Putative urinary pheromone of bulls involved with breeding performance of primiparous beef cows in a progestin-based estrous synchronization protocol

The objective of this study was to determine if factors associated with the biostimulatory effect of bulls alter breeding performance of primiparous, suckled beef cows using a progestin-based estrous synchronization protocol. We tested the hypotheses that the estrous synchronization response and AI pregnancy rates differ among cows exposed to bulls, continuously exposed to bull urine, and exposed to fence-line contact with bulls or cows not exposed to bulls or bull urine. Data were collected from 3 experiments performed over consecutive years. Cows were assigned to the following treatments: bull exposure (BE; n = 26) or no bull exposure (NB; n = 25) in Exp. 1, bull urine exposure (BUE; n = 19) or steer urine exposure (SUE; n = 19) in Exp. 2, and fence-line contact with bulls (BFL; n = 26) or no bull exposure (NB; n = 26) in Exp. 3. Synchronization protocols in each experiment included the use of a controlled internal drug release device (d -10), PGF(2alpha) (d -3), and GnRH and fixed-time AI (TAI; d 0). Cows that were observed in estrus by 60 h after PGF(2alpha) were inseminated 12 h later. Cows not observed in estrus by 60 h after PGF(2alpha) were TAI at 72 h and given GnRH (100 mug). Pregnancy was determined by ultrasonography 35 d after TAI. In Exp. 1, 2, and 3, cows were exposed directly to bulls, bull urine, or bull fence-line contact for 35, 64, and 42 d, respectively. Data were analyzed between treatments within each experiment. The proportion of estrous cycling cows did not differ between treatments at the beginning of each experiment; however, more (P < 0.05) BE and BFL cows were estrous cycling at the beginning of the estrous synchronization protocol than NB cows in Exp. 1 and 3. The proportion of cows that showed estrus and interval to estrus after PGF(2alpha) did not differ between treatments in Exp. 1 and 3. However, in Exp. 2, more BUE cows tended (P = 0.09) to have shorter intervals to estrus and to exhibit estrus after PGF(2alpha) than SUE cows. Overall, AI pregnancy rates were greater (P < 0.05) for BE and BUE cows than for NB and SUE cows in Exp. 1 and 2, respectively. There was no difference in AI pregnancy rates between BFL and NB cows in Exp. 3. The presence of bulls and exposure to bull urine appeared to improve breeding performance of primiparous beef cows using a progestin-based estrous synchronization protocol, whereas fence-line bull exposure was insufficient to cause this biostimulatory effect. We propose that a novel urinary pheromone of bulls may be responsible for the enhancement of fertility in the primiparous, postpartum cow.     

Synchronization of estrus in suckled beef cows for detected estrus and artificial insemination and timed artificial insemination using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone

We determined whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or estrous detection plus TAI, and whether adding a controlled internal device release (CIDR) to GnRH-based protocols would enhance fertility. Estrus was synchronized in 2,598 suckled beef cows at 14 locations, and AI was preceded by 1 of 5 treatments: 1) a CIDR for 7 d with 25 mg of PG F(2alpha) (PGF) at CIDR removal, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received 100 mug of GnRH and TAI at 84 h (control; n = 506); 2) GnRH administration, followed in 7 d with PGF, followed in 60 h by a second injection of GnRH and TAI (CO-Synch; n = 548); 3) CO-Synch plus a CIDR during the 7 d between the first injection of GnRH and PGF (CO-Synch + CIDR; n = 539); 4) GnRH administration, followed in 7 d with PGF, followed by detection of estrus and AI during the 84 h after PGF; cows not detected in estrus by 84 h received GnRH and TAI at 84 h (Select Synch & TAI; n = 507); and 5) Select Synch & TAI plus a CIDR during the 7 d between the first injection of GnRH and PGF (Select Synch + CIDR & TAI; n = 498). Blood samples were collected (d -17 and -7, relative to PGF) to determine estrous cycle status. For the control, Select Synch & TAI, and Select Synch + CIDR & TAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed using the AM/PM rule. Pregnancy was diagnosed by transrectal ultrasonography. Percentage of cows cycling at the initiation of treatments was 66%. Pregnancy rates (proportion of cows pregnant to AI of all cows synchronized during the synchronization period) among locations across treatments ranged from 37% to 67%. Pregnancy rates were greater (P < 0.05) for the Select Synch + CIDR & TAI (58%), CO-Synch + CIDR (54%), Select Synch & TAI (53%), or control (53%) treatments than the CO-Synch (44%) treatment. Among the 3 protocols in which estrus was detected, conception rates (proportion of cows that became pregnant to AI of those exhibiting estrus during the synchronization period) were greater (P < 0.05) for Select Synch & TAI (70%; 217 of 309) and Select Synch + CIDR & TAI (67%; 230 of 345) cows than for control cows (61%; 197 of 325). We conclude that the CO-Synch + CIDR protocol yielded similar pregnancy rates to estrous detection protocols and is a reliable TAI protocol that eliminates detection of estrus when inseminating beef cows.     

