Syncro-Mate-B Research Articles

Ovulation rate in ewes synchronized with Syncro-Mate-B (SMB) and follicle stimulating hormone

To achieve successful embryo transfer programs, ewes must be hormonally stimulated to induce multiple follicular development. Knowing the times of ovulation in these stimulated animals is critical for accurate timing of insemination. To determine the timing of ovulation in ewes treated with Syncro-Mate-B (SMB) and FSH, ewes ( n=13) were implanted with SMB for 14 days and were treated with FSH twice daily for 4 days, starting on day 11 after SMB implantation. Ewes underwent laparoscopy at 36, 48, and 60 h after SMB removal (day 0) to count corpora hemorrhagica (CH), followed by laparotomy on day 8 to count corpora lutea (CL). Blood samples were taken every 6 h to record plasma LH, estradiol-17β, and progesterone concentrations on days 1–3, and one sample was collected before laparotomy on day 8. Ovulation rates (number of CH expressed as a percentage of the total number of CL) increased ( P<0.01) from 4±2% at 36 h, to 50±7% at 48 h, to 67±7% at 60 h. Between 36 and 48 h after SMB removal, 50% of the follicles had ovulated, and between 48 and 60 h another 16% of the follicles had ovulated. However, at 60 h after SMB removal, approximately 30% of the follicles still remained unovulated. Plasma LH concentrations increased ( P<0.05) from 1.4 ng/ml at 7:00 a.m. on day 1 to 10.1 ng/ml at 1:00 a.m. on day 2 and then decreased ( P<0.05) to 0.6 ng/ml at the time of laparotomy (day 8). Plasma estradiol-17β concentrations increased ( P<0.05) from 8.5 pg/ml at 7:00 a.m. on day 1 to 24.3 pg/ml at 7:00 p.m. on day 1 and then decreased ( P<0.05) to 8.6 pg/ml on day 8. Progesterone concentrations were very low (<0.2 ng/ml) on days 1–3, but increased ( P<0.01) to 4.3 ng/ml on day 8, after formation of the CL. These results demonstrate that the ovulation in SMB- and FSH-treated ewes occurs over an extended period of time and that almost a third of follicles do not ovulate until more than 60 h after SMB removal.

Use of steroid hormone treatments prior to superovulation in Nelore donors

The objective of this study was to evaluate the effectiveness of synchronization of follicular wave emergence using steroid hormone treatments in Nelore cows. Donors were placed into three groups. Those that were between days 9 and 12 of their cycle (estrus=day 0) formed the TI group ( n=60), whilst those that were in any other stages of their estrus cycle constituted groups TII ( n=60) and TIII ( n=60). TI donors were submitted to a standard protocol of superovulation, however, TII and TIII donors were treated with the Syncro-Mate-B (SMB) or Controlled Internal Drug Releasing Device (CIDR-B) programs, respectively. Superovulation was induced with p-FSH, divided into eight decreasing doses at intervals of 12 h. The donors received cloprostenol 48 h after the beginning of the treatment and progestagens were removed 12 h later. Artificial inseminations (AI) were done at 12 and 22 h after the initiation of estrus and the embryo collections were done 7 days after AI. In the donors which displayed behavioral estrus, mean (±S.E.M.) total ova and viable (transferable) embryos were 15.8±1.4 and 8.3±1.0 (TI, n=56); 15.6±1.3 and 8.9±1.0 (TII, n=56); 17.3±1.0 and 9.9±0.9 (TIII, n=57), respectively, with no significant difference ( P≥0.05) among groups. In those animals that did not displayed behavioral estrus, the mean values of total ova and viable embryos were 3.5±1.6 and 0.7±0.5 (TI, n=4); 11.5±3.9 and 9.0±4.4 (TII, n=4); 8.7±5.0 and 5.0±2.9 (TIII, n=3), respectively, with no significant differences ( P≥0.05) among groups. Pregnancy rates of 62.2% (TI, n=235); 66.4% (TII, n=284) and 65.1% (TIII, n=244) were obtained with embryos transferred from these collections and did not differ significantly ( P≥0.05) among groups. It was concluded that the synchronization of the emergence of follicular waves in Nelore donors is usable and does not harm the efficiency of embryo transfer programs. In addition, in contrast to the standard superovulation protocol, this method permits the use of a large number of donors in a short time period, at any stage of the estrus cycle, minimizing the costs of embryo transfer.

