Absorbable deslorelin implants (Ovuplant) prolong postpartum anestrus in early ovulating dairy cows

Two experiments were conducted to investigate the use of a bioabsorbable implant of the GnRH agonist deslorelin to temporarily delay the resumption of postpartum ovulatory cycles in Holstein cows. In Experiment 1, recently calved cows were paired and received either a single implant (Ovuplant); Peptech Animal Health, Sydney, NSW, Australia) within 48 h of parturition (OVP; n=17), or remained as untreated controls (CON; n=17). Blood samples were collected for plasma progesterone assay three times weekly for 6 weeks to profile the pattern of resumption of ovulatory cycles. In Experiment 2, there were 15 CON and 15 OVP cows initially treated as for Experiment 1 as well as 15 OVP+SYNCH cows. Each cow in the CON and OVP+SYNCH groups received a progesterone vaginal insert (CIDR); Genetics Australia, Bacchus Marsh, Vic., Australia) for 7 days at 23 days postpartum (23 dpp) to synchronise estrus in cycling animals or to induce an ovulation with estrus in anestrus animals. Blood samples were collected weekly until removal of the CIDR insert, and then twice weekly until 56 dpp to monitor plasma P4 for retrospective determination of ovulation. Milk yield was monitored by twice daily electronic volume measurements and milk composition with once weekly milk composition analysis.In Experiment 1, CON cows began ovulating from 9 dpp; 15 of 17 had ovulated by the end of blood sampling at 42 dpp. None of the OVP cows ovulated until at least 24 dpp, and only 6 of 17 had ovulated by 42 dpp. The average day of first ovulation was extended from 22.4+/-2.7 dpp to 39.3+/-2.7 dpp (P<0.05). In Experiment 2, ovulation had occurred in 8 of 15 CON cows at the time of CIDR insertion (23 dpp), 0 of 15 OVP cows and 1 of 15 OVP+SYNCH cows. By 40 dpp (or 10 days following removal of the CIDR insert) every CON cow (15/15) had ovulated, but only 2 of 15 OVP+SYNCH cows and 1 of 15 OVP cows. None of these effects of treatment was associated with any changes in milk yield or composition in either experiment.In conclusion, inserting a bioabsorbable implant of deslorelin within 48 postpartum extended the interval to first ovulation to at least 24 dpp in 46 of 47 cows. Recovery periods were highly variable. This variability was not reduced by using a form of intravaginal progesterone supplementation that did produce a synchronised estrus with ovulation in anestrus animals that had not been treated with deslorelin.     

Efficacy of PGF(2alpha) to synchronize estrus in water buffalo cows (Bubalus bubalis) is dependent upon plasma progesterone concentration,corpus luteum size and ovarian follicular status before treatment

This study was conducted to identify factors affecting PGF(2alpha) efficacy to synchronize estrus in water buffalo cows. After detection of a corpus luteum (CL) by rectal palpation, cows were treated (im) with dinoprost (12.5, 25 or 50mg) or D(+) cloprostenol (75, 150 or 300 microg) in a total of 66 treatments. Blood samples were collected 0, 24 and 48 h after treatment and ultrasound examinations and observations for estrus were performed daily to the day of ovulation or to 6 days after treatment. No PGF(2alpha) dose-response pattern was observed and overall rates of luteal regression (progesterone <1.0 ng/ml at 48 h), estrus, no detected behavioral estrus with ovulation occurring, and ovulation were 71.2, 36.4, 19.7 and 54.5%, respectively. To analyze plasma progesterone concentrations and ovarian dynamics, cows were divided in three groups according to their response to treatment. Cows that failed to have ovulations from a follicle after treatment (Group A, n = 30) had (P < 0.05) a lower plasma progesterone concentration (2.98 ng/ml) and smaller CL area (CLA; 187.3 mm(2)) before treatment as compared with cows that had an ovulation from a follicle (4.43 ng/ml and 223.7 mm(2), respectively; Groups B and C, n = 36). In cows that failed to ovulate, plasma progesterone concentration decreased in the first 24 h, but did not decline further and was >1.0 ng/ml 48 h after treatment. Moreover, no significant change in CLA after treatment was detected, indicating that treatment induced only partial luteolysis. In cows that ovulated, plasma progesterone concentration and CLA decreased continuously from treatment to ovulation (consistent with complete luteolysis). Threshold values of 2.8 ng/ml for plasma progesterone concentration and 189 mm(2) for CLA were identified as the best predictors of ovulation before treatment (83.3 and 80.6% sensitivity and 58.6 and 65.5% specificity, respectively, with positive and negative predictive values around 71%). When the origin of the ovulatory follicle was investigated, the interval from treatment to ovulation was shorter (91.9 versus 113.3 h; P < 0.05), and the ovulatory follicle had a slower growth rate (1.02 versus 1.55 mm per day; P < 0.005), a lesser increase in diameter from treatment to ovulation (4.7 versus 8.0 mm; P < 0.001), and a greater maximum diameter (13.2 versus 12.1 mm; P < 0.05) in cows that ovulated from the largest follicle present in the ovary before treatment (Group B, n = 27) compared with cows that ovulated from the second largest follicle present in the ovary before treatment (Group C, n = 9). In summary, the efficacy of PGF(2alpha) for causing luteolysis and synchronizing estrus and ovulation in buffalo cows was dependent upon plasma progesterone concentration, CL size and ovarian follicular status before treatment.     

