Reproductive performance of lactating dairy cows following oestrus synchronisation with progesterone, oestradiol and prostaglandin

The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzoate 10 days prior to the planned start of the breeding season (Day 0). The device was removed 8 days later on Day -2 and a luteolytic dose of prostaglandin F2alpha was administered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (81.8% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p>0.0 1) by 1.3 days in synchronised cows (19.9 +/- 0.7 days; mean +/- SEM) compared to control cows (21.2 +/- 0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.     

Resynchrony of previously anoestrous cows and treatment of cows not detected in oestrus that had a palpable corpus luteum with prostaglandin F(2 alpha)

AIMS: To determine if resynchrony, using a progesterone (P4) / oestradiol benzoate (ODB) regime, of previously treated, anovulatory anoestrous (AA) cows would increase the probability of oestrus, conception and pregnancy compared to no resynchrony. Additionally, the effect of prostaglandin F2alpha (PG) treatment of cows not detected in oestrus, but in which a corpus luteum (CL) was palpable transrectally (NDO/CL+), was compared with no treatment. METHODS: Cows not detected in oestrus by 1 week before the start of the seasonal breeding programme were categorised as AA or NDO/CL+, based on absence or presence of a palpable CL, respectively. All AA cows were treated with an intravaginal device containing 1.36 g P4 (CIDR-B) for a period of 6 days, and with 1 mg ODB by intramuscular (I/M) injection 1 day after the device was removed (Day 0). Half the AA cows that were detected in oestrus between Days 0 and 3 were randomly assigned to be resynchronised by reinsertion of a clean used CIDR-B device on Day 15, for a period of 6 days, followed by an I/M injection of 0.5 mg ODB, 1 day after the device was removed (resynchrony, RS), while the other half were not resynchronised (no-RS). NDO/CL+ cows were alternately assigned to be either treated with 25 mg of the PG, dinoprost tromethamine, on Day 0 or left as untreated controls (Con). RESULTS: Resynchrony increased the percentage of cows detected in oestrus between Days 14 and 28 (212/282 = 75.2% vs 155/285 = 54.4%, for RS vs no-RS, respectively; p<0.001), but had no effect on conception rate to a service within the first 3 days of the mating period (146/397 = 36.8% vs 148/399= 37.1%, for RS vs no-RS cows, respectively; p>0.9), or to a service between Days 14 and 28 (84/159 = 52.8% vs 114/217 = 52.5%, for RS vs no-RS cows, respectively; p>0.9). Resynchrony increased the Day 28 pregnancy rate (264/432 = 61.1% vs 237/435 = 54.5%, for RS vs no-RS cows, respectively; p=0.03), but had no effect on the Day 56 or final pregnancy rates (p>0.1).Prostaglandin treatment of NDO/CL+ cows did not affect the percentage of cows detected in oestrus by Day 7 (43/106 = 40.6% vs 51/101 = 50.5%, for Con vs PG, respectively; p=0.15), or Day 28 (92/106 = 86.8% vs 91/101 = 90.1%, for Con vs PG, respectively; p>0.4). Treatment did not affect the Day 28 pregnancy rate (55/103 = 53.4% vs 54/98 = 55.1%, for Con vs PG, respectively; p>0.9), the Day 56 pregnancy rate (81/103 = 78.6% vs 74/98 = 75.5%, for Con vs PG, respectively; p>0.6), or the final pregnancy rate (98/103 = 95.1% vs 89/97 = 91.8%, for Con vs PG, respectively; p>0.3). CONCLUSIONS: Resynchrony of AA cows treated using the present protocol increased the proportion of non-pregnant cows detected in oestrus between Days 14 and 28 and increased the Day 28 pregnancy rate. This resynchrony protocol may be useful for increasing the proportion of the herd pregnant in the first month of the breeding programme, especially in herds that have a history of a low proportion of non-pregnant cows detected in oestrus between Days 14 and 28. There was no benefit in treating NDO/CL+ cows with PG compared to no treatment. KEYWORDS: Dairy cows, anoestrus, treatment, resynchrony, prostaglandin, progesterone, oestradiol benzoate.     

