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PubMed1996

The ovarian follicular wave pattern and induction of ovulation in the mated and non-mated one-humped camel (Camelus dromedarius).

Ovarian follicular wave patterns were studied ultrasonographically in three groups of dromedary. Group 1 camels (n = 20) were teased daily with a vasectomized male but mating was prevented; group 2 camels (n = 8) ran freely with a vasectomized male camel for 10 h each day and group 3 camels (n = 8) were kept completely separate from any males. In a second experiment (n = 63), when the diameter of the dominant follicle reached 0.5-0.9 cm, 1.0-1.9 cm, 2.0-2.9 cm or > 3 cm, the camel was given one of three treatments to induce ovulation: (i) natural mating; (ii) 20 micrograms of the GnRH analogue, buserelin; or (iii) 3000 iu hCG. The ovaries were re-scanned regularly to monitor ovulation, and daily blood samples were assayed for progesterone and oestradiol concentrations. The follicular cycle was divisible into a growth phase (10.5 +/- 0.5 days), a mature phase (7.6 +/- 0.8 days) and a regression phase (11.9 +/- 0.8 days). The dominant follicle reached a mean +/- SEM maximum diameter of 2.0 +/- 0.1 cm (range 1.5-2.5 cm) in 34 cycles (52%) before it began to regress. In the other 32 cycles (48%), however, the dominant follicle continued to grow to 4.2 +/- 0.2 cm (range 4.0-6.0 cm) before regression commenced. Group 2 camels were mated when their follicles reached 1.3 +/- 0.1 cm in diameter and the mean interval between successive matings was 13.8 +/- 1.0 days. Mean +/- SEM serum concentrations of oestradiol reached peak values at 39.0 +/- 1.8 pg ml-1, when the dominant follicle measured 1.7 +/- 0.1 cm and, after ovulation, mean serum concentrations of progesterone reached peak values at 2.6 +/- 0.3 ng ml-1 on day 8, before decreasing to < 1 ng ml-1 by day 10 or 11. When the dominant follicle measured 0.5-0.9 cm in diameter, 70%, 60% and 60% of them ovulated in response to mating, or treatment with buserelin or hCG, respectively. These ovulation rates increased to 85% (mating), 81% (buserelin) and 67% (hCG) when the follicle measured 1-1.9 cm, but they decreased again to 12.5% (mating), 29% (buserelin) and 13% (hCG) when the diameter had increased to 2.0-2.9 cm at the time of treatment. No follicles measuring > 3.0 cm ovulated in response to any of the treatments. These results indicated that the optimum time to mate or attempt to induce ovulation in the female dromedary is when the growing follicle measures 0.9-1.9 cm in diameter.

Animals↗

PubMed1997

Ovulation induction and gamete transport in the female tract of the musk shrew, Suncus murinus.

The musk shrew Suncus murinus was studied with regard to induction of ovulation, the genesis and role of the vaginal copulation plug, and the behaviour of gametes and embryos within the Fallopian tube. Ovulation occurred about 15 h after ejaculation, which required a mean of 5.2 (range 2-10) intromittent thrusts. Since ovulation occurred also after five thrusts without ejaculation, and after ejaculation without plug formation or sperm deposition, the primary stimulus for this seemed to be the thrust of the penis, the glans of which was covered by a dense field of spines. Neither vasectomized nor prostatectomized males formed a plug at ejaculation, and in the latter case the mean number of spermatozoa reaching the isthmus of the Fallopian tube, the number at the ampullary fertilization site and the rate of fertilisation were lower than in females mated to normal males. Thus both the vesicular gland on the vas deferens and the prostate are essential for formation of the copulation plug, which appears to enhance sperm transport within the female tract. At ejaculation, < or = 10(6) spermatozoa were incarcerated by the plug in the anterior vagina for 6-7 h, by which time a maximal population of several hundred had become established in posterior crypts of the isthmus of the Fallopian tube as small groups of free languidly moving spermatozoa. It remains to be established whether oviductal crypts in this and other shrews have a storage function for spermatozoa or sequester spermatozoa and so regulate the number that reach the fertilization site. Very few spermatozoa reached the ampulla of Suncus. Generally, only one or two spermatozoa had reached the ampulla by 4-5 h, and often less than ten had done so by 5-13 h after ovulation. As a probable correlate, few eggs were penetrated during the first 5 h, with a frequent delay of 10-13 h before most eggs were fertilized. Thereafter, unfertilized eggs were transported through the oviduct at the same rate as developing embryos, which entered the uterus about 85 h after ovulation at the 32-cell stage. There were highly significant differences between the larger KAT/SK strains and smaller OK strain with regard to Fallopian tube length (mean 6.9 mm versus 9.7 mm), as well as the rates of hCG-induced ovulation (5.6 versus 3.25) and of unilateral ovulation (6% versus 50%).

