Progestin and prostaglandin for estrous synchronization in beef heifers

Seventy-eight Simmental-Angus-Hereford crossbred yearling heifers, in 1983, and 99 similar heifers, in 1984, were used to compare two estrous synchrony regimens. One treatment group (SMB) was synchronized using the commercially available Syncro-Mate-B procedure, which involved placing a norgestomet implant in the ear for 9 d and giving an injection of norgestomet and estradiol valerate at the time of implantation. A second group (PR + PG) was given a norgestomet implant (PR) for 7 d and a 5-mg injection of alfaprostol (PG) at implant removal. Percentage of heifers cycling during the synchronization period and percent conceiving in 5 d or 30 d were not different (P greater than .10) due to treatment. The interval from implant removal to onset of behavioral estrus was shorter (P less than .01) for the heifers treated with SMB than for the heifers treated with PR + PG (42.8 vs 58.0 h). The group treated with SMB had a more uniform synchrony of estrus than the group treated with PR + PG. The effect of day of the estrous cycle at implantation on hours to estrus after implant removal was determined by a regression analysis, which showed a linear response for the SMB group with a slope of .78 (P = .09); the PR + PG group regression was cubic (P less than .01); this also indicated a more uniform response by the SMB group. These results indicate that the combination of norgestomet and alfaprostol produced more variation in interval from treatment to estrus than the Syncro-Mate-B procedure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship of pre- and post-ovulatory gonadotropin concentrations to subnormal luteal function in postpartum beef cattle

Early weaning of calves from anestrous cows results in formation of short-lived corpora lutea (CL) unless the animals are pretreated with a progestagen (norgestomet). This study was conducted to investigate the relationship between pre- and post-ovulatory gonadotropin secretion and luteal lifespan. Postpartum beef cows were assigned randomly into two groups, control (n = 5) and norgestomet (implant given at weaning for 9 d; n = 7). Calves from all cows were weaned 30 to 33 d postpartum. Coccygeal artery cannulas were placed into cows in the control group 1 d prior to weaning and 2 d before implant removal in cows in the norgestomet group. Plasma for determination of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol-17 beta (E) and progesterone (P) was collected daily at 10-min intervals for 6 h from weaning (control) or the day prior to implant removal (norgestomet) to estrus (d 0) and on d 2, 4 and 6 following estrus. Average interval (X +/- SE; P less than .05) from weaning to estrus or implant removal was 4.2 +/- .8 and 2.3 +/- .2 d for the control and norgestomet groups, respectively. Estrous cycle length for the control group was 12.4 +/- 1.8 d compared with 20.4 +/- .3 d for the norgestomet group (P less than .05). Four of five control cows had an estrous cycle length of 7 to 14 d; all cows in the norgestomet group and the remaining control cow had an estrous cycle of normal length (16 to 21 d).2+ estrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of termination of pregnancy or long-term progestogen exposure on subsequent estrous cycle length and concentration of progesterone in plasma of heifers

An experiment was conducted to determine whether short estrous cycles following abortion of heifers between 70 and 75 d of gestation are due to factors associated with the previous presence of a conceptus or long-term exposure of the uterus and(or) ovaries to a progestogen. Fifty crossbred heifers were randomly allotted at estrus (d 0) to five groups: control (n = 10), pregnant (Preg.; n = 14), progestogen (norgestomet) implant (Norg.; n = 9), progesterone-releasing intravaginal device (PRID; n = 9), or hysterectomy (Hyst.; n = 8). Control heifers were injected during the mid-luteal phase of an estrous cycle with 25 mg prostaglandin F2 alpha (PGF2 alpha) and length of the subsequent estrous cycle was determined. Beginning 6 to 8 d after estrus, heifers in the Norg. or PRID groups were given norgestomet ear implants or intravaginal coils, respectively, every 10 d for 70 d. Heifers were hysterectomized 5 to 8 d after estrus. Seventy to 75 d after conception, progestogen treatment or hysterectomy, heifers were injected (i.m.) with 25 mg PGF2 alpha and the last norgestomet ear implants or PRIDs were removed. Interval from PGF2 alpha injection to first estrus (means +/- SE) ranged from 2.5 +/- .2 to 4.4 +/- .7 d (P greater than .05). Length of the first estrous cycle means +/- SE) following PGF2 alpha-induced luteolysis or progestogen withdrawal was shorter (P less than .01) for the Preg. group (8.2 +/- .4 d) than for the control, Norg. and PRID groups (21.5 +/- .6 d; 19.3 +/- 1.4 d; and 18.2 +/- 1.3 d, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Calving rates in a tropical beef herd after treatment with a synthetic progestagen, norgestomet, or a prostaglandin analogue, cloprostenol

