Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate and PGF2alpha

A total of 402 two suckled postpartum beef cows at 2 locations (CSU and ECRC) were utilized in 3 trials to evaluate the effectiveness of a combination melengestrol acetate (MGA)-PGF2alpha estrus synchronization system in spring-calving cows. The cows were allocated by days post partum, body condition score (1 = emaciated; 9 = obese), sire breed, and dam age at the beginning of treatment to 1 of 2 treatments within location and trial: MGA-PGF2alpha (0.5 mg MGA/head/d for 14 d with 25 mg of PGF2alpha injected 17 d after MGA withdrawal), and unsynchronized controls. All cows were observed for estrus at 12-h intervals for at least 5 d post injection. Cows observed in standing estrus were inseminated 12 to 18 h later. There was a location effect on response to treatment that was attributed to differences in body condition score between locations so data were analyzed within a location. Body condition score at the CSU location was 5.7 compared with 4.0 at the ECRC location. The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 5-day estrus and 5-d pregnancy rates (78.6 and 61.0%, respectively) than the CSU controls (11.1 and 6.9%, respectively). Similar results for 5-d estrus and pregnancy rates but of decreased magnitude were also observed for the ECRC MGA-PGF2alpha treated (31.6 and 21.4%, respectively) cows compared with that of the ECRC controls (11.9 and 8.5%, respectively). The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 25- and 60-d pregnancy rates (82.5 and 94.8%) than the CSU controls (65.3 and 87.5%). The 25- and 60-d pregnancy rates were similar between the ECRC MGA-PGF2alpha treated cows and ECRC control cows. The MGA-PGF2alpha estrus synchronization system appears to contribute to pregnancy early in the breeding season in postpartum beef cows, although its effectiveness is limited by cow body condition.     

Comparison of two MGA-PGF2alpha systems for synchronization of estrus in beef heifers

Yearling beef heifers (n = 193) were used to evaluate reproductive performance attained with 2 MGA-PGF(2)alpha synchronization systems. These treatments were compared with an untreated control group. The 14-d MGA heifers were synchronized by feeding 0.5 mg MGA/h/d for 14 d. At 17 d after the last MGA feeding, these heifers were injected with PGF(2)alpha (25 mg, im). Heifers in the 7-d MGA treatment group were fed 0.5 mg MGA/h/d for 7 d and received a 25-mg, im injection of PGF(2)alpha on the last day of the MGA feeding period. Heifers in all 3 treatment groups were observed for estrus every 12 h for 7 d beginning 24 h after the PGF(2)alpha injection. Heifers observed in estrus during this 7-d period were artificially inseminated approximately 12 h after the onset of estrus. The percentages of heifers in estrus during the 7-d synchronized period were 75.4, 56.3 and 17.2% for the 14-d MGA, 7-d MGA and control groups, respectively. The estrous responses were significantly different in each treatment. The percentage of heifers in estrus during the peak 24-h period was higher (P < 0.05) in heifers synchronized with the 14-d MGA system than in heifers synchronized with the 7-d MGA system (75.5 vs 50.0%). The synchronized conception rate of the 14-d MGA heifers was significantly higher (65.3%) than that of both the 7-d MGA (41.7%) and control (45.4%) heifers. Synchronized conception rates were similar (P = 0.79) in the 7-d MGA and control treatments. Synchronized pregnancy rates were 55.2, 32.4 and 15.2% for the 14-d MGA, 7-d MGA and control groups, respectively. Both synchronization treatments resulted in significantly higher synchronized pregnancy rates compared with that of the controls. The synchronized pregnancy rate was higher (P < 0.05) in the 14-d MGA group than it was in the 7-d MGA group. The mean day of conception within the breeding season was 11.5 and 9.3 d shorter in the 14-d MGA heifers than in the 7-d MGA and control heifers, respectively. Our results indicate that using the 14-d MGA system to synchronize estrus in beef heifers results in better reproductive performance than that attained in heifers synchronized with the 7-d MGA system or in control heifers.     

Comparison of Melengestrol Acetate-Prostaglandin F(2)alpha to Syncro-Mate B for estrus synchronization in beef heifers

