.7 (Mean ± SEM; estrus = Day 0). In the 2-wave pattern, first and the second waves started on Days 1.8 ± 0.6 and 7.8 ± 2.0, respectively, and the dominant follicle in the second wave was the ovulatory follicle. The maximal size and growth rate of the dominant follicle in the first and second wave of the 2-wave cycles did not differ significantly. However, the growth rate of the ovulatory dominant follicle in the 2-wave cycles was greater (P < 0.05) than that in the single-wave cycles. On the day of estrus, the ovulatory follicle was always the largest follicle present on either ovary. In conclusion, this study shows that in buffalo the development of ovarian follicles ≥ 4 mm occurs in 1 or 2 waves per estrous cycle.

Pituitary function, ovarian follicular growth, and plasma concentrations of 17 beta-estradiol and progesterone in prepubertal heifers during and after treatment with the luteinizing hormone-releasing hormone agonist deslorelin.

Pituitary function, ovarian follicle growth, and plasma steroid concentrations were determined in prepubertal heifers during and after treatment with the LHRH agonist deslorelin. Brahman heifers, 13 mo of age and 204 +/- 5 kg, were allocated to 4 groups with treatments as follows: group C (n = 6), control, received no treatment; group C + LHRH (n = 6), control, received LHRH tests at the same times as group D + LHRH below; group D (n = 6), received deslorelin (approximately 300 micrograms/day) for 28 days; group D + LHRH (n = 6), received deslorelin for 28 days were given LHRH tests (50 micrograms LHRH i.m.) on Day 28 of treatment and on Days 2, 4, 8, 12, 16, and 20 after treatment. Number and size of ovarian follicles were determined by rectal ultrasonography. Deslorelin induced an increase in plasma concentrations of LH within 2 h (p < 0.001); LH remained greater (p < 0.05) for heifers treated with deslorelin for 48 h, but from Day 4 to 28 of treatment, LH in treated and control heifers did not differ. Ovarian follicles of heifers treated with deslorelin were characterized by increased (p < 0.05) maximum size, and also tended to have a greater rate of growth, compared with those of control heifers. Heifers treated with agonist had greater (p < 0.05) plasma concentrations of 17 beta-estradiol from Day 0 to 28 of treatment, and 17 beta-estradiol in these heifers showed cyclical fluctuations that appeared to be related to cycles of growth and regression of ovarian follicles. After cessation of deslorelin treatment, plasma LH was similar for heifers in group C and group D. Heifers in group C + LHRH had significant (p < 0.05) LH responses to exogenous LHRH at all times. In contrast, heifers in group D + LHRH did not show an LH release in response to exogenous LHRH on Day 28 of treatment and also failed to have a significant (p < 0.05) release of LH until Day 12 after treatment. A significant increase in plasma 17 beta-estradiol after LHRH injection also occurred on Day 12 after treatment in heifers in group D + LHRH. The findings indicated that LHRH agonist treatment in prepubertal heifers is associated with an acute LH response followed by a return of LH to concentrations similar to those of control heifers. Size of the largest ovarian follicle is greater in heifers treated with LHRH agonist and is associated with increased plasma concentrations of 17 beta-estradiol. After cessation of agonist treatment, the pituitary remains desensitized to LHRH for approximately 12 days. This study is the first demonstration of enhanced ovarian follicular growth and increased 17 beta-estradiol secretion during treatment with an LHRH agonist.