Maiden heifers and lactating cows of known ovarian status and of several breeds were treated with a synthetic prostaglandin, cloprostenol, or a synthetic progestagen, norgestomet, at the start of an artificial insemination (AI) program. Animals in the cloprostenol treatment received 2 injections 10 days apart. Over the next 26 days those animals that showed oestrous behaviour were inseminated. Synchronisation rates and calving rates to insemination over the first 7 days were calculated. Those in the norgestomet treatment received an implant of norgestomet plus an injection of norgestomet and oestradiol valerate. The implant was removed 10 days later and the animals were given an injection of pregnant mare serum gonadotrophin (PMSG). They were inseminated at 48 h (maiden heifers) or 56 h (lactating cows) after implant removal. Calving rates to fixed-time insemination were recorded. After completion of the AI program the animals in both treatments were joined with bulls. Overall calving rates (AI plus bulls) were calculated. By day 7 of the program, 82% of the maiden heifers and 76% of the lactating cows in the cloprostenol treatment had been detected in oestrus. By day 21 the respective figures were 99% and 81% Norgestomet treatment had an immediate and a prolonged effect on ovarian activity in those females classified as having inactive ovaries at the start of the AI program. Calving rates of those females to fixed-time AI and overall were similar to those of the females with active ovaries in both treatments. Their calving rates to fixed-time insemination, and overall calving rates for the lactating females, were significantly higher than the corresponding values of their contemporaries treated with cloprostenol and inseminated on observed oestrus over 7 days. For those females classified as having active ovaries at the start of the AI program, calving rates to first insemination and overall were similar for both treatments. Overall calving rates of lactating cows of each breed were, with one exception, higher in the norgestomet treatment than in the cloprostenol treatment. Although norgestomet treatment was more expensive than cloprostenol treatment, the advantage in calf crop resulted in an overall monetary advantage to the norgestomet treatment.     

Relationship between size of the ovulatory follicle and pregnancy success in beef heifers

Previous research indicated that the size of the ovulatory follicle at the time of insemination significantly influenced pregnancy rates and embryonic/fetal mortality after fixed-timed AI in postpartum cows, but no effect on pregnancy rates was detected when cows ovulated spontaneously. Our objective was to evaluate relationships of fertility and embryonic/fetal mortality with preovulatory follicle size and circulating concentrations of estradiol after induced or spontaneous ovulation in beef heifers. Heifers were inseminated in 1 of 2 breeding groups: (1) timed insemination after an estrous synchronization and induced ovulation protocol (TAI n = 98); or (2) AI approximately 12 h after detection in standing estrus by electronic mount detectors during a 23-d breeding season (spontaneous ovulation; n = 110). Ovulatory follicle size at time of AI and pregnancy status 27, 41, 55, and 68 d after timed AI (d 0) were determined by transrectal ultrasonography. Only 6 heifers experienced late embryonic or early fetal mortality. Interactions between breeding groups and follicle size did not affect pregnancy rate (P = 0.13). Pooled across breeding groups, logistic regression of pregnancy rate on follicle size was curvilinear (P < 0.01) and indicated a predicted maximum pregnancy rate of 68.0 +/- 4.9% at a follicle size of 12.8 mm. Ovulation of follicles < 10.7 mm or > 15.7 mm was less likely (P < 0.05) to support pregnancy than follicles that were 12.8 mm. Ovulatory follicles < 10.7 mm were more prevalent (28% of heifers) than ovulatory follicles > 15.7 mm (4%). Heifers exhibiting standing estrus within 24 h of timed AI had greater (P < 0.01) follicle diameter (12.2 +/- 0.2 mm vs. 11.1 +/- 0.3 mm) and concentrations of estradiol (9.9 +/- 0.6 vs. 6.6 +/- 0.7) and pregnancy rates (63% vs. 20%) than contemporaries that did not exhibit behavioral estrus. However, when differences in ovulatory follicle size were accounted for, pregnancy rates were independent of expression of behavioral estrus or circulating concentration of estradiol. Therefore, the effects of serum concentrations of estradiol and behavioral estrus on pregnancy rate appear to be mediated through ovulatory follicle size, and management practices that optimize ovulatory follicle size may improve fertility.     