Reproductive performance of post-partum anoestrous dairy cows treated with progesterone and oestradiol benzoate

Abstract

Extract

Recent studies have shown that the anoestrous condition of post-partum dairy cows can be treated with a combination of progesterone (for 5–7 days) and oestradiol benzoate (ODB, 1 mg injected at 24 or 48 h after termination of the progesterone treatment)(1) McDougall, S, and Macmillan, KL. 1993. Follicle waves, ovulation and oestrus in the postpartum cow. Proceedings of the 13th Seminar for the Society of Dairy Cattle Veterinarians of the New Zealand Veterinary Association, : 33–47.  [Google Scholar]. However, published data on the performance of this anoestrus treatment programme in commercial dairy herds is limited(2) Macmillan, KL,, Taufa, VK,, Day, AM, and McDougall, S. 1995. Some effects of using progesterone and oestradiol benzoate to stimulate oestrus and ovulation m dairy cows with anovulatory anoestrus. Proceedings of the New Zealand Society of Animal Production, 55: 239–241.  [Google Scholar]. During the 1994–95 and 1995–96 breeding seasons, performance of this anoestrus treatment programme was determined in nine and six spring-calving herds, respectively. In each herd, cows that had not been detected in oestrus using the tailpainting technique by Day -7 (Day 0 = start of the breeding season) were examined per rectum by each herd owner's attending veterinarian for the presence of a palpable corpus luteum (CL) on the ovary. Cows with a palpable CL or with an enlarged or infected uterus were excluded. Throughout the trial period, anoestrous cows were managed together with the cycling cows.     

Treatment of anovulatory anoestrous postpartum dairy cows with a gonadotropin-releasing hormone (GnRH), prostaglandin F2 alpha, GnRH regimen or with progesterone and oestradiol benzoate

AIM: To compare 2 treatments for anovulatory anoestrus (AA) in postpartum dairy cows. The treatments were combinations of gonadotropin-releasing hormone (GnRH) and prostaglandin F2 (PG) or progesterone (P4) and oestradiol benzoate (ODB). METHODS: Forty AA cows from each of 5 herds were blocked by age (2 or 2 years old) and randomly assigned to 1 of 2 treatments. The first group (GPG) were treated with 250 mug of a GnRH analogue, gonadorelin, followed 7 days later by 15 mg of the PG analogue, luprostiol. Two days later the cows were injected with 250 mug of gonadorelin. Cows were artificially inseminated 16-24 h after the second GnRH injection. The second group (P4+ODB) were treated with an intravaginal P4 releasing device for 6 days, followed 24 h after device removal by injection of 1 mg of ODB. Cows were pregnancy tested 35-40 days after the initial insemination and twice again at 6-8 week intervals thereafter. RESULTS: There was no significant difference between P4+ODB and GPG groups in the percentage of cows submitted for insemination in the first 7 days (94.0% vs 100% for P4+ODB vs GPG, respectively; p>0.3), in conception rate to first insemination within the first 7 days (43.6% vs 35.0% for P4+ODB vs GPG, respectively; p>0.2), in the percentage of cows conceiving in the first 28 days of the breeding period (68.0% vs 58.3%, P4+ODB vs GPG, respectively; p>0.1), or in median interval from the end of treatment to conception (20 vs 21 days; p>0.1). CONCLUSIONS: No differences in the reproductive performance of AA cows treated with either P4+ODB or GPG were detected. However, given the small number of animals enrolled, further data are required before the GPG protocol can be recommended for treatment of AA cows.     

