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1.
Angus x Hereford heifers were used to determine endocrine and ovarian function preceding nutritionally induced anovulation. Six heifers were fed to maintain body condition score (M), and 12 heifers were fed a restricted diet (R) until they became anovulatory. Starting on d 13 of an estrous cycle, heifers were given PGF2alpha every 16 d thereafter to synchronize and maintain 16 d estrous cycles. Ovarian structures of M and R heifers were monitored by ultrasonography daily from d 8 to ovulation (d 1 of the subsequent cycle) until R heifers became anovulatory. Concentrations of LH and FSH were quantified in serum samples collected every 10 min for 8 h on d 2 and 15 (48 h after PGF2alpha), and estradiol and IGF-I were quantified in daily plasma samples from d 8 to 16 during the last ovulatory cycle (Cycle -2) and the subsequent anovulatory cycle (Cycle -1). During the last two cycles before anovulation, M heifers had 50% larger (P < .0001) ovulatory follicles than R heifers and 61% greater (P < .0001) growth rate of the ovulatory follicles. There was a treatment x cycle x day effect (P < .001) for concentrations of estradiol. The preovulatory increase in estradiol occurred in the R and M heifers during Cycle -2 but only in M heifers during Cycle -1. A treatment x cycle x day effect (P < .05) influenced LH concentrations. During Cycle -2, LH concentrations were similar for M and R heifers, but during Cycle -1, M heifers had greater LH concentrations than did R heifers. Concentrations of FSH were greater (P < .05) in R than M heifers after induced luteolysis when R heifers failed to ovulate. There was a treatment x cycle interaction (P < .05) for IGF-I concentrations, and M heifers had 4.7- and 8.6-fold greater IGF-I concentrations than did R heifers during Cycle -2 and -1, respectively. We conclude that growth rate and diameter of the ovulatory follicle, and concentrations of LH, estradiol, and IGF-I are reduced before the onset of nutritionally induced anovulation in beef heifers.  相似文献   

2.
Heifers treated with ivermectin at weaning have been reported to reach puberty at a younger age and lighter weight than untreated heifers. We tested the hypothesis that heifers administered ivermectin would respond with earlier follicular development and a greater LH response to a 1-mg estradiol-17beta challenge (E2C) than untreated heifers. Fall-born Angus heifers (n = 32) were randomly assigned on 284 +/- 9 d of age (215.5 +/- 20.8 kg) to receive ivermectin (IVR) or albendazole (ALB), IVR + ALB, or to remain as untreated controls (CONT). Each group (n = 8) was housed separately in adjacent pens throughout the trial and managed to gain .8 kg/heifer on a ration containing 13.2% CP, 58.8% TDN, and 49.9% DM. The CONT heifers received an additional 2.27 kg/heifer of corn silage and 1.59 kg/heifer of corn daily to maintain ADG at comparable levels. Individual body weight was recorded weekly, and nematode eggs per gram (EPG) of feces were measured every 21 d. Ultrasonography was performed on alternate days starting 2 wk prior to E2C to characterize follicular wave patterns. Follicles were separated into classes (C1 [3 to 5 mm], C2 [6 to 9 mm], and C3 [10 mm]) and sizes (largest [LF], second [SLF], third [TLF], and fourth largest follicles [FLF]). The sizes of the regressing dominant follicle 1 (DF1) and the progressing dominant follicle 2 (DF2) were also determined. Serum concentrations of LH were determined from hourly jugular blood samples collected 8 to 24 h after injection of E2C. The IVR + ALB treatment group had more C3 follicles than ALB and CONT (P < .07). The IVR-treated heifers had larger TLF than ALB and CONT (P < .04). The IVR- and IVR + ALB-treated heifers had larger FLF and DF2 than ALB and CONT (P < .1). Least squares means for DF2 were 9.5 +/- .5, 8.0 +/- .4, 9.5 +/- .3 and 8.3 +/- .3 mm, for IVR, ALB, IVR + ALB and CONT, respectively (P = .02 for treatment effect). The E2C-induced serum LH concentration did not differ with respect to treatment. We conclude that heifers administered IVR display increased follicular development, supporting our earlier investigations regarding reduced age at puberty in heifers treated with IVR near weaning.  相似文献   