Animals↗

PubMed1997

Influence of insemination-ovulation interval and sperm cell dose on fertilization in sows.

This experiment was conducted to determine the effects of sperm dose at insemination on fertilization rates and accessory sperm cells attached to day 5 embryos. Multiparous sows (n = 115) were artificially inseminated once with 1 x 10(9), 3 x 10(9) or 6 x 10(9) sperm cells between 3 h and 48 h before ovulation. Transrectal ultrasonography was performed at intervals of 4 h to determine the time of ovulation and sows were killed at 120 +/- 5 h after ovulation to assess the results of fertilization. The insemination-ovulation interval had a major influence on the fertilization rate and accessory sperm count. A nonsignificant but consistent increase in fertilization rate and in number of accessory sperm cells due to the sperm dose was observed. During the insemination-ovulation interval of 12-24 h, the median fertilization rates were 95%, 100% and 100%, and the median accessory sperm counts were 11, 17 and 31 for the 1 x 10(9), 3 x 10(9) and 6 x 10(9) doses, respectively. During the insemination-ovulation interval of 24-36 h, the median fertilization rates were 88%, 95% and 97%, and the median accessory sperm counts were 6, 8 and 11 for the 1 x 10(9), 3 x 10(9) and 6 x 10(9) doses, respectively. No direct relationship was detected between embryo quality and the accessory sperm count but there was a relationship between insemination-ovulation interval and accessory sperm count. The fertilization rate was positively correlated with the breeding value for litter size of the sows. In conclusion, the effects of sperm dose on fertilization rate and on accessory sperm count in sows were small and nonsignificant, indicating only small effects of sperm dose on the functioning of the sperm reservoir in the sow.

Animals↗

PubMed2004

Sperm distribution in the genital tract of the bitch following artificial insemination in relation to the time of ovulation.

In the present study, sperm distribution in the genital tract of the bitch following artificial insemination (AI) in relation to the time of ovulation was investigated by histology, scanning electron microscopy (SEM) and flushing. Ten bitches were inseminated intravaginally with 500 x 10(6) spermatozoa: three dogs before ovulation, four dogs during ovulation and three dogs after ovulation. Ovariohysterectomy was performed 24 h after AI. Half of the genital tract was divided into nine segments (cervix, corpus uteri, caudal, middle and cranial uterine horn (UTH), utero-tubal junction (UTJ), isthmus, ampulla and infundibulum), which were processed for histology and SEM. The contralateral UTH and uterine tube (UT) were flushed, and several sperm characteristics were assessed. Histology revealed that the spermatozoa were mainly located in the uterine glands and at the UTJ, while very few spermatozoa were detected in the UT. Insemination during ovulation resulted in higher percentages of glands with spermatozoa in the different parts of the uterus (P < 0.05). Evaluation by SEM showed higher numbers of spermatozoa in several parts of the uterus for bitches inseminated during ovulation (P < 0.05). The mean number of spermatozoa flushed from the UTH and the UT was low. No significant differences in the evaluated sperm quality parameters were found between the flushings of the UTH and the UT. In conclusion, based on our findings, the uterine glands and the UTJ might act as sperm reservoirs in the bitch and sperm transport in the genital tract is affected by the time of AI in relation to ovulation.