Synchronising oestrus with oestradiol benzoate after using a two-dose prostaglandin treatment to synchronise luteolysis in dairy heifers

OBJECTIVE: To compare the reproductive performance and pattern of onset of oestrus in dairy heifers in which oestrous cycles were synchronised with two doses of prostaglandin (PG) F2alpha and oestrus was synchronised with oestradiol benzoate (ODB). PROCEDURE: Dairy heifers in two herds (herd A, n = 192; herd B, n = 267) were treated with two doses of an analogue of PGF2alpha (cloprostenol, 375 microg, IM) 12 days apart. Heifers not detected in oestrus 48 h after the last dose of PGF2alpha were either left untreated (No ODB, n = 147) or treated with ODB (0.75 mg IM, n = 126). Onset of oestrus was monitored at 0, 24, 48, 80, 96 and 120 h after the last dose of PGF2alpha Heifers were inseminated on detection of oestrus. RESULTS: After the last dose of PGF2alpha, oestrous detection rates at 80 h (43.5 vs 72.6%, P < 0.001), 96 h (74.1 vs 84.9%, P =0.025) and 120 h (78.2 vs 86.3%, P = 0.082) were less in the No ODB compared to the ODB heifers, respectively. Conception rates (percentage pregnant that were inseminated) were greater in the No ODB compared to the ODB heifers (64.3% vs 47.6%, respectively; P = 0.006), while pregnancy rates (percentage pregnant that were treated) were also greater in the No ODB compared to the ODB heifers, but differences were not significant (50.3% vs 41.1%, respectively; P = 0.068). CONCLUSION: Administration of ODB to heifers not in oestrus 48 h after a two-dose PGF2alpha treatment increases the percentage of heifers detected in oestrus by 80 h, 96 h and 120 h after treatment, by an estimated 29%, 11% and 8%, respectively. However, administration of ODB decreases conception rates by an estimated 17%, and may decrease pregnancy rates (estimated 9% difference). Results are consistent with the hypothesis that ODB can increase submission rates but reduce conception rates following a two dose treatment with PGF2alpha.     

Comparison of two doses of oestradiol benzoate administered at a resynchronised oestrus on reproductive performance of dairy cows

OBJECTIVE: To compare the effects of two doses of oestradiol benzoate (ODB) administered as part of a treatment designed to resynchronise returns to oestrus on the reproductive performance of cows in a controlled breeding program. DESIGN: Cohort study. PROCEDURE: Lactating dairy cows on two farms were treated to synchronise three successive oestrous cycles. An intravaginal progesterone releasing insert (IVP4) was used to synchronise the first oestrous cycle. The cows were then treated 15 days after the first treatment by reinsertion of an IVP4 that had been used to synchronise the first oestrus and administration of 1.0 mg of oestradiol benzoate (ODB) i.m. at device insertion. The IVP4 device was removed 8 days later and either 0.5 (n = 421) or 1.0 mg of ODB (n = 446) was administered 24 h later. Injections of (ODB) with or without the use of an IVP4 were used to synchronise the third oestrous cycle. Different synchronisation treatments were used to synchronise first and third oestrous cycles but differences were included in statistical models to account for variation in the data. This enabled examination of effects due to differences in the dose of ODB used to synchronise the second synchronised oestrus. RESULTS: The dose of ODB (0.5 or 1.0 mg) administered just before the second synchronised oestrus did not significantly (P > 0.10) affect the cumulative pregnancy rates over three successive rounds of artificial insemination, the mating start date to the conception intervals, the conception rates to the first or second insemination, the proportion of cows submitted for insemination at the second synchronised oestrus or the proportion of cows that were not pregnant yet failed to show signs of oestrous (phantom cows) identified within each herd. CONCLUSION: There was no difference in reproductive performance between cows receiving either 0.5 mg or 1.0 mg ODB after removal of used IVP4 devices that had been inserted to resynchronise them for a second insemination.     

Synchronization of lactating dairy cows with prostaglandin F2 alpha: insemination on observed oestrus versus timed artificial insemination

The effect of two insemination policies after synchronization of oestrus on reproductive performance in two groups of cows was investigated. Oestrus was synchronized by two treatments with prostaglandin F2 alpha (PGF2 alpha) at a 14-day interval. Cows in Group 1 (n = 234) were inseminated twice on appointment 66 and 90 h after the second treatment. Cows in Group 2 (n = 222) were intensively watched for signs of oestrus after the synchronization protocol and inseminated on observed oestrus. Cows with abnormal discharge after synchronization were excluded from breeding and inseminated later during the study period. Service rate within 1 week after synchronization was higher in Group 1 than in Group 2 (89.3 versus 67.1%). Conception rates on first service did not differ between groups (33.2 versus 30.0%). Days to first service and days open were shorter in Group 1 (P < 0.05). The number of cows culled for infertility did not differ between the groups. Endometritis 14-20 days post-partum decreased the percentage of cows pregnant at the end of the study period in both groups but did not have a significant effect on conception rates and days open. It is concluded that additional inseminations required in the timed artificial insemination protocol were economically justified by the reduction in days open in comparison with insemination on observed oestrus after synchronization.     