Three hundred and ten yearling heifers of various breeds were used in five trials to compare two estrus synchronization treatments. Treatment 1 consisted of Melengestrol Acetate-Prostaglandin F(2)alpha (MGA-PGF(2)alpha). Heifers were fed 0.5 mg MGA/head/d for 14 to 16 d. Sixteen or 17 d after the final MGA feeding, heifers were injected i.m. with 25 mg PGF(2)alpha. Treatment 2 consisted of Syncro-Mate B (SMB). Heifers were given a 9-d norgestomet implant plus an injection containing 3 mg norgestomet and 5 mg estradiol valerate i.m. at implant insertion. Heifers were observed for estrus at 6-h intervals for 120 h after the end of treatments and were artificially inseminated 12 to 18 h after observed estrus. Heifers synchronized with MGA-PGF(2)alpha and SMB had a similar (P > 0.10) estrous response (83.4 vs 90.2%) and a similar (P > 0.10) degree of synchrony (71.8 vs 79.0%) following treatment. However, the synchronized conception rate (68.7 vs 40.6%) and the synchronized pregnancy rate (57.3 vs 36.6%) were higher (P < 0.01) in MGA-PGF(2)alpha than SMB heifers. Breeding season pregnancy rates were similar in both treatment groups. Heifers in both groups that were classified as cycling prior to initiation of treatment had improved reproductive performance following synchronization compared with those classified as noncycling. Based on higher synchronized conception and pregnancy rates and lower labor requirements and drug costs, the MGA-PGF(2)alpha system appears to be a better method to synchronize estrus in beef heifers than the SMB system.     

Estrus synchronization in beef heifers with progestin-based protocols. I. Differences in response based on pubertal status at the initiation of treatment

Two progestin-based protocols for estrus synchronization in replacement beef heifers were compared on the basis of estrous response, interval to and synchrony of estrus, and pregnancy rate. The objective was to determine, whether addition of GnRH to a melengestrol acetate (MGA)-prostaglandin F2alpha (PGF2alpha) estrus synchronization protocol would improve synchrony of estrus without compromising fertility in yearling beef heifers. Heifers at two locations (Location 1, n = 60 and Location 2, n = 64) were assigned randomly to one of two treatments by breed and pubertal status. Heifers were defined as, pubertal when concentrations of progesterone in serum were elevated (> or = 1 ng/mL) in either one of two samples obtained 10 and 1 day prior to treatment initiation. Prior to MGA administration, 18/60 (30%) and 36/64 (56%) of the heifers at Locations 1 and 2, respectively, were pubertal. Heifers in both treatments were fed MGA (0.5 mg/head/day in 1.8 kg/head/day supplement) for 14 days followed by 25 mg of PGF2alpha i.m. (MGA-PGF2alpha) 19 days after MGA withdrawal (Day 33 of treatment). One-half of the heifers at each location received 100 microg of GnRH i.m. 12 days after MGA withdrawal (Day 26 of treatment; MGA Select). The control group received only MGA-PGF2alpha. Heifers were observed for signs of behavioral estrus continuously during daylight hours for 7 days beginning on the day PGF2alpha was administered. Heifers were inseminated 12 h after observed estrus. There was a treatment by location by pubertal status interaction (P < 0.05) for interval to estrus. Compared to the respective control treatment at each location, prepubertal heifers assigned to the MGA Select protocol at Location 1 had longer intervals to estrus, whereas at Location 2, prepubertal heifers assigned to the MGA-PGF2alpha protocol had longer intervals to estrus. The higher number of pubertal heifers at Location 2 was associated with a reduced variance in the interval to estrus among MGA Select treated heifers. Total estrous response and synchronized conception rates were similar between treatments at both locations. These data suggest that addition of GnRH to the MGA-PGF2alpha protocol may improve synchrony of estrus, however, the degree of synchrony may be influenced by pubertal status of heifers at the time treatments are imposed. Further studies are needed to define production systems in which the MGA Select protocol is warranted for use in beef heifers.     

Synchronization of estrus in yearling beef heifers with melengestrol acetate and prostaglandin F(2alpha)

This study was designed to test the efficacy of melengestrol acetate (MGA) in combination with prostaglandin F(2alpha) (PGF(2alpha)) in synchronizing estrus in cyclic and noncyclic heifers. One hundred thirty-one cyclic and prepubertal crossbred heifers were randomly assigned to three treatment groups: Controls (n = 43); MGA (0.5 mg/d for 7 d) and PGF(2alpha) (25 mg i.m. on Day 7; n = 44); and PGF(2alpha) (25 mg i.m. on Day 7; n = 44). Observations for estrus were made at 6-n intervals throughout the 7-d treatment period followed by a 34-d artificial insemination breeding season. A greater percentage (P < 0.05) of MGA-PGF(2alpha) noncyclic heifers showed behavioral estrus (91%) than did Control (67%) or PGF(2alpha) heifers (61%) during the 34-d artificial insemination period. There was no difference (P > 0.05) between synchronization rates of the MGA-PGF(2alpha) heifers and PGF(2alpha) heifers 7 d after PGF(2alpha) administration. The percentage of control animals in estrus during the first 25 d of the breeding season did non differ from the synchronized rates of MGA-PGF(2alpha) and PGF(2alpha) heifers (P > 0.05). Conception rates (heifers pregnant/heifers inseminated) did not differ (P > 0.05) for cyclic or prepubertal heifers among Control, MGA-PGF(2alpha) or PGF(2alpha) heifers. Though conception rates did not differ, there was a trend toward lowered conception rates in MGA-PGF(2alpha) heifers.     