Animals↗

PubMed1976

The interrelationship between progesterone and luteinizing hormone during the ovulation cycle of the hen (Gallus domesticus).

The existence of a circadian rhythm in the sensitivity of the hypothalamus of the laying hen to stimulation by progesterone was investigated by injecting 0.5 mg progesterone subcutaneously during the proposed period of maximum insensitivity. Following this treatment increases in plasma concentrations of both LH and progesterone were observed which were comparable to the spontaneous preovulatory rises in the plasma levels of the hormones. The ability of either progesterone or luteinizing hormone releasing hormone (LH-RH) to induce premature ovulation varied according to the stage of follicular development. Neither hormone was more than 28% effective when injected within 6.5 h of the previous ovulation, whereas both hormones were 100% effective approximately 27 h after the terminal ovulation of a clutch sequence. Failure to ovulate in response to LH-RH given 6.5 h after ovulation was associated with a lack of progesterone secretion. Both LH and progesterone were secreted when ovulation was induced by injections of either LH-RH or progesterone, and LH was secreted in response to progesterone given 6.5 h after ovulation. These results demonstrate that progesterone stimulates the secretion of LH and LH stimulates the secretion of progesterone. The precise physiological role of these two hormones, however, was not established.

Animals↗

PubMed1983

Co-operation of progesterone and prostaglandins in ovulation induced by human chorionic gonadotrophin in immature rats primed with pregnant mare serum gonadotrophin.

Serial injections of a mixture of prostaglandin (PG) E2 and F2 alpha 0, 2, 4, and 6 h after simultaneous injection of human chorionic gonadotrophin (hCG) and indomethacin incompletely restored the ovulation that would have been blocked by indomethacin in immature rats treated with pregnant mare serum gonadotrophin followed by hCG. Serial injections of another mixture of PGE2 and PGF2 alpha 6, 8, 10 and 12 h after simultaneous injection of hCG and indomethacin similarly reversed, in part, the inhibitory effects of indomethacin on hCG-induced ovulation. In contrast, serial injections of the mixtures of PGE2 and PGF2 alpha 0, 2, 4, 6, 8, 10 and 12 h after simultaneous injection of hCG and indomethacin completely restored the indomethacin-blocked ovulation, suggesting that the prostaglandins mediate the action of hCG on ovulation both in the earlier and later stages of the preovulatory process. Six hours after simultaneous injection of hCG and indomethacin serial injections of a mixture of PGE2 and PGF2 alpha reproduced the acute and temporary increase in concentrations of progesterone and testosterone in plasma which would have been abolished by indomethacin. Progesterone given concurrently with hCG and indomethacin partially antagonized the inhibitory action of indomethacin on ovulation. Serial injections of a mixture of PGE2 and PGF2 alpha 6, 8, 10 and 12 h after concurrent administration of progesterone with hCG and indomethacin completely restored the indomethacin-blocked ovulation, suggesting that progesterone can substitute the action of prostaglandins injected serially in the first half of the preovulatory process. It was concluded that the co-operation of progesterone in the earlier stage and of prostaglandins in the later stage of the preovulatory interval is required to mediate the action of hCG on ovulation.

Animals↗

PubMed1983

Maturation of ovarian follicles after inhibition of ovulation in rats.