3.
The follicle and hormone aspects of diameter deviation and development of one dominant (≥28 mm) follicle (1DF) vs two dominant follicles (2DF) were studied in 32 ovulatory follicular waves in mares. Follicles were ranked each day as F1 (largest) to F3. The beginning of deviation was designated day 0 and preceded the first increase in the differences in diameter between F1 and F2 in the 1DF group and between a combination of F1 and F2 vs F3 in the 2DF group. One dominant follicle and 2DF developed in 21 (66%) and 11 (34%) waves, respectively. Double ovulations occurred in only one of the waves with 2DF. In 8/11 waves with 2DF, a second deviation occurred between F1 and F2 on 2.5 ± 0.4 days after the first deviation. On day 0, 1DF and 2DF waves were similar in number of days after ovulation, number of follicles, difference in diameter between F1 and F2, and plasma concentrations of LH, estradiol and immunoreactive inhibin. The interval from maximum FSH concentration to day 0 was longer (p < 0.05) and FSH concentration was lower (p < 0.05) on days -1 to 4 in the 2DF group. The similarities on day 0 in the characteristics of 1DF and 2DF waves despite the differences in the declining portions of the FSH profile indicated that a specific day of the FSH decline or a specific concentration were not factors in initiating deviation. Unlike reported results in heifers, the results in mares did not indicate a hormonal basis for the development of 2DF or two deviations.  相似文献   

4.
The effects of estradiol-17beta (E-17beta) or estradiol benzoate (EB) on gonadotrophin release, estrus and ovulation in beef cattle were evaluated in two experiments. In experiment 1, 16 ovariectomized cows received a previously used CIDR insert from days 0 to 7 and 1mg of EB on day 8; they also received 5mg of E-17beta on days 0 or 1, or 5mg of E-17beta+100mg of progesterone on day 0. There was only an effect of time (P<0.0001) on plasma concentrations of progesterone, estradiol, FSH, and LH. Following treatment with E-17beta, plasma FSH concentrations were suppressed for approximately 36 h, whereas plasma LH concentrations were reduced (P<0.05) for 6 h, but surged within 24 h. Injecting 1mg of EB 24 h after CIDR removal decreased (P<0.02) plasma LH concentrations for 6h, followed by an LH surge at 18 h. In experiment 2, ovary-intact heifers (n=40) received a used CIDR and 5mg of E-17beta+100mg of progesterone on day 0. On day 7, CIDR were removed, PGF given, and heifers received nothing (control) or 1mg of EB 12, 24, or 36 h later. In these groups, plasma LH peaked (mean+/-SEM) 78.0+/-23.0, 37.8+/-8.5, 44.4+/-10.3, and 51.0+/-5.1 h after CIDR removal (means, P<0.001; variances, P<0.001) and intervals from CIDR removal to ovulation were 102.0+/-6.7, 63.6+/-3.6, 81.6+/-3.5, and 78.0+/-4.1h (P<0.05). The interval from CIDR removal to ovulation was shorter and less variable in EB-treated groups; the interval from EB to ovulation was shortest (P<0.05) in the 12-h group. In summary, E-17beta or EB decreased both FSH and LH, but LH increased after 6h (despite elevated progesterone concentrations). Following CIDR removal, 1mg of EB effectively synchronized LH release, and ovulation (in intact cattle), but the interval from CIDR removal to EB treatment affected the time of ovulation.  相似文献   

5.
The working hypotheses in this experiment were: that ovarian estradiol would inhibit luteinizing hormone (LH) secretion in heifers that were anestrus as a result of restricted dietary energy intake and the responsiveness of LH secretion to estradiol negative feedback would decrease during the period when restoration of estrous cycles occurred following feeding of diets adequate in energy. Fifteen heifers weighing 341 +/- 12 (mean +/- SE) kg were fed a diet containing 50% of the energy required for maintenance until 40 to 50 d following cessation of estrous cycles. Heifers were assigned to intact control (C, n = 5), ovariectomized (OVX, n = 5) or ovariectomized-estradiol-17 beta-implanted (OVX + E2, n = 5) treatments. Heifers were subsequently provided a high-energy (HE) diet until termination of the study. Progesterone concentrations indicating cessation of corpus luteum function were detected after heifers had lost 71 +/- 8 kg body weight over 186 +/- 28 d. Control heifers re-initiated estrous cycles as indicated by increased progesterone concentrations in serum at 49 +/- 9 d after initiation of feeding the HE diet (360 +/- 18 kg body weight). Initiation of pulsatile LH secretion was observed in heifers by d 12 following OVX. Estradiol suppressed LH secretion in OVX + E2 heifers during the period of nutritional anestrus in C heifers. Suppressive effects of E2 on LH secretion continued in OVX heifers after C heifers had initiated corpus luteum function. Therefore, the working hypothesis that LH secretion is inhibited by E2 in the nutritionally anestrous heifer is accepted but responsiveness to estradiol does not subside with re-initiation of estrous cycles, thus this working hypothesis is rejected.  相似文献   