Factors affecting pregnancy rate to estrous synchronization and fixed-time artificial insemination in beef cattle

Application of AI in extensive beef cattle production would be facilitated by protocols that effectively synchronize ovarian follicular development and ovulation to enable fixed-time AI (TAI). The objectives were to determine whether use of a controlled internal drug release (CIDR) device to administer progesterone in a GnRH-based estrous synchronization protocol would optimize blood progesterone concentrations, improve synchronization of follicular development and estrus, and increase pregnancy rates to TAI in beef cows. Beef cows (n = 1,240) in 6 locations within the US Meat Animal Research Center received 1 of 2 treatments: 1)?an injection of GnRH [100 μg intramuscularly (i.m.)] followed by PGF(2α) (PGF; 25 mg i.m.) 7 d later (CO-Synch), or 2) CO-Synch plus a CIDR during the 7 d between GnRH and PGF injections (CO-Synch + CIDR). Cows received TAI and GnRH (100 μg i.m.) at 60 h after PGF. Progesterone was measured by RIA in blood samples collected 2 wk before and at initiation of treatment (d 0) and at PGF injection (d 7). Estrous behavior was monitored by Estrotect Heat Detectors. Pregnancy was diagnosed by ultrasonography 72 to 77 d after TAI. Plasma progesterone concentrations did not differ (P > 0.10) between synchronization protocols at first GnRH injection (d 0), but progesterone was greater (P < 0.01) at PGF injection (d 7) in cows receiving CO-Synch + CIDR vs. CO-Synch as a result of fewer CIDR-treated cows having progesterone ≤1 ng/mL at PGF (10.7 vs. 29.6%, respectively). A greater (P < 0.01) proportion of CO-Synch + CIDR vs. CO-Synch cows were detected in estrus within 60 h after PGF (66.7 vs. 57.8 ± 2.6%, respectively) and a greater (P < 0.01) proportion were pregnant to TAI (54.6 vs. 44.3 ± 2.6%, respectively). For both synchronization protocols, cows expressing estrus within 60 h before TAI had a greater pregnancy rate than cows without estrus. For cows with plasma progesterone ≤1 ng/mL at PGF injection, CO-Synch + CIDR increased pregnancy rate (65.2 ± 5.9 vs. 30.8 ± 3.4% with vs. without CIDR), whereas pregnancy rates did not differ (P > 0.10) between protocols (52.1 ± 2.1 vs. 50.0 ± 2.4%, respectively) when progesterone was >1 ng/mL (treatment × progesterone; P < 0.01). Inclusion of a CIDR in the synchronization protocol increased plasma progesterone concentration, proportion of cows detected in estrus, and pregnancy rate; however, the increase in pregnancy rate from inclusion of the CIDR was primarily in cows with decreasing or low endogenous progesterone secretion during treatment.     

Evaluation of human chorionic gonadotropin as a replacement for gonadotropin-releasing hormone in ovulation-synchronization protocols before fixed timed artificial insemination in beef cattle

Two experiments were conducted during 2 yr to evaluate differences in ovulation potential and fertility in response to GnRH or hCG. In Exp. 1, 46 beef cows were given 100 microg of GnRH or 500, 1,000, 2,000, or 3,000 IU of hCG. Ovulation incidence was not different between GnRH and any of the hCG doses, indicating that ovulatory capacity of at least 500 IU of hCG was equivalent to GnRH. In Exp. 2, beef cows (n = 676) at 6 locations were assigned randomly to a 2 x 3 factorial arrangement of treatments. Main effects were: 1) pre-timed AI (TAI) treatment (GnRH or hCG) and 2) post-TAI treatment (saline, GnRH, or hCG) to initiate resynchronization of ovulation in previously inseminated cattle. Blood samples were collected (d -21 and -10) to determine progesterone concentrations and assess cyclicity. Cattle were treated with a progesterone insert on d -10 and with 100 microg of GnRH or 1,000 IU of hCG. A PGF(2alpha) injection was given at insert removal on d -3. Cows were inseminated 62 h (d 0) after insert removal. On d 26 after first TAI, cows of unknown pregnancy status were treated with saline, GnRH, or hCG to initiate a CO-Synch protocol. Pregnancy was diagnosed 33 d after first TAI to determine pregnancies per AI (P/AI). Nonpregnant cows at 6 locations in yr 1 and 1 location in yr 2 were given PGF(2alpha) and inseminated 56 h later, concurrent with a GnRH injection. Five weeks later, pregnancy diagnosis was conducted to determine pregnancy loss after first TAI and pregnancy outcome of the second TAI. Injection of pre-TAI hCG reduced (P < 0.001) P/AI compared with GnRH, with a greater reduction in cycling cows. Post-TAI treatments had no negative effect on P/AI resulting from the first TAI. Serum progesterone was greater (P = 0.06) 7 d after pre-TAI hCG than after GnRH and greater (P < 0.05) after post-TAI hCG on d 26 compared with saline 7 d after treatment in association with greater frequency of multiple corpora lutea. Compared with saline, injections of post-TAI GnRH and hCG did not increase second insemination P/AI, and inconsistent results were detected among locations. Use of hCG in lieu of GnRH is contraindicated in a CO-Synch + progesterone insert protocol. Compared with a breeding season having only 1 TAI and longer exposure to cleanup bulls, total breeding season pregnancy rate was reduced by one-third, subsequent calving distribution was altered, and 50% more AI-sired calves were obtained by applying 2 TAI during the breeding season.     

Effectiveness of GnRH plus prostaglandin F2alpha for estrus synchronization in cattle of Bos indicus breeding

Postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding at three locations were studied to determine the efficacy of GnRH + PGF2alpha combinations for synchronization of estrus and(or) ovulation. Cows were equally distributed to each of three treatments by body condition score at the start of the experiment (d 0). All cows received 100 microg of GnRH on d 0 and 25 mg of PGF2alpha 7 d later. The three insemination protocols included 1) AI 12 h after exhibiting estrus during d 7 to 12 of the experiment (Select-Synch; n = 197); 2) timed-AI + 100 microg of GnRH on d 9 of the experiment (CO-Synch; n = 193); 3) AI 12 h after exhibiting estrus during d 7 to 10 of the experiment. Cows not exhibiting estrus by d 10 were timed-AI and injected with 100 microg of GnRH on d 10 of the experiment (Hybrid-Synch; n = 200). The percentage of cows exhibiting estrus during d 7 to 12 of the experiment was lower (P < 0.05) for CO-Synch (17.6%) cows than for Select-Synch or Hybrid-Synch (45.2 and 33.0%, respectively) cows, which did not differ (P > 0.05). For the Select-Synch and Hybrid-Synch cows that exhibited estrus during d 7 to 10 of the experiment and were artificially inseminated, conception rates were similar across treatments (50.5%). Pregnancy rates were greater (P < 0.01) for CO-Synch and Hybrid-Synch (31.0 and 35.5%, respectively) cows than for Select-Synch (20.8%) cows. A greater (P < 0.01) percentage of cycling cows became pregnant (34.5%) than noncycling cows (25.9%) across all treatments. The CO-Synch and Hybrid-Synch synchronization protocols resulted in greater pregnancy rates compared with the Select-Synch protocol in postpartum and lactating crossbred cows containing a percentage of Bos indicus breeding.     