The present investigation was performed to elucidate the mechanism of the initiation of follicular maturation after inhibition of ovulation in rats treated with pentobarbitone sodium at 13.30 h and progesterone at 14.00 h on the day of pro-oestrus (day 0 denotes the day of these treatments). Ovulation was completely inhibited and the next spontaneous ovulation occurred on day 5, the expected day of the next oestrus. Follicular responsiveness to injection of human chorionic gonadotrophin (hCG) indicated that preovulatory follicles at the time of treatment with pentobarbitone and progesterone regressed by 05.00 h on day 2. Maturation of a new set of follicles began from 17.00 h on day 2 and all rats were induced to ovulate by hCG injection by 17.00 h on day 3, the number of oocytes ovulated being comparable to normal ovulation. In the animals receiving pentobarbitone sodium and progesterone treatment, two selective rises in plasma FSH, which had peak levels at 05.00 h on day 1 and 11.00 h on day 2, were observed without a rise in LH. Preovulatory surges of FSH and LH occurred on the afternoon of day 4. These results suggest that the second rise in FSH was induced by regression of Graafian follicles present at the time of treatment with pentobarbitone sodium and progesterone and that this surge of FSH was responsible for initiation of maturation of a new set of follicles destined to ovulate in the subsequent cycle. The mechanism of induction and the role of the first rise of FSH from the night of day 0 to the morning of day 1 cannot be explained at present.

Animals↗

PubMed1984

Ovarian steroid concentrations in rats approaching first ovulation.

Steroid concentrations were studied in ovarian tissue obtained by means of unilateral ovariectomy during a 10-day period preceding first ovulation. Furthermore, the levels of progesterone were measured in this period in the serum of simultaneous intact control rats. Ovarian concentrations of testosterone and oestradiol were at about 70 and 15 fmol/mg ovary respectively from 10 to 4 days before first ovulation; they clearly increased to a maximum of 170 and 120 fmol/mg ovary during the last 1-3 days before first ovulation. Ovarian concentrations of 5 alpha-reduced androgens (i.e. androsterone and 5 alpha-androstane-3 alpha,17 beta-diol) were high (up to 2500 fmol/mg ovary) from 7 to 4 days before first ovulation, whereas low levels (500-750 fmol/mg ovary) were present during the last 3 days before ovulation. Both ovarian and serum concentrations of progesterone were constantly low (at 500-1000 fmol/mg ovary and at 17-32 nmol/l respectively) from 10 days to 1 day before first ovulation. An inverse correlation was observed between the ovarian content of 5 alpha-reduced androgens and that of oestradiol, which is in agreement with the existence of a prepubertal shift in pathways of steroid production; this shift seems to take place between 4 and 3 days before first ovulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Androstane-3,17-diol↗

PubMed1992

Noradrenergic peripheral denervation of the female rat accelerates the positive feedback mechanisms resulting in pubertal ovulation, and blocks the modifications induced by administration of testosterone propionate at birth.

The noradrenergic innervation of the ovary of prepubertal rats causes an inhibitory response of the follicles to gonadotrophins, leading to ovulation. We investigated the possibility that noradrenergic peripheral denervation at birth, produced by treatment with guanethidine, modifies the positive feedback effects of gonadotrophins and oestradiol in prepubertal rats, and also the possibility that peripheral denervation can modify the anovulatory syndrome induced by androgenization at birth. Noradrenergic peripheral denervated rats of 18 days of age treated with pregnant mare serum gonadotrophin (PMSG) ovulated 96 h later, while normal animals did not ovulate (4/9 vs 0/12, P < 0.05) and the number of ova shed was lower than in rats which ovulated spontaneously at first vaginal oestrus (3.5 +/- 0.6 vs 8.3 +/- 0.4 (S.E.M.), P < 0.01). Oestradiol benzoate (10 micrograms) did not induce ovulation in either normal or denervated animals (0/11 and 0/11). The anovulatory syndrome induced by the administration of testosterone propionate (75 micrograms) at birth was partially blocked by noradrenergic peripheral denervation (4/7 ovulated vs 0/10). The results suggest that some neural information arising from the ovary modulates, in an inhibitory way, the stimulatory feedback mechanisms required to induce ovulation. Partial inhibition of the anovulatory syndrome resulting from androgenization caused by peripheral noradrenergic denervation suggests that noradrenergic neural information sent by the ovary to the hypothalamus results in a decreased concentration of noradrenaline in the hypothalamus and in the aromatization of androgens to oestrogens.

Animals↗

PubMed1991

Prediction of breeding values for twinning rate and ovulation rate with a multiple trait, repeated records animal model.