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 PGF2α 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 PGF2α 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 PGF2α had a greater pregnancy rate at 5 d compared to controls (P = .0672). Interval to estrus, estrous response, and pregnancy rate to AI at d 28 or end of breeding season were not affected by administration of PGF2α in conjunction with SMB when compared to the standard SMB protocol.

Hormonal control of estrouscyclicity and attempted superovulation in wood bison ( Bison bison athabascae)

The wood bison ( Bison bison athabascae) is a threatened Canadian species that has faced extinction twice in the last 100 yr. Development of assisted reproductive technologies could help ensure the long-term propagation and genetic management of this species. The objectives of this study were to refine estrus synchronization techniques and evaluate superovulatory responses after FSH or eCG administration. In Experiment 1, females were fitted with Syncro-mate B (SMB) implants for 9 d and received an injection of either estradiol valerate (E 2V; n = 9) or cloprostenol (PGF; n = 9) at implant insertion (Day -9). In Experiment 2, estrus was synchronized with SMB implants and a PGF injection on Day -9, and superovulation was attempted on Day -2 with either 2500 IU eCG (n = 5) or 400 mg Folltropin-V (n = 5). In each experiment, bison were examined daily for estrual behavior. Ultrasonography was used during the luteal phase to detect ovulation and assess ovarian status; feces were analyzed by ELISA for immunoreactive progestogens (P) to study ovarian endocrine responses. In Experiment 1, a closer synchrony of estrus was observed between Days 2 to 4 among the PGF-treated (77.8%) than the E 2V-treated (66.7%) females. Corpora lutea (CL) were detected in 55% of E 2V- and PGF-treated females. In Experiment 2, neither treatment successfully induced superovulation, with only a single female per treatment producing ≥ 1 CL. In both experiments, progestogen profiles were similar for each treatment (P>0.05).

Retention of a functional corpus luteum and peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F2alpha following metestrus administration of Syncro-Mate-B.

This study was conducted to examine the effects of metestrus administration of SyncroMate-B (SMB) on PGF2alpha secretion and corpus luteum (CL) development. In a study replicated over 2 yr, cows were observed for spontaneous estrus in yr 1, and cows received an injection of 25 mg of PGF2alpha and were observed for subsequent estrus in yr 2. At standing estrus (estrus = d 1), cows were randomly allotted to receive either the standard SMB regimen (n = 40) on d 3 of the estrous cycle or no treatment (n = 8). Fifty percent (n = 20) of SMB-treated cows were administered PGF2alpha on d 10 of the estrous cycle 48 h prior to implant removal. Twice-daily blood samples were collected in the morning (AM) and evening (PM) from d 2 AM through d 14 AM of the treated estrous cycle and subsequently analyzed for progesterone (P4) and PGF2alpha metabolite (PGFM). Prior to statistical analysis, SMB- and SMB/PGF2alpha-treated cows were sorted according to P4 concentration at d 10 of the treated estrous cycle to either a CL functional group (P4 > or = 1 ng/mL; n = 20) or a CL nonfunctional group (P4 < 1 ng/mL; n = 17). Following d 10 AM administration of PGF2alpha, functional and nonfunctional groups were further subdivided based on treatment. The groups were as follows: untreated control cows (n = 8); SMB-treated cows retaining a functional CL (SMB-F; n = 8); SMB-treated cows with a nonfunctional CL (SMB-N; n = 11); SMB/PGF2alpha-treated cows retaining a functional CL (SMB/PG-F; n = 12); and SMB/PGF2alpha-treated cows with a nonfunctional CL (SMB/PG-N; n = 6). Of all SMB-treated cows, 54% retained a functional CL through d 10 AM of the treated estrous cycle. Mean serum P4 concentrations increased for cows in all groups until d 7, after which P4 concentrations increased for cows in SMB/PG-F, SMB-F, and control groups and decreased for cows in SMB/PG-N and SMB-N groups. Following PGF2alpha administration on d 10, mean serum P4 concentrations remained < 1 ng/mL for cows in SMB/PG-N and SMB-N groups, decreased to < 1 ng/mL for cows in the SMB/ PG-F group, and remained > 1 ng/mL for cows in SMB-F and control groups. Mean serum PGFM concentrations tended (P = .06) to increase in cows with nonfunctional CL compared with control cows on d 8 AM and were greater (P < .05) in cows with functional CL on d 8 PM through d 9 PM. These results indicate that retention of a functional rather than a nonfunctional CL following metestrus administration of SMB is dependent on a premature release of uterine PGF2alpha.