Effect of days postpartum and exogenous GnRH on reproductive hormone and ovarian changes in postpartum suckled beef cows

Two experiments were conducted to determine the effect of days postpartum and exogenous gonadotropin releasing hormone (GnRH) on reproductive hormone and ovarian changes in postpartum suckled beef cows. In experiment 1, eight suckled cows were bled at .5 hour intervals for 4 hours on days 7, 14, 21 and 28 postpartum. Although mean concentrations of plasma luteinizing hormone (LH) were positively correlated with days postpartum, mean concentrations did not differ. The mean maximum change and the variance of plasma LH were low on days 7, 14, 21 and 28 postpartum. Although the number of cows with an ovarian follicle and follicular size increased with days postpartum, mean concentrations of estradiol-17beta did not change. The interval from parturition to the first detected ovarian follicle and the first postpartum estrus was 17.5 +/- 2.6 days and 36.0 +/- 2.2 days, respectively. An elevation in plasma progesterone was detected about one week prior to the first postpartum estrus in 6 of the eight cows in the absence of corpora lutea. In experiment 2, gonadotropin releasing hormone (GnRH) induced ovulation in 4 of the 8 cows treated on day 27, 28 or 29 postpartum whereas none of the 8 saline treated cows ovulated to treatment. The interval from parturition to first estrus and conception were similar for both groups (P >.10).     

Gonadotropin-releasing hormone (GnRH) inhibits ovulation induced with luteinizing hormone (LH) in proestrous hypophysectomized rats

In this paper we present evidence that a single low dose of the natural synthetic gonadotropin-releasing hormone (GnRH), inhibits ovulation induced by LH in proestrous-hypophysectomized rats. Rats hypophysectomized by the parapharyngeal route in the morning of proestrus received an intravenous injection of 100 or 300 ng GnRH at 1400 h immediately followed by 1.0 microgram LH per 100 g bw. In control groups, either one or both hormones were replaced with 0.9% NaCl. Ovulation was assessed the following morning by counting the ova present in oviductal flushings. All the rats treated with LH alone ovulated, and the addition of GnRH reduced significantly the number of ovulating rats and the number of ova per ovulating rat. In other groups of rats hypophysectomized in the morning of proestrus and treated in the same way, ovarian or adrenal secretory rates of estradiol and/or progesterone were measured after cannulation of the corresponding vein, in the afternoon of proestrus. In these animals, GnRH failed to inhibit either the ovarian progesterone surge observed 2 h after LH administration, or the adrenal progesterone secretion. All hypophysectomized rats showed lower ovarian secretory rate of estradiol than intact rats; this rate was not affected by treatment with LH or LH plus GnRH. The systemic estradiol levels in plasma of hypophysectomized rats were distributed within a range of 20 pg/ml to 50 pg/ml. The number of rats whose levels were above 21 pg/ml on estrus day was significantly higher in rats receiving 300 ng GnRH as compared to those receiving 100 ng GnRH, reaching values that surpassed the concentration found in intact, untreated animals at the same time of estrus. This effect did not depend on LH administration.     

