Effect of gonadotrophin releasing hormone on levels of luteinising hormone in cattle synchronised with dinoprost

Interval from Oestrus to Ovulation in Dairy Cows-A Key Factor for Insemination Time: A Review

This review describes the oestrus-to-ovulation interval, the possibility of predicting the time of ovulation, and the optimum time for insemination relative to oestrus in dairy cows. The duration of oestrus in dairy cows is approximately 8-20 h, with differences possibly related to the methods of oestrus detection and the frequency of observations. Most cows ovulate approximately 24-33 h after the onset of oestrus and 15-22 h after the end of oestrus. The interval from the preovulatory luteinising hormone (LH) surge to ovulation is approximately 4-30 h. Ovulation occurs when follicle diameter averages 18-20 mm. When it is possible to correctly determine the beginning of oestrus, artificial insemination can be performed utilizing the "a.m.-p.m. rule", and only one insemination may be applied. In cows with too long or too short oestrus-to-ovulation intervals, fertility can be compromised. One important factor that can alter the oestrus-to-ovulation interval is acute or chronic heat stress during the warm season. When there is a risk that insemination may occur too early or too late with respect to the time of ovulation, GnRH administration can be considered.

Effect of prostaglandin F2α and GnRH administration at the time of artificial insemination on reproductive performance of dairy cows

The present study aimed to determine the effect of administrating prostaglandin F2α (PGF2α) and GnRH at the time of artificial insemination (AI) on the pregnancy per artificial insemination (P/AI) and the pregnancy survival rate of dairy cows. A number of 830 lactating Holstein cows were randomly divided into four groups. Cows in group 1 (n=200) treated with 150 µg d-cloprostenol. In group 2 (n=212), cows received 10 µg buserelin acetate, and group 3 (n=205) was treated with both 150 µg d-cloprostenol and 10 µg buserelin acetate. In addition, 213 cows were assigned as control group which received normal saline as placebo (group 4). To measure progesterone, milk samples were collected at the insemination day and five days later. Pregnancy diagnosis was performed 28 and 60 days after the insemination, and the size and number of corpus luteum (CL) and twin pregnancies were recorded. Hormone therapies had no effect on the P/AI, pregnancy survival rate, and the size and number of CL. The P/AI ratio in groups 1, 2, 3 and 4 were 38.50%, 42.92%, 41.46% and 40.84%, and the pregnancy survival rates in groups 1, 2, 3 and 4 were 84.42%, 86.81%, 88.23% and 83.91%, respectively. The probability of a twin pregnancy was significantly higher in group 1 (15.58%) than other groups. There was no significant difference between groups in terms of the offspring gender. In conclusion, the administration of d-cloprostenol or buserelin acetate at the time of AI had no effect on P/AI and pregnancy survival rate in dairy cattle under no heat stress condition, while the administration of d-cloprostenol increased the probability of twin pregnancies.

The effect of administration of different levels of GnRH on the day 0, 5 and 12 post-insemination on progesterone concentration in dairy heifers

This study was carried out to evaluate the effects of different levels of GnRH in different days of reproductive cycle on progesterone concentration in dairy heifers. Two hundred heifers were divided into ten experimental treatment: control group with no injection (1) administration of 2.5 mL Gonadorelin (a GnRH analogue) in day of insemination (2) administration of 5 mL GnRH in day of insemination (3) administration of 10 mL GnRH in day of AI insemination (4) administration of 2.5 mL GnRH in day 5 post-insemination (5) administration of 5 mL GnRH in day5 post-insemination (6) administration of 10 mL GnRH in day5 post-insemination (7) administration of 2.5 mL GnRH in day 12 post-insemination (8) administration of 5 mL GnRH in day 12 post-insemination (9) administration of 10 mL GnRH in day 12 post-insemination. Blood samples were collected in days 0, 5, 12 and 19 post insemination (AI = Day 0) for analysis of serum P4 concentration. There was no significant difference among experimental groups on day of insemination. Evaluation of P4 concentration on day 19 illustrated differences in progesterone concentration between groups on day 19 post-insemination. P4 concentration of serum in the day 19 post-insemination significantly increased in groups either by 5 or 10 mL injection of GnRH whether in day 5 or 12 post-insemination versus control group (9.24 +/- 2.2, 8.6 +/- 1.96, 9.43 +/- 2.15 and 9.42 +/- 2.14 versus 5.5 +/- 0.8, respectively; p < 0.05). GnRH administration in the day 5 and 12 post-AI significantly increased progesterone concentration that may decline early embryonic death and improve pregnancy rate.

Veterinary clinical application of GnRH—questions of efficacy

The efficacy of GnRH treatments are reviewed in relation to prevention of embryo mortality, control of follicle development in synchronization programmes using PG as luteolysin, induction of ovulation in post-partum anoestrus and in bovine cystic ovarian disease. It is suggested that in cattle that GnRH is effective in increasing pregnancy rates when given either at the time of insemination (first or repeat) or between days 11 and 14 after insemination. Evidence is also presented for positive effects on pregnancy rates in sheep, mares and sows. Use of GnRH as an integral part of synchronising regimens where it is given 7 days before PG and then again 48-60 h after PG appears to be effective in increasing the synchrony of ovulation in controlled breeding programmes. The main synchronizing effect seems to reside in the second GnRH injection whereas the importance of the first is in prolonging the luteal phase in those cows treated late in the cycle. The published work on the potential use of GnRH to induce ovulation in anovulatory cattle is reviewed. Neither bolus dose injections, pulsatile, continuous infusion, nor controlled release formulations of GnRH, have yet proved effective in inducing fertile ovulations in a predictable or consistent manner. It is suggested that this is due to the variability of follicular status when treatment is initiated. GnRH is commonly used in the treatment of bovine cystic ovarian disease. However, although stimulating ovulation/luteinisation of a new follicle and luteinisation of the cyst, fertility of treated cattle remains very poor and it is suggested that a better understanding of the disease is needed before more effective treatments can be developed.