Prolonging the MGA-prostaglandin F2 alpha interval from 17 to 19 days in an estrus synchronization system for heifers

Our objective was to determine whether extending the interval from 17 to 19 d between removal of melengestrol acetate (MGA) feed and administration of PGF2 alpha would alter conception rates, pregnancy rates and the degree of synchrony in replacement beef heifers. A commercial heifer operation in north-central Kansas purchased 591 Angus x Hereford heifers from 12 sources. Prior to the spring breeding season, 14% of the heifers were culled. The remaining heifers were assigned randomly to 2 MGA-PGF2 alpha synchronization systems. All heifers were fed MGA (0.5 mg/head/d) for 14 d, and PGF2 alpha was administered either 17 or 19 d after the completion of MGA feeding. Heifers were inseminated artificially for 30 d followed by 30 d of natural mating. Based on each source, first-service conception rates ranged from 66 to 90%, whereas overall pregnancy rates ranged from 91 to 100%. Heifers given PGF2 alpha on Day 17 after MGA had first-service conception rates of 75.9% compared with 81.4% for heifers receiving PGF2 alpha on Day 19. In response to the PGF2 alpha injection, 99% of the Day 19 heifers that were detected in estrus were inseminated artificially by 72 h after the PGF2 alpha injection, whereas 74% of the heifers in the Day 17 treatment were inseminated by that time. Average interval to artificial insemination (AI) after PGF2 alpha was greater (P < 0.01) for the Day 17 heifers (73.1 +/- 1.1 h) than for the Day 19 heifers (56.2 +/- 1.1 h). No differences in conception rates or overall pregnancy rates occurred; however, heifers receiving PGF2 alpha on Day 19 after MGA had shorter intervals to estrus, and a greater proportion was inseminated within 72 h after PGF2 alpha, thus possibly facilitating successful timed insemination of the remaining heifers not yet inseminated by that time.     

Estrus synchronization with an oral progestogen prior to superovulation of postpartum beef cows

Ovarian follicular dynamics and steroid secretion patterns were monitored in postpartum beef cows that were synchronized for estrus with melengestrol acetate (MGA) or prostaglandin F(2alpha) (PGF) prior to superovulation. Twenty-four muhiparous Angus cows were stratified by number of days postpartum to an MGA or PGF treatment prior to superovulation. Cows in the MGA group were fed 0.5 mg MGA/d for 14 d in a grain carrier. Superstitnulatory treatments began 14 d after withdrawal of MGA from feed or 11 d after administering a single injection of 500 microg cloprostenol (PGF). Supersthnulatory treatments (FSH) were administered twice daily in decreasing doses (7.5, 5, 5, 2.5 mg) over 4 d. Sixty and 72 h after initiating the superstimulatory treatments, all cows were treated with 750 microg and 500 microg PGF, respectively Cows were inseminated at 0, 12, and 24 h from the onset of standing estrus with semen from 2 proven sires. Cows within treatment were inseminated with 1, 2 and 1 (single) or 2, 4 and 2 units (double) of semen at the designated insemination times. Blood sampling and transrectal ultrasonography of ovaries were performed daily beginning 2 d prior to the initiation of FSH treatment and were continued through embryo recovery. Ovaries were examined daily to determine the number and size of follicles. Plasma samples were analyzed for progesterone and estradiol. Follicles were counted and categorized based on a 5 to 9 mm range or >/= 10 mm. At the end of superovulatory treatment there were more (P /= 10 mm among cows that were estrus synchronized with MGA (75 +/- 1.2) than with PGF (3.9 +/- 1.2) These differences were reflected in higher (P 相似文献   

Change in morphology of corpora lutea, central luteal cavities and steroid secretion patterns of postpartum suckled beef cows after melengestrol acetate with or without prostaglandin F2alpha

Change in morphology of the corpus luteum (CL) and patterns of progesterone and estradiol secretion after treatment with melengestrol acetate (MGA) were monitored in postpartum beef cows. Twenty Angus cows were randomly assigned to MGA or MGA + prostaglandin F(2alpha) (PGF) treatments. All cows were fed 0.5 mg of MGA per cow per day for 14 d. The MGA-treated cows (n = 10) were allowed to return to estrus spontaneously at the second estrus after withdrawal of MGA from the feed. The MGA + PGF-treated cows (n = 10) received an injection containing 25 mg of PGF(2alpha) 17 d after the last feeding of MGA. Cycle 1 was defined as the first luteal phase after MGA feeding and Cycle 2 represented the subsequent cycle or luteal phase after PGF. Blood sampling and transrectal ultrasonography of the ovaries was done daily through the completion of 2 estrous cycles upon removal of MGA from the feed. Blood samples were analyzed for plasma progesterone and estradiol concentrations. Area of CL and fluid-filled cavities within each CL were determined by ultrasonography. Concentrations of progesterone and area of CL were similar between cycles and treatments. Estradiol concentrations were higher (P < 0.05) in Cycle 2 than in Cycle 1. Fluid-filled cavities were larger (P < 0.001) in Cycle 1 than in Cycle 2 for both mid-luteal (Days 5 to 9) and late-luteal (Days 10 to 14) phases. Multiple CL (2 or more during 1 cycle) were observed in 5 cows. Progesterone concentrations and total area of luteal tissue did not change with respect to treatment or cycle, but CL morphology was altered in the first cycle after MGA treatment. Of the 19 cows that ovulated after withdrawal of MGA, 3 experienced a short luteal phase. These data characterize changes that occur among cows that are fed melengestrol acetate during the postpartum period and enhance observations from prior studies regarding MGA use.     

