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1.
The application of real-time ultrasonography to monitoring ovarian function in mammals has advanced the understanding of follicular dynamics and its regulation. Follicular development is a wave-like sequence of organised events. The waves consist of the synchronous growth of small (4 to 5 mm) antral follicles, followed by the selection and growth of one dominant follicle which achieves the largest diameter and suppresses the growth of the subordinate follicles. In the absence of luteal regression, the dominant follicle eventually regresses (becomes atretic) and a new follicular wave begins. The dominant follicle regulates the growth of the subordinate follicles, because the appearance of the next wave is accelerated if the dominant follicle is ablated, and delayed if the lifespan of the dominant follicle is prolonged. During bovine oestrous cycles, two or three successive waves emerge, on average, on the day of ovulation (day 0) and day 10 for two-wave cycles, and on days 0, 9 and 16 for three-wave cycles. During the oestrous cycle there are thus two or three successive dominant follicles, and the last of these ovulates. Ovarian folliculogenesis is a complex process involving interactions between pituitary gonadotrophins, ovarian steroids and non-steroidal factors. Subtle changes in the hormonal milieu regulate folliculogenesis and the emergence of a follicular wave is preceded by a small increase in the concentration of plasma follicle-stimulating hormone. The mechanisms that promote the selection of a dominant follicle have not been elucidated, but considerable progress has been made in understanding follicular development and its regulation. Most treatments designed to control the development of follicular waves have been based on the physical or hormonal removal of the suppressive effect of the dominant follicle, and the consequent controlled induction of the emergence of a new follicular wave. The studies reviewed here describe current methods for regulating the bovine ovarian cycle, interesting models for future studies, and information that may be used for improving reproductive efficiency.  相似文献   

2.
Gonadotropins determine the follicle selection and ovulation rate. Follicle growth is independent of gonadotropins until antrum formation, at which time recruitment occurs. Once recruited, follicles will continue to grow or degenerate. In gilts, visible surface follicles are classified as small (<3mm), medium (3-6.9 mm) and large (> or =7.0mm). At estrus (day 0), there are approximately 15 small and medium follicles, and approximately 15 large follicles. By day 3, there may be approximately 30 small, 5 medium and no large follicles. During the remainder of the luteal phase, the pool of follicles increases and peaks at day 11-13 with approximately 50 small, and 30 medium, but with no large follicles observed. By the start of the follicular phase at day 15, numbers of small and medium follicles rapidly decline, while a pool of medium follicles is selected for the ovulation. The size of large follicles at estrus is heterogeneous (6.5-10.0 mm) but their number is reflective of the subsequent number of corpora lutea found following the ovulation. However, the time of medium follicle selection for ovulation is variable during the late luteal and early follicular phases. Suppression of FSH before and at the time of luteolysis reduces medium and large follicles but does not reduce the ovulation rate. In contrast, suppression of FSH for 3 days or unilateral ovariectomy after 3 days of the follicular phase prevents full ovulatory compensation. Therefore, FSH appears to be involved in the maintenance of a pool of medium follicles that can be selected by LH to mature and ovulate.  相似文献   

3.
Ovarian follicular growth, function and turnover in cattle: a review   总被引：3，自引：0，他引：3  
Studies in cattle assessing changes in number and size of antral follicles, concentrations of estradiol, androgens and progesterone in serum and follicular fluid, and numbers of gonadotropin receptors per follicle during repetitive estrous cycles and postpartum anestrus are reviewed. The rate of growth of small follicles (1 to 3 mm) into larger follicles increases as the estrous cycle progresses from d 1 to 18 (d 0 = estrus). Size of the largest antral follicle present on the ovary also increases with advancement of the estrous cycle. Most large follicles (greater than 10 mm) persist on the ovarian surface for 5 d or more between d 3 and 13 of the bovine estrous cycle. After d 13, most of these large follicles are replaced more frequently by new growing follicles (turnover) with an increased probability for recruitment of the ovulatory follicle after d 18. More research is needed to determine the time required for growth of bovine follicles from small to large antral size and evoke recruitment of the ovulatory follicle. Factors that regulate selection of the ovulatory follicle are unknown but may involve increased frequency of LH pulses in blood, altered blood flow and(or) changes in intrafollicular steroids and proteins. Quantitative evaluation of ovarian follicles indicated occurrence of consistent short-term changes in fluid estradiol and numbers of luteinizing hormone receptors in cells of large follicles only during the pre-ovulatory period. Presumably, low concentrations of follicular estradiol found during most of the estrous cycle are not due to a lack of aromatizable precursor or follicle-stimulating hormone receptors. Follicular fluid concentrations of progesterone increase only near the time of ovulation. Little is known about changes in follicular growth, turnover and function during postpartum anestrus in cattle. However, preliminary data suggest that the steroidogenic capacity of large follicles changes markedly during the postpartum period.  相似文献   

