Progress 09/01/00 to 06/30/05
Outputs
Project 1: Timed artificial insemination (Ovsynch; OVS) is a convenient method to facilitate artificial insemination, however GnRH administered during the follicular phase, as occurs in OVS, causes a premature decline in estradiol secretion. Our objective was to determine the effect of 0.25 mg of ECP at the time of the second GnRH injection on expression of estrus and conception rates in beef cattle. One hundred eighty-two beef cows received (i.m.) injection of 25 mg PGF (d -14). Fourteen days later 100 ug GnRH was administered (i.m.;d 0) followed by 25 mg PGF on d 7. On d 9 cows were assigned randomly to receive either GnRH + 0.25 mg ECP (OVS-ECP; n=90) or GnRH + vehicle (OVS-C; n=92). All cows were inseminated 12 to15 h post-treatment. Estrus activity was monitored 2 times daily after second PGF administration and pregnancy determined by ultrasonography 40 d post-insemination. More cows (P < 0.05) were detected in estrus in the OVS-ECP group (43.5%) compared with
OVS-C (25%). Mean serum progesterone concentrations did not differ between treatment groups on any day. OVS-ECP tended (P = 0.14) to have a higher conception rate compared with OVS-C (68% vs. 57.5%, respectively). These results suggest that incorporation of a low dose of ECP into conventional OVS increased estrous behavior and may improve conception rate in beef cattle. Project 2: Two experiments were conducted to determine the effect of ECP, when incorporated into OVS, on systemic estradiol (E2), time and incidence of ovulation, and conception rate in Holstein cows. Our objective was to determine if administration of 0.25 mg of ECP at the time of the second GnRH injection would effectively synchronize ovulation and increase conception rate. In Exp 1, lactating Holstein cows (n = 23) were synchronized with PGF (d -10). Ten days later, OVS was initiated with the administration of 100 ug GnRH (d 0) followed by PGF on d 7. On d 9, cows were assigned randomly to be treated with either
GnRH + 0.25 mg ECP (OVS-ECP; n = 11) or GnRH and 1 mL of cottonseed oil (OVS-C; n = 12). To determine the time of ovulation, ultrasound examinations were conducted at 12 and 20 h post-treatment and then at least every 3 h until either 36 h post-treatment or ovulation was observed. Blood samples were collected at the time of treatment (d 9, 0 h) and at 6, 12, 20, and 28 h for E2 analysis. Incidence of ovulation did not differ between treatments. Mean ovulation time relative to the second GnRH administration was similar between treatments. Serum E2 concentration was not different at the time of treatment (0 h); however, E2 concentration was greater for the OVS-ECP at 6 and 12 h after treatment compared with OVS-C. In Experiment 2, lactating dairy cows (n = 333) in 3 commercial herds were assigned randomly to be treated with OVS-ECP (n=169) or OVS-C (n=164). Cows were inseminated 22 to 24 h post-treatment. Conception rates did not differ between treatments. ECP treatment was successful
in increasing serum E2 when administered at the time of the second dose of GnRH in the Ovsynch protocol. Conception rates, however, were not affected by treatment in dairy cow.
Impacts
ECP treatment was successful in increasing serum E2 when administered at the time of the second dose of GnRH in the Ovsynch protocol. While ECP tended to improve conception rates in beef cattle; however this effect was not observed in dairy cows. More research needs to be conducted in dairy cattle to further explore the role of increased E2 during proestrus on fertility.
Publications
- Sellars C. B., J. C. Dalton, R. Manzo, J. Day, and A. Ahmadzadeh. 2006. Time and Incidence of Ovulation and Conception Rates after Incorporating Estradiol Cypionate into a Timed AI Protocol. J. Dairy Sci. 89: 89: 620-626.