Synchronization of estrus in dairy goats given norgestomet and estradiol valerate at various stages of the estrous cycle.

Dairy goats were given subcutaneous implants with 3 mg of norgestomet (NOR) and IM injections of 0.625 mg of estradiol valerate and 0.375 mg of norgestomet on day 0 of the estrous cycle (estrus; NOR 0, n = 18), on postestrus day 4 (NOR 4, n = 18), or on postestrus day 11 (NOR 11, n = 15). Ear implants were removed after 9 days. Mean (+/- SE) hours from removal of ear implants to onset of estrus and proportion of goats responding were 36 +/- 3.8 and 83%, 33 +/- 4.0 and 61%, and 36 +/- 2.7 and 93% for groups NOR 0, NOR 4, and NOR 11, respectively. There were no significant differences between treatment groups in time to onset of estrus. The percentage of goats in group NOR 11 that had signs of estrus was significantly greater than the percentage of goats in group NOR 4. Of the goats in groups NOR 0, NOR 4, and NOR 11 that had signs of estrus, 53, 55, and 86%, respectively, had onset of behavioral estrus between 24 and 48 hours after implant removal. All goats that had signs of estrus had onset of behavioral estrus between 12 and 72 hours after implant removal. Mean (+/- SE) hours from removal of ear implants to time of peak concentrations of luteinizing hormone (LH) were 49 +/- 4.1, 49 +/- 3.8, and 49 +/- 4.0 for groups NOR 0, NOR 4, NOR 11, respectively (not different). The percentage of goats in group NOR 11 that had LH peaks was significantly greater than the percentage of goats in group NOR 4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Timing of preovulatory endocrine events, estrus and ovulation in Brahman x Hereford females synchronized with norgestomet and estradiol valerate

The purpose of these studies was to investigate the pattern and timing of preovulatory endocrine events, estrus and ovulation in Brahman X Hereford (F1) heifers synchronized with norgestomet and estradiol valerate. In Exp. 1, 66 nulliparous and 191 primiparous Brahman X Hereford (F1) heifers were used to estimate the interval from norgestomet implant removal to onset of estrus. The mean interval from implant removal to onset of estrus was 29.8 +/- .5 h, with 80.9% exhibiting estrus within 48 h. Endocrine and reproductive characteristics were examined in detail during Exp. 2 with 37 primiparous heifers. Continuous observation for estrus, 6-h or 2-h blood sampling and ovarian palpation per rectum were employed. All animals were artificially inseminated 48 h after implant removal. Mean interval from implant removal to onset of estrus and to onset of the luteinizing hormone (LH) surge were closely related (r = .91; P less than .0001). Mean intervals from implant removal to ovulation, onset of estrus to ovulation and onset of LH surge to ovulation were 59.1 +/- 2.5 h, 23.3 +/- 1.4 h and 23.1 +/- 1.6 h, respectively. Approximately 73% of heifers exhibited estrus within 54 h after implant removal (optimal timing); conception rate was 59.3% in this subgroup. Conception rate of heifers that did not exhibit estrus within 54 h after implant removal or exhibited an LH surge later than 12 h after estrus (delayed timing) was 10%. Assessment of plasma estradiol-17 beta concentrations suggested that retarded selection and(or) maturation of the preovulatory follicle following implant removal delayed estrus and lowered conception in up to 28% of females timed-inseminated at 48 h.     