4.
The association between conception rate at first service and numbers of follicles developed during a follicular wave was examined in 102 suckled beef cows and 14 heifers. Follicular development was monitored using ultrasonography for either two (trial 1) or three (trial 2) consecutive oestrous cycles (pre-breeding, breeding and post-breeding equivalent). Animals were examined on alternate days from day 6 after first oestrus (day 0) until ovulation and from day 6 after insemination until next ovulation or day 24 of pregnancy and were observed for oestrus twice daily and inseminated artificially at either the second (trial 1) or third oestrus (trial 2). Cows were classified as having two or three waves of follicular development for each oestrous cycle. Numbers of follicles >or=4 mm per wave were determined, and based on the maximum diameter they attained, were classified as small (4-6 mm), medium (7-10 mm) or large (>or=11 mm) follicles. Total numbers of follicles, and primarily numbers of small and medium follicles, were affected by trial and within trial by cow, oestrous cycle and follicular wave. Heifers had more small and total numbers of follicles, but fewer large follicles than cows in trial 1 (p < 0.05). The average number of antral follicles per wave in the breeding cycle or post-breeding period did not affect conception rates, which averaged 84%. Repeatability of the total numbers of antral follicles between and among oestrous cycles and follicular waves ranged from 0.01 to 0.97. In conclusion, fertility was not affected by the numbers of antral follicles >or=4 mm in diameter in a single follicular wave.  相似文献   

5.
Cystic ovarian disease (COD) is one of the main causes of infertility in dairy cattle. It has been shown that intra‐ovarian factors may contribute to follicular persistence. Transforming growth factor‐beta (TGFB) isoforms are important paracrine and autocrine signalling molecules that regulate ovarian follicle growth and physiology. Considering the importance of these factors in the ovarian physiology, in this study, we examined the expression of TGFB isoforms (TGFB1, TGFB2 and TGFB3) in the ovary of healthy cows and animals with spontaneous and adrenocorticotrophic hormone (ACTH)‐induced COD. In the oestrous‐synchronized control group, the expression of TGFB1 in granulosa and theca cells was higher in spontaneous cysts than in atretic or tertiary follicles. When we compared TGFB2 expression in granulosa cells from atretic or tertiary follicles from the oestrous‐synchronized control group with that in ACTH‐induced or spontaneous follicular cysts, we found a higher expression in the latter. The expression of the TGFB isoforms studied was also altered during folliculogenesis in both the spontaneous and ACTH‐induced COD groups. As it has been previously shown that TGFB influences steroidogenesis, ovarian follicular proliferation and apoptosis, an alteration in its expression may contribute to the pathogenesis of this disease.  相似文献   

6.
The aim of this study was to prove if oxidation-reduction levels in the follicular fluid were new functional indices of follicular health and whether there was a high level of accordance with endocrinological parameters and with the growth stage as detected by ultrasound monitoring of individual follicles during the oestrous cycle in mares. Follicles were classified as growing and regressing follicles using ultrasonography. Altogether 48 follicles with a diameter from 20 to 56 mm were aspirated by transvaginal ultrasound guided follicular aspiration. Follicular concentration of oestradiol and progesterone in relation to the diameter of growing follicles showed correlations of r = 0.64 and r = 0.57, respectively. The redox potential derived index D2 varied from -448 to +431 in the collected fluids of the follicles. The accordance of the judgement of all follicles using both complexes of methods - endocrinological and ultrasonographic parameters vs. analysis of oxidation and reduction levels - reached 72.5%. This finding has shown that parameters of redox reactions do not correlate closely with the stage of follicular growth or regression as determined by in vivo scanning of ovaries or by assessment of follicular steroid concentrations. However, the measurement of redox potentials offers an opportunity to examine the whole process of metabolism in follicular cells and to forecast impairments of cellular performances. Changes of redox parameters in growing follicles enable an earlier prediction of their further development. The data demonstrate that growing and regressing follicles do not represent nonatretic, early atretic and atretic follicles, respectively.  相似文献   