6.
An experiment was conducted to test the hypothesis that 17 beta-estradiol (E2) would not suppress secretion of luteinizing hormone (LH) in heifers fed a diet limited in energy during the period before the onset of nutritionally induced anestrus. Sixteen of 20 heifers that had been exhibiting normal estrous cycles (20 mo of age, 409 +/- 6 kg body weight) were ovariectomized, and half of them were assigned at random to receive an E2 implant. The ovariectomized heifers were assigned at random to receive diets that contained low (L; 5.8 Mcal X animal-1 X d-1, n = 8) or high levels of energy (H; 20.0 Mcal X animal-1 X d-1, n = 8) for 100 d. The other four heifers remained intact and were fed the L-diet. The intact heifers were utilized to determine the status of reproductive function in animals fed the L-diet. Heifers lost body weight rapidly after initiation of feeding the L-diet. Heifers fed the L-diet then stabilized at a lighter weight until the latter part of the experiment. One of the four intact heifers fed the L-diet became anestrus near the end of the study. Mean concentrations of LH in blood serum increased linearly (P less than .05) in ovariectomized heifers fed the L- and H-diet. Mean concentration of LH in heifers fed the H-diet that were implanted with E2 was similar to ovariectomized heifers fed the H-diet that received no E2. Mean LH in serum of ovariectomized heifers implanted with E2 fed the L-diet was suppressed and remained low throughout the study. Frequency of pulses of LH in ovariectomized heifers fed the L-diet was less (P less than .01) than that in ovariectomized heifers fed the H-diet. Estradiol decreased the number of pulses of LH in heifers fed the L-diet. We conclude that dietary energy restriction in beef heifers has a direct action on the hypothalamo-pituitary axis to lower the number of pulses of LH in the absence of ovarian steroids. However, ovarian E2 appears to suppress further secretion of LH in heifers fed limited levels of dietary energy before the onset of nutritional anestrus occurs, therefore, our working hypothesis is rejected.  相似文献   

7.
Two homologous radioimmunoassays for bovine follicle stimulating hormone (bFSH) were utilized in comparing the differential regulation of FSH and luteinizing hormone (LH) in response to ovariectomy or administration of gonadal steroids in cattle. There appeared to be significant LH cross-reactivity in one of the bFSH systems (bFSH-HS-2-17), but not in the other (bFSH-BP3). Concentrations of FSH in plasma measured by these two systems suggested both qualitative and quantitative differences. Following ovariectomy in heifers, LH concentrations in plasma were increased by 7.5 h, while FSH (measured in the bFSH-BP3 system) was not significantly elevated until 18 h. Administration of 200 micrograms of estradiol-17 beta to ovariectomized heifers inhibited levels of FSH in plasma but large doses of testosterone (100 mg), androstenedione (400 mg) and dihydrotestosterone (800 mg) had no effect. Similarly, LH was not affected by the androgens, while estradiol induced LH surges, leading to increased mean LH concentrations. In contrast to the results in heifers, LH concentrations in plasma from steers were inhibited by administration of androgens as well as by estradiol. In steers, FSH (bFSH-BP3) was marginally inhibited by estradiol and not at all by the androgens. Differences in the secretory patterns of FSH and LH also occurred in intact heifers during the estrous cycle. The 72-h period preceding estrus (follicular phase) was characterized by rapidly declining serum progesterone concentrations, followed by concurrent increases in both LH and estradiol. The circulating levels of bFSH (BP3) tended to decline during this interval. Overall, during the estrous cycle, progesterone levels were positively correlated with bFSH-BP3 (r = .37) and negatively correlated with LH (r = -.39). The gonadotropins were not significantly related (r = -.15). These relationships are consistent with the concept that LH controls the final stages of follicular development in cattle and that FSH may exert only a permissive effect.  相似文献   