Estrus synchronization and pregnancy rates in beef cattle given CIDR-B, prostaglandin and estradiol, or GnRH

Two experiments were conducted to determine estrous response and pregnancy rate in beef cattle given a controlled internal drug release (CIDR-B) device plus prostaglandin F2 alpha (PGF) at CIDR-B removal, and estradiol or gonadotropin releasing hormone (GnRH). In Experiment I, crossbred beef heifers received a CIDR-B device and 1 mg estradiol benzoate (EB), plus 100 mg progesterone (E + P group; n = 41), 100 micrograms gonadotropin releasing hormone (GnRH group; n = 42), or no further treatment (Control group; n = 42), on Day 0. On Day 7, CIDR-B devices were removed and heifers were treated with PGF. Heifers in the E + P group were given 1 mg EB, 24 h after PGF, and then inseminated 30 h later. Heifers in the GnRH group were given 100 micrograms GnRH, 54 h after PGF, and concurrently inseminated. Control heifers were inseminated 12 h after onset of estrus. The estrous rate was lower (P < 0.01) in the GnRH group (55%) than in either the E + P (100%) or Control (83%) groups. The mean interval from CIDR-B removal to estrus was shorter (P < 0.01) and less variable (P < 0.01) in the E + P group than in the GnRH or Control groups. Pregnancy rate in the E + P group (76%) was higher (P < 0.01) than in the GnRH (48%) or Control (38%) groups. In Experiment II, 84 cows were treated similarly to the E + P group in Experiment I. Cows received 100 mg progesterone and either 1 mg EB or 5 mg estradiol-17 beta (E-17 beta) on Day 0 and either 1 mg of EB or 1 mg of E-17 beta on Day 8 (24 h after CIDR-B removal), in a 2 x 2 factorial design, and were inseminated 30 h later. There were no differences among groups for estrous rates or conception rates. The mean interval from CIDR-B removal to estrus was 44.2 h, s = 11.2. Conception rates were 67%, 62%, 52%, and 71% in Groups E-17 beta/E-17 beta, E-17 beta/EB, EB/E-17 beta, and EB/EB, respectively. In cattle given a CIDR-B device and estradiol plus progesterone, treatment with either EB or E-17 beta effectively synchronized estrus and resulted in acceptable conception rates to fixed-time artificial insemination.     

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)     

The use of a progesterone-releasing device (CIDR-B) or melengestrol acetate with GnRH,LH, or estradiol benzoate for fixed-time AI in beef heifers

The objective of this experiment was to compare two progestins and three treatments for synchronizing follicular wave emergence and ovulation in protocols for fixed-time AI in beef heifers. On d 0 (beginning of the experiment), Angus and Angus-Simmental cross beef heifers at random stages of the estrous cycle either received a CIDR-B device (n = 257) or were started on 0.5 mg x anima(-1) x d(-1) melengestrol acetate (MGA; n = 246) and were randomly assigned to receive i.m. injections of 100 microg GnRH, 12.5 mg porcine LH (pLH), or 2 mg estradiol benzoate (EB) and 50 mg progesterone (P4). The last feeding of MGA was given on d 6 and on d 7, CIDR-B devices were removed and all heifers received 500 microg cloprostenol (PG). Consistent with their treatment groups on d 0, heifers were given either 100 microg GnRH or 12.5 mg pLH 48 h after PG (and were concurrently inseminated) or 1 mg EB 24 h after PG and were inseminated 28 h later (52 h after PGF). Estrus rate (combined for both progestins) in heifers receiving EB (92.0%) was greater (P < 0.05) than that in heifers receiving GnRH and pLH (combined) and a CIDR-B device (62.9%) or MGA (34.3%). Although the mean interval from PG treatment to estrus did not differ among groups (overall, 47.8 h; P = 0.85), it was less variable (P < 0.01) in MGA-fed heifers (SD = 2.5 h) than in CIDR-B-treated heifers (SD = 8.1 h). Pregnancy rates (determined by ultrasonography approximately 30 d after AI) did not differ (P = 0.30) among the six treatment groups (average, 58.0%; range, 52.5 to 65.0%). Although fixed-time AI was done, pregnancy rates were greater in heifers detected in estrus than in those not detected in estrus (62.6 vs 51.9%; P < 0.05). In conclusion, GnRH, pLH, or EB treatment in combination with a CIDR-B device or MGA effectively synchronized ovulation-for fixed-time AI, resulting in acceptable pregnancy rates in beef heifers.     