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Progress 01/01/04 to 12/31/04
Outputs
Increased understanding of follicular dynamics, luteal function, and time of ovulation led investigators to develop a timed artificial insemination (AI) breeding program (GnRH-7d -->PGF2a- 2d-->GnRH--> Timed AI; OvSynch or CO-Synch), in which ovulation is synchronized, thereby allowing timed AI of all cows without estrus detection. There is evidence that induction of ovulation by GnRH during proestrus, as occurs in both OvSynch or CO-Synch, may impair ovarian estradiol secretion and shortens subsequent luteal phase in cattle. It was hypothesized that administration of a small dose of estradiol cypionate (ECP) at the time of the second GnRH injection would effectively synchronize ovulation and increase conception rate. The objectives were to determine the effect ECP incorporation into OvSynch on ovulation time, ovulation rate, luteal development, and conception rate in Holstein cows. In Exp 1 twenty-three lactating Holstein cows (58 DIM) were synchronized with 25mg
PGF2a (d -10). Ten days later 100 ug GnRH was given (d 0) followed by 25mg PGF2a on d 7. On d 9 cows were assigned randomly to receive either GnRH + 0.25mg ECP (OVS-ECP; n=11) or GnRH + vehicle (OVS; n=12). Using an ultrasound, ovarian activities were monitored on d 0, 7, 9 and also at 12, 20 and every 3h until 35h post-treatment. Presence of a CL was determined on d 16. Blood samples were collected on d 0, 7, 9, 10, and 16 for serum progesterone (P4). In Exp 2, 282 lactating cows in three farms were assigned randomly to either OVS-ECP (n=143) or OVS (n=139) as described in Exp 1. Cows received AI 12-22 h post treatment. Pregnancy was determined by rectal palpation at 40 d post AI. In Exp 1, serum P4 concentration did not differ between groups at any time. All ovulated cows had CL on d 16. Ovulation rate did not differ between groups (100% OVS-ECP vs. 92% OVS). Mean ovulation time relative to last injection was not different between groups (26.3 +/- 0.5 OVS-ECP vs. 27.3 +/- 0.5 h
OVS). Conception rate was 29.4% and 35.2% for OVS-ECP and OVS, respectively and was not different between treatment groups. Although incorporation of ECP into the OvSynch protocol did not change ovulation time, ovulation rate, or luteal development, no improvement in conception rate was observed.
Impacts
Estradiol plays an important role in fertility. For the purpose of estrous synchronization and breeding in cattle, GnRH is routinely used to induce ovulation. Exogenous GnRH may impair ovarian estradiol secretion prematurely. Therefore, administering of a low dose E2 where GnRH is used to induce ovulation may overcome the premature GnRH-induced estradiol suppressions and improve fertility in dairy cattle. Based on the encouraging results in beef cattle further investigation of the use of estradiol in a timed artificial insemination protocol is warranted. Coupling exogenous estradiol with GnRH, and AI in a Co-Synch protocol may exploit the potential effect of maximally elevated serum estradiol on fertility, as measured by fertilization status, sperm accessibility to the ovum as measured by accessory sperm number per embryo(ovum), and embryo quality.
Publications
- Ahmadzadeh, A., and J. C. Dalton. 2003. Estrous synchronization: A tool to improve reproductive efficiency. 2003. Proceedings, Intermountain Cow Symposium. p 33.
- Sellars, C. B. , A. Ahmadzadeh, R. Manzo, J.C. Dalton, and J. Day. 2002. Incorporating Estradiol cypionate (ECP) into the OvSynch (OVS) protocol to improve conception rates in dairy cows. J Dairy Sci. 85(Suppl 1): 307.