Reproductive performance in the subsequent lactation of dairy cows previously treated for failure to be detected in oestrus

AIM: To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation. METHODS: Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesterone-releasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or "late-calving") in the previous lactation, to examine the potential "carryover" effects of previous status on the reproductive performance in the subsequent lactation. RESULTS: Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207-221, vs 224, 95% CI=220-228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactation's breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses. CONCLUSIONS: Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous season's status was still important in the subsequent season's reproductive performance, despite adjusting for known confounders of fertility. CLINICAL RELEVANCE: The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.     

Reproductive performance of anovulatory anoestrous postpartum dairy cows following treatment with two progesterone and oestradiol benzoate-based protocols, with or without resynchrony

AIMS: (a) To compare the reproductive performance of anovulatory anoestrous (AA) postpartum dairy cows following treatment with 1 of 2 progesterone (P4) and oestradiol benzoate (ODB)-based treatment regimens; (b) To determine whether resynchronisation of cows initially treated for AA would improve reproductive performance and; (c) to determine whether cows not detected in oestrus but with a corpus luteum (CL) present (NDO/CL+), treated with P4 and ODB, would conceive earlier than untreated controls. METHODS: Cows (n=1386) from 11 herds, that had not been detected in oestrus before the start of the seasonal mating period (PSM) and in which a CL was not detected were diagnosed AA, blocked by age (2 or >2 years old), then randomly assigned to be treated with an intravaginal P4-releasing device for either 6 (6-Day group) or 8 days (8-Day group). Cows in the 8-Day group were injected intramuscularly (IM) with 2 mg ODB at device insertion and all cows were injected with 1 mg ODB 24 h after device removal (Day 0). Cows detected in oestrus from Days 0-3 were subsequently assigned to be either resynchronised or left as untreated controls. Resynchronised cows had a used P4-releasing device reinserted on Day 14 for 8 days and were injected with 1 mg ODB at device reinsertion and again 24 h after device removal. NDO/CL+ cows were assigned to be either treated the same as the 8-Day group or left as untreated controls. All cows were inseminated on detection of oestrus and pregnancy tested approximately 10 weeks after the PSM and again 6-8 weeks after the end of the mating period. RESULTS: For AA cows, the 14-day submission rate was similar between 6-Day and 8-Day groups (p0.1). However, the pregnancy rate by Day 14 was higher for the 8-Day than the 6Day group (43.0% vs 35.2%; p=0.006). Resynchrony treatment decreased the 14-day pregnancy rate compared with untreated controls (35.2% vs 42.5%; p=0.026). The resynchrony treatment increased the submission rate between Days 14-28 for non-pregnant cows compared with untreated controls (80.6% vs 57.4%; p=0.049). However, conception rate to resynchronised heats was lower than for cows that returned to oestrus naturally (56.6% vs 67.9%; p=0.025). Neither initial treatment type nor resynchrony treatment increased the 28-day pregnancy rate (p>0.1). There were no differences between treatment groups in the final non-pregnant rate (4.5% vs 4.6%; p>0.1). Treated NDO/CL+ cows had a higher 14-day submission rate (88.1% vs 49.4%; p>0.001), higher 14-day and 28-day pregnancy rates (42.9% vs 20.7%, p>0.001 and; 56.0% vs 42.5%, p=0.094, respectively) and conceived earlier (21 vs 36 days from PSM to median day of conception; p>0.05), than untreated NDO/CL+ cows. CONCLUSIONS: The 8-Day, ODB-P4-ODB treatment regimen resulted in a higher pregnancy rate by 14 days but not 28 days than the 6-Day, P4-ODB treatment. The resynchrony treatment increased the proportion of non-pregnant cows inseminated on days 14-28, but did not increase the 28-day pregnancy rate or final pregnancy rate. Treatment of NDO/CL+ cows with the 8-Day, ODB-P4-ODB treatment improved reproductive performance compared with no treatment.     