Ovulation, ovarian function, and reproductive performance after treatments with GnRH in postpartum suckled cows

Two experiments were conducted to determine whether treatments with gonadotropin releasing hormone (GnRH) during the early postpartum period in suckled cows would induce ovulation and initiate regular estrous cycles. In Experiment I, 0, 100 or 200mug of GnRH was given to 22 suckled Angus x Holstein cows at three and again at five weeks postpartum. Serum luteinizing hormone (LH) responses did not differ between cows given 100 or 200mug of GnRH. Treatment with GnRH tended to increase the percentage of cows exhibiting estrus by 30 and 60 days postpartum, but reproductive performance during the breeding season did not differ among groups. In Experiment II, 70 suckled Hereford cows were given either no treatment or 200mug of GnRH at 7 weeks postpartum. Cows given GnRH received either no treatment prior to GnRH or were separated from their calves for 24 hr prior to GnRH treatment. Half of the cows that were separated from their calves also received progesterone via a progesterone intravaginal device (PRID) for 12 days prior to calf removal. Treatment with GnRH alone tended to increase the percentage of anestrous cows which ovulated by 8 days after treatment. Calf removal did not increase the ovulatory response to GnRH, but PRID treatment did. More estrous periods were detected in GnRH-treated cows than in control cows during 20 days after GnRH treatment.     

Simultaneous injection of PGF2alpha and GnRH into diestrous dairy cows delays return to estrus

Simultaneous injections of prostaglandin F2alpha (PGF) and gonadotropin releasing hormone (GnRH) or saline were given to 32 diestrous dairy cows to test the ability of GnRH to improve estrous and ovulation synchrony beyond that of PGF alone. Cows were randomly assigned to receive PGF on Day 8 or Day 10 of the estrous cycle (estrus = Day 0), and all cows were further assigned to simultaneous injection of GnRH or saline. Corpus luteum (CL) regression, return to estrus and follicular activity were monitored by plasma progesterone assay, twice-daily estrous detection and ultrasonographic examination, respectively. Plasma progesterone concentrations declined to <1.0 ng/ml at 24 hours after PGF in all cows and were not affected by GnRH. Gonadotropin releasing hormone inducted premature ovulation or delayed return to estrus in 7 of 8 cows treated with PGF/GnRH on Day 8 and 3 of 8 cows treated with PGF/GnRH on Day 10. Further, cows with premature GnRH-induced ovulations failed to develop and maintain a fully functional CL, and all returned to estrus 7 to 13 days after the induced ovulation. These data indicate that GnRH administered simultaneously with a luteolytic dose of PGF disrupts follicular dynamics and induces premature ovulation or delays normal return to estrus and, therefore, does not improve the synchrony of estrus and ovulation achieved with PGF alone.     

Influence of lameness on follicular growth, ovulation, reproductive hormone concentrations and estrus behavior in dairy cows

The objective of this study was to examine the effect of a chronic stressor, lameness, on reproductive parameters. Seventy cows 30-80 days post-partum were scored for lameness and follicular phases synchronized with GnRH followed seven days later by prostaglandin (PG). Fifteen Lame animals did not respond to GnRH ovarian stimulation. Milk progesterone for 5 days prior to PG was lower in the remaining Lame cows than Healthy herdmates. Fewer Lame cows ovulated (26/37 versus 17/18; P = 0.04) and the interval from PG to ovulation was shorter in Lame cows. In Subset 1 (20 animals), the LH pulse frequency was similar in ovulating animals (Lame and Healthy) but lower in Lame non-ovulators. An LH surge always preceded ovulation but lameness did not affect the interval from PG to LH surge onset or LH surge concentrations. Before the LH surge, estradiol was lower in non-ovulating cows compared to those that ovulated and estradiol concentrations were positively correlated with LH pulse frequency. In Subset 2 (45 cows), Lame ovulating cows had a less intense estrus than Healthy cows, although Lame cows began estrus and stood-to-be-mounted earlier than Healthy cows. In conclusion, we have identified several parameters to explain poor fertility in some chronically stressed animals. From 30 to 80 days post-partum, there was a graded effect that ranged from 29% Lame cows with absence of ovarian activity, whereas another 21% Lame cows failed to express estrus or ovulate a low estrogenic follicle; in 50% cows, many reproductive parameters were unaffected by lameness.     