Intervals from norgestomet withdrawal and injection of equine chorionic gonadotropin or P.G. 600 to estrus and ovulation in ewes

Synchronization of estrus and ovulation is essential for AI of ewes during a predetermined time frame, and progestogen-eCG treatments are typically used to prepare the ewes. However, eCG is not readily available in the United States, but P.G. 600 (400 IU of eCG and 200 IU of hCG) is available. Thus, we conducted a study to determine the effects of eCG and P.G. 600 on the timing of estrus and ovulation after progestogen withdrawal. Ewes were assigned to two replicates of an experiment with the following treatments: 1) 3-mg norgestomet implant (i.e., one-half of a Syncro-Mate-B [SMB] implant) for 10 d, plus 2 mL of saline i.m. at SMB removal (n = 11); 2) 3-mg SMB implant for 10 d, plus 400 IU of eCG i.m. at SMB removal (n = 13); and 3) 3-mg SMB implant for 10 d, plus P.G. 600 i.m. at implant removal (n = 9). On d 6 after SMB insertion, PGF2alpha was used to induce luteolysis. Beginning 12 h after implant removal, vasectomized rams were used at 12-h intervals to check for estrus. When a ewe was detected in estrus, each ovary was evaluated ultrasonically. Ovaries were evaluated again 16 h later and then at 8-h intervals until ovulation. Treatment altered the interval from implant removal to estrus (less [P < 0.05] in SMB + eCG than in the other two groups) and to ovulation (greatest [P < 0.05] in SMB). However, the treatment x replicate interaction was significant for the intervals from implant removal to estrus (P < 0.03) and from implant removal to ovulation (P < 0.05). An inconsistent response in the SMB-treated ewes seemed to be primarily responsible for the interaction. The intervals to estrus and to ovulation for the SMB-treated ewes were shorter (P < 0.05) in Replicate 1 than in Replicate 2. Also, both intervals seemed to be less consistent between replicates for the SMB + P.G. 600- than for the SMB + eCG-treated ewes; that is, eCG seemed to increase the predictability of the intervals to estrus and to ovulation. Neither the main effects of treatment and replicate nor their interaction were significant for the interval from estrus to ovulation (38.4 /- 3.3 h), size of the ovulatory follicle (7.7 +/- 0.8 mm), or ovulation rate (1.6 +/- 0.2). We concluded from this experiment that eCG is a better choice than P.G. 600 as the gonadotropin to use at the time of progestogen withdrawal to prepare ewes for AI during a predetermined interval.     

Comparison of three approaches for synchronization of ovulation for timed artificial insemination in Bos indicus-influenced cattle managed on the Texas gulf coast

Our objectives were to compare the relative efficacies of three protocols designed to synchronize ovulation for timed artificial insemination (AI) of predominantly Brahman-influenced cows and heifers. In Exp. 1, 273 Brahman x Hereford (F1) cows at three locations were stratified by BW, body condition score (BCS), age, and days postpartum and assigned randomly to three treatments: 1) Syncro-Mate-B (SMB), 2) norgestomet-prostaglandin (NP), and 3) Ovsynch. The management goal required that cows have a minimum BCS of 5 and be at least 36 d postpartum (PP) at treatment onset. However, final results included 23 cows (8.4%) whose BCS fell below 5. In Exp. 2, 286 pubertal beef heifers were stratified by BW and BCS and allocated randomly to the three treatments. Heifers were predominantly Brahman crossbred (n = 265; Brahman x Hereford, F1; Santa Cruz) or purebred Brahman-influenced (Santa Gertrudis) with a smaller number (n = 21) of Hereford heifers also included. For both experiments, SMB treatment consisted of a 9-d norgestomet ear implant plus an estradiol valerate/norgestomet injection on d 0. Norgestomet-prostaglandin-treated females were implanted with a SMB implant without the estradiol valerate/norgestomet injection at the time of implant insertion and received 25 mg prostaglandin F2alpha (PGF) i.m. 2 d before implant removal. Ovsynch consisted of 100 microg GnRH i.m. on d 1, 25 mg PGF i.m. on d 8, and a second GnRH injection on d 10. Beginning on d 9, calves were removed for 48 h in Exp. 1. Cattle in SMB and NP groups in both experiments were timed-inseminated 48 to 54 h after implant removal and at 12 to 24 h after the second GnRH injection (Ovsynch). Timed AI conception rates did not differ between the SMB (45.1%) and Ovsynch (42.4%) groups; however, conception rate in the NP group tended (P < 0.12) to be lower overall than in the other groups due to a reduced (P < 0.05) conception rate in cows that were < 60 d PP at treatment onset. Conversely, timed-AI conception was greatest (P < 0.056) in NP (54.7%) compared with SMB (40.4%) and Ovsynch (39.1%) for heifers in Exp. 2. We conclude that in mature, suckled beef cows with Brahman genetic influence, SMB and Ovsynch perform similarly when cow eligibility relies primarily on BCS and minimum days PP. The NP treatment results in lower conception in cows < 60 d PP compared with SMB and Ovsynch. However, in nulliparous Brahman-influenced heifers that are confirmed to be pubertal, NP may be superior to the other two treatments for timed AI.     