7.
Estrous cycles of heifers (n = 137) were synchronized with prostaglandin (PGF2α) and follicular development stimulated with follicle stimulating hormone. Twenty-eight animals were administered Norgestomet implants 12 hr prior to the initial PGF2α injection to suppress the LH surge that initiates ovulation. Animals were ovariectomized every 12 hr after the initial PGF2α (7–9/time, 12–108 hr and at 192 and 240 hr post PGF2α) and divided into three treatment groups to consist of: 1) animals exhibiting a normal luteinizing hormone (LH) surge (n = 86), 2) animals in which no LH surge was detected (n = 23), and 3) suppression of the LH surge via Norgestomet implants (72–108 hr, n = 28). Follicular diameter was measured and follicular fluid was collected for analysis of prolactin, estradiol, progesterone and glycosaminoglycan concentrations. Progesterone concentrations were increased in animals exhibiting an LH surge as compared to animals in which no LH surge was detected; primarily in large follicles (> 8 mm diameter) after the LH surge. Animals not exhibiting an LH surge also had increased follicular progesterone concentrations compared to Norgestomet-implanted animals (242.3 ± 36.3 vs 86.7 ± 6.4 ng/ml, respectively, P < .01), indicating some LH stimulation. Follicular estradiol in animals exhibiting an LH surge increased up to the time of LH surge detection and then declined whereas animals with no LH surge detected had follicular estradiol concentrations that declined after the PGF2α injection. No differences were noted between those that did not exhibit an LH surge or in which the LH surge was suppressed with Norgestomet in relation to follicular estradiol concentrations. Follicular estradiol concentrations increased with follicular size in all treatment groups (P < .01). Follicular concentrations of prolactin were increased in small follicles (P < .05; ≤ 4 mm diameter) and follicular prolactin increased from 12 to 36 hr post PGF2α injection, then declined after the LH surge. Follicular glycosaminoglycan concentrations decreased with increases in follicular size (P < .01) and were higher in animals that did not exhibit an LH surge (P < .01). No differences in follicular glycosaminoglycans were noted between Norgestomet-implanted animals and those not exhibiting an LH surge. In the animals representing days 4 and 6 of the subsequent estrous cycle (192 and 240 hr post PGF2α), numbers of small-sized follicles were increased. Follicular progesterone and estradiol concentrations were related to atretic large follicles unovulated from the prior estrus and a wave of growth in small and medium follicles. Follicular prolactin and glycosaminoglycans increased with time of the new estrous cycle and were increased in smaller follicles (P < .01). Suppression of LH with progestin implants (Norgestomet) may relate to early effects of progesterone, which may not be totally eliminated at target tissues and subsequently alters the LH surge, steroidogenesis of the follicle, and ovulation. Oocytes were predominantly found in the follicular fluid from animals in which an LH surge was detected and in the buffer wash of follicles in which no LH surge was detected. Oocyte viability was higher in animals exhibiting an LH surge (75% viable) whereas the oocytes of Norgestomet-implanted animals were 75% degenerate.  相似文献   

8.
Because IGFBP inhibit IGF-stimulated cellular proliferation and differentiation, it is hypothesized that variations among IGFBP in individual follicles might contribute to the regulation of recruitment, selection, dominance, and turnover of ovarian follicles. Sources of IGFBP in fluid of bovine follicles are not well established; thus, objectives of this study were to determine levels of IGFBP binding activities and messenger RNA (mRNA) in granulosa and theca interna cells at different stages of follicular development (small [< 6 mm], medium [6 to < 8 mm], and large [> or = 8 mm]) and to characterize associations of these levels measured in the cells with levels of IGFBP and steroids in follicular fluid. Thecal and granulosa cells from large healthy follicles contained two- to twentyfold less (P < 0.05) IGFBP-2, -3, and -5 than cells from small, medium, and large atretic follicles. Thecal cells from small, medium, and large atretic follicles contained more (P < 0.05) IGFBP-3 and -4 than granulosa cells from these follicles, whereas granulosa cells from these follicles contained more IGFBP-2 activity than thecal cells. Differences in IGF binding activity were paralleled by differences in levels of mRNA for the respective IGFBP. Developmental differences in IGFBP activity in follicular fluid were positively associated with activity in granulosa and/or thecal cells, with the exception of IGFBP-4, which was low in fluid from large healthy follicles but markedly increased (mRNA and binding activity) in granulosa cells from these follicles. It is concluded that developmental changes in follicular fluid IGFBP-2 and -5 binding activities seem to be controlled in part by alterations in synthesis of these IGFBP by granulosa and thecal cells, whereas diminished IGFBP-4 in fluid from large healthy follicles occurs concomitantly with increased levels of IGFBP-4 mRNA and activity in granulosa cells, implicating posttranslational regulation by specific proteases.  相似文献   