Follicular dynamics during the ovulatory season in goats

Growth and regression of ovarian follicles ≥3 mm were studied by transrectal ultrasonography for 4 interovulatory intervals in each of 5 Saanen goats. The observed number of growing identified 4-mm follicles per day differed (P<0.05) from randomness, indicating that follicles, on the average, emerged in groups (waves). Averaged over all interovulatory intervals, the number of 3-mm follicles on each day that later reached ≥6 mm followed a pattern of significant peaks on Days 0 (ovulation), 4,8 and 14. A follicular wave was defined by consecutive days of entry of follicles ≥6 mm into the wave, and the day of emergence was defined as the first day that the ≥6 mm follicles were 3 mm. In 15 of 20 (75%) interovulatory intervals, 1 wave emerged during each of Day −2 to Day 1 (Wave 1); Days 2 to 5 (Wave 2); Days 6 to 9 (Wave 3); and Days 10 to 15 (Wave 4). Ovulation occurred during Wave 4. The mean days of emergence of Waves 1 to 4 were Days −1, 4, 8 and 13, respectively. However, in 5 of these 15 interovulatory intervals, 50% of the apparent waves merged or were continuous so that a distinction could not be made between 2 waves. The largest follicle grew to a larger (P<0.05) maximum diameter for Waves 1 (8.7±0.3 mm) and 4 (9.7±0.3 mm) than for Waves 2 (7.2±0.2 mm) and 3 (7.3±0.2 mm). The following observations suggested that the phenomenon of follicular dominance was more common during Waves 1 and 4 than during Waves 2 and 3: 1) the interwave intervals (days) were longer (P<0.05) for Waves 1 (3.4±0.2) and 4 (4.3±0.6) than for Waves 2 and 3 (2.5±0.2 for each wave) and 2) the correlation between maximum diameter of largest follicle and the subsequent interwave interval was significant for Waves 1 and 4 but not for Waves 2 and 3. The 5 remaining interovulatory intervals were irregular and involved more than 4 waves, including 2 interovulatory intervals with prolonged follicular phases (14 and 21) and failures of ovulation. In conclusion, the predominant follicular-wave pattern was 4 waves with ovulation from Wave 4, and apparent follicular dominance was expressed during some follicular waves, especially during Waves 1 and 4.

Patterns of growth and regression of ovarian follicles during the oestrous cycle and after hemiovariectomy in mares

SummaryTo increase our understanding of the regulation of ovarian follicular development during the oestrous cycle, 13 mares were used in two experiments. In Experiment 1, the pattern of growth and regression of individual follicles, 15 mm or more in size, was monitored daily during 17 oestrous cycles by real‐time ultrasonography. Each examination was recorded on videotape to ensure accurate monitoring of individual follicles. Results indicated that the development of such follicles occurs in waves, with the most common pattern being one follicular wave per oestrous cycle (12 of 17 cycles). An alternative pattern of two follicular waves per cycle was observed in mares with (n=3) and without (n=2) dioestrous ovulations. The ovulatory follicle appeared earlier in the cycle in mares with one wave than in mares with two waves (Day 6.3 ± 0.9 vs Day 11.0 ± 1.2, respectively; p&lt;0.01). Also, the ovulatory follicle was the largest follicle for a longer period of time in mares with one wave than in mares with two waves per cycle (9.5 ± 0.6 vs 5.8 ± 0.3 days, respectively; p&lt;0.01). Mares with one follicular wave had shorter cycles than those with two waves per cycle (18.2 ± 0.6 vs 21.6 ± 0.5 days, p&lt;0.001). In both cases, the interval between the appearance of the ovulatory follicle and its ovulation was, on average, 10 to 12 days. Overall, a negative correlation was found between the relative size of the ovulatory follicle at the beginning of the follicular phase and the length of the follicular phase (r=‐0.91, p&lt;0.001). To study the control of follicular recruitment, patterns of follicular growth were monitored in nine mares following removal of the ovary bearing the presumptive ovulatory follicle (Experiment 2). Hemiovariectomies were performed between Day 14 of dioestrus and the fourth day of oestrus. Follicular dynamics were characterised by the development of one follicular wave that produced one to three ovulatory follicles in seven of nine mares. The ovulatory follicle reached 15 mm or more 6.3 ± 1.5 days following surgery and the interval from hemiovariectomy to ovulation was 13.7 ± 1.3 days. Two of nine mares hemiovariectomised on Day 14 failed to undergo complete luteolysis after the ovary bearing the ovulatory follicle, but not the corpus luteum, was excised. These mares had not ovulated by 30 days after surgery, although follicular waves producing ovulatory size follicles were observed. This study indicated that the development of ovarian follicles 15 mm or larger in the mare occurs in waves, with a more common pattern of one wave and an alternative pattern of two waves per oestrous cycle.