8.
In domestic animals limited data are available concerning levels of pituitary luteinizing hormone-releasing hormone (LHRH) receptors during various physiological states. The objectives of this study were to quantify anterior pituitary gonadotropin and LHRH receptor concentrations in cycling, noncycling and early pregnant beef heifers. To accomplish these objectives, five heifers each were slaughtered, after synchronization with prostaglandin F2 alpha (PGF2 alpha), on d 0 (estrus), 7 and 14 of the estrous cycle and d 40 of pregnancy. Four heifers determined to be noncycling were also slaughtered. Pituitaries were collected and analyzed for LHRH receptor and gonadotropin concentrations. Pituitary luteinizing hormone (LH) concentrations were low on d 0 (1.4 +/- .2 micrograms/mg pituitary, mean +/- SE) and remained low on d 7 (1.4 +/- .1 micrograms/mg pituitary) before increasing (P less than .01) on d 14 (2.6 +/- .5 micrograms/mg pituitary). Luteinizing hormone concentrations, compared with d 0, were also elevated (P less than .01) in noncycling (NC; 2.6 +/- .2 micrograms/mg pituitary) animals and in 40-d pregnant (PG; 2.5 +/- .2 micrograms/mg pituitary) heifers. Pituitary follicle stimulating hormone (FSH) concentrations, though similar (P greater than .05) for all groups, paralleled changes in LH concentration. Pituitary LHRH receptor binding affinity did not differ (P greater than .05) among groups, with an overall Kd = .64 +/- .02 X 10(-9) M. Luteinizing hormone-releasing hormone receptor concentrations were highest on d 0 (1.09 +/- .12 fmol/mg pituitary) and fell (P less than .01) to low levels on d 7 (.75 +/- .11 fmol/mg pituitary).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

9.
In cattle, prolonged progestogen treatments following luteolysis result in persistent dominant follicles (DF) that are associated with precise onset of estrus but marked reductions in pregnancy rate (PR). The aim was to determine whether increasing duration of dominance of the ovulatory follicle in heifers affected 1) precision of onset of estrus and 2) the timing and nature of the decline in PR. In Exp. 1, duration of dominance of the ovulatory follicle was controlled by causing corpus luteum (CL) regression at emergence of the second follicle wave (mean duration of dominance of 2.1+/-.3 d, Dm2, n = 11) or first day of dominance of the second DF of the cycle; the latter was combined with insertion of a 3-mg norgestomet ear implant for 2 to 10 d to maintain the second DF for 4 (Dm4, n = 32), 6 (Dm6, n = 19), 8 (Dm8, n = 49), 10 (Dm10, n = 28), or 12 d (Dm12, n = 20). Heifers detected in estrus were inseminated approximately 12 h later with frozen-thawed semen. Durations of dominance of the ovulatory follicle of up to 8 d did not affect (P>.05) PR (Dm2 8/9, Dm4 19/28, Dm6 14/18, and Dm8 34/48 heifers pregnant), but PR in Dm10 heifers (12/23 heifers pregnant) was reduced (P = .05) compared with Dm2 heifers; PR in Dm12 heifers (2/17 pregnant) was less compared with all other treatments (P<.01). Fitting a logistic regression model to the pooled PR data to examine the trend in PR showed that extending the duration of dominance from 2 to 9 d and from 10 to 12 d resulted in a predicted decline in PR of 10 to 25% and a further decline of 35 to 75%, respectively. Onset of estrus was delayed in heifers assigned to Dm4 treatment relative to all other treatments (P<.001); it was less variable than that for heifers on Dm6, Dm8, and Dm10 treatments (P<.1). In Exp. 2, heifers received a PGF2alpha analogue and a norgestomet implant on d 12 of the cycle for 3 or 7 d to give approximate durations of dominance of the preovulatory follicle of 2 to 4 d (Dm2-4, n = 29) or 6 to 8 d (Dm6-8, n = 24), respectively. The PR did not differ (P>.05) between heifers on Dm2-4 (22/29) and Dm6-8 (15/24) treatments, but the interval to onset of estrus was delayed (P<.05) by 7 h in the Dm2-4 heifers. In conclusion, restricting the duration of dominance of the preovulatory follicle to < or =4 d at estrus, results in a precise onset of estrus and a high PR following a single AI at a detected estrus.  相似文献   