9.
Large multiple cystic ovarian follicles were induced in three sows and small multiple cystic ovarian follicles were induced in three other sows by injections of adrenocorticotrophic hormone (ACTH) during the follicular phase of the oestrous cycle. Plasma progesterone levels in sows with large cysts were relatively high, while those of sows with small cystic follicles were low. Removal of the ovaries with large cysts from one sow resulted in a precipitous drop in progesterone levels indicating that the large cysts were primarily the source of progesterone. The method by which ACTH may induced cystic ovaries was also investigated. Plasma progesterone levels in two ovariectomised sows during ACTH treatment fluctuated markedly during a 24 h period achieving peak values of 4 or 5 ng/ml. The results suggest that progesterone of adrenal cortical origin may be a factor in the development of the cystic ovarian condition.  相似文献   

10.
Several studies have clarified that the follicular cysts degenerate and are replaced by newly growing follicles that develop into new follicular cysts without ovulation, i.e., turnover of ovarian follicular cysts in cows. However, the relativity of endocrinological changes, including the inhibin profile during turnover of spontaneous follicular cysts in dairy cows, is still unclear. In the present study, the relationship between turnover of follicular cysts and changes in the peripheral blood concentrations of progesterone (P), estradiol-17beta (E(2)), luteinizing hormone (LH), follicle stimulating hormone (FSH) and inhibin were examined in lactating dairy cows. Five cows diagnosed with follicular cysts (follicles of more than 25 mm in diameter in the absence of a corpus luteum) were investigated. Their ovarian dynamics were monitored using ultrasonography, and blood samples were collected at 2- or 3- day intervals throughout the experiment. The day when a follicle fated to become a follicular cyst reached more than 8 mm in diameter was defined as the start of a cystic follicular wave. Four of the 5 cows exhibited a similar patterns of cystic follicular changes and hormone profiles. The data from the 4 cows was used for analysis of the relationships between turnover of cystic follicles and the hormone profiles. Two or three new cystic follicular waves occurred in each cow during the experimental period. The mean diameter of the cystic follicles was more than 25 mm 13 to 15 days after the start of the cystic follicular wave, and it began to decrease 1 to 6 days before the start of the subsequent cystic follicular wave. The levels of E(2) and inhibin tended to decrease for 7 to 9 days before the start of a new cystic follicular wave and to increase concomitantly with new follicular cyst growth. The levels of FSH rose for 1 to 3 days before the start of a new cystic follicular wave. The present study clarified the relationship between FSH and inhibin during turnover of spontaneous follicular cysts in dairy cows and found that it was very similar to previous results for cows. The present results suggest that an increase in FSH secretion following a reduction in inhibin secretion triggers turnover of cystic follicles in cows with spontaneous follicular cysts.  相似文献   