Influence of GnRH infusion on endocrine parameters and duration of postpartum anestrus in beef cows

The effect of an intravenous infusion of gonadotrophin releasing hormone (GnRH) on the duration of postpartum anestrus in suckled beef cows was studied. Twenty-eight, mature, suckled beef cows were assigned in equal numbers to one of four treatment groups which were based on infusion with saline or GnRH (15ug/hour for 12 hours) and stage postpartum (pp) (20 or 35 days). Serum LH and progesterone were determined by radioimmunoassay for the period which began 5 days pre-infusion and ended at 55 days postpartum (ie: 35 or 20 days post-infusion). Serum LH remained below 5ng/ml during infusion in all control cows. Peak serum LH values, times of LH peaks, and duration of LH responses (means +/- SE) during infusion were 49 +/- 12 ng/ml, 162 +/- 42 minutes and 7.8 +/- 1.3 hours for the 20 day group and 44 +/- ng/ml, 144 +/- 6 minutes, and 8.2 +/- 1.1 hours for the 35 day group respectively. Serum progesterone levels indicated that the proportion of cows showing the onset of estrous cycles within 10 days of infusion was greater in the 20 day pp GnRH group (4/7) than the 20 day pp saline group (0/7) (p < .05) but was not significantly different between the 35 day pp GnRH (4/7) and 35 day pp saline (2/6) groups. The incidence of estrus was not affected by GnRH treatment and was 37% in all cows prior to 55 days pp. It was concluded that infusions of GnRH for 12 hours at a rate of 15 ug/hour could induce estrous cycles in suckled beef cows treated at 20 days postpartum.     

Conception rates and serum progesterone concentration in dairy cattle administered gonadotropin releasing hormone 5 days after artificial insemination

The objectives of this study were to determine the effect of administration of exogenous GnRH 5days after artificial insemination (AI) on ovarian structures, serum progesterone concentration, and conception rates in lactating dairy cows. In experiment 1, 23 Holstein cows were synchronized using the Ovsynch protocol. Five days after AI (day 0) cows were assigned randomly to receive either saline (saline; n=11) or 100microg GnRH (GnRH; n=12). To examine ovarian structures, ultrasonography was performed on day 1 and every other day beginning on day 5 until day 13. On days 5 and 13 blood samples were obtained to measure serum progesterone concentrations. All cows in the GnRH-treated group developed an accessory corpus luteum (CL), whereas cows in the saline group did not. Mean serum progesterone concentrations did not differ between GnRH and saline groups on day 5 (1.64+/-0.46ng/ml versus 2.04+/-0.48ng/ml). On day 13 serum progesterone concentrations were greater (P<0.05) in the GnRH group compared with saline (5.22+/-0.46ng/ml versus 3.36+/-0.48ng/ml). In experiment 2, 542 lactating cows, at two different commercial dairies, were used to test the effect of administering GnRH 5 days after AI on conception rates. Cows were synchronized and detected for estrus according to tail chalk removal. Cows detected in estrus received AI within 1h after detection of estrus. Five days after AI, cows were assigned randomly to receive either GnRH (n=266) or saline (n=276). Pregnancy status was determined by palpation per rectum of uterine contents approximately 40 days after AI. There was no effect of farm on conception rate. There was no effect of treatment as conception rates did not differ between GnRH and saline groups (26.7% GnRH versus 24.3% saline). Regardless of treatment, days in milk, parity, milk yield, and number of services had no effect on the odds ratio of pregnancy. In summary, the results of this study indicated that GnRH administered 5 days after AI increased serum progesterone by developing an accessory CL but did not improve conception rates in dairy cattle.     

Temporal relationships among estrus, body temperature, milk yield, progesterone and luteinizing hormone levels, and ovulation in dairy cows

Estrous cycles of 10 postpartum cyclic Holstein cows were synchronized using prostaglandin f(2alpha) (PGF(2alpha)) given twice 12 d apart to study the relationship of the onset of estrus, body temperature, milk yield, luteinizing hormone (LH) and progesterone concentration to ovulation. Blood samples and body temperatures (vaginal and rectal) were taken every 4 h until ovulation, starting 4 h prior to the second PGF(2alpha) treatment. All cows were observed for estrus following the second administration of PGF(2alpha). Ultrasound scanning of the ovaries commenced at standing estrus and thereafter every 2 h until the disappearance of the fluid filled preovulatory follicle (ovulation). Two cows failed to ovulate and became cystic following the second PGF(2alpha) treatment. The remaining eight cows exhibited a decline in progesterone to <1.0 ng/ml within 28 h, standing estrus and a measurable rise (> 1.0 degrees C) in vaginal but not rectal temperature, and ovulated 90 +/- 10 h after the second PGF(2alpha) treatment. Onset of standing estrus, LH peak and vaginal temperature were highly correlated (P<0.05) with time of ovulation (0.82, 0.81 and 0.74, respectively). Intervals to ovulation tended to depend upon parity. Pluriparous (n = 4) and biparous (n = 4) cows ovulated within 24 and 30 +/- 3 h from the onset of standing estrus; 22 and 31 +/- 2 h from the LH peak; and 22 and 27 +/- 3 h from peak vaginal temperature (mean +/- standard error of the mean), respectively. The results indicated that the onset of standing estrus and rise in vaginal temperature are good practical parameters for predicting ovulation time in dairy cattle.     

