Estrus synchronization and superovulation with a subcutaneous gestagen implant (Norgestomet, Intervet) in suckler cows and heifers

Four trials were conducted to investigate the suitability of a gestagen implant (Norgestomet, Intervet) for estrus synchronization and superovulation in suckler cows and heifers kept under field conditions in Germany. In trial 1 out of 17 heifers treated 12 responded with one ovulation each. In trial 2 57 suckler cows were treated at the University experimental farm. Of 23 cows treated sooner and 34 cows treated later than 50 days post partum one (4 %) and 16 (47 %) respectively calved at the expected time. Trial 3 was a field trial involving 126 suckler cows and 21 heifers. Of 24 cows treated sooner and 102 cows treated later than 50 days post partum 17 % and 52 % respectively calved at the expected time. Of the 21 heifers only 19 % calved at the expected time. In trial 4 superovulation of 13 cows and 17 heifers resulted in 62 % and 94 % responding with 10.0 +/- 2.5 and 11.1 +/- 3.0 (x +/- SD ) ovulations per animal respectively.     

Embryo production from superovulated Holstein-Friesian dairy heifers and cows after insemination with frozen-thawed sex-sorted X spermatozoa or unsorted semen

The aim of this study was to evaluate embryo production in superovulated Holstein-Friesian dairy heifers and cows inseminated with either X-sorted spermatozoa (2 million/dose) or unsorted semen (15 million/dose). Experiment 1 at the research farm involved eight heifers, six cows and semen of one Holstein bull. All transferable embryos were diagnosed for sex. Experiment 2 included embryo collections on commercial dairy farms: X-sorted spermatozoa from three Holstein bulls were used for 59 collections on 28 farms and unsorted semen from 32 Holstein bulls were used for 179 collections on 79 farms. Superovulations were induced by eight declining doses of FSH (total of 12 ml for heifers and 19 ml for cows) starting on days 8-12 of the estrus cycle. Inseminations began 12h after the onset of estrus and were performed two to four times at 9-15 h intervals. Low-dose X-sorted inseminates were deposited into uterine horns and unsorted semen was placed into the uterine body. In Experiment 1, on average 70.3 and 75.0% of embryos recovered from heifers, and 48.4 and 100% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. The proportion of transferable female embryos produced approximately doubled when insemination was with X-sorted spermatozoa compared to insemination with unsorted semen (heifers 96.4% versus 41.1%; cows 81.1% versus 39.8%). In Experiment 2, estimated 53.9 and 65.5% of embryos recovered from heifers, and 21.1 and 64.5% of embryos recovered from cows were of transferable quality in X-sorted and unsorted groups, respectively. Proportions of unfertilized oocytes were 21.1 and 10.6% for heifers and 56.0 and 14.4% for cows in X-sorted and unsorted groups, respectively. Consequently, cows inseminated with X-sorted spermatozoa produced significantly smaller proportions of transferable embryos (p<0.005) and significantly larger proportions of unfertilized oocytes (p<0.001) than those inseminated with unsorted semen. Proportions of quality 1 or degenerated embryos were similar for the two treatments in both heifers and cows. Within treatments, bulls did not significantly affect the proportions of transferable, unfertilized or degenerated oocytes/embryos. It was concluded that using low-dose X-sorted spermatozoa rather than normal-dose unsorted semen for the insemination of superovulated embryo donors can improve the proportion of transferable female embryos produced but this potential may not be achieved in commercial practice, particularly in cows, because of reduced fertilization rates when using low doses of X-sorted spermatozoa.     

Estrus synchronization and pregnancy rates in cyclic and noncyclic beef cows and heifers treated with syncro-mate B or Norgestomet and Alfaprostol

Postpartum lactating cows (N=118) and virgin heifers (N=60) were treated with subcutaneous Norgestomet implants for nine days and received either an intramuscular injection (im) of 5 mg estradiol valerate and 3 mg Norgestomet at the time of implant insertion or an im injection of 5 mg Alfaprostol 24 hr before implant removal. Animals were artificially inseminated 12 hr after detection of estrus. Of the cows and heifers, 78% and 88%, respectively, were in estrus within five days after implant removal (P<0.09). There was no difference between treatments in the proportion of animals in estrus or in the timing of estrus (P<0.85). Estrus was detected in a greater (P<0.05) proportion of animals that were cyclic prior to treatment (88%) than among those that were anestrous prior to treatment (77%). Pregnancy rates after five days were similar between heifers that were cyclic (42%) or anestrous (47%) prior to treatment; however, the five-day pregnancy rate in cows that were anestrous prior to treatment was 38% lower than that in cows that were cyclic prior to treatment (17 vs 55%, P<0.01). Although the treatments synchronized or induced estrus in both cyclic and anestrous animals, marked variability in estrous response and fertility among previously cyclic or anestrous postpartum cows limited the effectiveness of the treatments.     