Dose response effects of PMSG on ovulation rate and follicular development in Pelibuey ewes treated with Syncro-mate-B implants

The effect of dose of pregnant mare serum gonadotropin (PMSG) was determined on the superovulatory response and follicular development in 50 cycling, mature Pelibuey ewes following treatment with Syncro-mate-B (SMB) implants. A randomized complete block design with five treatments was utilized; all ewes were treated for 10 days with SMB implants and at the end of the treatment, groups of 10 ewes each were randomly allocated and treated with 1-500, 2-1000, 3-2000, 4-3000 or 5-4000 IU of PMSG, 24 h prior to SMB removal. Ovarian responses were recorded as the number of corpora lutea (CL) and the number and size of follicles present 5–6 days after estrus, by means of a midventral laparotomy. The percentage of ewes responding to treatment, determined by the presence of unovulated follicles, was significantly different ( p<0.01) among treatments, these values were 50, 60, 90, 80 and 100%, respectively, for the groups 1–5. The number of unovulated follicles was also different ( p<0.05), among the treatment groups, the corresponding means (±SEM) were 0.7±0.63, 2.4±4.07, 8.0±4.7, 9.4±7.03 and 9.0±5.6 follicles per ewe, respectively, for the treatment groups 1–5. The overall percentage of ewes ovulating was 80%. The percentage of ewes ovulating at least once per group was also different ( p<0.01) among the treatment groups, the corresponding values per group were 70, 60, 100, 80 and 90%; whereas the percentage of ewes ovulating at least twice was 48% and the corresponding treatment group values were 30, 20, 80, 60 and 50%, respectively. These values were significantly different ( p<0.01). The mean number of CL for the ewes with two or more CL among the treatment groups was different ( p<0.05); the values being 1.5±2.4, 1.0±2.1, 6.9±6.1, 4.4±4.2 and 4.6±5.4 CL per ewe. It is concluded from these results, that Pelibuey ewes can be effectively superovulated with a dose of PMSG of 2000 IU.

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 2α (second PGF 2α 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.

Flumethasone delays or prevents estrus in ovariectomized and intact heifers given Syncro-Mate B ®

This study was conducted to determine if a glucocorticoid (flumethasone) affects the expression of behavioral estrus in heifers given Syncro-Mate B (SMB). Ten ovariectomized heifers and 10 intact cyclic heifers were given the SMB treatment. The ovariectomized heifer trial was replicated 4 times and the intact heifer trial twice. The SMB treatment involved giving an injection containing 3 mg norgestomet and 5 mg estradiol valerate (EV). An implant containing 6 mg norgestomet was placed subcutaneously under the outer surface of one ear at the time of injection and was removed 9 d later. At the time of implant removal, half of the heifers in each replicate were given 5 mg of flumethasone. Heifers were checked for estrus, and blood was collected and measured for estradiol-17β (E 2) concentration every 8 h for 72 h after implant removal. Flumethasone reduced (P = 0.06) the number of intact (100 versus 70%) and ovariectomized heifers (65 versus 35%) that exhibited estrus. Heifers that exhibited estrus after treatment with flumethasone did so later than controls in both the intact (42 ± 3 h versus 36 ± 2 h; P = 0.11) and the ovariectomized (53 ± 3 versus 40 ± 2%; P < 0.005) groups. Flumethasone did not alter mean concentrations of E 2 in intact or ovariectomized heifers. Apparently, flumethasone suppresses or delays the expression of estrus in most treated heifers. However, the effect is not caused by mechanisms at the ovarian level or by decreased concentrations of E 2 in the serum.

Induction of luteal regression, ovulation and development of new luteal tissue during early pregnancy in heifers