Profiles of LH, FSH and progesterone in postpartum dairy cows and their relationship to the commencement of cyclic functions

In 25, 3-to-13 year old, dairy cows (Braunvieh and Hoehenfleckyieh) FSH, LH and progesterone plasma profiles were determined by RIA. Blood was sampled at 6-hour intervals from parturition to 40–78 days postpartum, and the results correlated with the commencement of cyclic functions. For FSH, generally basic values were recorded, without characteristic features associating any values with the onset of cyclic ovarian activities or the occurrence of the first heat. LH profiles varied greatly between individuals with regard to the onset of elevations, regularity of patterns and peak values. The first preovulatory LH peak was recorded 17.3±9.8 days (range 4–46) postpartum. The first heat occurred on day 28.4±16 (range 6–55) postpartum, indicating that 13/23 cows ovulated without behavioral estrus, as reproductive cycles were re-established. Peak LH values increased with progressive cycles (1st peak 5.7±4.8 ng/ml; 2nd peak 11.8±8.7 ng/ml; 3rd peak 13.5±9.9 ng/ml plasma). Progesterone values also showed great variations in the profile of their first postpartum elevation. In 13/25 cows the first cycle was shortened (13.1±2.9 days), prolonged in 3 animals (34±4 days) and normal in 7 cows (20.4±1.9 days). Heat, preovulatory LH peak and progesterone profile were normal in all animals on subsequent cycles. Two animals did not start cycling.     

Influence of intrauterine infections and follicular development on the response to GnRH administration in postpartum dairy cows

The effects of intrauterine infections and prior follicular development on the response to gonadotropin releasing hormone (GnRH) administration in postpartum dairy cows were studied. Fifty lactating Holstein cows were assigned at random to one of two groups after calving. Group I (control) consisted of 25 cows given a single intramuscular injection of saline on Day 15 postpartum. Group II (treated) consisted of 25 herdmates given a single i.m. injection of 100 mug of GnRH on Day 15 postpartum. Palpation per rectum and real-time ultrasonography were used to monitor ovarian activity, and endometrial swabs were cultured to determine the presence of uterine infection. Blood samples were collected for progesterone (P(4)) and luteinizing hormone (LH) analysis. Fourteen cows (control, n = 5; treated, n = 9) did not ovulate during the first 60 d postpartum. Ovaries in these cows contained 4 to 8-mm size follicles and both P(4) and LH remained at basal concentrations. Fourteen other cows (control, n = 6; treated, n = 8) ovulated by Day 15 postpartum. Follicles >/= 10 mm were demonstrable in the ovaries of these cows before or by Day 12 postpartum. GnRH treatment had no effect on the lifespan of the existing corpus luteum in these cows. In the remaining cows, 7 of 14 Control and all 8 Treated cows ovulated within 3 d of treatment. All cows ovulating within this period were free of uterine infection and the ovaries contained follicles 相似文献   

Hormone response of dairy cows with ovarian cysts after treatment with HCG or GnRH

Twenty lactating Holstein and Guernsey cows, diagnosed by rectal palpation as having ovarian cysts, were randomly divided within breed into two groups to receive either a single intramuscular injection of 100 μg of synthetic gonadotropin releasing hormone (GnRH) or an intravenous injection of 10,000 IU of human chorionic gonadotropin (HCG). The objective was to compare hormonal and clinical changes in cows with ovarian cysts following treatment with GnRH and HCG. Eight of ten and nine of ten cows given either GnRH and HCG, respectively, responded to treatment and subsequent fertility was not different between the two groups. Pre-injection plasma levels of LH, progesterone, and estradiol were highly variable. Mean plasma levels of LH, progesterone and estradiol did not differ between groups either following treatment (days 1–17 post-treatment), at the subsequent estrus, or during days 1–13 following the subsequent estrus. Mean LH levels did not differ significantly on the days either post-treatment or post-estrus except that levels were higher (P < .01) at the subsequent estrus as compared to the other days. Mean progesterone levels increased after treatment with either GnRH or HCG and were higher on days 5, 9 and 13 post-estrus and post-treatment as compared to the subsequent estrus. Mean levels of estradiol were higher (P < .05) at the subsequent estrus than any other time post-treatment or post-estrus. No other days were significantly different. In conclusion, GnRH and HCG are effective treatments for ovarian cysts in cattle. Endocrine response on days following treatment are similar for both compounds.     

