Synchronization of estrus in beef cows with Norgestomet-Alfaprostol or Syncro-Mate B

In the spring of 1986, 506 beef cows were used to evaluate the effectiveness of two estrus synchronization systems. Cows were synchronized with either a 6-mg Norgestomet implant placed in the ear for 14 d followed by a 6-mg Alfaprostol injection given 16 d after implant removal (Norgestomet-Alfaprostol) or with Syncro-Mate B (6-mg Norgestomet implant for 9 d with an injection containing 5 mg estradiol valerate and 3 mg Norgestomet at the time of implantation). The Alfaprostol injection in the Norgestomet-Alfaprostol group was given the same day as implant removal in the Syncro-Mate B group. These treatment groups were compared to a group of untreated controls. Cows were allotted to treatments by days postpartum, age and breed. Syncro-Mate B cows had a higher estrous response within 5 d after treatment (78.6 vs 64.0%) and a shorter interval to estrus (39.2 vs 66.7 h) than did Norgestomet-Alfaprostol cows (P < 0.05). Controls had a significantly lower estrous response compared to either of the synchronized groups (27.1%). The degree of estrus synchrony was identical in both synchronization systems (72.7%). Synchronized conception rate tended to be higher (P = 0.06) in the Norgestomet-Alfaprostol cows than in the Syncro-Mate B cows (74.5 vs 62.5%). Synchronized, 21-d, 25-d and breeding season pregnancy rates were 51.2, 70.8, 76.8 and 92.9% for Norgestomet-Alfaprostol cows; 48.5, 63.0, 73.2 and 87.8% for Syncro-Mate B cows; and 15.6, 56.3, 61.3 and 86.9% for control cows. The four pregnancy rates were not different between the two synchronization treatments (P > 0.10). Controls had lower synchronized and 25-d pregnancy rates when compared to either of the synchronized groups (P < 0.05). Days postpartum had no effect on the reproductive performance of cows synchronized with Norgestomet-Alfaprostol. Our results indicate that the Norgestomet-Alfaprostol system is as effective as Syncro-Mate B in synchronizing estrus in beef cows.     

Synchronization of estrus in embryo transfer recipients after using a combination of PRID or CIDR-B plus PGF2alpha

The use of CIDR-B or PRID in combination with prostaglandin F2alpha (PGF2alpha) for synchronizing estrus in embryo transfer recipients was evaluated in 2 experiments. In Experiment 1, virgin heifers (n=263) were synchronized using either a PRID (including estradiol benzoate capsule) or a CIDR-B in a combined program in which devices were inserted on Day 1, an injection of prostaglandin was given on Day 6, and devices were withdrawn on Day 7. The interval from device removal to the onset of estrus was significantly shorter for CIDR-B than for PRID-treated animals (50.44 vs 55.50 hours; P<0.003). The CIDR-B treatment resulted in a similar degree of synchrony to the PRID treatment (74.0 vs 70.4%; P=0.68). InExperiment 2, cows (n=95) and heifers (n=93) were allocated at random to be synchronized using a PRID (excluding estradiol benzoate capsule) plus PGF2alpha or a CIDR-B device plus PGF2alpha. The devices were inserted on Day 1, an injection of prostaglandin was given on Day 10 and the devices were removed on Day 12. Estrus was observed earlier following the CIDR-B treatment (43.50 vs 47.04 hours; P=0.01), but the degree of synchrony was similar (76.2 vs 76.3%; P>0.10) for the CIDR-B and PRID-treated animals. In both experiments, there were no significant differences in the proportions of animals observed in estrus, selected as embryo transfer recipients, or which achieved pregnancy consequent on embryo transfer between those synchronized using CIDR-B or PRID regimens. We conclude that the CIDR-B is a suitable device for synchronizing estrus in embryo transfer recipients.     

Effect of estrous cycle stage at Syncro-Mate B treatment on conception and time to estrus in cattle