Induction of estrus in suckled female yaks (Bos grunniens) and synchronization of ovulation in the non-sucklers for timed artificial insemination using progesterone treatments and Co-Synch regimens

The objectives of the present study were to evaluate the induction of estrus and fertility in yak cows treated with Co-Synch regimens or progesterone (P(4)). In Experiment 1, postpartum suckled yaks were assigned to three treatments: (1) A (n=28), insertion of an intravaginal device containing P(4) (CIDR) on Day 0, PGF(2alpha) (i.m.) on Day 6 and PMSG (i.m.) at the time of CIDR removal on Day 7 (P(4)-PGF(2alpha)-PMSG); (2) B (n=21), PGF(2alpha) (i.m.) on Day 6 and PMSG on Day 7; (3) C (n=26), control group. Seven yak bulls were grazed with the cows for natural breeding. Rate of estrus within 96h of the end of treatment was greater (P<0.05) in A (100.0%) than in B (28.6%) or C (0.0%). First service conception rate (CR) determined by serum P(4) on Day 21 after breeding was greater (P<0.05) in A (78.6%) than in B (22.2%). Also, pregnancy rate (PR) during the breeding season was greater (P<0.05) in A (82.1%) than in B (19.0%) and C (7.7%). In Experiment 2, non-suckled yaks that calved in previous years but not in the current year were assigned to three treatments: (1) A (n=31), GnRH (i.m.) on Day 0, followed by PGF(2alpha) on Day 7 and timed artificial insemination (TAI) concurrently with GnRH treatment on Day 9 (Co-Synch regimen); (2) B (n=50), a CIDR device for 7 days plus PGF(2alpha) and PMSG at the time of CIDR withdrawal on Day 7 and TAI on Day 9 (P(4)-PGF(2alpha)-PMSG); (3) C (n=50), yak cows were artificially inseminated at spontaneous estrus. Frozen semen of Holstein and Jersey were used for insemination in Experiment 2. The CR assessed by rectal palpation 35 days after TAI was not different in A (22.6%), B (30.0%) and C (33.3%), but PR was greater in A and B than in C, when based on those cows presented for estrous synchronization programs. It is concluded that P(4)-PGF(2alpha)-PMSG protocol could efficiently induce estrus and result in an acceptable pregnancy rate in postpartum suckled yak cows. This technique and Co-Synch regimen can be applied successfully for TAI of non-suckled yak cows.     

Efficacy of either a single or split treatment of PGF2alpha after a 14 day melengestrol acetate treatment to synchronize estrus and induce luteolysis in Bos indicus x Bos taurus heifers

Two experiments evaluated a modified delivery of prostaglandin F2alpha (PGF2alpha) after a melengestrol acetate (MGA) treatment in Angus and Bos indicus x Bos taurus (BI) heifers. Experiment 1 was replicated three times with yearling BI heifers (n = 695). Heifers received MGA (0.5 mg head(-1) day(-1)) for 14 days. In Replications 1 and 2, heifers received either 25 mg of PGF2alpha im 19 days after MGA (single) or 12.5 mg of PGF2alpha im 19 and 20 days after MGA (split). In Replication 3, heifers received the same treatments, with PGF2alpha initiated either 18 or 19 days after MGA. Estrus was detected for 72 h after PGF2alpha, with AI commencing 8-12 h after a detected estrus. Heifers not observed in estrus by 72 h were timed-AI concomitant with GnRH (100 microg im). Heifers from Replication 2 (n = 146) had blood samples collected at the initial PGF2alpha and at timed-AI to determine corpus luteum (CL) regression by evaluating plasma progesterone concentrations. The interval from MGA withdrawal to PGF2alpha did not have a significant effect on any variable in Replication 3 and there were no treatment by replication effects for any variables, therefore data were pooled. Modifying the PGF2alpha treatment from a single treatment to two treatments on consecutive days increased (P < 0.05) 72 h estrous response (43.2% versus 50.1%), timed-AI (23.9% versus 33.5%) and total-AI pregnancy rates (34.5% versus 42.5%), and CL regression (79.1% versus 92.5%), respectively. In Experiment 2, yearling Angus (n = 66) and 2-year-old BI (n = 68) heifers were synchronized as per Experiment 1 (with the initial PGF2alpha 19 days after MGA). Neither breed nor PGF2alpha treatment effected (P > 0.05) 72 h estrous response, total-AI pregnancy rate, or CL regression rate. In conclusion, treating yearling BI heifers with split treatments of PGF2alpha (given on two consecutive days) improved estrous response and pregnancy rates by increasing PGF2alpha-induced luteolysis.     