Estrous response of early postpartum beef heifers to progesterone and estradiol-17beta during restricted dietary energy

A study was conducted to determine reproductive response of primiparous beef heifers to an ovulation induction regimen during restricted dietary energy intake. Thirty-seven Barzona x Hereford heifers, maintained under drylot conditions, were utilized. Heifers were restricted in TDN on a pen basis to approximately 50% of N.R.C. recommendations for the first 90 days postpartum, then received 120% for 80 days thereafter. All animals received control injections (C) or 30 mg progesterone on day 15 postpartum followed in 48 hours by 2 mg estradiol-17beta (PE). Treated heifers not ovulating at first treatment and/or not cycling, were re-treated at 60 day postpartum, with non-cycling C heifers receiving control injections. Intact fertile bulls were maintained with the heifers from day 1 to 170 days postpartum, with visual observations for signs of estrus and breeding activity conducted twice daily during this period. At first treatment, seven of 18 heifers ovulated, one conceived and four continued to cycle. At second treatment, three of 13 conceived and seven returned to a synchronized estrus 15 to 21 days later. Although intervals to first estrous behavior and estrus favored PE heifers (P< .05), by 90 and 170 days postpartum no advantage in interval to conception or number conceiving was observed.     

Reproductive responses of early postpartum dairy cattle to continuous treatment with a GnRH agonist (deslorelin) for 28 days to delay the resumption of ovulation

An experiment was conducted to investigate the potential of chronic delivery of a potent GnRH agonist (deslorelin) via subcutaneous implants to delay the resumption of ovulatory cycles in postpartum dairy cattle. Cows received either a single deslorelin implant (n=40; DES) within 7 days of calving or were untreated (n=24; CON). Blood samples were collected thrice weekly during the period the implants were in place. Plasma concentrations of progesterone (P4) and 17beta-oestradiol (E2) were measured along with selected serum metabolites. Implants were removed after 28 days and cattle monitored daily for behavioral oestrus. Serial weekly blood samples were collected to detect the occurrence of ovulation. Cows were artificially inseminated as they were detected in oestrus from 30 days after implant removal. Pregnancy status was subsequently determined by manual palpation of uterine contents at strategic intervals.Insertion of implants induced ovulation in 3/40 cows as determined by a rise in progesterone 7 days later. Deslorelin implants delayed the onset of ovulatory cycles compared with untreated herdmates (mean 43.4+/-4.2 versus 57.3+/-1.6 days postpartum; P<0.001). A noticeable delay of at least 12 days was observed between implant removal and the first animals ovulating. Mean plasma E2 concentrations during the period the implants were in place were similar for DES and CON cows that experienced a prolonged spontaneous postpartum anoestrus (low P4 >60 days), although both groups had concentrations only 20% of CON cows that had ovulated prior to 30 days postpartum.The patterns of recovery following implant removal were highly variable. A number of DES cows showed a low and transient rise in plasma progesterone around 21 days after implant removal. Some cows displayed oestrus but did not appear to form a fully functional corpus luteum with this phenomenon being more prevalent among DES cows (7 of 37 versus 1 of 21; P<0.05). Overall, significantly more DES cows were detected in oestrus without ovulating compared to CON cows. Final pregnancy rates did not differ between DES and CON groups. The mean time to conception for DES cows was longer (21.2+/-5.6 versus 41.1+/-7.4 days, CON versus DES; P<0.01). This difference was not present if the time from first ovulation to conception was compared (50.5+/-5.3 versus 43.5+/-9.3 days, CON versus DES; P>0.05). Deslorelin implants provided a reliable method of inducing anoestrus when treatment was initiated prior to 3 days postpartum. A variable pattern of recovery was observed which delayed conception but did not ultimately reduce the final proportion pregnant at the completion of mating. The study demonstrates the potential of GnRH agonists to control postpartum reproductive function to manipulate the fertility of dairy cows.     