A genetic correlation near unity between ovulation rate in heifers and later twinning frequency led to consideration of using measures of ovulation rate in heifers for each estrous cycle, beginning at puberty, to increase accuracy of selection for twinning rate. An initial evaluation with a multiple trait animal model for predicting breeding values included six genetic groups: 1) selected Scandinavian bulls, 2) transfers from other populations at the Research Center to a twinning project, 3) early-purchased Holsteins, 4) late-purchased Holsteins, 5) early purchases-other breeds, and 6) late purchases-other breeds. For ovulation and twin measures, heritabilities of .100 and .070 and repeatabilities of .120 and .092 were assumed. Assumed phenotypic correlation between ovulation and twin measures of .08 was accounted for by genetic correlation of .89 and permanent environmental correlation of .19. The number of animals evaluated was 1,745; 6,912 estrous cycles were measured for ovulation rate on 840 heifers and 1,929 parturitions were observed for occurrence of twinning on 851 cows, of which 346 had ovulation rate measured as heifers. The remaining 400 animals were foundation animals that created relationships among those with records or were sires of animals with records. The Scandinavian genetic group effect was substantially greater than that of the others. Joint evaluations were compared to evaluations using only twinning measures. For animals with twin evaluations based only on parents but with ovulation rates measured, the multiple trait evaluation increased accuracy of evaluation from .62 (twin information only) to .81.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1992

Effects of gonadotropin-releasing hormone infused in a pulsatile or continuous fashion on serum gonadotropin concentrations and ovulation in the mare.

Studies were conducted to compare continuous vs pulsatile i.v. infusion of GnRH on serum gonadotropin concentrations and ovulation in seasonally anestrous mares and in cycling mares. Anestrous mares (Exp. 1) received no treatment (control; n = 3), 2, or 20 micrograms of GnRH/h continuous infusion (CI) (n = 4 and n = 6, respectively), or 20 micrograms of GnRH/h pulsatile infusion (PI) (n = 5). After initiation of GnRH infusion, serum LH levels increased earlier, and to a greater extent, in the PI group than in other groups (P less than .05). In contrast, serum FSH concentrations did not differ among groups. The number of days to development of the first 35-mm follicle was not different among GnRH treatment groups; however, mares receiving PI ovulated on d 9.4 of treatment, 2.8 d earlier than those receiving 20 micrograms of GnRH/h CI (P less than .05). Mares given 2 micrograms of GnRH/h CI failed to ovulate spontaneously after 16 d of treatment, but each one ovulated within 2 to 4 d after injection of 2,000 IU of hCG on d 16. Control mares did not ovulate or show any significant follicular development throughout the experiment. Cycling mares (Exp. 2) received no treatment (control; n = 6), 20 micrograms of GnRH/h CI, or 20 micrograms of GnRH/h PI (n = 4) beginning on d 16 of an estrous cycle (d 0 = day of ovulation). Serum LH concentrations in all groups increased after initiation of treatment; however, on the day of ovulation LH concentrations were lower in the CI group than in the PI or control groups (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1997

Evidence for quantitative trait loci affecting ovulation rate in pigs.

Fifty-five microsatellite markers were scored in an F2 population of pigs (n = 114 females) developed at the University of Nebraska. The population was produced by crossing a line previously selected for 10 generations using an index of ovulation rate and embryonal survival and a line selected at random. The lines were from a common base population and differed by 6.7 ovulations and 3.1 fetuses at 50 d of gestation. Ovulation rate and number of fully formed and mummified pigs were recorded for each female. Data were analyzed with regression models that included random animal effects. Likelihood-ratio tests were used to test for quantitative trait loci (QTL) effects by deviating the log-likelihood for the full model that included additive and dominance QTL effects from the log-likelihood for the reduced model that did not contain QTL effects. A QTL for ovulation rate was found on chromosome 8 (P < .001) with an additive effect of 3.07 ovulations. Other evidence of potential QTL affecting ovulation rate was found on chromosomes 4 (P < .10), 13, and 15 (P < .05). Effects on chromosomes 4, 13 and 15 were not significant for fan experiment-wise threshold value of P < .001. No significant QTL for litter size or number of mummified pigs were found. Additional data are needed to confirm the location and the effect of QTL found for ovulation rate before markers associated with them can be used in marker-assisted selection.