10.
In beef heifers weaned between 3 and 4 mo of age and fed a high-concentrate diet, approximately 50% reach puberty before 300 d of age (precocious puberty). The objectives of this experiment were 1) to determine whether precocious puberty could be induced experimentally by weaning heifers early and feeding a high-concentrate diet, and 2) to determine the dynamics of secretion of LH associated with precocious puberty. Crossbred Angus and Simmental heifer calves were weaned at 73 +/- 3 d of age and 115 +/- 3 kg of BW and fed a high-concentrate (60% corn; HI, n = 9) or control diet (30% corn; CONT, n = 9). Heifers were fed individually, and target BW gains were 1.50 and 0.75 kg/d for the HI and CONT treatments, respectively. Heifers were weighed every 2 wk. Blood samples were collected weekly and assayed for progesterone concentration to determine age at puberty. Serial blood samples were collected at 20-min intervals for 24 h at mean ages of 102, 130, 158, 172, 190, 203, 217, 231, and 259 d and assayed for LH concentration to evaluate the dynamics of secretion of LH. Heifers fed the HI diet exhibited greater BW gain (P < 0.01) than CONT heifers (1.27 +/- 0.05 vs. 0.85 +/- 0.05 kg/d, respectively). As a result, BW in the HI treatment was greater (P < 0.01) than in the CONT treatment by 188 d of age and remained different through the end of the experiment. Precocious puberty occurred in 8 of 9 heifers fed the HI diet and 0 of 9 heifers fed the CONT diet. Age at puberty was reduced in the HI (P < 0.01) compared with the CONT heifers (262 +/- 10 vs. 368 +/- 10 d of age, respectively). Body weight at puberty was also reduced in the HI (P < 0.05) compared with the CONT treatment (327 +/- 17 vs. 403 +/- 23 kg, respectively). Heifers attaining puberty during the experiment continued with subsequent luteal phases as evidenced by cyclic patterns of progesterone concentrations. Frequency of pulses of LH (pulses/24 h) increased with age (P < 0.01) for both treatments. Heifers in the HI treatment exhibited a greater number of pulses of LH (P < 0.01) than those in the CONT treatment by 190 d of age and in all subsequent collection periods (treatment x age, P < 0.05). Mean LH concentrations also increased with age (P < 0.01) for both treatments but did not differ between treatments. In conclusion, precocious puberty induced by early weaning and feeding of a high-concentrate diet is preceded by increasing frequency of pulses of LH.  相似文献   

11.
Postpubertal beef heifers (n = 55) were used to examine the effects of high-fat diets, independently of energy intake, on nonesterified fatty acid and lipoprotein metabolic patterns, ovarian follicular dynamics, and embryo recovery/viability after FSH superstimulation. High-lipid (HL) diets (5.4% added fat) increased (P < .01) serum concentrations of cholesterol, but not of nonesterified fatty acids, during the 35-d period before FSH treatment. Development of medium-sized (5 to 9.9 mm) follicles was enhanced (P < .05) during this period in heifers fed the HL diet. The HL diet increased total cholesterol (P < .05) and progesterone (P = .14) concentrations in follicular fluid obtained at ovariectomy (n = 10) 60 h after the onset of FSH treatment, but neither estradiol-17 beta nor androstenedione was affected. Granulosa cells recovered from FSH-induced, estrogen-active follicles in heifers fed the HL diet produced greater quantities of progesterone (P = .06) and less estradiol-17 beta (P < .05) in vitro than did granulosa cells from heifers fed the normal lipid diet. Dietary treatment did not influence FSH-stimulated recruitment of medium and large follicles, number of ovulations, embryo recovery, or embryo viability. Data suggest that increments in dietary fat intake can alter specific aspects of ovarian steroidogenic potential and can increase the population of medium-sized follicles theoretically available for maturation and harvest during the estrous cycle. However, conditions that limited the latter process in the current experiment are not understood and require further investigation.  相似文献   

12.
A 3-d extension of the luteal phase occurs in interovulatory intervals (IOIs) with a contralateral relationship between the corpus luteum (CL) and preovulatory follicle with 3 follicular waves (Contra-3W group). Concentrations of FSH, progesterone, LH, and estradiol-17β for the ipsilateral versus contralateral CL and/or follicle relationship and 2 versus 3 waves per IOI were studied in 14 heifers. Follicular waves and FSH surges were designated 1, 2, or 3, according to order of occurrence in the IOI. The day (day 0 = ovulation) of the FSH peak in surge 2 occurred earlier (P < 0.02) in 3-wave IOIs (day 6.3 ± 0.5) than in 2-wave IOIs (day 8.5 ± 0.5). Mean FSH was higher in 3-wave than in 2-wave IOI on 82% of the days in the IOI. Repeatability or individuality in FSH concentration was indicated by a correlation (r = 0.54, P < 0.04) in FSH concentrations between ovulations at the beginning and at the end of the IOI. Concentrations of LH and estradiol increased (P < 0.05) near the beginning of the luteolytic period in 2-wave IOI regardless of the CL and/or follicle relationship. In the Contra-3W group, LH and estradiol remained at basal concentrations concurrently with FSH surge 3 and extension of the luteal phase. The hypotheses were supported that FSH surge 2 occurs earlier in 3-wave IOIs than in 2-wave IOIs and that the development of 3-wave IOIs occurs in individuals with greater FSH concentrations. Extension of the luteal phase in the Contra-3W group was temporally associated with lower concentrations of LH and estradiol.  相似文献   