Endocrine response of postpartum anestrous beef cows to GnRH or PMSG

Forty-one postpartum anestrous Hereford cows, maintained under range conditions, were used to determine the influence of gonadotropin releasing hormone (GnRH) or pregnant mare serum gonadotropin (PMSG) on ovarian function. Anestrous cows were identified by estrous detection with sterile bulls and concentrations of progesterone in plasma obtained weekly. At 45 +/- 2 days postpartum, cows were allotted to the following treatments: (1) control (saline), (2) 100 mug GnRH, (3) 200 mug GnRH, (4) 200 mug GnRH in carboxymethyl cellulose (CMC), (5) 500 IU PMSG, (6) 1,000 IU PMSG or (7) 2,000 IU PMSG. Cows were bled frequently the first day after treatment and then every other day until 85 days postpartum. The LH responses after 100 and 200 mug of GnRH were not significantly different and mixing 200 mug GnRH with CMC before injection did not significantly alter the LH response. During the first 20 days after treatment, neither GnRH nor 500 IU PMSG altered estradiol concentrations in plasma, but treatment of cows with 1,000 or 2,000 IU PMSG resulted in increased (P<0.01) concentrations of estradiol. The time postpartum required for concentrations of progesterone in plasma to exceed 1 ng/ml was reduced (P<0.05) by all treatments except 100 mug GnRH. These data indicate that GnRH causes LH release in anestrous range cows and that treatment with 1,000 or 2,000 IU PMSG initiates ovarian activity as evidenced by increased concentrations of estradiol in plasma.     

Ovarian follicular wave synchronization and induction of ovulation in postpartum beef cows

An experiment was designed to evaluate a) the effect of a progesterone-estradiol combined treatment on ovarian follicular dynamics in postpartum beef cows, and b) ovulation and the subsequent luteal activity after short-term calf removal and GnRH agonist treatment. Multiparous Angus cows (25 to 40 d after calving) were assigned to the following treatments: untreated (Control, n = 9); short term calf removal (CR, n = 8); progesterone (CIDR, n = 9) and progesterone plus estradiol-17 beta (CIDR + E-17 beta, n = 9). Progesterone treatment (CIDR) lasted 8 d and the day of device insertion was considered as Day 0. Cows in the CIDR + E-17 beta group also received an i.m. injection of 5 mg of E-17 beta on Day 1. On Day 8, calves were removed for 48 h (CR, CIDR and CIDR + E-17 beta groups) and 6 h before the end of calf removal these cows also received an i.m. injection of 8 micrograms of Busereline (GnRH). Anestrus was confirmed in all cows by the absence of luteal tissue and progesterone concentrations below 1 ng ml-1 at the beginning of the experiment. Although mean (+/- SEM) interval from the beginning of the experiment (Day 0) to wave emergence did not differ (P > 0.05) among treatment groups (Control, 1.9 +/- 1.0, range -2 to 7 d; CR, 3.9 +/- 0.7, range 0 to 6 d; CIDR, 2.8 +/- 0.5, range 0 to 4 d and CIDR + E-17 beta, 4.1 +/- 0.2, range 3 to 5), the variability was less (P < 0.05) in the CIDR + E-17 beta group. The proportion of cows ovulating 24 to 48 h after GnRH administration tended (P = 0.08) to be higher in cows from CIDR + E-17 beta group (8/9) than in those of CR (5/8) or CIDR (6/9) groups, respectively and was associated with a higher proportion (P < 0.05) of CIDR + E-17 beta treated cows (9/9) that had a dominant follicle in the growing/early static phase at the time of GnRH treatment compared to the other GnRH treated groups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows ovulated 0-24 h after GnRH and only one Control cow ovulated the day before the time of GnRH administration. Cows pretreated with progesterone had longer (P < 0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR + E-17 beta, 13.9 +/- 0.6 d) than those not treated with CIDR (Control, 5, CR, 4.0 +/- 0.4). We conclude that progesterone plus estradiol treatment results in tightly synchronized wave emergence and high GnRH-induced ovulation rate with normal luteal activity in postpartum beef cattle.     