A study was conducted to determine whether luteal tissue formed after administration of exogenous luteinizing hormone (LH) was capable of maintaining pregnancy in the absence of the original corpus luteum (CL) of pregnancy in heifers. Nineteen beef heifers, confirmed pregnant by ultrasonography approximately 28 days after breeding, were randomly assigned to one of two groups. Nine heifers remained as untreated controls to determine the incidence of spontaneous embryonic or fetal loss. Each of the remaining ten heifers was given two Syncro-Mate-B (SMB) ear implants (12 mg of norgestomet) between 30 and 35 days after breeding (day of SMB implant was Day 1). An additional SMB was implanted on Day 8 and another on Day 15. All implants were removed on Day 20. On Day 2, SMB-implanted heifers were given an intramuscular (i.m.) injection of 500 μg of cloprostenol to induce luteal regression. On Day 5, regression of the CL was confirmed by ultrasonography and these heifers received a highly purified porcine LH preparation (50 mg Armour, i.m.); an additional 25 mg was injected i.m. on Day 6. Ovulation occurred in all ten LH-treated heifers and was detected on Day 7.2±0.1 (mean±SEM). In five of ten LH-treated heifers, the induced CL regressed, and was last detected by ultrasonography on Day 15.8±0.4 (range, Day 15–17). Pregnancy was not maintained in these heifers after SMB implants were removed. Pregnancy was maintained until Day 40 (end of experiment) in the remaining five LH-treated heifers and in all nine control heifers. In all five heifers in which the induced CL regressed, this CL had formed in the ovary contralateral to the original CL of pregnancy. In contrast, in four of five heifers in which the induced CL was maintained, this CL had formed in the ovary ipsilateral to the original CL of pregnancy. Although LH induced ovulation and CL formation in the absence of the CL of pregnancy and in the presence of continuous progestagen support, short-lived CL were formed in five of ten heifers.

Role of luteal regression in embryo death in cattle

Inseminated crossbred beef cows and heifers were used in 2 experiments to investigate embryo survival after prostaglandin-induced or spontaneous luteal regression. In Experiment 1, luteal regression was induced by an intramuscular (im) injection of cloprostenol (500 μg) on Day 15 (day of ovulation = Day 0). Progestagen was replaced 24 or 36 h later either by one-and-a-half Syncro-Mate-B (SMB) ear implants (9 mg of norgestomet) and norgestomet solution (2.25 mg, im) containing no estradiol in 1 replicate or by 2 SMB implants (12 mg of norgestomet) and progesterone (100 mg, im) in the second replicate. Combined for both replicates, the Day-24 pregnancy rate in an untreated control group (Group 1, 16/19; 84%) was higher (P < 0.01) than in the 24-h group (Group 2, 9/20; 45%), which also was higher (P < 0.02) than in the 36-h group (Group 3, 3/23; 13%). In Experiment 2, 15 or 16 d after breeding, cattle with a corpus luteum at least 16 × 16 mm were given either 2 SMB implants or no treatment. At 24 to 26 d after breeding, pregnancy rates (48/65, 74% versus 49/68, 72%) were not significantly different, and all but 1 of the pregnant progestagen-supplemented cattle had a functional corpus luteum.

Effects of metestrous administration of a norgestomet implant and injection of norgestomet and estradiol valerate on luteinizing hormone release and development and function of corpora lutea in suckled beef cows.

Sixteen suckled beef cows were used to determine effects of Syncro-Mate-B (SMB) on the development and function of corpora lutea (CL) and LH release. Twelve cows were treated 2 d after estrus with the standard SMB treatment regimen, a 6-mg Norgestomet ear implant (in situ 9 d) and a 2-mL i.m. injection of 3 mg of Norgestomet and 5 mg of estradiol valerate at time of implant insertion. Four cows served as untreated controls. In cows treated with SMB with subsequently nonfunctional CL (n = 5), mean concentrations of progesterone (P4) were lower on d 9, 12 (implant removal), and 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL (n = 7), mean concentrations of P4 were lower only on d 12 of the treated cycle than those in control cows (P < .01). In cows treated with SMB with subsequently nonfunctional CL, CL were smaller from d 9 through 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL, CL were smaller on d 9 and 11 of the treated cycle than in control cows (P < .01). Regardless of subsequent CL function, mean concentrations of LH and numbers of LH pulses were lower in cows treated with SMB than in control cows on d 3 and 4 of the treated cycle (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

A preliminary study of growth, serum prolactin and reproductive performance of beef heifers grazing [formula omitted][formula omitted]-infected tall fescue