Ovarian Follicular Dynamics during the Estrous Cycle in Heifers Monitored by Real-Time UItrasonograph1

It is not clear whether the turnover of ovarian follicles during the estrous cycle in cattle is continuous and independent of the phase of the cycle, or whether waves of follicular growth occur at specific times of the cycle. To clarify this controversy, the pattern of growth and regression of ovarian follicles was characterized during a complete estrous cycle in ten heifers by daily ultrasonographic examinations. Follicles greater than or equal to 5 mm were measured and their relative locations within the ovary were determined in order to follow the sequential development of each individual follicle. Results indicated the presence of either two (n = 2 heifers), three (n = 7), or four (n = 1) waves of follicular growth per cycle. Each wave was characterized by the development of one large (dominant) follicle and a variable number of smaller (non-dominant) follicles. In the most common pattern observed (three waves/cycle), the first, second, and third waves started on Days 1.9 +/- 0.3, 9.4 +/- 0.5, and 16.1 +/- 0.7 (X +/- SEM), respectively. The dominant follicle in the third wave was the ovulatory follicle. The maximal size and the growth rate of the dominant follicle in the second wave were significantly lower than in the other waves, but no significant difference was observed between the first and third waves. For the two heifers that had two follicular waves/cycle, the waves started on Days 2 and 11, whereas in the remaining heifer (four waves/cycle), the waves began on Days 2, 8, 14, and 17, respectively. At 0, 1, 2, 3, and 4 days before estrus, the ovulatory follicle was the largest follicle in the ovaries in 100%, 95%, 74%, 35%, and 25% of follicular phases monitored, respectively. The relative size of the preovulatory follicle at the completion of luteolysis (progesterone less than 1 ng/ml) was negatively correlated (r = -0.90; p less than 0.0001) with the interval of time between the end of luteolysis and the luteinizing hormone surge, suggesting that the length of proestrus is determined by the size of the pre-ovulatory follicle at the beginning of proestrus. In conclusion, this study shows that the development of ovarian follicles greater than or equal to 5 mm in heifers occurs in waves and that the most common pattern is three waves per estrous cycle.

Growth and regression of ovarian follicles during the follicular phase of the oestrous cycle in heifers undergoing spontaneous and PGF-2 alpha-induced luteolysis.

Ultrasonography was used to monitor the growth, ovulation and regression of individual ovarian follicles greater than or equal to 5 mm during the late luteal and follicular phases of the oestrous cycle in heifers treated with injections of PGF-2 alpha to induce luteolysis and in heifers undergoing spontaneous luteolysis. Six heifers were given a single injection of PGF-2 alpha between Day 12 and 15 of the oestrous cycle and their ovaries were examined daily by transrectal ultrasonography until ovulation occurred. Another group of 5 heifers was examined daily by ultrasound from Day 14 or 15 of the cycle through spontaneous luteolysis and ovulation. Blood samples were taken twice daily from this group and analysed for progesterone to determine when luteolysis occurred. All heifers were checked for oestrous behaviour twice daily. Mean diameters of ovulatory follicles on each of the 3 days before oestrus were not different between PGF-2 alpha-treated and untreated heifers. In both groups there was large variation among heifers in the sizes and growth rates of the ovulatory follicles. At 3 days before oestrus the diameters of ovulatory follicles were between 7.5 and 11 mm in PGF-2 alpha-treated heifers and between 6 and 11.5 mm in untreated heifers. Non-ovulatory follicles decreased in size during the 3 days before oestrus and the number of non-ovulatory follicles within the size ranges of ovulatory follicles decreased. The ovulatory follicle was not consistently the largest follicle on the ovaries until the day of oestrus but was always one of the 2 largest follicles during the 3 days before oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)