Synchronization of estrus in virgin beef heifers using melengestrol acetate and PGF2alpha: an efficacy comparison of cloprostenol and dinoprost tromethamine

This study compared the efficacy of two sources of PGF2alpha on the reproductive performance of virgin beef heifers, after synchronization of estrus using melengestrol acetate (MGA) and PGF2alpha. Angus-based heifers (n = 1002) in five herds were fed 0.5 mg per head per day of MGA for 14 days. Nineteen days after the last day of MGA feeding, heifers were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (n = 504; Estrumate, E) or 25 mg dinoprost tromethamine (n = 498; Lutalyse, L) as a source of exogenous PGF2alpha. Heifers were observed twice daily for 5 days for signs of estrus and artificially inseminated 8-12 h later, except in herd A, wherein animals not detected in estrus by 80 h after PGF2alpha were mass-mated and no longer monitored for signs of estrus. Estrumate and Lutalyse were equally (P > 0.1) effective among all response variables evaluated, including estrus response (E, 89% and L, 86%), conception rate (E, 67% and L, 67%), and synchronized pregnancy rate (E, 61% and L, 57%). Synchrony of estrus was not affected (P > 0.1) by PGF2alpha source, and peak estrus response occurred 60 h post-PGF for both treatments. Conception rate to timed insemination was not different (P > 0.1) among Estrumate- and Lutalyse-treated heifers within herd A (14%, 4/28 and 7%, 2/29, respectively). Herd had a significant (P < 0.05) effect on all indicators of reproductive performance. Conception rates within herds A and D were influenced by technician (P < 0.05), however, this effect was balanced across treatments and no treatment by technician interaction was detected. In conclusion, when administered 19 days after a 14-day MGA feeding period, cloprostenol and dinoprost tromethamine are equally efficacious for synchronous induction of a fertile estrus in virgin beef heifers.     

Estrus synchronization in beef cows: comparison between GnRH+PGF2alpha+GnRH and PRID+PGF2alpha+eCG

The aim of this study was to compare two protocols for estrus synchronization in suckled beef cows over a 2 years period. The population studied consisted of 172 Charolais and 168 Limousin cows from 12 and 14 beef herds, respectively. In each herd, cows were allotted to groups according to parity, body condition score and calving difficulty. Cows in Group 1 (n=174) received PRID on Day-8 with estradiol benzoate (10mg, vaginal capsule), dinoprost on Day-4 (25mg i.m.), eCG on Day 2 (500 IU i.m.). The PRID was removed on Day-2 and cows were inseminated on Day 0, 56 h after PRID was removed. Cows in Group 2 (n=166) received GnRH on Day-10 (100 microg i.m.), dinoprost on Day-3 (25mg i.m.) and GnRH on Day-1 (100 microg i.m.), and were inseminated on Day 0, 16-24h after the last GnRH treatment. Plasma progesterone concentrations were measured to determine cyclicity prior to treatment (Days-20 and -10), to confirm the occurrence of ovulation (Days 0 and 10) and to determine the apparent early pregnancy rate (Days 0, 10 and 24). Pregnancy diagnosis was performed by ultrasonography between Days 35 and 45. The effects of various factors on ovulation, apparent early pregnancy and pregnancy rates were studied using logistic mixed models. There was no significant difference between Groups 1 and 2, respectively, for the cyclicity rate before treatment (80.5% versus 80.1%), for apparent pregnancy rate on Day 24 (62.1% versus 54.8%, P=0.09) and for pregnancy rate on Days 35-45 (53.8% versus 46.3%, P=0.16). Ovulation rate was higher (P<0.01) in Group 1 (90.8%) than in Group 2 (77.1%) and was affected by cyclicity prior to treatment in Group 2 but not in Group 1 (Group 1: 88.2% in anestrous cows versus 91.4% in cyclic cows; Group 2: 45.5% in anestrous cows versus 85.0% in cyclic cows, P interaction=0.05). Apparent pregnancy rates on Day 24 were influenced by the year of study (52.4% versus 68.8%, OR=2.12, P<0.01) and by the cyclicity before treatment (anestrous cows 46.3% versus cyclic cows 61.5%, OR=1.86, P<0.05). Pregnancy rates at 35-45 days were influenced by the year of study (44.2% versus 59.8%, OR=1.92, P<0.01). In conclusion, although pregnancy rates were similar for the two treatments, the combination of GnRH+PGF2alpha+GnRH in suckled beef cows induced a lower rate of ovulation than treatment with PRID+PGF2alpha, particularly in anestrous cows.     