Resynchronization of estrus in cattle of unknown pregnancy status using estrogen,progesterone, or both

Our objective was to develop treatments applied to cattle of unknown pregnancy status that would resynchronize the repeat estrus of nonpregnant females. In Exp. 1, previously inseminated dairy and beef heifers were assigned randomly to each of three treatments 13 d after AI: 1) no treatment (controls; n = 44); 2) 0.5 mg of estradiol cypionate (ECP) i.m. on d 13 and 20 at the time of insertion and removal of a used intravaginal progesterone (P4)-releasing insert (CIDR; P4 + ECP; n = 44); and 3) same as P4 + ECP without injections of ECP (P4; n = 42). The P4 + ECP (>90%) and P4 (>75%) protocols effectively synchronized repeat periods of estrus to 2 d and did not harm established pregnancies. In Exp. 2, treatments similar to those in Exp. 1 were applied to previously inseminated beef heifers (n = 439). Feeding 0.5 mg of melengestrol acetate (MGA) from d 13 to 19 after AI replaced the CIDR as a source of progestin. Of those heifers not pregnant (n = 65) after the initial AI, more than 86% were reinseminated, but conception was decreased (P < 0.05) by 28 to 39% compared with controls. In Exp. 3, previously inseminated lactating beef cows at four locations were assigned within herd to each of three treatments: 1) no treatment (control; n = 307); 2) same as in Exp. 1, but with P4 + 1 mg of estradiol benzoate on d 13 and 20 (P4 + EB; n = 153); and 3) same as in Exp. 1, P4 + ECP (n = 149). Treatments with P4 plus estrogen did not decrease conception rates in pregnant cows at any location, but increased (P < 0.05) the percentage of nonpregnant cows returning to estrus between 19 and 23 d after timed AI from 29% in controls to 86% in P4 + EB and 65% in P4 + ECP cows. Conception rates at the return estrus were not decreased when treatments occurred between d 13 and 20. In Exp. 4, lactating beef cows were assigned as in Exp. 3 to each of three treatments: 1) no treatment (controls; n = 51); 2) P4 + ECP (n = 47), as in Exp. 1; and 3) a single injection of ECP on d 13 (n = 48). Previously established pregnancies were not harmed (P = 0.70), and return rates of nonpregnant cows did not differ (P = 0.78) among treatments. In summary, in both heifers and lactating beef cows, the P4-based resynchronization treatments increased synchronized return rates when estrus detection rates were low, had no negative effects on established pregnancies, and decreased or tended to decrease conception rates at the resynchronized estrus.     

The strategic use of estradiol to enhance fertility and submission rates of progestin-based estrus synchronization programs in dairy herds