Alleles↗

PubMed2007

Luteinizing hormone release after administration of the gonadotropin-releasing hormone agonist Fertilan (goserelin) for synchronization of ovulation in pigs.

The generic GnRH agonist, Fertilan (goserelin), was tested for the ability to induce an LH surge and ovulation in estrus-synchronized gilts. Three experiments were performed to 1) examine the effect of various doses of Fertilan on secretion of LH in barrows, to select doses to investigate in gilts (Exp. 1); 2) determine doses of Fertilan that would induce a preovulatory-like rise of LH in gilts (Exp. 2); and 3) determine the time of ovulation after Fertilan treatment (Exp. 3). In Exp. 1, 10 barrows were injected on d 1, 4, 7, 10, and 13 with 10, 20, or 40 microg of Fertilan; 50 microg of Gonavet (depherelin; GnRH control) or saline (negative control); and sequential blood samples were collected for 480 min. There was a dose-dependent stimulation (P < 0.05) of LH release. Maximal plasma concentrations of LH (LH(MAX)) were 2.1 +/- 0.2, 4.1 +/- 0.3, 2.6 +/- 0.4, and 3.4 +/- 0.3 ng/mL after 10, 20, and 40 microg of Fertilan and 50 microg of Gonavet, respectively, and duration of release was 78 +/- 9, 177 +/- 12, 138 +/- 7, and 180 +/- 11 min, respectively. Fertilan doses of 10 and 20 microg were deemed to be the most suitable for testing in gilts. In Exp. 2, 12 gilts received (after estrus synchronization with Regumate and eCG) injections of 10 or 20 microg of Fertilan or 50 microg of Gonavet 80 h after eCG to stimulate a preovulatory-like LH surge and ovulation. An LH surge was induced in 3 of the 4 gilts in both of the Fertilan groups and in all of the Gonavet-treated gilts. Characteristics of induced release of LH did not differ among groups: LH(MAX), 5.0 +/- 0.9 vs. 4.6 +/- 1.8 vs. 6.6 +/- 1.1 ng/mL; duration, 11.7 +/- 2.0 vs. 12.3 +/- 2.2 vs. 14.3 +/- 0.5 h; interval from GnRH injection to LH(MAX), 4.0 +/- 2.0 vs. 6.7 +/- 1.3 vs. 5.8 +/- 1.6 h. In Exp. 3, estrus-synchronized gilts were injected with 20 microg of Fertilan (n = 8) or 50 microg of Gonavet (n = 4), and the time of ovulation was determined by repeated endoscopic examination. Time of ovulation ranged from 34 to 42 h postGnRH; however, ovulation occurred earlier in the Gonavet compared with the other groups (P < 0.05). Results of these experiments indicate that 1) barrows are an appropriate model for determining GnRH doses that can be effective in inducing a preovulatory-like LH surge in females; 2) the generic GnRH agonist Fertilan, at doses of 10 to 20 microg, can stimulate an LH surge in gilts, with subsequent ovulation; and 3) Fertilan at doses of 10 and 20 microg should be examined further for use in fixed-time insemination protocols.

Animals↗

PubMed2002

The relationship between estrous behavioral score and time of ovulation in dairy cattle.