13.
Precocious puberty (<300 d of age) can be induced in beef heifers by early weaning and feeding a high-concentrate diet. The objective of this experiment was to determine whether precocious puberty occurs as a result of a hastened reduction of estradiol negative feedback on secretion of LH. Thirty crossbred Angus and Simmental heifers were weaned at 83 +/- 2 d of age and 114 +/- 3 kg of BW, blocked by BW, and randomly assigned to receive a high-concentrate (60% corn; H) or control (30% corn; C) diet and to receive ovariectomy (OVX), OVX plus an estradiol implant (OVXE), or to remain intact (INT). Residual ovarian tissue after OVX necessitated withdrawal of 6 heifers during the course of the experiment, resulting in the following treatment groups: OVX-C, n = 3; OVX-H, n = 5; OVXE-C, n = 4; OVXE-H, n = 2; INT-C, n = 5; INT-H, n = 5. To determine concentrations of progesterone and estradiol, blood samples were collected weekly beginning at a mean age of 160 d. To characterize LH concentrations, serial blood samples were collected at 12-min intervals for 12 h at mean ages of 119, 149, 188, 217, 246, 281, 323, 365, 407, and 449 d. By a mean age of 202 d, heifers fed the H diet were heavier (P < 0.05) than those fed the C diet. Heifers in the INT-H treatment attained puberty earlier (P < 0.05) than in the INT-C treatment (275 +/- 30 vs. 385 +/- 14 d of age, respectively). Overall mean concentrations of estradiol did not differ between OVXE-H and OVXE-C, between INT-H and INT-C, or between OVXE and INT treatments. The OVX treatments exhibited greater LH pulse frequency than the OVXE and INT treatments by the first serial blood collection (treatment x age, P < 0.05). The frequency of LH pulses was greater (P < 0.05) in the INT-H than the INT-C treatment by a mean age of 246 d and was greater (P < 0.05) in the OVXE-H than the OVXE-C treatment by a mean age of 281 d. In the OVXE-H treatment, LH secretion increased and subsequently "escaped" from estradiol negative feedback (detection of > or = 1 LH pulse/h) earlier (P < 0.05) than in the OVXE-C treatment (307 +/- 30 and 420 +/- 21 d of age, respectively). It is concluded that advancing the reduction of estradiol negative feedback on secretion of LH is the mechanism by which early weaning and feeding a high-concentrate diet results in precocious puberty in heifers.  相似文献   

14.
The objective of the present study was to examine the involvement of opioid neuropeptides and E2 in regulating circulating concentrations of gonadotropins during sexual maturation in the bovine female. Prepubertal (immature) and postpubertal (mature) bovine females were used. Mean concentrations of luteinizing hormone (LH) and follicle- stimulating hormone (FSH) in circulation before and after administration of naloxone were determined in ovariectomized heifers administered E2 and ovariectomized heifers not administered E2. A linear decline (P<0.01) in opioid suppression of LH and FSH occurred during the experimental period in immature heifers receiving E2. This decline in opioid suppression of LH and FSH occurred during the same period of time that intact control heifers were initiating estrous cycles at puberty. Little change of opioid suppression of LH and FSH occurred during the experimental period in immature heifers not receiving E2 and mature heifers receiving E2. Our research indicates that opioid neuropeptides and E2 act together to regulate LH and FSH secretion during sexual maturation in the bovine female.  相似文献   

15.
This study was designed to test the effects of active immunization against estrogen and progesterone on patterns of luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion, ovarian characteristics and growth rate of heifers. Heifers were randomly assigned to four treatments: 1) control injection (n = 10); 2) ovariectomy (n = 9); 3) immunization against estrogen (anti-E, n = 10); and 4) immunization against estrogen and progesterone (anti-E+P4, n = 10). Three booster immunizations were administered at 1, 1.5 and 6 mo after primary immunization. Progesterone antibody binding was 40% (34 fmol at 1:600 final dilution) in the anti-E+P4 heifers, and estradiol-17 beta binding was 35% (30 fmol) and 60% (52 fmol at 1:100 final dilution) in the anti-E+P4 and anti-E heifers, respectively, after the final immunization. Anti-E+P4 heifers had more pulses of LH and higher basal concentrations of LH than anti-E or control heifers (P less than .05). Concentrations of LH in anti-E+P4 heifers did not increase to concentrations found in ovariectomized heifers (P less than .05). Immunization against steroids did not alter the secretion of FSH. The number of large follicles (greater than 15 mm diameter) in anti-E+P4 and anti-E heifers was greater than in control heifers (P less than .05). Ovarian weight was increased in anti-E+P4 heifers (P less than .05). Average daily gain was not different among groups (P greater than .05). It was concluded that active immunization against estrogen and progesterone in heifers increased LH secretion and stimulated ovarian function.  相似文献   