11.
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12.
To determine influences of insulin and body condition on follicular growth, prepuberal gilts (n = 16) treated with pregnant mare's serum gonadotropin (PMSG) were used in a 2 X 2 factorial experiment with main effects of insulin (0 or .4 IU/kg every 12 h beginning at 1800 on the day before PMSG) and backfat depth (moderate, 25 +/- .8; high, 32 +/- .7 mm; P less than .0001). Body weights were similar. Blood sampling was at 6-h intervals for analyses of LH, FSH, growth hormone (GH), glucagon, cortisol, insulin, insulin-like growth factor-I (IGF-I), plasma urea nitrogen (PUN), nonesterified fatty acids (NEFA), testosterone, estradiol-17 beta, and progesterone. Ovaries were removed 75 h after PMSG treatment, and visible small (less than or equal to 3 mm), medium (4 to 6 mm), large (greater than or equal to 7 mm), and macroscopically atretic follicles were counted. Administration of insulin increased IGF-I in fluid of medium follicles (108.8 vs 60.7 ng/ml; SEM = 13.3; P less than .05). Neither insulin nor fatness affected hCG binding by granulosa cells (12.5 +/- 1.6 ng/10(6) cells) or numbers of large (16.7 +/- 2.6) and medium (10.4 +/- 2.3) follicles. However, insulin increased the number of small follicles (58.9 vs 29.9; SEM = 9.7; P less than .05) and reduced the number of atretic follicles (3.8 vs 11.3; SEM = 1.1; P less than .05). The predominant effect of insulin on reducing number of atretic follicles was in the small size class (.6 vs 6.9; SEM = .6, P less than .01). Follicular fluid estradiol and progesterone were not affected by treatments; however, testosterone concentrations in large follicles were lower in gilts with higher backfat (32.5 vs 59.9 ng/ml; SEM = 4.0; P less than .05). Systemic LH, FSH, glucagon, cortisol, PUN, NEFA, estradiol, and testosterone were not affected by insulin or level of feeding. However, GH was lower in gilts that had higher backfat (overall average of 3.2 vs 2.8 ng/ml; SEM = .1; P less than .05). Insulin reduced atresia and altered intrafollicular IGF-I independently of body condition and without sustained effects on other hormones.  相似文献   

13.
To investigate some biochemical changes during bovine follicle development, ovaries were obtained from cyclic heifers (7 to 11 heifers/d on each day of the 21-d estrous cycle; N = 152). Follicular fluid from the two largest follicles from both ovaries and a pool from small follicles (N = 30/cow) were collected from each animal and analyzed for ionic, enzymatic and endocrine changes in relation to day of the estrous cycle, follicle size, rank and atretic or growing status. Follicular fluid alkaline phosphatase activity and ascorbate concentrations were highest in all follicular sizes during the earlier portion of the estrous cycle (d 1 to 12; P less than .05), then decreased to the lowest levels (d 13 to 21). As follicular size (diameter) increased lactate dehydrogenase (LDH), acid and alkaline phosphatase activity was reduced in follicular fluid (P less than .05). Alkaline phosphatase and LDH activity tended to be increased in atretic follicles (P less than .10), and was correlated with increased progesterone and androgen concentrations of follicular fluid (r = .4, P less than .05). Both albumin and total protein concentrations decreased as follicular diameter increased (P less than .05). Sodium concentrations in follicular fluid were greater in growing-antral than atretic follicles, and increased with follicular enlargement (P less than .05). Follicular potassium concentrations increased as the estrous cycle progressed (P less than .05), and tended to be elevated in atretic follicles (nonsignificant). Both Ca and Mg concentrations increased with follicular enlargement (P less than .05). Dehydroepiandrosterone and testosterone were the predominant androgens in follicular fluid (androstenedione, the lowest concentration); their concentration decreased with follicle development (P less than .05), but were quite variable. Estradiol was increased in growing follicles (P less than .01). Estrone and estradiol concentrations increased as ovulation approached, particularly in small follicles (less than or equal to 4 mm diameter). Changes of biochemical components found in follicular fluid that relate to the growth and atresia process may provide a more sensitive and accurate method to classify follicle status, and thus aid in understanding the complexity of events associated with maturation of the bovine follicle and oocyte.  相似文献   

14.
The potential reproduction power of domestic animals is limited by a complicated follicular atresia process. P53, caspase-9 (Casp9), Bax, Bcl-2 and Fas play a crucial role in the ovarian mitochondrion-dependent apoptosis and death receptor pathway. In accordance with this study, the expression levels of Casp9, Bax, Bcl-2 and Fas were analysed in ovaries and oviducts of yak by immunohistochemistry (IHC). P53 and the above in ovarian granulosa cells (GCs) from atretic (3–6 mm) to healthy follicles (6–8 mm) and in oviducts were examined from the luteal phase to the follicular phase during the oestrous circle by Western blot (WB) and real-time PCR (RT-PCR). Results demonstrated that typical classic apoptotic factors Casp9, Bax, Bcl-2 and Fas were expressed in the cytoplasm and zonal pellucida of oocytes, primordial follicles, primary follicles, ovarian surface epithelium, ovarian GCs, granular lutein cells, surface epithelia in oviduct uterotubal junction and oviduct ampulla during the luteal phase. RT-PCR and WB revealed that P53 and Fas significantly increased in GCs of atretic follicles. P53 and Casp9 increased in oviduct epithelium during the luteal phase, but Fas was unchanged. A contrary tendency was noted in Bcl-2 and Bax expression. Overall, P53 and Fas play an essential role in inducing GC apoptosis, and Bax, Bcl-2, Casp9 and P53 are involved in oviduct epithelial regeneration in yak.  相似文献   