Superovulatory responses of Holstein cows

Approximately 1000 registered cows and heifers were superovulated one to 10 times. Nonsurgical embryo recoveries were performed on all donors which exhibited estrus. Healthy donors produced more total ova and cleaving embryos and had a higher ovum recovery rate, fertilization rate and pregnancy rate from embryos transferred than did cows classified as infertile. While ovum number was not affected during 10 repeated superovulations, fertilization rate and embryo number decreased. The number of ova recovered from healthy cows was affected by season, and from infertile cows by the day of the estrous cycle on which FSH was started and by the number of days since calving. More ova were recovered from infertile cows synchronized with prostaglandins prior to superovulation than following a natural estrous cycle. The number of embryos recovered from infertile cows was affected by age and from healthy cows by daily milk production. Fertilization rates in both healthy and infertile cows were affected by age, time since calving, daily milk production, day of cycle FSH was injected and season. There was no effect of the day of recovery on the number of ova or embryos recovered from healthy or infertile cows.     

Embryo yield and plasma progesterone profiles in superovulated dairy cows and heifers.

This study was conducted to compare the superovulatory (SOV) response of dairy cows (n=172) and heifers (n=172), with two SOV treatments started at the mid-luteal-phase of the estrus cycle. Donors were randomly treated either with equine chorionic gonadotrophin (eCG) plus neutra-eCG serum (eCG+N group, n=167) or follicle stimulating gonadotrophin (FSH-P group, n=177).No significant differences were observed among groups in the percentage of superovulatory responsive donors (SR donors; corpora lutea (CL) >/=2), the mean number of total ova, fertilized ova and viable embryos recovered. Cows yielded significantly less total ova and less fertilized ova (P<0.05) and tended to yield less viable embryos (P<0.06) than heifers.Plasma progesterone (P4) concentrations (n=135 donors) on the day of PGF(2alpha) (PGF) injection and on the day of SOV estrus were significantly higher (P<0.01) in eCG+N than in FSH-P donors and, the increase between those 2 days was also significantly higher (P<0.05) in group eCG+N than in group FSH-P, suggesting a higher luteotrophic effect of eCG than FSH-P. SR donors had P4 levels significantly higher (P<0.001) than non-SR donors only on day 5 after the SOV estrus and on the day of embryo recovery. Plasma P4 concentrations at 5 days after the SOV estrus and at embryo recovery correlated significantly (r=0.76, P<0.001).Heifers had significantly higher P4 levels than cows at gonadotrophin injection (P<0.01), PGF injection (P<0.001), 5 days (P<0.01) and 7 days (P<0.001) after the SOV estrus. At day 7 after the SOV estrus, P4 concentrations per ova recovered were significantly higher in heifers than in cows (P<0.01). The increase of plasma P4 per ova recovered, between days 5 and 7 after the SOV estrus, was significantly (P<0.01) higher in heifers than in cows. Also, the increase of plasma P4 between injections of gonadotrophin and PGF was significantly higher (P<0.05) in heifers than in cows.These results suggest that heifers have higher plasma P4 concentrations at diestrus (either before or after the SOV treatment) and this is associated with a higher embryo yield and quality, as compared to lactating cows. These higher plasma P4 concentrations reflect not only differences in ovulation rate as well as the competence of the corpus luteum, which is potentialized by gonadotrophin stimulation.     

Influence of summer heat stress on pregnancy rates of lactating dairy cattle following embryo transfer or artificial insemination

Lactating Holstein cows were used to determine if pregnancy rate from embryo transfer (n = 113) differed from contemporary control cows (n = 524) that were artificially inseminated (AI). Holstein heifers (n = 55) were superovulated with FSH-P (32 mg total) and inseminated artificially during estrus and subsequently managed under shade structures. On Day 7 post estrus, embryos were recovered, and primarily excellent to good quality embryos (90.3%) were transferred to estrus-synchronized lactating cows. Cows were managed under conditions of exposure to summer heat stress. Pregnancy status was determined by milk progesterone concentrations at Day 21 and palpation per rectum at 45 to 60 d post estrus. Pregnancy rates of cows presented for AI (Day 21, 18.0%; Days 45 to 60, 13.5%) were typical for lactating cows inseminated during periods of summer heat stress in Florida. Pregnancy rates of embryo recipient cows were higher (P<0.001) than those of control cows (Day 21, 47.6%; Days 45 to 60, 29.2%). Summer heat stress had no adverse effect on heifer superovulatory response, but it increased (P<0.05) the incidence of retarded embryos (相似文献   