Effect of addition of a progesterone intravaginal insert to a timed insemination protocol using estradiol cypionate on ovulation rate, pregnancy rate, and late embryonic loss in lactating dairy cows

The objectives of this study were to determine the effects of incorporating a progesterone intravaginal insert (CIDR) between the day of GnRH and PGF2alpha treatments of a timed AI protocol using estradiol cypionate (ECP) to synchronize ovulation on display of estrus, ovulation rate, pregnancy rate, and late embryonic loss in lactating cows. Holstein cows, 227 from Site 1 and 458 from Site 2, were presynchronized with two injections of PGF2alpha on study d 0 and 14, and subjected to a timed AI protocol (100 mixrog of GnRH on study d 28, 25 mg of PGF2alpha on study d 35, 1 mg of ECP on study d 36, and timed AI on study d 38) with or without a CIDR insert. Blood was collected on study d 14 and 28 for progesterone measurements to determine cyclicity. Ovaries were scanned on d 35, 37, and 42, and pregnancy diagnosed on d 65 and 79, which corresponded to 27 and 41 d after AI. Cows receiving a CIDR had similar rates of detected estrus (77.2 vs. 73.8%), ovulation (85.6 vs. 86.6%), and pregnancy at 27 (35.8 vs. 38.8%) and 41 d (29.3 vs. 32.3%) after AI, and late embryonic loss between 27 and 41 d after AI (18.3 vs. 16.8%) compared with control cows. The CIDR eliminated cows in estrus before the last PGF2alpha injection and decreased (P < 0.001) the proportion of cows bearing a corpus luteum (CL) at the last PGF2alpha injection because of less ovulation in response to the GnRH and greater spontaneous CL regression. Cyclic cows had greater (P = 0.03) pregnancy rates than anovulatory cows at 41 d after AI (33.8 vs. 20.4%) because of decreased (P = 0.06) late embryonic loss (16.0 vs. 30.3%). The ovulatory follicle was larger (P < 0.001) in cows in estrus, and a greater proportion of cows with follicles > or = 15 mm displayed estrus (P < 0.001) and ovulated (P = 0.05) compared with cows with follicles <15 mm. Pregnancy rates were greater (P < 0.001) for cows displaying estrus, which were related to the greater (P < 0.001) ovulation rate and decreased (P = 0.08) late embryonic loss for cows in estrus at AI. Cows that were cyclic and responded to the presynchronization protocol (high progesterone at GnRH and CL at PGF2alpha) had the highest pregnancy rates. Incorporation of a CIDR insert into a presynchronized timed AI protocol using ECP to induce estrus and ovulation did not improve pregnancy rates in lactating dairy cows. Improvements in pregnancy rates in cows treated with ECP to induce ovulation in a timed AI protocol are expected when more cows display estrus, thereby increasing ovulation rate.     

Effects of standing estrus and supplemental estradiol on changes in uterine pH during a fixed-time artificial insemination protocol

Cows that exhibit estrus within 24 h of fixed-time AI have elevated concentrations of estradiol and greater pregnancy rates compared with cows not in estrus. Our objective was to determine whether estradiol, estrus, or both had an effect on uterine pH during a fixed-time AI protocol. Beef cows were treated with the CO-Synch protocol (100 mircog of GnRH on d -9; 25 mg of PGF(2alpha) on d -2; and 100 mircog of GnRH on d 0). One-half of the cows received an injection of estradiol cypionate (ECP; 1 mg) 12 h after PGF(2alpha). Cows detected in standing estrus within 24 h of the second GnRH injection were considered to be in standing estrus. Uterine pH was determined in all animals 12, 24, and 48 h after the PGF(2alpha) injection. For Exp. 1, pH was also determined 72 and 96 h after the PGF(2alpha) injection; in Exp. 2, pH was also determined at 54, 60, 66, 72, 78, 84, 90, and 96 h after the PGF(2alpha) injection or until ovulation. A treatment x time interaction (P < 0.01) influenced concentrations of estradiol. All cows had similar (P > 0.15) concentrations of estradiol at the time of ECP administration, but after ECP treatment all cows treated with ECP and control cows that exhibited estrus had greater (P < 0.01) concentrations of estradiol compared with nontreated cows that did not exhibit estrus. In all animals, estradiol diminished 48 h after the PGF(2alpha) (time of the second GnRH injection), but ECP-treated cows, regardless of estrus, had elevated (P < 0.02) concentrations of estradiol compared with control cows. There was a treatment x time interaction (P < 0.001) on uterine pH. All cows had similar uterine pH (P > 0.19) 24 h after the PGF(2alpha) injection. Control cows that did not exhibit estrus had a greater uterine pH compared with control cows that exhibited estrus (P < 0.01) and ECP cows that exhibited estrus (P = 0.05) 48 h after the PGF(2alpha) injection (7.0 +/- 0.1 vs. 6.7 +/- 0.1 and 6.8 +/- 0.1, respectively). Estradiol cypionate-treated cows not exhibiting estrus were intermediate (6.8 +/- 0.1; P > 0.05). All cows had similar uterine pH 72 h after the PGF(2alpha) injection through ovulation (P > 0.06). In summary, uterine pH was similar among all animals that exhibited estrus, regardless of treatment with ECP.     