Estrus and pregnancy after synchrony with lutalyse in conjunction with Syncro-Mate-B.

Estrous response and pregnancy rates are decreased for cows given Syncro-Mate-B (SMB) during metestrus (Day 1 to 5 of an estrous cycle). Data indicate these decreases are due, in part, to retention of a functional corpus luteum (CL). Our objective was to determine whether PGF2alpha administered in conjunction with SMB would improve estrous response and pregnancy rates in metestrous cows with no detrimental effects to cows in other stages of the estrous cycle. Three hundred seventy-three suckled beef cows were observed for estrus for 21 d before SMB administration to determine stage of an estrous cycle. Blood samples were collected 14 and 7 d before treatment and at SMB administration. Serum was assayed for concentration of progesterone to verify stage of estrous cycle or noncyclicity. All cows received the standard SMB regime and were allotted by age and stage of cycle to one of two groups. Cows denoted SMB + L received 25 mg of PGF2alpha 8 d after implantation, whereas cows denoted SMB served as controls. On Day 10, SMB implants were removed and females were observed for subsequent estrus. At this time, calves were removed from their dams for 48 h. Artificial insemination was performed 12 hr after observation of a standing estrus. Timed insemination was performed at 48 hr after implant removal for cows not inseminated at 24 or 36 hr after implant removal. Interval to synchronized estrus (within 5 d of implant removal) was lengthened for metestrous cows compared to cows in other stages of the cycle irrespective of treatment (P < 0.001). Cows receiving PGF2alpha had a greater pregnancy rate at 5 d compared to controls (P = .0672). Interval to estrus, estrous response, and pregnancy rate to A1 at d 28 or end of breeding season were not affected by administration of PGF2alpha in conjunction with SMB when compared to the standard SMB protocol.     

Reproductive performance of synchronized beef cows as affected by inhibition of suckling with nose tags or temporary calf removal

A study was conducted to determine whether presence of the calf during suckling inhibition influences the response to estrus synchronization in beef cows. Angus or Hereford cows (n=89) were administered Syncro-Mate-B (SMB), which consisted of a 6-mg norgestomet ear implant (in situ 9 d) in conjunction with 5 mg of estradiol valerate and 3 mg (im) of norgestomet. Cows were allotted by breed, body condition, stage of the estrous cycle, parity and date of parturition to 1 of 3 treatments: 48-h calf removal; ad libitum suckling; or inhibition of suckling with a nose tag for 48 h. Calves were weighed at time of SMB implant removal, 48 h later and at weaning. Cows were mated via AI approximately 12 h after detection of estrus during a 30-d period after implant removal followed by a natural service period of 35 d. At 48 h after implant removal, calf removal and nose tag calves had lost an average of 3.6 and 0.9 kg, respectively, while the suckled calves gained 1.8 kg (P < 0.01). Mean calf weight at weaning did not differ among treatments. Synchronized estrous response (within 5 d of implant removal) was not different among treatments. Pregnancy rate for cows exhibiting a synchronized estrus (5 d AI) for calf removal, nose tag and suckled cows was 76, 48 and 48%, respectively (P>0.10). Treatment did not affect the 30-d AI or overall 65-d pregnancy rate. In this study, there were no differences observed in the percentage of synchronized or pregnant cows following suckling inhibition by either a nose tag or calf removal. Transient reductions of calf body weight during the 48-h calf removal period did occur in both the nose tag and calf removal groups.     

Synchronization of estrus with PGF2 alpha administered 18 days after a progesterone treatment in lactating dairy cows

In a previous study we showed that estrus synchronization with 2 treatments of PGF2 alpha 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2 alpha treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2 alpha was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2 alpha (25 mg, i.m., Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2 alpha treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.     

Attenuation of premature estrous behavior in postpartum beef cows synchronized to estrus using GnRH and PGF2alpha