Collection of two-cell pig embryos and their culture in media containing different protein components

Eggs were flushed from the oviducts of slaughtered gilts that had been inseminated after synchronization of estrus and ovulation with pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG). Of 347 eggs collected at a recovery rate of 73.8%, 41.8% had not cleaved by 32 h after expected ovulation time. Of those cleaved, 86.9% were at the two-cell stage.Two-cell embryos were cultured in Dulbecco's medium containing either no protein or 20% of one of the following: lyophilized bovine serum albumin, lyophilized fetal calf serum or heat-inactivated serum from slaughter heifers, rabbits or barrows. Dulbecco's medium without protein did not support further development of embryos. Addition of heat-inactivated blood serum from slaughter heifers, rabbits or barrows resulted in development rates similar to those obtained by using commercially available products. Optimal embryonic development rates of 54.5% were obtained with addition of heat-inactivated bovine serum. Of the two-cell embryos only three (2.1%) developed past the four-cell stage in these culture media.     

Superovulation and embryo recovery from peripubertal Holstein heifers

The use of peripubertal donors in embryo transfer (ET) programs presents significant opportunity to accelerate genetic gain in domestic livestock by reducing the generation interval. These studies were designed to evaluate feasibility of superovulation and embryo recovery in peripubertal heifers (starting at 7.8 months of age), and to determine whether subsequent reproductive and lactational performance of donor heifers were impaired. Study 1 utilized 10 pairs of contemporary full-sibling heifers in which one heifer in each pair was assigned to receive a superovulation regimen and her full-sibling contemporary received placebo. Treated heifers were artificially inseminated at estrus and embryos were flushed transcervically 4-6 days later. Based on recovery of oocytes and/or embryos, 9 of 10 heifers responded to the hormonal regimen and 12 total embryos were recovered. Seven embryos (58%) were transferred into recipients resulting in five pregnancies. Control and treated heifers remained in the herd and were bred at a natural estrus by AI at 15 months of age. Lactation records, i.e., 305 days mature equivalent (305 d ME) were obtained, and all animals were evaluated for udder conformation traits between 32 and 38 months of age. Reproductive traits (age at first calving and days to conception) and lactational traits of heifers subjected to embryo transfer and their non-treated full-siblings did not differ (P > 0.05). Study 2 was conducted to establish the commercial feasibility of hormonally programming peripubertal heifers ranging in age from 7.8 to 9.9; 10 to 11.9; 12 to 13.9 and >/= 14 months. In total, 3982 embryos were recovered from 520 heifers, with 2419 (60.7%) of those categorized as viable (transferable). The number of ova/embryos obtained per flush (5.6 +/- 1.0) and the number of transferable embryos (2.8 +/- 0.5) was reduced (P < 0.05) in heifers of age 7.8-9.9 months compared to all other age groups. There was no difference (P > 0.05) in the number of ova/embryos recovered (7.8 +/- 0.3), or the number of transferable embryos (4.8 +/- 0.2), among heifers that were >/=10 months of age. The number of unfertilized ova did not differ by age, however, more degenerate embryos tended to be recovered from heifers <10 months of age compared to heifers >/=14 months of age. These data indicate that transferable embryos can be safely recovered from heifers beginning at 10 months of age without compromising subsequent reproductive or lactational performance of the donor.     

Effects of GnRH on superovulated cattle

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF(2)alpha or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 mug i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed. No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.     

Seasonal effects on caprine response to synchronization of estrus and superovulatory treatment

Nubian doelings (n = 21, 7 of which were repeats) were synchronized and superovulated with Norgestomet ear implants and follicle stimulating hormone-pituitary (FSH-p) and were then mated during early and late periods of their breeding season in the southeastern United States. A 100% response rate to estrus synchronization treatment was found in doelings (n = 15, 2 of which were repeats) treated early in the breeding season, and the superovulation regimen resulted in the surgical collection of an average of 15.1 viable embryos per doeling. But only a 66.7% response rate to estrus synchronization treatment was observed in doelings (n = 6, 5 of which were repeats) treated late in the season; only 50% of these doelings (or 33.3% of the initial doelings treated) responded to superovulatory treatment, resulting in an average of 3.33 viable embryos collected surgically per doeling. Thus, a significantly higher number of viable embryos can be obtained from Nubian doelings when treated for estrus synchronization and superovulation early in the breeding season.     