Methods to reduce or eliminate detection of estrus in a melengestrol acetate-PGF2alpha protocol for synchronization of estrus in beef heifers

Three experiments were conducted to evaluate methods to decrease or eliminate the detection of estrus inherent to a melengestrol acetate (MGA)-PGF2alpha (PGF) protocol for synchronization of estrus in heifers. In each experiment, all heifers received 0.5 mg of MGA x animal(-1) x d(-1) for 14 d (d -32 to -19) and PGF (25 mg, i.m.; d 0, 0 h) 19 d after the last feeding of MGA (MGA-PGF protocol). In Exp. 1, heifers (n = 709) were assigned to each of the following protocols: 1) the MGA-PGF protocol with AI 6 to 12 h after detection of estrus (estrus AI; MGA-PGF); 2) MGA-PGF plus 100 microg, i.m. of GnRH on d -7 (1x GnRH) and estrus AI; or 3) MGA-PGF, GnRH on d -7, and GnRH (100 microg, i.m.) at 48 h after PGF, coincident with insemination (2x GnRH-TB48). In Exp. 2, heifers (n = 559) received the MGA-PGF protocol and were inseminated by either estrus AI or fixed-time AI (TAI) at 60 h, coincident with an injection of GnRH (GnRH-TB60). In Exp. 3, all heifers (n = 460) received the MGA-PGF protocol and were inseminated by estrus AI when detected up to 73 h. Heifers not observed in estrus by 73 h received TAI between 76 and 80 h. Half the heifers inseminated by TAI received no further treatment (TB80), and the remaining half was injected with GnRH at insemination (GnRH-TB80). Variance associated with the interval to estrus and the proportion in estrus from d 0 to 5 was similar for 1x GnRH and MGA-PGF treatments in Exp. 1. Pregnancy rate (d 0 to 5) did not differ for the MGA-PGF and 1x GnRH treatments (62.5 and 60.4%, respectively), and both were greater (P < 0.05) than TAI pregnancy rate in the 2x GnRH-TB48 treatment (42.3%). In Exp. 2, the peak estrous response occurred 60 h after PGF. Pregnancy rate during the synchrony period was greater (P < 0.05) for the MGA-PGF (255/401; 63.6%) than the GnRH-TB60 (74/158; 46.6%) treatment. In Exp. 3, 75.7% of heifers (348/460) were detected in estrus by 73 h and were inseminated, with a conception rate of 74.4%. Pregnancy rates after TAI did not differ between TB80 and GnRH-TB80 (14/56 = 25% and 19/ 56 = 33.9%, respectively). Total pregnancy rate was 63.5% for heifers inseminated after detected estrus and by TAI. Collectively, these data indicate that the exclusive use of TAI for heifers treated with the MGA-PGF protocol resulted in lower pregnancy rates than when AI was performed after detection of estrus. However, estrus AI for 3 d and TAI at the end of d 3 could result in pregnancy rates similar to those achieved after a 5-d period of detecting estrus.     

JSAR Innovative Technology Award. Development of ovulation synchronization and fixed time artificial insemination in dairy cows

Recently, reproductive management has become more difficult as a result of increased herd size. Problems with missing estrous signs and decrease in conception rate by artificial insemination (AI) performed at wrong timing have caused low AI conception rates. In 1995, ovulation synchronization and fixed-time AI (Ovsynch/TAI) was developed in the USA as a new reproductive technology, which was accepted as an useful reproductive management tool in many countries. However, no information on the use of Ovsynch/TAI was available in Japan. It was, therefore, warranted to show the ovulation rate and conception rate after Ovsynch/TAI using gonadotropin releasing hormone analogue (GnRH-A, fertirelin acetate) and prostaglandin F2alpha (PGF2alpha)-THAM, both were commercially available in this country. The conception rate after Ovsynch/TAI has been known to vary among different herds and individuals. Investigation and analysis of factors affecting the conception rate was also warranted to improve the conception rate. A series of experiments were carried out to establish Ovsynch/TAI using domestically produced GnRH-A and PGF2alpha and to study factors affecting conception rate after Ovsynch protocol. Ovsynch using 100 microg GnRH-A and 25 mg PGF2alpha were observed using ultrasonography. As a result, a high synchronization rate of ovulation at 16 to 20 h after the second GnRH injection was confirmed. The conception rate after Ovsynch/TAI was compared in 87 cows with the conception rate after AI at estrus induced by PGF2alpha (139 cows). Conception rate after Ovsynch/TAI was higher than the figure after AI at induced estrus (59.1% vs 20.9%, P<0.05). The dose of GnRH-A was also studied and a practical dose of GnRH-A was found to be 50 microg per cow. To clarify some factors affecting the conception rate after Ovsynch/TAI, 1,558 cows were investigated for the state of their ovaries, days after calving, parity, season, ovarian cyclicity postpartum and nutritional state at the day of Ovsynch. The overall conception rate after Ovsynch/TAI was 51.5%. Fifty-six cows (3.6%) showed estrus at 6 to 7 d after the first injection of GnRH-A. The conception rate after Ovsynch/TAI was low in cows that were 40 to 60 d postpartum, those in their 5th lactation or more, those bred in July to August, and those recovering ovarian cyclicity later than 56 d postpartum. The conception rate after Ovsynch/TAI was high in cows in which body condition score (BCS) was 3.75 at dry period and 3.0 at the day of Ovsynch. In conclusion, Ovsynch/TAI is an effective tool for the reproductive management of dairy cows. A steady and sufficient conception rate after Ovsynch/TAI could be expected by taking the factors affecting the conception rate into the consideration.     