The effects of a post partum injection of prostaglandin F2 alpha on return to oestrus and pregnancy rates in dairy cows

The interval from calving to conception is unnecessarily long in dairy cows. Post partum administration of prostaglandin F2 alpha can reduce the calving to conception interval, but it is not known whether this is due to advanced return to oestrus, increased oestrus intensity and/or increased pregnancy rates. In two experiments, the treatment of dairy cows with prostaglandin F2 alpha 21 days post partum reduced the interval to first oestrus and first service by about 10 days. The intensity of oestrus was not affected. Pregnancy rates to first service were increased from (on average) 60 to 80%, and the number of services/conception was reduced from 2.0 to 1.3.     

Treatment of anovulatory anoestrous postpartum dairy cows with a gonadotropin-releasing hormone (GnRH), prostaglandin F2𝛂, GnRH regimen or with progesterone and oestradiol benzoate

AIM: To compare 2 treatments for anovulatory anoestrus (AA) in postpartum dairy cows. The treatments were combinations of gonadotropin-releasing hormone (GnRH) and prostaglandin F_2𝛂 (PG) or progesterone (P4) and oestradiol benzoate (ODB).

METHODS: Forty AA cows from each of 5 herds were blocked by age (2 or >2 years old) and randomly assigned to 1 of 2 treatments. The first group (GPG) were treated with 250 𝛍g of a GnRH analogue, gonadorelin, followed 7 days later by 15 mg of the PG analogue, luprostiol. Two days later the cows were injected with 250 𝛍g of gonadorelin. Cows were artificially inseminated 16–24 h after the second GnRH injection. The second group (P4+ODB) were treated with an intravaginal P4 releasing device for 6 days, followed 24 h after device removal by injection of 1 mg of ODB. Cows were pregnancy tested 35–40 days after the initial insemination and twice again at 6–8 week intervals thereafter.

RESULTS: There was no significant difference between P4+ODB and GPG groups in the percentage of cows submitted for insemination in the first 7 days (94.0% vs 100% for P4+ODB vs GPG, respectively; p>0.3), in conception rate to first insemination within the first 7 days (43.6% vs 35.0% for P4+ODB vs GPG, respectively; p>0.2), in the percentage of cows conceiving in the first 28 days of the breeding period (68.0% vs 58.3%, P4+ODB vs GPG, respectively; p>0.1), or in median interval from the end of treatment to conception (20 vs 21days;p>0.1).

CONCLUSIONS: No differences in the reproductive performance of AA cows treated with either P4+ODB or GPG were detected. However, given the small number of animals enrolled, further data are required before the GPG protocol can be recommended for treatment of AA cows.     

Factors affecting the monetary return from programmes for synchronising oestrus in dairy cows with gonadotrophin-releasing hormone and prostaglandin F2alpha

Synchronisation, using a combination of gonadotrophin-releasing hormone and prostaglandin F2alpha injections, is commonly used to control the reproductive cycle of dairy cows. A simple model that could predict the monetary return from synchronisation would be a valuable tool in determining whether it would be worthwhile. This study used data from three controlled clinical trials to investigate the effects of six factors (interval between calving and synchronisation, 21-day submission rate, number of cows synchronised, average age, pregnancy rate of non-synchronised cows and season) on the return from synchronisation. The results suggests that the herd's submission and pregnancy rates, the time between calving and synchronisation, and the number of cows synchronised can all significantly affect the return from synchronisation, but only time since calving significantly affected the return in all three trials. They also suggest that there is no simple linear relationship between these factors and the return from synchronisation.     