FSH and LH variations in beef cows during the postpartum period

To study the plasma gonadotrophin profiles of 9 cows after parturition, blood samples were obtained every 20 min for 12 hrs on three occasions between 5 and 50 days postpartum and analysed by RIA techniques. The time of the first ovulation, as judged by plasma progesterone levels, varied from 30 to more than 60 days postpartum. Variations in mean levels of FSH and LH were not significantly correlated with the postpartum interval. However, the mean levels of plasma FSH and number of LH pulses were lower in females which had not ovulated than in those which had. The cows could be classified into four groups: group 1 with less than 4 LH pulses in 12 hrs and a mean plasma FSH level less than 138 ng/ml; group 2 with more than 4 LH pulses in 12 hrs and varying plasma FSH levels; group 3 with less than 4 LH pulses in 12 hrs and a mean plasma FSH level greater than 138 ng/ml; group 4 which had ovulated. This classification indicated that the LH and FSH levels progressed significantly (2.46 to 3.56 ng/ml, P less than 0.05; 120 to 159 ng/ml, P less than 0.01, respectively) from groups 1 to 3, and that they decreased in the females which had ovulated (group 4). Since the time of the first ovulation after parturition varied, it was not possible to demonstrate any relationship between that interval and the mean plasma gonadotrophin profiles. However, when ovulation was considered as time zero there was a clear increase in plasma gonadotrophin before ovulation.     

Luteal activity at the onset of a timed insemination protocol affects reproductive outcome in early postpartum dairy cows

This study was designed to compare two timed insemination protocols, in which progesterone, GnRH and PGF2alpha were combined, with the Ovsynch protocol in presynchronized, early postpartum dairy cows. Reproductive performance was also evaluated according to whether cows showed high or low plasma progesterone concentration, at the onset of treatment. One hundred and six early postpartum dairy cows were presynchronized with two cloprostenol treatments given 14 days apart, and then assigned to one of the three treatment groups. Treatments for the synchronization of estrus in all three groups started 7 days after the second cloprostenol injection, which was considered Day 0 of the actual treatment regime. Cows in the control group (Ovsynch, n=30) were treated with GnRH on Day 0, PGF2alpha on Day 7, and were given a second dose of GnRH 32 h later. Cows in group PRID (n=45) were fitted with a progesterone releasing intravaginal device (PRID) for 9 days, and were given GnRH at the time of PRID insertion and PGF2alpha on Day 7. In group PRID/GnRH (n=31), cows received the same treatment as in the PRID group, but were given an additional GnRH injection 36 h after PRID removal. Cows were inseminated 16-20 h after the administration of the second GnRH dose in the Ovsynch group, and 56 h after PRID removal in the PRID and PRID/GnRH groups. Ovulation rate was determined on Day 11 postinsemination by detecting the presence of a corpus luteum in the ovaries. Lactation number, milk production, body condition at the onset of treatment and treatment regime were included as potential factors influencing ovulation and pregnancy after synchronization. Logistic regression analysis for cows with high and low progesterone concentration on treatment Day 0 revealed that none of the factors included in the models, except the interaction between progesterone and treatment regime, influenced the risk of ovulation and pregnancy significantly. In cows with high progesterone concentration at treatment onset, Ovsynch treatment resulted in a significantly improved pregnancy rate over values obtained following PRID or PRID/GnRH treatment. In cows with low progesterone concentration, PRID or PRID/GnRH treatment led to markedly increased ovulation and pregnancy rates with respect to Ovsynch treatment. These findings suggest the importance of establishing ovarian status in early postpartum dairy cows before starting a timed AI protocol, in terms of luteal activity assessed by blood progesterone.     

Reproductive hormones associated with the ovarian cyst response to GnRH

Eighteen cows with ovarian cysts were administered 100 mug of GnRH and bled prior to treatment, at half hour intervals for 4 hours posttreatment and on days 1, 5 and 9 posttreatment. Blood plasma was analyzed for estradiol-17beta, progesterone and LH by radioimmunoassay. Response to treatment was recorded as positive if ovulation was detected within 30 days posttreatment. Fourteen cows (78%) initiated ovarian cycles by 30 days posttreatment. Mean pretreatment concentrations of estradiol-17beta, progesterone and LH and the GnRH induced LH release were not different for positive or no response cows. However, all seven cows that had pretreatment progesterone concentrations greater than 1.0 ng/ml had a positive response to treatment. Eight of the remaining eleven cows had a progesterone response (mean progesterone concentrations on days 5 and 9 posttreatment) greater than 1.0 ng/ml; seven had a positive response to treatment. In summary, most cows with ovarian cysts administered GnRH will initiate ovarian cycles within 30 days if: 1) pretreatment progesterone concentrations are greater than 1.0 ng/ml or 2) if progesterone response is greater than 1.0 ng/ml.