Influence of a controlled internal drug release after fixed-time artificial insemination on pregnancy rates and returns to estrus of nonpregnant cows

We determined whether an ovulatory estrus could be resynchronized in previously synchronized, AI nonpregnant cows without compromising pregnancy from the previous synchronized ovulation or to those inseminated at the resynchronized estrus. Ovulation was synchronized in 937 suckled beef cows at 6 locations using a CO-Synch + progesterone insert (controlled internal drug release; CIDR) protocol [a 100-microg injection of GnRH at the time of progesterone insert, followed in 7 d by a 25-mg injection of PGF(2alpha) at insert removal; at 60 h after PGF(2alpha), cows received a fixed-time AI (TAI) plus a second injection of GnRH]. After initial TAI, the cows were assigned randomly to 1 of 4 treatments: 1) untreated (control; n = 237); 2) progesterone insert at 5 d after TAI and removed 14 d after TAI (CIDR5-14; n = 234); 3) progesterone insert placed at 14 d after TAI and removed 21 d after TAI (CIDR14-21; n = 232); or 4) progesterone insert at 5 d after TAI and removed 14 d after TAI and then a new CIDR inserted at 14 d and removed 21 d after TAI (CIDR5-21; n = 234). After TAI, cows were observed twice daily until 25 d after TAI for estrus and inseminated according to the AM-PM rule. Pregnancy was determined at 30 and 60 d after TAI to determine conception to the first and second AI. Pregnancy rates to TAI were similar for control (55%), CIDR5-14 (53%), CIDR14-21 (48%), and CIDR5-21 (53%). A greater (P < 0.05) proportion of nonpregnant cows was detected in estrus in the CIDR5-21 (76/110, 69%) and CIDR14-21 (77/120, 64%) treatments than in controls (44/106, 42%) and CIDR5-14 (39/109, 36%) cows. Although overall pregnancy rates after second AI service were similar, combined conception rates of treatments without a CIDR from d 14 to 21 [68.7% (57/83); control and CIDR5-14 treatments] were greater (P = 0.03) than those with a CIDR during that same interval [53.5% (82/153); CIDR5-21 and CIDR14-21 treatments]. We conclude that placement of a progesterone insert 5 d after a TAI did not compromise or enhance pregnancy rates to TAI; however, conception rates of nonpregnant cows inseminated after a detected estrus were compromised when resynchronized with a CIDR from d 5 or 14 until 21 d after TAI.     

Effect of GnRH pretreatment on reproductive performance of postpartum suckled beef cows following synchronization of estrus using GnRH and PGF2alpha

The effect of GnRH pretreatment on estrus detection rate, precision of estrus, and reproductive performance of postpartum beef cows synchronized to estrus using GnRH and PGF2alpha was evaluated. In Exp. 1, Angus cows (n = 87) were randomly assigned by parity, postpartum interval, and body condition score (BCS) to receive either 1) GnRH on d -7 and PGF2alpha on d 0 (GP) or 2) the GP treatment and an additional injection of GnRH on d -16 (GGP). Estrus detection and AI were conducted twice daily from d -3 to d 3. At 72 h after PGF2alpha, all animals not previously detected in estrus were bred by AI and received a concurrent injection of GnRH (TAI). Synchronized pregnancy rates were numerically increased (P = 0.15) in cows treated with GGP (55%) compared with those on the GP treatment (44%). In Exp. 2, 1,276 spring-calving, suckled beef cows in nine herds were randomized to treatments as described for Exp. 1, except that the initial GnRH injection for the GGP treatment was administered on d -14. Herd affected all indicators of reproductive performance (P < 0.05). The percentage of animals detected in estrus prematurely (d -3 to d 0; 7%) was not affected by treatment. Estrus response rate was influenced by postpartum interval (< 60 vs > or = 60; 61 vs 73%; P < 0.01) and a three-way interaction of parity, BCS, and treatment (P < 0.01). Within animals with a BCS > or = 5.5, the GGP treatment tended to increase the detection of estrus in primiparous cows (GP vs GGP; 76 vs 91%; P = 0.11) and decrease detection in multiparous cows (GP vs GGP; 78 vs 72%; P < 0.10). However, because conception rate to TAI in animals with a BCS > or = 5.5 was greater (P < 0.05) in the GGP than in the GP group (28 vs 8%, respectively), this interaction was interpreted to represent a shift in interval to estrus induced by the GGP treatment, rather than a reduction in the synchronization of ovarian function. Conception rates of animals inseminated to an observed estrus did not differ among treatments (P = 0.15). Synchronized pregnancy rate tended (P = 0.06) to be greater in GGP- (53%) than in GP-treated animals (47%). In conclusion, pretreatment with GnRH tended to increase pregnancy rates during a 6-d synchronization period, primarily through enhanced conception rates of cows bred by TAI. In contrast to our hypothesis, GnRH pretreatment did not increase the percentage of animals detected in estrus or the precision of estrus expression.     