In an experiment with a 2×2 factorial arrangement of treatments, 32 virgin Angus heifers were used to study effects of tall fescue endophyte Acremonium coenophialum and energy supplementation on reproductive performance. Treatments were feeding of endophyte-free (EF) or endophyte-infected (EI) tall fescue without (0%) and with energy supplementation at one percent group mean body weight (1%). Blood samples were collected at 28-day intervals for prolactin (PRL). Starting 21 days before the breeding season, blood was also collected weekly for progesterone (P 4) and PRL. After 99 days of grazing, heifers received Syncro-Mate-B (SMB) and were then artificially inseminated over a 30-day period. Heifers on EI-0% had a lower (P<0.05) average final body weight. Highest average daily gain was observed in heifers fed EF-1% (0.98 kg/day), whereas, heifers fed EI-0% had lowest average daily gain (0.53 kg/day; P<0.05). Endophyte-infected fescue depressed serum PRL concentrations (171 and 143 ng/ml vs 70 and 85 ng/ml; EF-0% and EF-1% vs EI-0% and EI-1%, respectively; P<0.05). No differences were observed among treatments in luteal activity before or after SMB, in pregnancy rates after a synchronized estrus or in overall pregnancy rates during the 30-day breeding season. Endophyte-infected fescue decreased average daily gain and depressed serum concentrations of prolactin, but had no effect on reproductive performance as measured in this study.

Performance of Bos indicus-influenced bulls in serving capacity tests and multiple-sire breeding groups

Three experiments were conducted with Santa Gertrudis (SG) or F1 (Gelbvieh x SG or Red Angus x SG) bulls to assess factors that influence copulatory activity and fertility of Bos indicus-influenced genotypes. In Exp. 1, 3-yr-old SG bulls (n = 20) with sexual experience and 20-mo-old virgin SG bulls (n = 34) were allotted in a split-plot design (age, bull within age group, test day, and heifer treatment). Number of mounts (Mt), intromissions (I), and ejaculations (E) were measured 14 d apart during two 30-min serving capacity (SC) tests. Estrus was either induced via progesterone+estradiol cypionate (PE) injections or synchronized with Syncro-Mate B (SMB). There were more (P less than .05) I and E on Test d 2 than on Test d 1. Heifers treated with SMB received more (P less than .001) Mt, I, and E than did heifers treated with PE. Sixteen 20-mo-old bulls from Exp. 1 were allotted to breeding pastures at a bull:heifer ratio of 4:119 +/- 3 for 50 d in Exp. 2. Breeding pasture treatments either included or excluded low-SC bulls. Neither pregnancy rate nor least squares mean day of conception differed between treatments. Experiment 3 evaluated copulatory activity with a 2 x 2 factorial arrangement (breed and test day) in 14- to 16-mo-old SG (n = 45) and F1 (n = 16) bulls. The F1 bulls had more Mt, I, and E than did the SG bulls (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Fixed-time insemination of bos indicus heifers following the use of syncro-mate-B (SMB) to synchronize estrus

Two-hundred and twenty-one Bos indicus and Bos indicus × Bos taurus cross heifers aged 12 to 24 months (Group I, n=67; Group II, n=74, yearlings; Group III, n=80, 2-year-olds) were selected to examine some of the factors influencing the fertility of females treated with the SMB system to synchronize estrus for the purpose of fixed-time insemination. Only heifers weighing more than 290 kg were selected for treatment. Estrus response was monitored using the dual tail paint-raddle system. Tail paint score was recorded at 29, 42 and 52 hours after implant removal. All heifers were inseminated at 42 hours after implant removal. Heifers with a tail paint score of 6 (nil paint or raddle removed) at 42 hours were re-inseminated at 52 hours after implant removal. The 2-year-old heifers (Group III) achieved a higher pregnancy rate (49%) than the yearling heifers (Group I, 39%; Group II, 35%). However, there was a significantly (P<0.05) higher proportion of heifers in Groups I and II, with a tail paint score of 4 (raddle removed, 70 to 90% paint remaining) or less at 42 hours after implant removal than in the Group III heifers. The pregnancy rate of the heifers with a tail paint score of 4 or less at 29 hours after implant removal (i.e., inseminated approximately 13 hours after the onset of standing estrus) was similar to the rate achieved in heifers with a tail paint score of 6 at 42 hours after implant removal (i.e., no evidence of standing estrus at the time of first insemination). It was concluded that insemination of well-grown Bos indicus heifers at a fixed time after treatment with the SMB system resulted in a satisfactory pregnancy rate (40%, n=221) despite the fact that many heifers lost weight around the time of insemination.

Luteal function and reproductive response in suckled beef cows after metestrus administration of a norgestomet implant and injection of estradiol valerate with various dosages of injectable norgestomet.