Two experiments were performed to evaluate the efficacy of a progestin-based estrus synchronization program that incorporated the use of estradiol at the initiation of progestin treatment and at 48 h after progestin withdrawal (Exp. 2). In Exp. 1, cyclic, lactating dairy cows (n = 112) were assigned to receive either 1 (1mg) or 2 (2mg) mg of estradiol benzoate via an i.m. injection on d -9 (d 0 = initiation of the breeding season). All cows received an intravaginal progesterone-releasing insert (IPI; CIDR-B) on d -9. On d -2, the IPI was withdrawn and all cows were administered 500 microg of cloprostenol sodium. Beginning on d 0, cows were bred by AI upon detection of estrus. Estrus was observed in similar proportions of cows in each treatment during the first 6 d of AI (90% across treatments), but the interval to estrus was shorter (P < .05) in 1mg (1.26 +/- .18 d) than in 2mg (1.77 +/- .18 d). Conception and pregnancy rates did not vary among treatments; however, cows in estrus on d 0 tended to be less fertile (P = .11) than those in estrus on d 1. In Exp. 2, 408 cyclic cows from three herds were assigned to receive either no synchrony treatment (Control, n = 214) or the treatments described in Exp. 1 (1mg, n = 100; 2mg, n = 94). Anestrous cows from all herds received an IPI from d -9 to -2 (n = 143; Anestrus). All cows in the 1mg, 2mg, and Anestrus groups, with the exception of those detected in estrus between d -1 and 0, also received 1 mg of estradiol benzoate on d 0. Greater than 90% of cows that received an IPI were in estrus between d -1 and 3, and 92.1% of cows in the Control group were in estrus by d 21. Conception rate to first service in 2mg (61.7%) was similar to Control (57.0%), tended to be higher (P = .06) than 1mg (49.0%), and was greater (P < .05) than Anestrus (39.9%). The mean day of conception was earlier (P < .05) in the 2mg (d 13.1 +/- 2.0) than the Control (d 23.2 +/- 1.6) and Anestrus (d 22.4 +/- 1.9) groups. Conception occurred earlier in 1mg (d 17.4 +/- 2.1) than in Control. The proportion of cows that were pregnant at the end of the breeding season tended (P = .09) to be greater in the 2mg and Anestrus groups. This regimen of estrus synchronization improved reproductive competence in cyclic cows and resulted in similar reproductive performance in anestrous cows and untreated cyclic cows inseminated at a spontaneous estrus.     

Method for obtaining bovine zygotes produced in vivo

A superovulatory and surgical protocol was developed for recovery of bovine zygotes. Holstein cows and heifers were given follicle-stimulating hormone and cloprostenol to induce superovulation. Surgical cannulation and lavage of the uterine tube was performed 40 to 48 hours after the start of standing estrus. In general, cows had more corpora hemorrhagica than did heifers, but a higher percentage (P less than 0.05) of ova recovered from cows were infertile. Several heifers were subjected to the procedure twice, and embryo recovery rates were equivalent both times.     

Influence of norgestomet in combination with gonadotropins on induction of estrus and ovulation in prepubertal gilts.

Our objective was to determine whether priming with the progestogen norgestomet for 9 d would enhance estrual and ovulatory responses of prepubertal gilts to PG600 (400 IU eCG + 200 IU hCG). Gilts (140 to 190 d old) were assigned by litter, age, and weight to one of three treatments: 1) 9 d of norgestomet implant with an injection of PG600 after implant removal on d 9 (N+PG; n = 43); 2) no implant and an injection of PG600 on d 9 (PG; n = 36); or 3) neither implant nor PG600 (control; n = 29). Beginning on d 0, gilts were exposed once daily to a boar and checked until estrus was observed or until d 45 after the start of the experiment. Ovaries were examined for number of corpora lutea (CL) after estrus or at 45 d. Greater proportions of N+PG (63%, P < .05) and PG (69%, P < .01) gilts expressed estrus than did controls (34%), but proportions did not differ between N+PG and PG (P > .10). Among gilts in estrus following treatment with N+PG or PG, 100% showed estrus within 6 d after PG600 injection. For gilts that expressed estrus within 45 d, the average age at estrus was reduced (P < .05) by PG to 172 +/- 2 d compared with 182 +/- 4 d for controls. Average age at estrus did not differ (P > . 10) between PG and N+PG (177 +/- 2 d). Greater proportions of N+PG (82%; P < .001) and PG (65%; P < .001) gilts ovulated than controls (13%), but proportions did not differ between N+PG and PG (P > .10). The number of CL (20 +/- 2) was not affected by treatment and ranged from 2 to 71. There was no increase in ovarian cysts in response to treatment. Results indicated that norgestomet before PG600 did not enhance estrus expression or ovulation compared with PG600 alone, but use of PG600 increased the proportions of gilts that expressed estrus and ovulated compared with controls.     

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.     