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Progress 01/01/03 to 12/31/03
Outputs
Timed artificial insemination (Ovsynch; OVS) is a convenient method to facilitate artificial insemination, however GnRH administered during the follicular phase, as occurs in Ovsynch, causes a premature decline in estradiol secretion. It was hypothesized that administration of estradiol cypionate (ECP) coupled with the second GnRH injection would improve conception rate. The objectives were to determine the effect of ECP incorporation into the Ovsynch protocol on Serum estradiol (E2) and progesterone (P4) concentrations, time of ovulation, and ovulation rate in dairy cows. Twenty-three lactating Holstein cows averaged 58.7 days in milk (DIM) were synchronized with 25 mg Prostaglandin F2 alpha (PGF;d -10). Ten days later the conventional Ovsynch protocol was initiated and 100 ug gonadotropin releasing hormone (GnRH) was given (d 0) followed by 25 mg PGF on d 7. On d 9 cows were assigned randomly to receive either GnRH or 0.25 mg ECP (ECP group; n=11) or GnRH and 1 ml
cottonseed oil (C group; n=12). Ovarian activity was examined by ultrasonography on d 0, 7, and 9. To determine time of ovulation, ultrasound examinations were conducted at 12 and 20 h post-treatment and then at least every 3 h until either 35 h post-treatment or ovulation was observed. Presence of a corpus luteum (CL) was determined on d 16. Blood samples were collected on d 0, 7, and 9, at 20 h post-treatment and on d 16 for serum progesterone (P4) analysis. Blood samples were collected at the time of treatment (d 9, 0 h) and at 6, 12, 20, and 28 h post-treatment for serum E2 analysis. Ovulation rate did not differ between groups (100% ECP vs. 92% C). Mean ovulation time relative to second GnRH administration was similar between groups (26.3 +/- 1.1 h ECP vs. 27.3 +/- 0.1 h C). Cows that ovulated exhibited CL on d 16. Serum P4 concentration did not differ between groups at any time. At 6, 12, and 28 h post-treatment mean serum E2 concentration was higher for the ECP group (P<0.05;
P=0 .05; and P=0.07, respectively). Serum E2 was not different at the time of treatment (0 h) or at 20 h post-treatment. Incorporation of a low dose ECP into the Ovsynch protocol elvated the serum E2 for the first 12 hours after injection but did not adversely affect time of ovulation, ovulation rate, or subsequent luteal function.
Impacts
Estradiol plays an important role in fertility. For the purpose of estrous synchronization and breeding in dairy cows, GnRH is routinely used to induce ovulation. Exogenous GnRH may impair ovarian estradiol secretion prematurely. Therefore, administering of a low dose E2 where GnRH is used to induce ovulation may overcome the premature GnRH-induced estradiol suppressions and improve fertility in dairy cattle.
Publications
- Ahmadzadeh, A., D. G. Falk, R. Manzo, C. B. Sellars, J. C. Dalton. 2003. Effect of incorporation of low dose of estradiol cypionate (ECP) into a timed artificial insemination protocol on estrous behavior and conception rates in beef cattle. J Anim Sci..81(Suppl.1):180.
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Progress 01/01/02 to 12/31/02
Outputs
There is evidence that the induction of ovulation by gonadotropin releasing hormone (GnRH) during proestrus, as occurs in the OvSynch (OVS; GnRH-- 7 days --> prostaglandin --2 days --> GnRH -- > Timed artificial insemination) breeding protocol may impair ovarian estradiol secretion and shorten the subsequent luteal phase in cattle. It was hypothesized that administration of estradiol cypionate (ECP) at the time of the second GnRH injection would effectively synchronize ovulation and improve conception rate. The objective was to determine the effect of low dose ECP incorporation into OVS on expression of estrus and conception rate in beef cattle. One hundred eighty two British cross-bred cows (55-60 d postpartum) received intramuscular (i.m.) injection of 25 mg prostaglandin F (PGF) (d -14). Fourteen days later 100 ug GnRH was administered (i.m.;d 0) followed by 25 mg PGF on d 7. On d 9 cows were assigned randomly to receive either GnRH + 0.25 mg ECP (OVS-ECP; n=90) or
GnRH + vehicle (OVS; n=92). All cows were artificially inseminated (AI) 12-15 h post treatment by a single AI technician. Estrus activity was monitored 3 times daily after PGF administration and pregnancy determined by ultrasonography 40 and 60 d post-insemination. More cows (P < 0.05) were detected in estrus in the OVS-ECP group (45%) compared to the OVS group (25%). Conception rate from AI was 68% and 57.5% for OVS-ECP and OVS, respectively (P < 0.15) and was not different between d 40 and d 60 post-insemination. These results suggest that incorporation of a low dose of ECP into conventional OVS increases estrous behavior and may improve conception rate.