One of the major contributors to poor fertility of a dairy herd is ineffective detection of estrus. Recently, it has become evident that cow factors contribute largely to low detection rates. Until now, standing behavior has been the symptom used to determine the right moment for insemination. However, standing behavior is not observed in over 50% of the cows in estrus in a number of herds, and no data are available to relate the moment of ovulation to other estrous symptoms. Therefore, in the present study, cows were observed for a number of visual signs of estrus, twice per day for 30 min, and the moment of ovulation was estimated by transrectal ultrasonographic scanning of the ovaries. In this study, 100 cows were detected in estrus visually, using a scoring system. Standing behavior was observed in 50% of those cows, although there was more than one cow in estrus at a time in most (85%) cases. There was no correlation between follicular size and ovulation time or estrous behavior score. Levels of 305-d milk yield and parity were also not correlated with estrous behavior scores. However, a significant correlation (0.31) was found between detection score and day of ovulation. A retrospective analysis revealed that cows that ovulated 0 to 24 h after artificial insemination (AD) scored almost three times the number of estrous behavior points compared to the ones that ovulated 24 to 48 h after AI. Ovulation more than 48 h after AI resulted in pregnancy in only 15% of the cows.

Animals↗

PubMed2003

Effects of GnRH administered to cows at the onset of estrus on timing of ovulation, endocrine responses, and conception.

Two experiments examined effects of GnRH administered within 3 h after onset of estrus (OE) on ovulation and conception in dairy cows. In experiment 1, 46 cows received either saline, 250 microg of GnRH, or 10 microg of the GnRH analogue, Buserelin. Cows were observed for estrus, blood samples were collected, and ovulations were monitored by ultrasound. In controls, 76% of cows had intervals from estrus to ovulation of < or = 30 h and 24% had intervals > 30 h. Treatment with either GnRH or GnRH analogue (data combined) increased magnitude of LH surges and decreased intervals from estrus to LH surge or to ovulation. Treated cows all ovulated < or = 30 h after OE. Among control cows, plasma estradiol concentrations before estrus correlated positively with amplitudes of LH surges. Higher plasma progesterone was observed in the subsequent estrous cycle in GnRH-treated cows compared to control cows with delayed ovulations. Experiment 2 included 152 primiparous and 211 multiparous cows in summer and winter. Injection of GnRH analogue at OE increased conception rates (CR) from 41.3 to 55.5% across seasons. In summer, GnRH treatment increased CR from 35.1 to 51.6%. Across seasons, GnRH increased CR from 36.0 to 61.5% in cows with lower body condition at insemination and GnRH increased CR (63.2 vs. 42.2%) in primiparous cows compared to controls. Use of GnRH eliminated differences in CR for cows inseminated early or late relative to OE and increased CR in cows having postpartum reproductive disorders. In conclusion, GnRH at onset of estrus increased LH surges, prevented delayed ovulation, and may increase subsequent progesterone concentrations. Treatments with GnRH increased conception in primiparous cows, during summer, and in cows with lower body condition.

Animals↗

PubMed2004

Use of estradiol cypionate as a substitute for GnRH in protocols for synchronizing ovulation in dairy cattle.

Our purpose was to determine whether estradiol cypionate (ECP) could be substituted for the second GnRH injection of the standard Ovsynch protocol (injection of GnRH given 7 d before and 48 h after PGF(2alpha), with timed AI [TAI] 12 to 20 h after the second GnRH injection). Lactating dairy cows ranging from 61 to 82 d in milk at TAI were studied in 14 replicates. Main effects were hormone (ECP vs. GnRH) to induce ovulation and exposure to progesterone (P4) or not during the week preceding PGF(2alpha)-induced luteolysis. Four treatments were: 1) 100 microg of GnRH at 48 h after PGF(2alpha) (Ovsynch; n = 27); 2) same as Ovsynch, plus a P4-releasing intravaginal insert (CIDR) placed for 7 d beginning at the first GnRH injection (Ovsynch + CIDR, n = 20); 3) same as Ovsynch, but substituting 1 mg of ECP for GnRH, and injecting ECP at 24 h after PGF(2alpha) (Heatsynch; n = 33); or 4) Heatsynch + CIDR (n = 26). The largest follicle was identified by ultrasonography 24 h after PGF(2alpha) and was monitored every 6 h until ovulation. Incidence of estrus was less after GnRH (54%) than after ECP (87%), but more GnRH-treated cows had LH surges detected (95 vs. 65%) and ovulated (100 vs. 86%). Duration of LH surges, but not peak concentrations, was less after GnRH than after ECP (6.1 +/- 0.7 vs. 12.2 +/- 0.9 h). Pre-treatment with P4 reduced the incidence of LH surges but had no effects on incidence of estrus or ovulation. Intervals to the LH surge and ovulation were less after GnRH than after ECP, but intervals between onset of the LH surge and ovulation did not differ (26 +/- 2 vs. 30 +/- 3 h). We concluded that substituting ECP for GnRH resulted in more cows in estrus and slightly fewer ovulating.