In an experiment replicated over 2 yr, 149 suckled beef cows were administered Syncro-Mate-B (SMB), a 6-mg Norgestomet (NOR) ear implant (in situ 9 d) in conjunction with an i.m. injection of 5 mg of estradiol valerate (EV), and either 3.0, 4.5, or 6.0 mg of NOR, 2 d after estrus. All cows were artificially inseminated at 48 h (timed insemination; TI) after implant removal (IR) and cows were reinseminated at any estrus subsequent to 24 h of TI through 30 d. Blood samples collected before treatment, every 3 d through IR, and at TI were assayed for progesterone (P4). At TI, 44, 39, and 12% of cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively, had serum concentrations of P4 greater than 1 ng/mL (3.0 and 4.5 mg vs 6.0 mg, P less than .01). Fifty-eight, 63, and 84% of cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively, exhibited a synchronized (within 5 d of IR) estrus (3.0 and 4.5 mg vs 6.0 mg, P less than .05). Pregnancy rates for the 5-d synchronized period were 38, 45, and 66% for cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively (3.0 and 4.5 mg vs 6.0 mg, P less than .05). First-service pregnancy rates were 66, 71, and 79% for cows treated with 3.0, 4.5, or 6.0 mg of NOR, respectively (P greater than .10).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of estradiol valerate on follicular dynamics and superovulatory response in cows with Syncro-Mate-B implants

Two experiments were designed to evaluate the effect of estradiol valerate on follicular dynamics and superovulatory response in cows with Syncro-Mate-B (SMB)implants. In Experiment 1, 5 mg estradiol valerate (E 2), injected at the same time as superstimulation treatments were initiated, resulted in fewer corpora lutea (CL), ova/embryos collected and fertilized ova (P<0.05) than if E 2 was administered with the SMB implant 7 days earlier. In Experiment 2, 31 beef cows and 26 Holstein cows were placed in one of four treatment groups. Group I (control) cows were superstimulated on Day 9 (estrus=Day 0). On Day 2, cows in Groups II, III, and IV received SMB and cows in Group III received E 2. On Day 9, cows in Group IV received E 2, and all cows were superstimulated with Folltropin. The number of CL did not differ (P>0.19) among groups. However, there were more follicles < 10 mm and fewer fertilized ova and transferable embryos (P<0.02) in Group IV cows. Ovarian ultrasonography revealed that the diameter of the largest follicle in Group III cows declined from Day 2 to Day 7 and subsequently increased until Day 13. In contrast, Groups I, II and IV were characterized by apparently linear growth between Days 2 and 13. Differences (P<0.05) were detected between Days 5 and 9. Mean diameter of the largest follicle was smaller for cows in Group III than for the remaining groups on Day 9. It was concluded that SMB did not adversely affect superovulatory response and that E 2 administration resulted in atresia of the antral follicles in the cows with SMB implants.

Luteal function, estrous response, and pregnancy rate after treatment with Norgestomet and various dosages of estradiol valerate in suckled cows.

Two experiments were conducted to determine whether dosage of estradiol valerate (EV) or day of estrous cycle when treatment was administered affected response to Syncro-Mate-B (SMB). Suckled beef cows received a 6-mg Norgestomet (NOR) ear implant (in situ 9 d) and a 3-mg NOR i.m. injection. In Exp. 1, 74 cows received NOR treatments concurrently with either 5 or 6 mg of EV administered i.m. on either d 1, 3, or 5 of an estrous cycle (estrus = d 1). In Exp. 2, 169 cows received NOR treatments concurrently with either 5, 7, or 9 mg of EV administered i.m. on either d 3 or 9 of an estrous cycle. In Exp. 1, 67, 50 and 92%, respectively, of cows receiving 5 mg of EV on d 1, 3, or 5 had functional corpora lutea (CL) at implant removal, whereas 42, 75, and 77%, respectively, of cows receiving 6 mg of EV had functional CL at implant removal (dosage P greater than .10; day P less than .05). Synchronized estrous responses were 50, 33, and 23%, respectively, when cows received 5 mg of EV on d 1, 3, or 5, and 67, 33, and 38%, respectively, when cows received 6 mg of EV (dosage P greater than .10; day P less than .05). First-service pregnancy rate was decreased (P less than .05) in cows treated on d 5 (33%) compared with cows treated on d 1 (63%), but dosage of EV had no effect on pregnancy rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Melengestrol Acetate (MGA) and Prostaglandin F2α Program Compared to Syncro-Mate-B (SMB) for Estrous Synchronization Utilizing Al or Natural Service