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.

Development of a gonadotrophin-releasing hormone and prostaglandin regimen for the planned breeding of dairy cows

Four studies were carried out to determine the ovarian responses of dairy cows undergoing natural oestrous cycles to sequential injections of gonadotrophin-releasing hormone (GnRH), followed seven days later by prostaglandin and, 48 to 72 hours later, by a second injection of GnRH. In study 1, of 60 cows so treated, 47 were in the intended periovulatory phase when a fixed-time insemination was given 72 hours after the prostaglandin. In study 2, detailed observations were made in 32 cows treated as in study 1, using ultrasound to determine the optimum time to administer the second dose of GnRH. Ovulation was most effectively synchronised by giving GnRH 56 to 60 hours after the prostaglandin. Study 3 investigated the timing of ovulation when no initial dose of GnRH was given. Six cows were injected with prostaglandin on day 12 of the oestrous cycle, followed by GnRH 60 hours later. Five of the six cows ovulated 24 to 36 hours after GnRH, an equivalent timing and synchrony to that in study 2, in which a dose of GnRH had been given seven days before prostaglandin. In study 4, an initial dose of GnRH was given to six cows late (day 17) in the oestrous cycle, and prostaglandin seven days later. The GnRH treatment delayed luteolysis in five of the cows so that they were responsive to the prostaglandin and ovulated 24 to 36 hours after the second dose of GnRH. The use of GnRH (day 0) - prostaglandin (day 7) - GnRH (day 9.5) appears to be an effective means of synchronising ovulation in most cows.

Ovarian and hormonal responses of cows to treatment with an analogue of gonadotrophin releasing hormone and prostaglandin F2 alpha

Blood samples were taken from 11 cows and their ovaries were scanned by ultrasound at least daily. Around day 5 of an induced cycle, they were injected with 10 micrograms buserelin, an analogue of gonadotrophin releasing hormone, and on day 12 they received 0.5 mg cloprostenol, an analogue of prostaglandin F2 alpha (PGF2 alpha). Two days later six of the cows (the treated group) received a second injection of 10 micrograms buserelin, but the remaining five received no further treatment (control group). The dominant, that is, the largest follicle in each cow disappeared after the first buserelin injection and was replaced by a new one which grew synchronously in all the cows until after the treatment with PGF2 alpha. Ovulation occurred significantly earlier after PGF2 alpha in the treated group than in the control group (72 to 96 hours v 96 to 120 hours; P < 0.05). Plasma progesterone concentrations then increased more rapidly in the treated group than in the control group and were significantly higher on days 3 and 4 after ovulation (P < 0.05).

Comparison of pregnancy rates of repeat-breeder dairy cows given gonadotropin releasing hormone at or prior to the time of insemination

A total of 585 repeat-breeder dairy cows was used to study the effect of GnRH treatment, either at or prior to insemination, on the pregnancy rate. The cows were divided into 6 treatment groups. Cows in Group 1 (n = 142) were observed in estrus, and 11 +/- 0.42 hours (mean +/- SEM) later they were given 100 ug, i.m. gonadotropin releasing hormone (GnRH) and were inseminated. Cows in Group 2 (n = 139) were observed in estrus and were inseminated 11.4 +/- 0.43 hours later. Cows in Group 3 (n = 33) were monitored for estrus with an activated heatmount detector but were not observed in estrus; they were inseminated 1.5 +/- 0.87 hours later and were given 100 ug, i.m. GnRH. Cows in Group 4 (n = 35) were not observed in estrus, but they did activate the heatmount detector and were inseminated 2.2 +/- 0.87 hours later. Cows in Group 5 (n = 107) were observed in estrus, given 100 ug, i.m. GnRH 2.0 +/- 0.40 hours later, and were inseminated 9 +/- 0.60 hours after GnRH treatment. Cows in Group 6 (n = 129) were observed in estrus and were inseminated 10 +/- 0.50 hours later. Pregnancy rates were analyzed by Chi-square. Interactions between pregnancy rate, treatment and time of insemination were evaluated using ANOVA and LSM (P < 0.05). There was no effect on pregnancy rate when GnRH was given at or prior to insemination. Cows inseminated on the basis of observed estrus had a higher pregnancy rate (P < 0.05) than cows inseminated on the observation of an activated heatmount detector. From the results of this study, it is concluded that treatment with GnRH at or prior to insemination did not improve the pregnancy rate of repeat-breeder dairy cows.

Plasma gonadotrophin responses in beef cows two progesterone plus prostaglandin treatment

Progesterone Releasing Intravaginal Devices (Prids) were inserted into six post-partum beef cows for nine days and 0.5 mg cloprostenol was injected i m on day eight. Blood samples were taken via jugular venous catheters at frequent intervals for seven days after Prid removal and assayed for LH, FSH and progesterone. The induced pre-ovulatory type LH and FSH surges occurred between 35 and 123h after Prid withdrawal in five of the cows. In four cows which underwent surges during the time of most intensive sampling, LH levels were significantly higher during the 30h period prior to the LH surge than during the 30h period after the surge. FSH values were low for the 30h period preceding and the 14h period following the time of maximum FSH/LH concentrations. 16 - 30h after the FSH and LH surges, FSH values were again significantly raised compared with the period immediately after the surge. Despite the success of this Prid/PG regime in inducing ovulation, the variability in time between progestagen withdrawal and the LH surge and ovulation is such that the use of fixed time artificial insemination may give poor results.