The value of progesterone, oestradiol benzoate and cloprostenol in controlling the timing of oestrus and ovulation in dairy cows and allowing successful fixed-time insemination

The relative merits of three hormone treatments of dairy cows: (1) intravaginally administered progesterone and oestradiol benzoate; (2) intravaginally administered progesterone and injected cloprostenol; and (3) injected cloprostenol; begun 35-75 days after calving and designed to synchronize oestrus and ovulation and allow successful artificial insemination (AI) at fixed times, have been assessed utilizing information from progesterone concentrations in milk. From this it was concluded that 89% of the cows had ovulated one to three times between calving and the beginning of treatment. Treatment (2) was more effective than (1) in synchronizing ovulation. This was due to the fact that when treatments began early in the ovulation cycle, the requirement for a rapidly effective luteolytic agent was provided by cloprostenol but not by oestradiol benzoate. Treatment (2) was also more effective than (3) in synchronizing ovulation. This is interpreted as meaning that progesterone treatment for 12 days had a beneficial effect in restoring normal cyclic ovarian function in the cows after calving. Whilst cloprostenol administered alone did not have this beneficial effect, there is no evidence that it had a detrimental effect. Based on all cows in treatment groups, the proportion that became pregnant to the fixed-time AI was significantly greater after treatment (2) than after (1), but when based on numbers of cows with synchronized ovulation, there were no significant differences among treatments in the proportions becoming pregnant. The progesterone/cloprostenol treatment had a disadvantage in that when begun during the 11-22 day period of the ovulation cycle, so resulting in a long, total period of suppression of ovulation (mean, 32.1 days), fertility to the fixed-time AI was poor despite effective synchronization of ovulation. Ovulation cycles immediately following the failed, fixed-time AI were normal, both in length and in maximum, luteal-phase progesterone concentration and indicated normal corpus luteum function. Thus the infertility could be ascribed neither to poor timing of AI nor to gross degeneration of follicles prior to their synchronized ovulation following the prolonged suppression of ovulation. The 12-day progesterone treatments when given to anovulatory cows gave, within 5.5 h of their beginning, a concentration of progesterone in milk that was not significantly different from the maximum reached. This concentration declined during the 12 days of the treatment but remained above pretreatment level until 5.5 h after treatment withdrawal; the maximum reached was about half that in normal ovulation cycles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Synchronisation of oestrus and reproductive performance of dairy cows following administration of oestradiol benzoate or gonadotrophin releasing hormone during a synchronised pro-oestrus

OBJECTIVE: To compare the use of gonadotrophin releasing hormone (GnRH) and oestradiol benzoate (ODB) administered following a synchronised pro-oestrus on reproductive performance of lactating dairy cows and the submission rates of non-pregnant cows following resynchronisation. DESIGN: Cohort study. PROCEDURE: Lactating Holstein cows enrolled in a controlled breeding program were first treated with an intravaginal progesterone releasing insert (IVP4) for 8 days, 2.0 mg of ODB intramuscular (i.m.) at device insertion (Day 0), an analogue of PGF2alpha at device removal and either 1.0 mg of ODB i.m., 24 h after device removal (ODB group, n = 242), or 0.25 mg of a GnRH agonist (GnRH group, n = 152) injected i.m. approximately 34 h after device removal. Every cow was artificially inseminated between 49 and 56 h after removal of its insert (Day 10). Cows detected in oestrus 1 day after artificial insemination (AI) that were not detected in oestrus on the previous day were re-inseminated on that day. All cows treated on Day 0 were resynchronised for reinsemination by insertion of a used IVP4 device on Day 23. Oestradiol benzoate at a dose of 1.0 mg was administered i.m. at the time of device insertion. Inserts were removed 8 days later (Day 31) and 1.0 mg of ODB was injected i.m. 24 h later. Those cows detected in oestrus between Days 31 and 35 were artificially inseminated. On Day 46 these cows were resynchronised for a third round of AI by insertion of an IVP4 device, used previously to synchronise cows for the first and second rounds of AI, and administration of 1.0 mg of ODB i.m.. Eight days later inserts were removed. Cows detected in oestrus between Days 54 and 58 were artificially inseminated. Bulls were run with the herd between rounds of AI and removed after 21 weeks of mating. RESULTS: Treatment with ODB or GnRH at the first synchronised pro-oestrus did not significantly alter the reproductive performance over three rounds of AI or over a 21-week breeding period. Treatment also did not alter submission rates at the second round of AI or the proportion of non-pregnant and non-return cows ('phantom' cows) detected and did not result in significant differences in concentrations of progesterone in plasma 10 and 18 days after removal of inserts at the first round of AI. Treatment with GnRH reduced the proportion of cows detected in oestrus at the first round of AI (36.2 vs 97.5%; P < 0.001). CONCLUSION: Administration of GnRH compared to ODB at a synchronised pro-oestrus results in similar reproductive performance. Treatment with GnRH reduced the proportion of cows detected in oestrus following treatment. This may offer advantages to the way AI is managed by enabling insemination at a fixed-time and removing the need for the detection of oestrus.     