15.
Microdialysis System (MDS) is a novel technique used for investigation of molecule secretion between different cell populations. Local hormonal secretion at follicular wall has been still unclear. This MDS study was used to determine progesterone (P4), androstenedione (A4), estradiol-17beta (E2) and Prostaglandin F2alpha (PGF2alpha) release in mare pre-ovulatory follicles. Follicles larger than 30 mm were isolated from the ovary and follicular fluid aspirated for hormone assay. Follicular fluid collected from small, middle and large follicles were analyzed by EIA. The concentrations of P4 and PGF2alpha were similar among the different sizes of follicles. The release of A4 was observed in middle and large follicles. E2 concentration was observed in middle follicles and was higher in large follicles compared with middle follicles. Follicular wall was cut and incubated for MDS and when LH was infused, there was an increase in P4 and A4 release. PGF2alpha release was considerably high after LH infusion compared to the control group. Infusion of PGF2alpha increased P4 and A4 release but there was no change in E2 release. This results suggest that in pre-ovulatory follicles, LH stimulates theca interna cells and also PGF2alpha seemed to have a mediator role to induce steroid hormone production and luteinization of follicular cells. The nature of the mechanisms involved in selection of large follicles is still a perplexing research problem in reproduction.  相似文献   

16.
Impaired reproductive performance exhibited by the domestic sow during the late summer and early autumn months is referred to as seasonal infertility. This study was carried out to determine whether there are changes in ovarian morphology and follicular steroidogenesis associated with season, which may be associated with seasonal infertility. Ovaries were collected in pairs from sows sourced from two farms and slaughtered 4 days after weaning during winter and summer. The mean progesterone concentration in follicular fluid (FF) collected from small follicles was lower in summer (701.3 ± 115.54 nm) compared with winter (1235.55 ± 164.47 nm; p<0.001). The mean progesterone concentration in the FF of large follicles was also lower in summer (1469.2 ± 156.51 nm) compared with winter (2470.9 ± 169.13 nm; p<0.001). The number of large surface antral follicles (5-8 mm in diameter) on the ovaries recovered from Farm A sows was higher during summer (17.76 ± 0.56) than in winter (15.38 ± 0.54; p<0.05). Similarly, the number of small follicles (3-4 mm in diameter) on Farm A sow ovaries was higher in summer (8.46 ± 0.66) than in winter (4.63 ± 0.53; p<0.001). In contrast, the number of small follicles on the surface of ovaries recovered from Farm B sows was higher during winter (10.17 ± 1.50) than in summer (6.45 ± 1.00; p<0.01). The number of pre-ovulatory follicles (>8 mm in diameter) was also higher in winter (1.23 ± 1.68) when compared to summer (0.51 ± 0.3; p<0.001) on the ovaries of sows from Farm B. The results suggest that there are seasonal differences in follicular steroidogenesis and ovarian dynamics. These findings add support to the theory that altered follicular steroidogenesis and ovarian morphology may possibly be the mechanism behind reduced reproductive performance during the period of seasonal infertility in sows.  相似文献   

17.
Factors that affect ovarian follicular dynamics in cattle.   总被引：1，自引：0，他引：1  
Studies of ovarian follicular dynamics in cattle may lead to methods for improving fertility, for synchronizing estrus with more precision, and for enhancing superovulatory responses. Within an estrous cycle, two or three large (> 10 mm) follicles develop during consecutive waves of follicular growth. The last wave provides the ovulatory follicle, whereas preceding wave(s) provide follicles that undergo atresia. The life span of large follicles seems to depend on the pulsatile secretion of LH; decreased frequency of LH pulses results in atresia of large follicles. Aromatase activity in the walls of the largest follicles is greatest during the first 8 d of the estrous cycle and decreases by d 12. Steroidogenesis of the largest and second-largest ovarian follicles differs on d 5, 8, and 12 of the estrous cycle. Follicular dynamics are altered by negative energy balance and lactation. The number of large follicles and concentration of estradiol during the preovulatory period differs between postpartum lactating and nonlactating cows. Dietary fats stimulate follicular growth when they are fed to increase energy balance. Administration of bovine somatotropin decreases energy balance and has a differential effect on ovarian follicular responses; growth of the largest follicle does not change, but growth of the second-largest follicle is stimulated by somatotropin. Studies of follicular dynamics in lactating cows demonstrate changes in ovarian function associated with energy balance that may be related to inefficient reproductive performance of cows producing high yields of milk.  相似文献   