The efficacy of GnRH and PGF2alpha (7-day injection interval) for estrus synchronization is diminished by estrous expression before PGF2alpha (premature estrus; PE). Effects of modifications to GnRH-PGF2alpha protocols on the incidence of PE and other indicators of reproductive performance were evaluated. In Experiment 1, Angus-based crossbred cows (n=51) received 25 mg of PGF2alpha i.m. on Day 0. Animals were randomly assigned by parity and interval postpartum to receive GnRH 100 microg i.m. on either Day -7 or Day -6. Estrous detection and AI were conducted from Day -3 to Day 5. Treatment had no effect on the incidence of PE, estrous response, conception rate per AI or synchronized pregnancy rate (6- vs. 7-day interval; 8 vs. 15%; 92 vs. 93%; 77 vs. 76%; 71 vs. 70%, respectively). In Experiment 2, Angus cows (n=150) received GnRH 100 microg i.m. on Day -7 and 25 mg PGF2alpha i.m. on Day 0. Animals were randomly assigned by parity, interval postpartum, and body condition score to receive either no further treatment (Control) or 0.5 mg melengestrol acetate/hd/d from Day -7 to Day -1 (MGA). Estrous detection and AI were conducted from Day -2 to Day 7. Fewer (P < 0.05) MGA-treated cows were detected in PE (0%) compared to controls (7%). Treatment had no effect on estrous response or synchronized pregnancy rates (Control vs. MGA; 78 vs. 84%; 52 vs. 60%, respectively). Conception rate per AI of cows > or = 60 days postpartum were not affected by treatment (Control vs. MGA; 79 vs. 73%) however, control cows < 60 days postpartum tended (P < 0.10) to have lower conception rates per AI (39%) than did their MGA-treated counterparts (69%). In summary, 6- and 7-day GnRH-PGF2alpha injection intervals resulted in similar synchronized reproductive performance. Inclusion of MGA feeding between GnRH and PGF2alpha injections eliminated the occurrence of premature estrus and improved conception rate per AI of late-calving cows.     

Pregnancy rate following GnRH + PGF 2alpha treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment

Anestrous and lactating Bos taurus by Bos indicus crossbred cows with minimum body condition were studied to determine the efficacy of GnRH+PGF 2alpha combinations for induction of estrus and/or ovulation on pregnancy rate during the months of the year when temperatures are greater. On day 0 (start of treatment), cows were assigned randomly to either treatment or control groups. Treated cows (n = 74) received i.m. 200 microg of GnRH on day 0 and 150 microg of PGF 2alpha 7 days later (day 7). On day 7, treated cows were equally distributed to each of three protocols: (1) Select Synch (n = 25), artificial insemination (AI) 12 h after exhibiting estrus from day 7 (PGF 2alpha injection) until day 12; (2) Ovsynch (n = 24), 200 microg of GnRH at 48 h after PGF 2alpha (day 9) + timed-AI (TAI) 16-20 h later; (3) CO-Synch (n = 25), 200 microg of GnRH + TAI at 48 h after PGF 2alpha (day 9). Control cows (n = 25) received no treatment + AI 12 h after exhibiting estrus from days 0 to 12. Detection of estrus was performed daily during the early morning and evening hours from days 0 to 7 in all the cows, and from days 7 to 12 in the cows treated with Select Synch and in the control group, with the aid of a sterilized bull. Palpation per rectum and transrectal ultrasonography were used on days -30, -20, -10 and 0 to confirm anestrus (absence of CL and no signs of estrus at each evaluation) but with ovarian follicles > or = 10 mm on day 0. Pregnancy rate was 0% for Select Synch, 21% for Ovsynch and 28% for CO-Synch (P < 0.05). In conclusion, the Ovsynch and CO-Synch protocols resulted in greater pregnancy rates compared with the Select Synch protocol in Bos taurus/Bos indicus cows with minimum body condition that were anestrous and lactating during the summer months in a tropical environment.     

Effect of sequential treatment with prostaglandin F2 alpha and/or oxytocin on estrus and pregnancy rate of lactating dairy cows

A total of 335 lactating dairy cows was used to determine the effect of oxytocin or PGF2a given 8 h after treatment with a luteolytic dosage of PGF2a on the percentage of cows exhibiting estrus within 7 d after treatment, and the pregnancy rate to a single insemination at this time. On the initial day of treatment (Day 0), cows with a palpable corpus luteum on the ovary were treated with 25 mg, im of PGF2a. At 8 h later, the cows were divided into 3 groups. Cows in Group 1 (n = 112) were treated with oxytocin (0.33 IU/kg bwt im); cows in Group 2 (n = 112) were treated with 25 mg, im of PGF2a; and cows in Group 3 (n = 111) served as the untreated controls. Cows in all 3 groups were continuously observed for estrus visually or by way of an activated heatmount detector within 7 d after treatment, and were inseminated within 12 h of the observed estrus.Plasma progesterone (P4) concentration was determined using radioimmunoassay on Day 0 and Day 2. Of the cows with P4 greater than 1 ng/ml on Day 0, the percentage of cows observed in estrus within 7 d after treatment was 75, 89 and 72% for cows in Group 1, Group 2 and Group 3, respectively. When all cows were evaluated, the percentage of cows observed in estrus within 7 d after treatment was 60, 70 and 55% for cows in Group 1, Group 2 and Group 3, respectively. In both instances, the value for cows in Group 2 was significantly higher than that for either cows in Group 1 or Group 3. The pregnancy rate for cows inseminated within 7 d was similar for cows in all 3 groups. The results of this study demonstrated that treatment of dairy cows with 2 luteolytic dosages of PGF2a at an 8-h interval resulted in more cows being observed in estrus within 7 d than with 1 treatment with PGF2a, or with oxytocin given at an 8-h interval after a luteolytic dosage of PGF2a.     