Two trials involving 85 heifers and 67 cows were conducted to determine the effect of estrous cycle stage at the time of Syncro-Mate-B((R)) (SMB) treatment on interval to estrus following implant removal and on conception rate at the synchronized estrus. In Trial 1, 57 beef and 28 dairy heifers were treated with SMB on each representative day of a 22-d estrous cycle (estrus = Day 0). Beef heifers were artificially inseminated approximately 48 h after implant removal, whereas dairy heifers were inseminated 0 to 12 h after detection of estrus. Inseminations were scored by the inseminator according to their difficulty. Interval to the onset of estrus was not different between heifers treated early ( Day 11) in the cycle (35.2 +/- 7.2 h). Conception rate at the synchronized estrus was slightly higher in early-cycle heifers (22 47 = 47% ) compared to late-cycle heifers (14 38 = 37% , P = 0.2). Heifers that were difficult to inseminate had lower (P < 0.01) conception rates (2 11 = 18% ) at the synchronized estrus than heifers considered normal (21 51 = 41% ) or easier than normal to inseminate (13 23 = 57% ). In Trial 2, of the 131 beef cows synchronized, 67 that were estimated to be either early or late in the estrous cycle by progesterone analysis were utilized. Cows were treated with SMB and inseminated without regard to estrus 48-h after implant removal. Inseminations were scored as in Trial 1. Calves were separated from cows from the time of implant removal to insemination. Conception rate was higher (P < 0.05) in cows treated with SMB early ( Day 11, 16 35 = 46% ). Cows that were difficult to inseminate had a lower (P < 0.01) conception rate (0 8 = 0% ) than cows that were normal (43 94 = 46% ) or easier than normal to inseminate (13 29 = 45% ).     

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.     

Synchronization of estrus and fertility in zebu beef heifers treated with three estrus synchronization protocols

The effects on estrus and fertility of 3 estrus synchronization protocols were studied in Brahman beef heifers. In Treatment 1 (PGF protocol; n=234), heifers received 7.5 mg, i.m. prostianol on Day 0 and were inseminated after observed estrus until Day 5. Treatment 2 (10-d NOR protocol; n = 220) consisted of norgestomet (NOR; 3 mg, s.c. implant and 3 mg, i.m.) and estradiol valerate (5 mg, i.m.) treatment on Day -10, NOR implant removal and 400 IU, i.m. PMSG on Day 0, and AI after observed estrus through to Day 5. Treatment 3 (14-d NOR+PGF protocol; n = 168) constituted a NOR implant (3 mg, sc) on Day -14, NOR implant removal on Day 0, PGF on Day 16, and AI after observed estrus through to Day 21. All heifers were examined for return to estrus at the next cycle and inseminated after observed estrus. The heifers were then exposed to bulls for at least 21 d. During the period of estrus observation (5 d) after treatment, those heifers treated with the PGF protocol had a lower (P<0.01) rate of estrual response (58%) than heifers treated with the 10-d NOR (87%) or 14-d NOR+PGF (88%) protocol. Heifers treated with the 10-d NOR protocol displayed estrus earlier and had a closer synchrony of estrus than heifers treated with either the PGF or the 14-d NOR+PGF protocol. Heifers treated with the 14-d NOR+PGF protocol had higher (P<0.05) conception and calving rates (51 and 46%) to AI at the induced estrus than heifers treated with the PGF (45 and 27%) or the 10-d NOR (38 and 33%) protocol. Calving rate to 2 rounds of AI was greater (P<0.05) for heifers treated with the 14-d NOR-PGF (50%) protocol than heifers treated with the 10-d NOR (38%) but not the PGF (43%) protocol. Breeding season calving rates were similar among the 3 protocols. The results show that the 14-d NOR+PGF estrus synchronization protocol induced a high incidence of estrus with comparatively high fertility in Brahman heifers.     

Synchronization of estrus following 7 or 9 day treatment with chlormadinone acetate (CAP)

Synchronization of estrus and fertility were determined in a series of 8 trials. Various levels of chlormadinone acetate (CAP) were fed for either 7 or 9 days. An injection of 5 mg of estradiol valerate and CAP was given at the start of the feeding period. In some trials estradiol 17β was injected near the end of the feeding period. In trial 1, 98% of the CAP-treated heifers were in estrus in a 5-day period, but only 46% conceived at first service compared to 80% in the non-synchronized heifers (P<.01).In trials 2 through 6, 0.25 mg estradiol 17β injected either 60 or 72 hours after the last CAP feeding reduced the interval to ovulation in heifers that ovulated. However, use of estradiol 17β reduced the number of heifers ovulating in most trials.In trials 7 and 8, estrus was effectively synchronized with either 7- or 9-day feeding of 7.5 or 10 mg of CAP daily followed by .5 mg estradiol 17β, 72 hours after the last CAP feeding. Pregnancy rates at first service varied from 21 to 45% in heifers in the synchronized groups, compared to 58% in the controls in trial 7 (P<.05). In trial 8 pregnancy rates at 1st service varied from 29 to 47% in treated heifers compared to 72% in controls (P<.01).In this series of trials, fertility was reduced from 24 to 43% with the use of CAP and estradiol valerate. Conception rates at first service were not improved by varying the length of feeding (7 or 9 days), level of CAP (7.5 or 10 mg) or by attempting to reduce the variation in ovulation time with estradiol 17β. None of the combinations of these three drugs used increased fertility in these trials.     