18.
The aim of the study was to investigate the histological characteristics and steroid concentrations in follicular fluid of different populations of follicles at different stages of development, during pregnancy and the oestrous cycle in cows. Follicles from ovaries collected at a slaughterhouse were allocated into three size categories (small, 2–5.9 mm; medium, 6–13.9 mm; and large, 14–20 mm) in pregnant and non-pregnant cows. Slices were stained with HE and PAS for histological analysis. Follicular fluid was pooled according to size and pregnancy status and estradiol, testosterone and progesterone concentrations in follicular fluid were determined by RIA. Characteristics of healthy follicles did not differ, regardless of follicle size or pregnancy status. Total histological atresia was significantly higher in pregnant cows than in non-pregnant cows (p < 0.05). Estradiol increased and testosterone decreased significantly, while follicles increased in size, in both non-pregnant and pregnant cows (p < 0.05). Nonpregnant cows had the highest estradiol values in follicles of all sizes. Medium and large follicles from pregnant cows showed the lowest testosterone concentration (p < 0.05). Progesterone levels increased with follicle size only in non-pregnant animals. In large follicles, progesterone concentration was significantly higher in non-pregnant cows than in pregnant cows (p < 0.05). Considering steroid concentration and histological findings, most large follicles might be atretic during pregnancy in cattle.  相似文献   

19.
The reproductive cycle of the domestic dog features a long period of relative ovarian inactivity or anestrus. The mechanism of anestrous termination/oestrous resumption is not yet fully understood, which presents a challenge to the development of oestrous induction protocols. In this study, we assess the possibility that anti‐Müllerian hormone (AMH) might play a role in this transition by characterizing its patterns of expression in the circulation during the transition from anestrus to oestrous and in all stages of ovarian follicular growth. Serum samples from five beagles (2.0–4.5 years) were collected three times per week at least 30 days prior to the onset of oestrous and assessed for AMH concentrations. Serum AMH concentration increased significantly during the transition from anestrus to proestrus and then declined back to the anestrous baseline beginning on day ?4 before the luteinizing hormone surge, which was determined by changes in serum progesterone concentrations. Cortical sections of ovaries from females undergoing routine ovariohysterectomy (aged 8 months–5 years, n = 4) were evaluated for AMH by immunohistochemistry. Pre‐antral and small antral follicles were most strongly immunoreactive for AMH. These data suggest that the increase in the number of antral follicles is associated with the rise in serum AMH as the anestrous period comes to an end. The rise in AMH might be useful in predicting the onset of oestrus and therefore assist with the optimization of oestrous induction protocols and possibly other assisted reproductive technologies.  相似文献   

20.
As dogs experience oestrus only once or twice a year, it is necessary to establish an effective method of oestrous induction for efficient breeding. In the present study, we evaluated inhibin antiserum (IAS) on oestrous induction in anoestrous females. Bitches were administered 0.5 ml/kg IAS or a mixture of 50 IU/kg equine chorionic gonadotropin (eCG) and 0.5 ml/kg IAS and 500 IU human chorionic gonadotropin (hCG) administered 7 days after the mixture injection. As a control, bitches received 50 IU/kg eCG, with 500 IU hCG administered 7 days after eCG injection. Blood-tinged vaginal discharge, vulvar swelling, plasma progesterone concentrations and ovarian follicular development were assessed from day 0 to day 14. IAS alone injection did not induce oestrus in bitches at the anoestrous stage. Conversely, vulvar swelling, blood-tinged vaginal discharge and an estimated luteinizing hormone (LH) surge appeared on days 3–7, days 3–6 and days 7–9 after the IAS+eCG mixture injection, respectively, in all five bitches at the anoestrous stage. The average number of developing and ovulated follicles in bitches administered IAS+eCG was 8.8 and 9.6 respectively. A single eCG injection followed by hCG induced oestrous signs, with an average of 8.3 developing follicles and 4.5 ovulated follicles. This study revealed that IAS alone did not induce oestrus, but when IAS was used in combination with eCG, it induced oestrus and promoted a considerable number of ovulations in anoestrous dogs.  相似文献   

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