Administration, Intravaginal↗

PubMed1996

Neonatal androgenization potentiates the inhibitory effects of blood withdrawal on ovulation in the rat.

Rats treated on Day 5 of life with testosterone propionate (TP) were tested for their ovulatory response to pregnant mare's serum gonadotropin (PMSG) on the 30th day of life with and without cardiac puncture under ketamine/xylazine anesthesia. TP without cardiac puncture in doses of 0.625, 1.25, or 2.5 microg did not inhibit ovulation, but 5.0 microg of TP inhibited ovulation in 15 of 16 rats. When cardiac puncture was performed at 1900 hr in rats not given TP, seven of eight ovulated on Day 33. However, none of the rats that received either 1.25 or 2.5 microg of TP ovulated after cardiac puncture at 1900 hr, and only one of seven given the 0.625-microg dose ovulated. Thus, the stress of bleeding greatly enhanced the inhibitory effect of otherwise ineffective doses of TP. The preovulatory luteinizing hormone (LH) surge was delayed and diminished by neonatal TP in a dose-related manner in animals from which blood was drawn from a previously inserted catheter. When blood drawn from similarly TP-treated animals by cardiac puncture, serum levels of LH were further reduced. Progesterone, given at 1100 hr on Day 32, was capable of partially overcoming the inhibitory effects of the combined treatments on both ovulation and serum LH levels at all but the highest dose of TP tested (5.0 microg). We conclude that neonatal exposure to androgen sensitizes rats to ovulation-inhibiting factors, such as bleeding, in a manner which appears to delay as well as inhibit the preovulatory release of LH. Such early exposure to androgen, therefore, may determine the susceptibility of individuals to reproductive failure in adult life.

Animals↗

PubMed1985

Ovine luteinizing hormone-induced steroid and luteinizing hormone secretion, and ovulation in intact and pregnant mare serum gonadotropin-primed hens.

Studies were conducted to investigate the effect of ovine luteinizing hormone (LH) treatment on steroid and LH secretion and ovulation in intact, saline-primed hens and in pregnant mare serum gonadotropin (PMSG)-primed hens. Intact, saline-primed hens, injected 12 hr prior to the first (C1) ovulation of the sequence, responded with fully potentiated preovulatory surges of progesterone (P4) (peak value was 371% above preinjection values), estradiol-17 beta (E2) (117% above baseline), LH (220% above baseline), and premature ovulation. By comparison, those hens injected at the same time prior to the second (C2) ovulation responded with a lesser increase in plasma P4 (peak value was 305% above baseline) and E2 (72% above baseline), and there was no significant increase in plasma LH. Within this group, 4 of 5 hens failed to ovulate prematurely. All groups of PMSG-primed hens had significantly higher preinjection concentrations of P4 and E2, and lower basal concentrations of LH, compared to saline-primed hens. Subsequent to treatment of PMSG-primed hens with 25 or 100 micrograms ovine LH, there was a significant increase in plasma P4 to approximately 200% above preinjection concentrations. By contrast, there was a nonsignificant increase in plasma LH (50% above baseline values) and no significant increase in plasma E2. The ovulatory response following PMSG-priming was greatest in hens injected with 100 micrograms ovine LH (5 of 5 hens ovulated), while 3 of 5 hens injected with 25 micrograms ovine LH and 6 of 6 saline-challenged hens failed to ovulate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