Ovsynch plus CIDR protocol for timed embryo transfer in suckled postpartum Japanese Black beef cows

We compared synchronization and pregnancy rates, and the increase in blood progesterone concentrations during luteal development, between (1) Ovsynch plus an intravaginal controlled internal drug release (CIDR) device protocol followed by timed embryo transfer (timed ET), and (2) a conventional estrus synchronization method using PGF(2 alpha) and ET in suckled postpartum Japanese Black beef cows. Cows in the PGF group (n=18) received a PGF(2 alpha) analogue when a CL was first palpated per rectum at 10-d intervals after 1 to 2 month postpartum. Cows (n=11), which showed estrus (Day 0) within 5 d of the PGF(2 alpha), and had a CL on Day 7, received ET. Cows in the Ovsynch+CIDR group (n=19) underwent the Ovsynch protocol plus a CIDR for 7 d (GnRH analogue and CIDR on Day-9, PGF(2alpha) analogue with CIDR removal on Day-2, and GnRH analogue on Day 0), with ET on Day 7. The ovulation synchronization (100%) and embryo transfer (100%) rates in the Ovsynch+CIDR group were greater (P<0.01) than the estrus synchronization (66.7%) and the embryo transfer (61.1%) rates in the PGF group. The postpartum interval at ET in the Ovsynch+CIDR group (62.5 +/- 2.5 d) was shorter (P<0.01) than in the PGF group (74.9 +/- 3.9 d). The pregnancy rate in the Ovsynch+CIDR group (57.9%) did not differ significantly from that in the PGF group (50.0%). Plasma progesterone concentrations were not significantly different in the two groups on Days 0, 1, 2, 5, 7, 14 and 21. In summary, higher synchronization and transfer rates, and shorter postpartum interval to ET, can be achieved with timed ET following the Ovsynch plus CIDR protocol than after estrus with the single PGF(2 alpha) treatment followed by ET in suckled postpartum recipient beef cows. Pregnancy rates were similar. Also, the increase in blood progesterone concentrations during luteal development following ovulation synchronized by the Ovsynch plus CIDR protocol was similar to that after estrus induced by the PGF(2 alpha) treatment.     

Synchronization of estrus in postpartum beef cows and virgin heifers using combinations of melengestrol acetate, GnRH, and PGF2alpha

The efficacy of various combinations of melengestrol acetate (MGA), GnRH, and PGF2alpha for the synchronization of estrus in Angus-based beef cattle was compared. Hormones were administered as follows: MGA, 0.5 mg x animal(-1) x d(-1) mixed in a grain carrier; GnRH, 100 microg i.m.; PGF2alpha, 25 mg i.m. In Exp. 1, 2, and 3, cows were randomly assigned to treatments by parity and interval postpartum. The detection of estrus and AI were conducted from d -2 until 72 to 96 h after PGF2alpha, at which time cows not detected to be in estrus received GnRH and fixed-time AI (TAI). Data were analyzed separately for primiparous and multiparous cows. In Exp. 1, cows (n = 799) at three locations received GnRH on d -7 and PGF2alpha on d 0 and either no further treatment (GnRH-PGF) or short-term MGA from d -6 through d -1 (STMGA). Among multiparous cows, conception rate at TAI was greater (P < 0.05) for STMGA (41%, 47/115) than for GnRH-PGF treated cows (26%, 24/92). Across herds and parity, synchronized AI pregnancy rate (SPR) was not affected (P > 0.10) by treatment (GnRH-PGF vs. STMGA; 54%, 210/389 vs. 57%, 228/402). In Exp. 2, cows (n = 484) at three locations received either STMGA or long-term MGA from d -32 through d -19, GnRH on d -7, and PGF2alpha on d 0 (LTMGA). Among primiparous cows, SPR was greater (P < 0.01) in LTMGA (65%, 55/85) than STMGA-treated cows (46%, 40/87). Treatment had no effect (P > 0.10) on SPR among multiparous cows (STMGA vs. LTMGA; 59%, 92/155 vs. 64%, 101/157). In Exp. 3, cows (n = 838) at four locations received the LTMGA treatment and either no further treatment or an additional period of MGA exposure from d -6 through d -1 (L&STMGA). Among primiparous cows, SPR tended to be influenced (P < 0.10) by the herd x treatment interaction and was greater (P < 0.01) among L&STMGA (86%, 19/22) than LTMGA-treated cows (56%, 14/25) at a single location. Among multiparous cows, SPR was lower (P < 0.05) in L&STMGA (46%, 165/358) than LTMGA-treated cows (55%, 184/336). In Exp. 4, Angus heifers (n = 155) received either STMGA or 14 d of MGA (d -32 through d -19) and PGF2alpha on d 0 (MGA-PGF). The detection of estrus and AI were conducted from d -2 to d 6. Interval to estrus was greater (P < 0.05) and estrous response was lower (P < 0.05) in STMGA than MGA-PGF-treated heifers. In conclusion, primiparous cows responded more favorably to longer-duration MGA treatments than did multiparous cows. All protocols achieved sufficient SPR to justify their use for improved reproductive management of postpartum beef cows.     

Follicular dynamics and steroid profiles in cows during and after treatment with progestin-based protocols for synchronization of estrus

Two progestin-based protocols for the synchronization of estrus in beef cows were compared. Cyclic, nonlactating, crossbred, beef cows were assigned by age and body condition score to one of two treatments. Cows assigned to the MGA Select protocol were fed melengestrol acetate (MGA; 0.5 mg x cow(-1) x (-1)) for 14 d, GnRH was administered (100 microg i.m. of Cystorelin) 12 d after MGA withdrawal, and PGF2alpha (25 mg of i.m. Lutalyse) was administered 7 d after GnRH. Cows assigned to the 7-11 Synch protocol were fed MGA for 7 d and were injected with PG on d 7 of MGA, GnRH on d 11, and PG on d 18. Transrectal ultrasonography was performed daily to monitor follicular dynamics from the beginning of MGA feeding through ovulation after the synchronized estrus. All cows exhibited estrus in response to PG. Mean interval to estrus was shorter (P < 0.01) for 7-11 Synch-treated cows (56 +/- 1.5 h) than for cows assigned to the MGA Select protocol (73 +/- 4.7 h). Mean interval from estrus to ovulation did not differ between treatments (P > 0.10). Variances for interval to estrus differed (P < 0.01) between treatments. Mean follicular diameter at GnRH injection, PG injection, and estrus did not differ (P > 0.10) between treatments. Relative to MGA Select, serum estradiol-17beta concentrations were higher (P < 0.01) for 7-11 Synch 2 d and 1 d before, on the day of GnRH injection, in addition to 4 d after GnRH, and 24 h after PG. Mean progesterone concentrations were greater (P < 0.01) for MGA Select cows from 4 d before to 7 d after GnRH. Forty-four percent of the variation in interval to estrus between treatments was explained by differences in estradiol-17beta concentrations 24 h after PG. This study suggests that follicular competence is likely related to steroidogenic capacity of the follicle and the endocrine environment under which growth and subsequent ovulation of the dominant follicle occurs.     