AbstractTwo hundred crossbred yearling heifers were used in a 3 x 2 factorial experiment to compare the effectiveness of two estrous synchronization programs (MGA-prostaglandin F2α and Syncro-mate-B) with a control group utilizing two types of breeding programs (Al or natural service). Heifers were stratified by estrous status (prepuberal or post-puberal) to one of six treatments. The MGA treatment group received MGA for 14 d followed by an injection of prostaglandin F2α (PGF2α), 16 d after the last day of MGA feeding. The Syncro-mate-B (SMB) group received the standard 9-d procedure. A third group served as the controls. One-half of the heifers in each of the three treatment groups were bred by Al and the other half by natural service. Yearling bulls were used in a ratio of 1 to 20 females and were rotated among treatment groups at 12-h intervals during the synchronization period. Estrous response rates did not differ (P>.05) between the MGA and SMB treatment groups for either the Al or natural service heifers. No differences (P>.05) were found in pregnancy rates during the first 6 d of breeding between MGA and SMB groups whether bred by Al (56 vs. 59%) or natural service (67 vs. 74%). First-service conception rates did not differ (P>.05) between treatments whether bred by Al or natural service. A higher percentage of the prepuberal heifers exhibited estrus following SMB treatment (100%) compared with controls (38%). Pregnancy rates in 6 and 30 d were slightly higher (P>.05) in heifers bred by natural service compared with Al. These data indicate both treatments were effective in inducing and synchronizing estrus, and natural service is a viable alternative to Al in synchronization programs.

Syncro-mate B ® induces estrus in ovariectomized cows and heifers

Eleven ovariectomized Hereford × Simmental cows and 10 ovariectomized crossbred heifers (primarily Angus and Hereford) were given the Syncro-Mate B (SMB) estrous synchronization treatment. The SMB treatment consisted of a 2 ml i.m. injection containing 5 mg of estradiol valerate and 3 mg of norgestomet plus a hydron ear implant containing 6 mg of norgestomet. The ear implant was removed 9 d later. Cows and heifers were considered in estrus only if they stood for mounting by a herdmate or a bull. Observations for estrus were made four or six times each day for 3 d after implant removal. The 21 animals were used in eight trials. Each trial involved 9 or 11 cows or 5 or 10 heifers. Four days to three weeks elapsed between implant removal and implant insertion for the next trial. No ovariectomized cow or heifer was observed in estrus for 21 d before treatment with SMB. In the eight trials, 3 of 9, 7 of 9 and 6 of 11 cows exhibited estrus, whereas 5 of 10, 1 of 5, 3 of 5, 3 of 5 and 5 of 5 heifers exhibited estrus after treatment. When data were pooled, 16 of 29 (55.2%) cows and 17 of 30 (56.7%) heifers exhibited estrus after treatment. Our data indicate that the SMB treatment can induce estrus in cows and heifers, independently of the ovaries.

Factors affecting mating activity and pregnancy rates with beef bulls mated to estrus synchronized females

Ninety-two beef bulls and 2,316 estrus synchronized beef females were used in single-sire mating trials to evaluate effects of age and breed of bull, bull-to-female ratios, number of females exhibiting estrus, and number of times a heifer or cow was serviced on mating activity and pregnancy rates. Bulls ranged in age from 1 to 7 yr and were either Angus or Hereford. Each bull received a breeding soundness examination and was exposed twice to a libido/serving capacity test. Females received either the Syncro-Mate B (SMB) treatment or the double injection treatment of Prostaglandin F 2α (PGF). Bull-to-female ratios ranged from 1:7 to 1:51. Bulls were joined with their groups of females at 27 h (SMB) or 48 h (PGF) posttreatment, and sexual activity was observed continuously for 30 and 48 h, respectively. Each bull remained with his group of females until the end of a 120-h posttreatment period. There were no differences between Angus and Hereford bulls in measurements of mating activity or pregnancy rate. It appeared that bulls became more efficient in mating activity as they increased in age up to 3 yr and older. Pregnancy rates based on number of females exhibiting estrus were lowest in yearlings (30.2 ± 5.1%), intermediate in 2-yr-olds (40.3 ± 6.0%) and highest in 3-yr and older bulls (50.7 ± 4.5%). Pregnancy rates were not affected by bull-to-female ratio or number of females exhibiting estrus per bull. However, females serviced two or more times had higher (P < 0.05) pregnancy rates than those serviced one time.