Superovulation in beef cattle with PMSG and prostaglandins or progestins

The ovarian response to 2000 I.U. PMSG of 76 suckler cows and 153 heifers synchronized by either progesterone (Abbovestrol-PRID/ CEVA), a synthetic gestagen (Norgestomet/ Intervet), prostaglandin F₂ (Dinolytic/ Upjohn) or a prostaglandin analog (Estrumate/ ICI) was recorded after slaughter. The proportion of animals responding with at least one ovulation was between 82 and 92% except for heifers treated with estrumate (56%). Heifers had nearly twice as many ovulations as cows (11.9 ± 0.9 vs 6.8 ± 0.8 (SEM)). The response was slightly more consistent in gestagen-synchronized animals: nevertheless, individual variation was considerable.     

Commercial aspects of bovine embryo transfer

Superovulated beef cows and heifers were nonsurgically collected 6 to 8 days post estrus. Commercial production results for 1976 through 1978 were 4979 pregnancies from 7814 embryos transferred for an overall pregnancy rate of 63%. In 1978, 519 superovulation procedures averaged 9.95 +/- 8.4 (S.D.) ova collected, 8.2 +/- 7.55 ova fertilized, 5.96 +/- 5.37 embryos transferred and 3.63 +/- 5.37 pregnancies per procedure. Embryos were transferred to recipient cows in estrus 12 hr before the donor (-12) the same time (0) or 12 hr after the donor (+12). The +12 group had a significantly lower pregnancy rate (61%, P<.05) than the 0 group (67%) or -12 group (66%). Transfer of early morula stage embryos resulted in a lower pregnancy rate (61%, P<.05) than late morula (67%) early blastocyst (67%) or late blastocyst (71%) stage embryos. A higher pregnancy rate (P<.05) was obtained with embryos of good morphological quality (71%) than with embryos graded fair and poor (55%). The pregnancy rate for embryos transferred nonsurgically was lower (44%) than the pregnancy rate for embryos transferred surgically during the same time period (66%). Pregnancy rates for three operators performing the nonsurgical transfers were 48%, 53%, 28%. No difference in pregnancy rate was found between embryos cultured 24 hr in BMOC-3 at 37C (62%) and embryos transferred the same day as collection (60%). Pregnancy rates for cultured embryos transferred to recipient cows in estrus 12, 24 or 36 hr after the donor were 68%, 62% and 60%, respectively. Embryos recovered on days 6, 7 and 8 were frozen in 1.5M DMSO and stored in liquid nitrogen several days to several weeks. Of 68 embryos frozen, 34 were viable post thaw. Upon transfer to recipient cows, the 34 viable embryos produced 23 confirmed pregnancies.     

Superovulatory response of dairy cattle (Bos taurus ) in a tropical environment

Dairy (Bos taurus) heifers and cows (n = 40) in a tropical environment were treated during mid-luteal phase using either SUPER-OV(R) or OVAGEN to induce superovulatory response after synchronization of the superovulatory estrus with a synthetic progestagen and cloprostenol (PG). Estrous cattle were inseminated twice using frozen-thawed semen, and embryos were recovered nonsurgically, on-farm, 7 d later. Between initiation of gonadotrophin treatment and recovery of embryos, 4 blood samples per animal were collected from 26 animals for determination of plasma progesterone (P4) concentration. Two (5%), 28 (70%) and 10 (22%) of the animals were observed in estrus 1.5, 2 and 2.5 to 3 d after PG, respectively. There was no difference (P = 0.7) in the number of palpable CL between animals treated with SUPER-OV (7.6 +/- 1.0; n = 18) and those treated with OVAGEN (7.9 +/- 1.1; n = 22). There was also no significant difference (P > 0.05) between Jersey vs Ayrshire breeds or heifers vs cows in the ovarian response as estimated by the number of palpable CL. However, a higher proportion of Ayrshire cattle and donors treated with OVAGEN yielded a higher total number and viable/transferable embryos than Jersey and SUPER-OV-treated cattle. There was a significant (P < 0.05) correlation between the number of CL and total number of embryos (r = 0.65); the number of transferable embryos was also significantly related to the total number of embryos per recovery (r = 0.85; P < 0.05). For 15 animals with normal P4 profiles, the mean (+/-SEM) plasma P4 concentration was 14.4 +/- 0.8, 0.5 +/- 0.2, 5.4 +/- 1.1 and 39.4 +/- 3.0 nmol L at initiation of gonadotrophin treatment, superovulatory estrus and Days 3 and 7, respectively. The mean (+/-SEM) interval between a PG injection given after embryo recovery and the induced estrus was 7.1 +/- 0.7 d (range 3 to 14 d) and the length of the superovulatory cycle was 24.1 +/- 3.2 d (range 12 to 35 d).     