持久黄体性不孕奶牛用复方缩宫素乳剂处理后血清中孕酮和雌二醇水平的变化

选择患持久黄体的不孕奶牛14头进行复方缩宫素乳剂的临床治疗试验,并利用放射免疫方法对部分患牛治疗前后血清孕酮（P     

Comparison of oestrus synchronisation programmes in dairy cattle using oestradiol benzoate, short-acting progesterone and cloprostenol, or buserelin and cloprostenol

AIM: To evaluate the efficacy of a programme using oestradiol benzoate, progesterone and the prostaglandin-F2 (PG) analogue, cloprostenol, to synchronise oestrus and ovulation in dairy cows, compared with a programme using a gonadotropinreleasing hormone (GnRH) agonist, buserelin, and cloprostenol. METHODS: Twenty non-lactating dairy cows, at random stages of the oestrus cycle, were randomly assigned to 1 of 2 treatments. In Treatment 1 ( OPPG; n=10), cows were injected with 2 mg oestradiol benzoate intramuscularly (IM) plus 200 mg progesterone subcutaneously (SC) on Day 0, followed by 500 microg cloprostenol IM on Day 9 and 1 mg oestradiol benzoate on Day 10. In Treatment 2 (GPG; n=10), cows were injected with 10 microg buserelin IM on Day 0, 500 microg cloprostenol IM on Day 7 and 10 microg buserelin on Day 9. The ovaries of all cows were examined by ultrasonography, using an 8 MHz probe, from 5 days before the initial treatment until ovulation. Cows were observed for oestrus 3 times daily for 7 days after cloprostenol treatment. Blood samples were collected daily for determination of progesterone, and 6-hourly for 36 h after the second oestradiol or buserelin injection for the determination of follicle stimulating hormone (FSH) and luteinising hormone (LH) concentrations. RESULTS: The percentage of cows observed in oestrus was higher in the OPPG group than in the GPG group (100% vs 55.6%, p=0.018). Treatment with either short-acting progesterone plus oestradiol benzoate or buserelin was followed by atresia or ovulation of the dominant follicle. Emergence of a new follicular wave occurred earlier (p>0.001) in the GPG group (2.2+/-0.2 days) than in the OPPG group (3.6+/-0.2 days). There was no significant difference between treatment groups in the variation of time of follicular wave emergence or size of the largest follicles at either the time of initial treatment (10.8+/-1.4 mm vs 11.1+/-0.8 mm), cloprostenol treatment (13.8+/-0.7 mm vs 14.0+/-1.3 mm) or of ovulation (15.4+/-0.7 mm vs 17.6+/-1.1 mm; p=0.10). The LH surge occurred sooner after the second injection of buserelin (4.0+/-1.0 h) than after the second injection of oestradiol benzoate (22.8+/-1.2 h; p>0.001). The interval between the second injection of oestradiol benzoate or buserelin and ovulation did not differ significantly between treatment groups (1.7+/-0.3 days vs 1.6+/-0.2 days; p=0.69). CONCLUSIONS: The use of short-term progesterone treatment, combined with oestradiol benzoate for follicular wave synchronisation, and cloprostenol to cause lysis of residual luteal tissue, is a promising alternative to established methods of oestrus synchronisation in cows.