Pregnancy rates in Holstein embryo transfer recipients: Effect of treatment with progesterone or clenbuterol and of natural versus induced cycles

Pregnancy rates were the same (59 and 50%; P > 0.05) in control recipients (n = 22) and recipients treated with 200 mg progesterone 4 h prior to nonsurgical transfer (n = 48) of previously frozen embryos. With small recipients and difficult transfer conditions, the same progesterone supplementation increased pregnancy rates (46 vs 21%; P < 0.05) after transfer of previously frozen embryos. The administration of the β₂-mimetic agent clenbuterol (4-amino- α [(tert. - butylamino) methyl] - 3,5,dichlorobenzyl-alcohol hydrochloride) 30 min prior to nonsurgical transfer resulted in pregnancy rates of 60.0% (n = 25) and 44.2% (n = 52) for Holstein heifers receiving fresh and previously frozen embryos, respectively. Pregnancy rates in untreated controls were 59.9% (n = 142) and 48% (n = 47) for fresh and frozen-thawed embryos. There was no effect (P > 0.05) of spontaneous versus prostaglandin-induced estrus on pregnancy rates for recipients of either fresh or previously frozen embryos.     

Synchronization of estrus and fertility in goats with norgestomet ear implants

Estrus was synchronized in 64 dairy goats in July with norgestomet ear implants. Half the does received ear implants that contained 6 mg norgestomet and the remaining does received implants that contained 3 mg. Implants were left in place for 11 days. Each doe received i.m. injections of 400 IU PMSG and 50 mug cloprostenol 24 hours prior to implant removal. Twenty-eight of 32 does (87.5%) that received 6 mg or 3 mg norgestomet exhibited onset of estrus within 24 hours of implant removal. All does had exhibited onset of standing estrus by 43 hours after implant removal. Does were hand-mated to fertile bucks twice daily while in standing estrus. There were no differences between does implanted with 6 mg or 3 mg in fertility to the induced estrus (74.2% vs 75% kidding), mean length of gestation (151.0 +/- 3.2 vs 151.6 +/- 2.0 days), mean number of kids per doe (2.1 +/- 0.8 vs 2.3 +/- 0.7) or in mean kid weights (3.10 +/- 0.80 vs 3.06 +/- 0.86 kg) (6 mg vs 3 mg, respectively). It was concluded that ear implants that contained 3 mg of norgestomet were equally as effective as implants that contained 6 mg for synchronization of estrus in dairy goats.     

Use of altrenogest to prepare ovariectomized mares as embryo transfer recipients

Altrenogest was administered to ovariectomized mares to determine if treatment would enable establishment and maintenance of pregnancy after transfer of a 7-d embryo. Three different treatment regimens were used: Group A received 22 mg altrenogest daily starting 5 d before transfer, Group B received 66 mg altrenogest daily starting 6 days before transfer, Group C received 300 mg progesterone in oil intramuscularly daily starting 5 d before transfer. Intact, ovulation-synchronized recipients were used as controls for transfer technique. Pregnancy rates were 1 6 , 2 6 , 2 5 , and 13 19 for Group A, Group B, Group C, and controls, respectively. The pregnancy rate in Group A was significantly different from controls and Group A mares had poor uterine and cervical tone. These results show that ovariectomized mares treated with altrenogest are capable of establishing pregnancy after embryo transfer. Treatment with 22 mg altrenogest appears to be insufficient for optimal pregnancy rates after transfer in ovariectomized recipients.     

Nutrition, synchronization, and management of beef embryo transfer recipients

A commercially viable cattle embryo transfer industry was established during the early 1970s. Initially, techniques for transferring cattle embryos were exclusively surgical. However, by the early 1980s, most embryos were transferred nonsurgically. For an embryo transfer program to be effective, numerous factors need to be in place to ensure success. Nutrition, estrous cycle control, and recipient management are all responsible for the success or failure in fertility for a given herd. Utilization of body condition scores is a practical method to determine nutritional status of the recipient herd. Prepartum nutrition is critical to ensure that cows calve in adequate body condition to reinitiate postpartum estrous cycles early enough to respond to synchronization protocols. Estrus synchronization for embryo transfer after detected estrus or for fixed-time embryo transfer without estrus detection are effective methods to increase the number of calves produced by embryo transfer. In addition, resynchronization of nonpregnant recipients effectively ensures that a high percentage of recipients will return to estrus during a 72 h interval and are eligible for subsequent embryo transfers. Numerous additional factors need to be assessed to ensure that the recipient herd achieves its reproductive potential. These factors include assessing the merits of nulliparous, primiparous, or multiparous cows, ensuring that facilities allow for minimal stress, and that the herd health program is well-defined and followed. Numerous short- and long-term factors contribute to recipients conceiving to a transferred embryo, maintaining the embryo/fetus to term, delivering the calf without assistance and raising and weaning a healthy calf.