Effect of melatonin on induction of estrous cycles in anestrous ewes

To examine the influence of melatonin on seasonality of reproduction, 97 multiparous Suffolk and Suffolk-cross ewes were randomly assigned to one of four treatment (TRT) groups in a 2 X 2 factorial arrangement. Treatments were as follows: 1) control (C); 2) melatonin (M); 3) progestogen (P) implant of norgestomet plus pregnant mare serum gonadotropin (PMSG) injection (P + PMSG) and 4) M plus TRT 3 (M + P + PMSG). From April 3 to June 24 an oral dose of 2 mg M was administered once daily at 1600 to each ewe in TRT groups M and M + P + PMSG. On April 30, ewes in groups P + PMSG and M + P + PMSG were implanted in the ear with 2 mg norgestomet for 13 d. Immediately following implant removal, each ewe was injected with 500 IU PMSG. Blood samples were collected from all ewes twice weekly from March 22 through June 24. Number of estrous cycles per ewe during the TRT period of 82 d (April 3 to June 24) was higher (P less than .05) for M + P + PMSG (2.1 +/- .2) than for C (.3 +/- .2), M (1.5 +/- .2) and P + PMSG (1.1 +/- .2). Control ewes had fewer (P less than .05) estrous cycles per ewe than either M or P + PMSG. Following the induced estrus, 40% of ewes in the M TRT had one estrous cycle; 32% had two or more cycles. For ewes treated with M + P + PMSG, 24% had one cycle, and 32% had two estrous cycles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estrous Characteristics and Pregnancy Rates of Beef Heifers Administered Two Synchronization Protocols,

Two estrous synchronization protocols were used to determine their effect on estrous characteristics, synchronization rates, and pregnancy rates in nulliparous beef heifers on a commercial cow-calf operation in western New Mexico. Fifty-three Red Angus and Angus × Hereford heifers were sorted by age and BW to compare heifers treated with gonadotropin-releasing hormone (GnRH) 7 d before treatment with prostaglandin F_2α [PGF_2α; SelectSynch (SS); n = 26] and heifers treated with two administrations of PGF_2α 14 d apart [Targeted Breeding™ (TB) (Pharmacia, Kalamazoo, MI); n = 27). An androgenized cow fitted with a chin-ball marker was placed in each pen of heifers, and a HeatWatch (HW) transmitter (DDx, Inc., Denver, CO) was attached to each heifer to monitor estrous characteristics. Heifers were artificially inseminated after estrus was determined by HW. Number of standing events tended (P=0.12) to increase for TB heifers compared with SS heifers (54.4 ± 7.4 and 37.5 ± 7.7, respectively). Duration of estrus was increased (P<0.05) in TB heifers (16.0 ± 1.3 h) compared with SS heifers (11.6 ± 1.3 h). However, overall synchronization and pregnancy rates were similar (P>0.10) between protocols. Androgenized cows identified 53% of the estruses detected by HW. When utilizing synchronization protocols, radiotelemetric estrous detection systems may identify more heifers in estrus than androgenized cows. Intensity of estrus was increased in TB heifers compared with SS heifers; however, synchronization and pregnancy rates were not influenced by synchronization protocol.     

Evaluation of luteolysis and estrous synchronization by a prostaglandin analog (Luprostiol) in Brahman cows and heifers

A trial was conducted to evaluate the ability of a prostaglandin analog, Luprostiol (LP), to synchronize estrus in Brahman cows and heifers. Animals were injected with either 0, 3.75, 7.5, 15 or 30 mg LP or 500 micrograms cloprostenol (CLP) on d 8 or 9 after estrus (d 0). All concentrations of LP (greater than 0 mg) and CLP caused luteolysis in cows and heifers, as indicated by a decline (P less than .01) in serum progesterone concentration after injection. Animals receiving 0 or 3.75 mg LP had a longer (P less than .04) interval to estrus after injection than did animals in other treatment groups. The proportion of animals exhibiting estrus by 120 h after injection was influenced by dose of LP (P less than .0001; 0, 3.75 mg less than 7.5, 15 and 30 mg and CLP) but not by age. Cows had a lower (P less than .01) progesterone concentration than heifers on d 10, 11 and 12 after LP-induced estrus. Progesterone concentration was lowest (P less than .01) on d 10, 11 and 12 after LP-induced estrus in cows given 15 mg LP or CLP. First-service conception rate was similar between cows and heifers, but it was lower (P less than .01) in animals given 15 or 30 mg LP. Both estrogen and LH concentrations were decreased (P less than .01) at the time of estrus by the 15 and 30 mg of LP. Luprostiol can cause luteolysis and estrous synchrony in Brahman cattle.(ABSTRACT TRUNCATED AT 250 WORDS)