Synchronizing estrus and(or) ovulation in beef cows after combinations of GnRH, norgestomet, and prostaglandin F2alpha with or without timed insemination

Three experiments were conducted to induce estrus and(or) ovulation in 1,590 suckled beef cows at the beginning of a spring breeding season. In Exp. 1, 890 cows at three locations were allotted to three treatments: 1) GnRH on d -7 + prostaglandin F2alpha (PGF2alpha) on d 0 (Select Synch); 2) GnRH on d -7 + PGF2alpha on d 0 (first day of the breeding season) plus a norgestomet implant (NORG) between d -7 and 0 (Select Synch + NORG); or 3) two injections of PGF2alpha given 14 d apart (2xPGF2alpha). More (P < 0.05) cycling cows were detected to have been in estrus after both treatments that included GnRH, whereas, among noncycling cows, the addition of norgestomet further increased (P < 0.05) the proportion in estrus. Pregnancy rates were greater (P < 0.01) among noncycling cows after treatments that included GnRH. For cows that calved >60 d before the onset of the breeding season, conception rates were greater (P < 0.01) than those that calved < or =60 d regardless of treatment, whereas days postpartum had no effect on rates of detected estrus. When body condition scores were < or =4 compared with >4, rates of detected estrus (P < 0.05) and conception (P = 0.07) were increased. In Exp. 2, 164 cows were treated with the Select Synch + NORG treatment and were inseminated either after estrus or at 16 h after a second GnRH injection (given 48 h after PGF2alpha). Conception and pregnancy rates tended (P = 0.08) to be or were less (P < 0.05), respectively, for noncycling cows inseminated by appointment, but pregnancy rates exceeded 53% in both protocols. In Exp. 3, 536 cows at three locations were treated with the Select Synch protocol as in Exp. 1 and inseminated either: 1) after detected estrus (Select Synch); 2) at 54 h after PGF2alpha when a second GnRH injection also was administered (Cosynch); or 3) after detected estrus until 54 h, or in the absence of estrus, at 54 h plus a second GnRH injection (Select Synch + Cosynch). Conception rates were reduced (P < 0.01) in cows that were inseminated by appointment. An interaction of AI protocol and cycling status occurred (P = 0.05) for pregnancy rates with differing results for cycling and noncycling cows. Across experiments, variable proportions of cows at various locations (21 to 78%) were cycling before the breeding season. With the GnRH or GnRH + NORG treatments, ovulation was induced in some noncycling cows. Conception rates were normal and pregnancy rates were greater than those after a PGF2alpha program, particularly when inseminations occurred after detected estrus.     

Ovarian and endocrine responses associated with the treatment of cystic ovarian follicles in dairy cows with gonadotropin releasing hormone and prostaglandin F2alpha, with or without exogenous progesterone

The objectives of this observational study were to document ovarian and endocrine responses associated with the treatment of cystic ovarian follicles (COFs) in dairy cows, using gonadotropin releasing hormone (GnRH) and prostaglandin F2alpha (PGF) with or without exogenous progesterone. A secondary objective was to determine pregnancy establishment following synchronization of ovulation and timed insemination in cows diagnosed with COFs. In trial I, 18 Holstein cows diagnosed with COFs received 2 injections of 100 microg GnRH, 9 d apart, with 25 mg PGF given 7 d after the 1st GnRH. A new follicle developed in all 18 cows after the 1st GnRH, and 83% of cows ovulated following the 2nd GnRH. Cows were inseminated 16 h after the 2nd GnRH. Of the 17 cows available for pregnancy diagnosis, 7 were confirmed pregnant. In trial II, 8 cows with COFs received GnRH and an intravaginal progesterone device (CIDR) concurrently, then PGF 7 d later. The CIDR was removed 2 d after PGF administration. Plasma estradiol concentrations declined following CIDR insertion. In all cows, a new follicle developed following GnRH treatment; estradiol-surge and estrus occurred spontaneously after CIDR-removal. Seven of 8 cows ovulated the new follicle. In dairy cows diagnosed with COFs, treatment with GnRH followed by PGF 7 d later, with or without exogenous progesterone, resulted in the recruitment of a healthy new follicle; synchronization of ovulation and timed insemination resulted in a 41% pregnancy rate.     

Supplemental norgestomet,progesterone, or melengestrol acetate increases pregnancy rates in suckled beef cows after timed inseminations