Use of short-term progestin treatment to resynchronize the second estrus following synchronized breeding in beef heifers

Two trials were conducted to evaluate the efficacy of short-term progestin administration to resynchronize the second estrus after artificial insemination in yearling beef heifers. In Trial 1 crossbred yearling heifers (n = 208) were synchronized with Syncro-Mate-B (SMB) and artificially inseminated (AI) between 48 and 54 h following implant removal. Implant removal is defined as Day 1. Following AI, the heifers were randomly assigned to 1 of 2 experimental groups. Group 1 heifers were fed melengestrol acetate (MGA) daily from Day 17 to 21 at a rate of 0.5 mg/head, while Group 2 control received no exogenous progestin during this period. Synchrony of estrus was defined as the 3-d period in which the highest number of heifers expressed behavioral estrus in each group. There was no difference (P < 0.05) in the pregnancy rate during the second estrus due to MGA supplementation. More MGA-treated heifers (P < 0.01) expressed estrus in a 3-d period than the controls. In Trial 2, yearling heifers (n = 108) were synchronized with 2 injections of PGF(2alpha) (second PGF(2alpha) injection is designated as Day 1) administered 14 d apart with AI 12 h after the onset of behavioral estrus. The heifers were then randomly assigned to 1 of the following 3 treatment groups after initial AI: 1) MGA fed at 0.5 mg/head daily from Days 17 to 21; 2) norgestomet administered in 6.0-mg implants from Days 17 to 21; 3) untreated control heifers. Blood samples were collected on Day 21 and analyzed for progesterone (P(4)). Elevated P(4) (> 1 ng/ml) on Day 21 indicated pregnancy to the first insemination. Synchrony among the 3 groups of heifers was similar (P > 0.10); however, the second estrus was less (P < 0.05) variable in the MGA and norgestomet treated heifers. During the resynchronized second estrus, conception rates were not affected by progestin treatment (MGA 40%, norgestomet 64%, and control 62%; P > 0.10). However, a proportion of heifers treated MGA 10% 4 36 and norgestomet 3% 1 36 expressed behavioral estrus during second estrus even though they were diagnosed as pregnant from first service by elevated P(4) levels on Day 21. We conclude that short-term use of progestin from Days 17 to 21 following AI causes closer synchrony of estrus; however, inseminating pregnant heifers that exhibit behavioral estrus may cause abortion.     

Estrus synchronization in cattle using estradiol, melengestrol acetate and PGF

In Experiment 1, all cattle were fed MGA (0.5 mg/head/d) for 7 d (designated Days 0 to 6) and given PGF on Day 6. One-half were administered estradiol valerate (EV; 5 mg, im) on Day 0. At Location 1, a higher proportion (P < 0.005) of EV-treated heifers were detected in estrus and bred by AI between Days 7 and 13 than control heifers not receiving EV (27 of 33 versus 15 of 32), but the number of pregnancies (12 vs 10) was not significantly different. Eighty-three of 104 EV-treated and 89 of 106 control cows were inseminated, resulting in 50 and 45 pregnancies, respectively (not significant). At Location 2, cattle were similarly treated and exposed to bulls on Days 7 to 49. Fall pregnancy rate was higher (P < 0.015) for EV-treated than control heifers (44 of 48 vs 33 of 46), but was not significantly different for cows (22 of 26 vs 19 of 23). In Experiment 2, estradiol 17beta (E17beta; 5 mg, im) and progesterone (100 mg, im) were administered on Day 0 (instead of EV). In a third group (designated the PGF group), cattle were bred on Days 0 to 6, and PGF was administered on Day 6 to those not yet bred. For 213 cows, the percentage pregnant to a synchronized estrus was greater in the PGF group (72%) than in either the control group treated with MGA (49%; P = 0.005) or the group receiving MGA and E17beta (54%; P < 0.025). Fall pregnancy rates were 91, 89, and 96% for the 213 cows (not significant) and 89, 93, and 98% for 131 heifers (not significant) in the PGF, MGA and E17beta groups, respectively. In cattle without a functional CL, the average diameter of the largest follicle at Day 6 was 1 to 2 mm smaller in the E17beta + MGA group than in the MGA group (difference significant only in cows at Location 1). Combined for both locations, the synchronized pregnancy rate in heifers without a functional CL on Day 6 was higher (P < 0.05) in the E17beta + MGA group than in the MGA group (11 of 21, 52% versus 4 of 20, 20%). Estrogen treatment caused regression of ovarian follicles with emergence of a new follicular wave. Including estrogen in an estrus synchronization program utilizing MGA and PGF significantly increased fall pregnancy rate in heifers (at 1 location) and the synchronized pregnancy rate of heifers without a functional CL at the time of PGF treatment (combined for both locations).