Impacts
A calf conceived in the first week of a breeding season would bring an additional $30/head compared to calf conceived 3-4 weeks later. In a five hundred head cow/calf operation and within two breeding cycle, a 10% increase in pregnancy rate in the first day of a breeding season may bring additional income of $2,000-$2,500. The proposed modified breeding protocol helps to keep cows conceiving early breeding season, provides more uniform calf crop, and helps to improve reproductive performance of herds during the following breeding season. Thus, the present breeding protocol has potential to have a major impact on managing reproduction of cows and enhancing profitability of cow calf operations.
Publications
- Ahmadzadeh, A.,G. A. Johnson, D. G. Falk, A. V. Grove, J. B. Glaze. 2002. Effect of incorporating a low dose of estradiol cypionate (ECP) into a timed artificial insemination protocol on estrous behavior and conception rates in beef cattle. Proceedings, Western Section, American Society of Animal Science (WSASAS). 53:464-467.
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Progress 01/01/01 to 12/31/01
Outputs
Using exogenous gonadotropin releasing hormone (GnRH) and prostaglandin F2a (PGF2a), a timed AI breeding program was developed (OvSynch) in which ovulation was reportedly synchronized in lactating dairy cows (24-32 hr after the second GnRH administration), thereby allowing timed AI of all cows without the need for estrus detection. Although OvSynch is a convenient method to facilitate AI, when compared to other conventional breeding programs, it has yielded lower conception rates in cows. There is evidence that induction of ovulation by GnRH during proestrus, as occurs in OvSynch, impairs ovarian estradiol secretion and shortens subsequent luteal phase in cattle. Therefore, lower fertility following OvSynch may be due to asynchronous timing of the GnRH-induced luteinizing hormone surge prior to estrus coupled with an abnormal decline in estradiol secretion. This experiment evaluated the use of estradiol cypionate (ECP) when incorporated into the conventional timed AI
breeding program (OvSynch) on pregnancy rates in beef cows. Specifically the objective was to compare conception rate of cows which were artificially inseminated after the conventional timed artificial insemination (OvSynch) breeding protocol and those artificially inseminated after the modified OvSynch, indicated above. Seventy British cross-bred mature cows, with a normal reproductive health status, were used for this experiment. Between 60 to 80 days after calving all cows received a luteolytic dose of PGF2a (day -14). Two weeks later (day 0), 100 ug GnRH was administered (i.m.) to all cows to cause luteinization or ovulation of a dominant follicle and development of a CL. On day 7 post-GnRH, cows received 25 mg PGF2a (i.m) to induce luteolysis of the developed CL. Forty-eight hours post-PGF2a , all cows were assigned to one of two treatments. Treatment group (35 cows) received GnRH (100 ug) + 0.25 mg estradiol cypionate (ECP; treatment group) and control group (n =35) received
GnRH (100 ug) + 1 mL of cottonseed oil. Estrus activity was monitored and twelve hours later all cows were artificially inseminated. Pregnancy status was examined by ultrasonography on day 40 and 70 post- insemination. Incorporation of ECP into the OvSynch protocol tended to increase (P < 0.15) pregnancy rate by 15 % compared to the control group. Further, more cows were detected in estrus (P < 0.05) in the treatment group compared to the control group. It appears that incorporation of ECP may increase pregnancy rate in beef cattle. However, this experiment needs to be repeated, using more cows, before we draw a definite conclusion. A fifteen percent increase in pregnancy rate, in the in the first week of the breeding season, has the potential to increase profit by $1,200 in a 100-cow beef herd.
Impacts
The modified protocol may have a major impact on managing reproduction of lactating cows and beef cows and enhancing profitability of dairy and beef producers regardless of the size of the farm.
Publications
- No publications reported this period
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