In Exp. 1, 187 lactating beef cows were treated with injections of GnRH 7 d before and 48 h after prostaglandin F2alpha (PGF2alpha; Cosynch) or with Cosynch plus a 7-d treatment with an intravaginal progesterone (P4)-releasing insert (CIDR-B; Cosynch + CIDR). In Exp. 2, 183 lactating beef cows were treated with the Cosynch protocol or with Cosynch plus a 7-d treatment with norgestomet (Cosynch + NORG). In Exp. 1 and 2, blood samples for later P4 analyses were collected on d -17, -7 (first GnRH injection), 0 (PGF2alpha injection), and at timed artificial insemination (TAI; 48 h after PGF2alpha). In Exp. 3, 609 lactating beef cows were treated with the Cosynch + CIDR protocol or were fed 0.5 mg of melengestrol acetate (MGA) per day for 14 d before initiating the Cosynch protocol 12 d after the 14th d of MGA feeding (MGA + Cosynch). Blood samples were collected as in Exp. 1 and 2, plus additional samples on d -33 and -19 before PGF2alpha. In Exp. 4, 360 lactating beef cows were treated with a Cosynch + CIDR protocol, with TAI occurring at either 48 or 60 h after PGF2alpha, while receiving either GnRH or saline to form four treatments. Blood samples were collected as in Exp. 1 and 2. In Exp. 1, addition of P4 reduced the ability of the first GnRH injection to induce ovulation in anestrous cows with low P4 before PGF2alpha but improved (P = 0.06) pregnancy rates (61 vs 66%). In Exp. 2, the addition of NORG mimicked P4 by likewise increasing (P < 0.01) pregnancy rates (31 vs 51%) beyond those after Cosynch. In Exp. 3, the Cosynch + CIDR protocol increased (P < 0.001) pregnancy rates from 46 to 55% compared to the MGA + Cosynch protocol. In Exp. 4, administration of GnRH at TAI improved (P < 0.05) pregnancy outcomes (50 vs 42%), whereas timing of TAI had limited effects. We conclude that a progestin treatment concurrent with the Cosynch protocol improved pregnancy outcomes in all experiments, but pretreatment of cows with MGA was not as effective as the CIDR insert or NORG implants in this Cosynch-TAI model. Most of the improvement in pregnancy rates was associated with the increase in pregnancy rates of anestrous cows, regardless of whether ovulation was successfully induced in response to GnRH 7 d before PGF2alpha. Injection of GnRH at TAI following the Cosynch + CIDR protocol increased pregnancy rates in cycling cows with high P4 before the PGF2alpha injection and in anestrous cows with low P4 before PGF2alpha injection.     

Timing of artificial insemination in postpartum beef cows following administration of the CO-Synch + controlled internal drug-release protocol

This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) at 54 or 66 h after administration of the CO-Synch + controlled internal drug-release (CIDR) protocol. Cows (n = 851) at 2 locations over 2 yr (yr 1, n = 218 and 206; and yr 2, n = 199 and 228 at the 2 locations, respectively) were stratified by age, BCS, and days postpartum to 1 of 2 FTAI intervals. Cows were administered GnRH (100 mug, i.m.) and were equipped with a CIDR insert (1.38 g of progesterone) on d 0. Controlled internal drug-release inserts were removed 7 d later at the time PGF(2alpha) (25 mg, i.m.) was administered (d 7). Continuous estrus detection was performed at location 2 by using the HeatWatch Estrus Detection System; the transmitters were fitted at the time of PGF(2alpha) and removed at the time of AI. Artificial insemination was performed at predetermined fixed times [54 h (FTAI 54; n = 424) or 66 h (FTAI 66; n = 427) after PGF(2alpha)] and all cows were administered GnRH (100 mug, i.m.) at AI. Two blood samples were collected on d -10 or -8 and immediately before treatment initiation to determine the pretreatment estrous cyclicity status of cows [progesterone >/=0.5 ng/mL (FTAI 54, 288/424 = 68%; FTAI 66, 312/427 = 73%; P = 0.07)]. Pregnancy rates were greater (P < 0.01) among cows that exhibited estrus than among those that did not (123/163 = 76% and 150/270 = 56%, respectively). There were no treatment x location interactions within year (P > 0.10) for age, days postpartum, or BCS; thus, the results were pooled for the respective treatments. Pregnancy rates were greater for FTAI 66 than FTAI 54 (P = 0.05; 286/426 = 67% vs. 257/424 = 61%, respectively). Pregnancy rates resulting from FTAI did not differ between year (P = 0.09), farm (P = 0.80), AI sire (P = 0.11), or technician (P = 0.64). There was no difference between pregnancy rates resulting from FTAI based on pretreatment cyclicity status (P = 0.30), and there was no difference between treatments in final pregnancy rates (P = 0.77). In summary, pregnancy rates resulting from FTAI following CO-Synch + CIDR at 66 h were greater than those resulting from FTAI at 54 h.     

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: replacement of gonadotropin-releasing hormone with human chorionic gonadotropin

Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 μg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.     

Influence of an agonist of gonadotropin-releasing hormone (buserelin) on estrus synchronization and fertility in beef cows.

The objective of this experiment was to determine the effect of sequential treatment with buserelin (a GnRH agonist) and cloprostenol (a prostaglandin F2 alpha analog) on estrous response and fertility in beef cattle with different ovarian conditions. On d 0 (1st d of treatment), the control group (n = 52, 10 heifers and 42 cows) and the GnRH group (n = 48, 10 heifers and 38 cows) received 2 mL of saline or 2 mL of Receptal (8 micrograms of buserelin), respectively. On d 6, all cows that had not exhibited spontaneous estrus were given i.m. 500 micrograms of cloprostenol (PGF). Ultrasonography on d 0 and assays of progesterone in blood on d -11, 0, and 6 were used to identify follicular and luteal status of animals. Cattle were observed for estrus from d 0 to 10. Cows showing estrus were bred artificially 12 h after onset of estrus. Over the 10-d period, the number of cows detected in estrus and pregnancy and conception rates were identical for the two groups. However, between d 0 and 6, the proportion of cows exhibiting estrus was lower (P less than .01) in the GnRH group than in the control group. Between d 6 and 10, the synchronization rate and precision of estrus were greater (P less than .01) in the buserelin-treated group than in the control group. Conception rate and interval from PGF injection to onset of estrus were not different between the two treatment groups. Presence of a large (greater than 10 mm) follicle on d 0 enhanced synchronization rate and precision of estrus.(ABSTRACT TRUNCATED AT 250 WORDS)