16.
Pituitaries from intact luteal phase (INT) and ovariectomized (OVX) cows were collected at slaughter to determine whether differences exist among regions of the bovine adenohypophysis in the concentrations of luteinizing hormone (LH), follicle stimulating hormone (FSH) and receptors for luteinizing hormone releasing hormone (LHRH). Each adenohypophysis was divided into three paired regions (anterior, AT; medial, M; posterior, PT) by first making a midsagittal cut followed by two transverse cuts of approximately equal size. Values for all variables were similar between paired regions. Mean LHRH receptor, LH and FSH concentrations were greater in OVX than INT adenohypophyseal regions. Receptor and gonadotropin concentrations differed among all three regions and were greatest in the AT, intermediate in the M and lowest in the PT regions of the adenohypophysis. There were significant correlations between LHRH receptor concentrations and concentrations of LH and FSH among the three adenohypophyseal regions for both INT and OVX cows. Therefore, to accurately characterize LHRH receptors from the bovine adenohypophysis, a midsagittal-half of the gland should be used for analysis.  相似文献   

17.
Effects of ewe body condition and level of feed intake on ovarian follicle populations and ovulation rates were studied in three groups of 12 to 15 Finnish Landrace cross ewes. Ewes were fed to achieve target body condition scores of either 2.0 (low, LM) or 2.5 (moderate, MM) and then fed a complete pelleted ration for three weeks before study so that they maintained liveweight. Ewes of a third group were also fed to achieve condition scores of 2.5 and then fed ad libitum (MAL). Neither ewe body condition nor level of feed intake significantly affected either the number of large follicles (greater than or equal to 4 mm diameter) or the ovulation rate. The proportion of estrogenic follicles was lower in MM than LM ewes (0.77 vs. 0.96; P less than 0.05), but there was no difference in this proportion between MAL and MM ewes. Insulin-like growth factor-I (IGF-I) concentrations in the follicular fluid were unaffected by ewe body condition or level of feed intake despite significant treatment differences in circulating concentrations. Inhibin concentrations were higher in estrogenic follicles of LM compared with MM ewes, and this difference was reflected in circulating profiles. Treatment differences in LH profiles were not associated with any difference in follicle populations or ovulation rate. There were no consistent treatment effects on FSH concentrations. It is concluded that the roles of inhibin and IGF-I in the control of follicle development cannot be adequately assessed on the basis of circulating concentrations alone and that there is a need to measure intrafollicular hormone profiles and associated effects on follicle physiology.  相似文献   

18.
Relatively few studies have been reported regarding the reproductive physiology of female Thai native cattle. Therefore, the objective of the present study was to evaluate the follicular dynamics and concentrations of follicle stimulating hormone (FSH), estradiol (E2) and progesterone (P4) during the estrous cycle in Thai native heifers (TNH) and to compare obtained results with those of European and Indian cattle breeds previously reported. For the detection of estrus, ovaries of all 20 heifers were examined twice daily (12 h intervals) by ultrasonography for three consecutive estrous cycles. From data of 60 estrous cycles (n = 60 estrous cycles from 20 heifers), it was found that 14 (70%) and 6 heifers (30%) had two (42 estrous cycles collected from 14 heifers) and three follicular waves (18 estrous cycles collected from 6 heifers), respectively. The days when estrus was detected, interovulatory intervals, life‐spans of corpus lutea (CL), and days for growing and regression of CLs were shorter in the two follicular waves than those in the three follicular waves (P < 0.05). In both two and thre follicular waves, larger maximum diameters and higher growth rates of the dominant follicle (DF) in an ovulatory wave were observed than those of the preceding waves without ovulation (P < 0.05). There was a progressive increase in follicular size and FSH and E2 production during follicular growth in each follicular wave. In addition, the FSH and E2 peak concentrations during the ovulatory wave were higher than those of the anovulation waves (P < 0.05). Moreover, although the ovarian follicular dynamic patterns in Thai native heifers were similar to those previously reported for European and Indian cattle breeds, the diameter of the largest preovulatory follicle (OF), subordinate follicles (SF) and CLs were smaller than those in European and Indian cattle breeds. In conclusion, when compared with European and some breeds of Indian cattle, the length of interovulatory intervals was shorter, and the sizes of dominant SF and CLs were smaller in Thai native heifers.  相似文献   

19.
To determine the influence of three levels of undegradable intake protein (UIP) supplementation on metabolic and endocrine factors that influence reproduction, 23 yearling crossbred heifers (body condition score = 4.5 +/- 0.5; initial BW = 362 +/- 12 kg) were stratified by BW and assigned randomly to one of three supplements: 1) low UIP (1,135 g x heifer(-1) x d(-1); 30% CP, 115 g UIP, n = 7); 2) mid UIP (1,135 g x heifer(-1) x d(-1); 38% CP, 216 g UIP, n = 8); or 3) high UIP (1,135 g x heifer(-1) x d(-1); 46% CP, 321 g UIP, n = 8). Heifers were estrually synchronized before initiation of supplementation. Supplement was individually fed daily for 30 to 32 d, at which time heifers were slaughtered (d 12 to 14 of the estrous cycle) and tissues collected. Heifers were fed a basal diet of sudan grass hay (6.0% CP) ad libitum. On d 28 of supplementation (d 10 of the estrous cycle), no differences were observed (P > 0.10) in serum insulin or IGF-I among treatments. At slaughter (d 10 to 12 of the estrous cycle), treatments did not influence corpus luteum weight, cerebral spinal fluid leptin, or IGFBP; serum estradiol-17beta, progesterone, leptin, IGF-I, and IGFBP; or anterior pituitary content of IGFBP (P > 0.10). Follicular fluid IGFBP-2 and IGFBP-4 were greater in high-UIP heifers than low- or mid-UIP heifers on d 12 to 14 of the estrous cycle (P < 0.05). Basal serum LH concentrations and LH area under the curve (every 15 min for 240 min) did not differ (P > 0.10) following 28 d of supplementation (d 10 of the estrous cycle); however, basal serum FSH concentrations were greater (P = 0.06) in low- and mid- vs. high-UIP heifers (5.2 and 5.2 vs. 4.6 ng/mL, respectively), and FSH area under the curve was greater (P = 0.03) in low- vs. high-UIP heifers. At slaughter (d 12 to 14 of the estrous cycle), anterior pituitary LH and FSH content and steady-state mRNA encoding alpha, LHbeta, and GnRH receptor did not differ (P > 0.10) among treatments. However, FSHbeta mRNA was increased approximately twofold (P = 0.03) in mid vs. low UIP. In summary, low and mid levels of UIP supplements fed to estrous cycling beef heifers seemed to enhance pituitary expression and/or secretion of FSH relative to high levels of UIP. Moreover, high-UIP supplementation was associated with increased low-molecular-weight IGFBP compared with supplementation of low and mid levels of UIP. These data suggest that differing levels of UIP supplementation may alter pituitary and ovarian function, thereby influencing reproductive performance in beef heifers.  相似文献   

20.
Three experiments were conducted to determine the effects of n-methyl-D,L-aspartate (NMA), an agonist of the excitatory amino acid glutamate, on secretion of hormones in boars. In Exp. 1, boars (185.0+/-.3 d of age; mean +/- SE) received i.v. injections of either 0, 1.25, 2.5, 5, or 10 mg of NMA/kg BW. There were no effects of NMA (P>.1) on secretion of LH and testosterone. Treatment with NMA, however, increased (P<.01) circulating GH concentrations in a dose-dependent manner. In Exp. 2, boars (401 d of age) received an i.v. challenge of NMA at a dose of 10 mg/kg BW or .9% saline. Treatment with NMA, but not saline (P>.1), increased serum concentrations of LH (P<.01), GH (P <.01), and testosterone (P<.06). In Exp. 3, boars that were 152, 221, or 336 d of age were treated i.v. with NMA (10 mg/kg BW). Across ages, treatment with NMA increased circulating concentrations of LH (P<.07) and testosterone (P<.01). However, NMA increased (P<.01) mean GH concentrations in only the oldest boars. Treatment with NMA had no effect (P>.1) on circulating concentrations of estradiol or leptin; however, estradiol concentrations increased (P<.03) with age. In summary, NMA increased secretion of LH, GH, and testosterone in boars. However, endocrine responses to treatment with NMA may be influenced by age of the animal. Finally, NMA did not influence circulating concentrations of estradiol or leptin.  相似文献   

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