Detrimental effects of high plasma urea nitrogen levels on viability of embryos from lactating dairy cows

High plasma urea nitrogen (PUN) concentrations are associated with decreased fertility in lactating dairy cows. Our objective was to evaluate the quality of embryos flushed from superovulated lactating cows having moderate or high PUN concentrations. Subsequent embryo survival was determined after transfer to recipient heifers with either low or high PUN. Lactating Holstein dairy cows (n = 23; 50-120 days in milk) were randomly assigned to one of two diets designed to result in moderate or high PUN concentrations (15.5 +/- 0.7 and 24.4 +/- 1.0 mg/dl, respectively; P < 0.001) and were fed for 30 days before embryo flushing and recovery. Embryos (n = 94) were evaluated morphologically, frozen and subsequently transferred into synchronized virgin heifers that were fed one of two diets designed to result in either low or high PUN concentrations (7.7 +/- 0.9 and 25.2 +/- 1.5 mg/dl, respectively; P < 0.001; 2 x 2 factorial design). The number, quality and stage of development of recovered embryos were similar for cows with moderate or high PUN. Transfer of embryos from moderate PUN donor cows resulted in a higher pregnancy rate (35%; P < 0.02) than the transfer of embryos from high PUN donor cows (11%). Pregnancy rate was not affected by either recipient diet or the interaction of donor and recipient diets (P > 0.05). These results indicate that high PUN concentrations in lactating dairy cows decrease embryo viability through effects exerted on the oocyte or embryo before recovery from the uterus 7 days after insemination.     

An instrument for transcervical recovery of embryos from heifers

A non-surgical system of embryo recovery is described. It consists of a rigid probe of small diameter (4 mm) for recovering the embryos from young heifers (10 to 12 days after estrus). An average of 6.35 eggs were recovered per donor from 64 heifers 15 to 22 month-old having more than two palpable corpora lutea after superovulation. Forty donors were slaughtered after recovery to determine the number of ovulations, the state of the uterus and to do a post-mortem perfusion. The average recovery rate of embryos was 56.4 % ; an additional 9 % were recovered after slaughter. We compared two recovery methods differing in mode of liquid return ; no significant differences were found. Twenty-four animals not slaughtered after recovery returned to heat a mean 23.8 days after induced estrus (control cycle).     

The effect of in vitro treatment of bovine embryos with IGF-1 on subsequent development in utero to Day 14 of gestation

Culture of bovine embryos with insulin-like growth factor-1 (IGF-1) can improve development to the blastocyst stage and embryo survival following transfer to heat-stressed, lactating dairy cows. Two experiments were conducted to determine whether IGF-1 could improve embryo survival and development at Day 14 after ovulation. In Experiment 1, non-lactating Holstein cows (n=58) were selected as recipients following synchronization for timed-embryo transfer. Embryos were produced in vitro and cultured with or without 100ng/mL IGF-1. At Day 7 after expected ovulation (Day 0), groups of 7-12 embryos were randomly transferred to each recipient. Embryos were recovered at Day 14. Embryo length and the presence or absence of an embryonic disc was recorded. Recovered embryos were cultured individually for 24h to determine interferon-tau (IFN-tau) secretion. There was no effect of IGF-1 on embryo recovery rate, embryo length or IFN-tau secretion. In Experiment 2, non-lactating (n=56) and lactating (n=35) Holstein cows were selected as recipients following synchronization for timed-embryo transfer. Embryos were produced as described in Experiment 1. At Day 7 after expected ovulation (Day 0), a single embryo was randomly transferred to each recipient. Embryos were recovered at Day 14. Embryo length and IFN-tau secretion were determined as in Experiment 1. Recovery rate at Day 14 tended (P=0.1) to be higher for recipients that received IGF-1 treated embryos compared to control embryos (43.2% versus 26.1%, respectively). There was no effect of IGF-1 on embryo length or IFN-tau secretion. In conclusion, results suggest that exposure to IGF-1 through Days 7-8 of development does not enhance capacity of embryos to prevent luteolysis. Results of the single embryo-transfer experiment suggested that IGF-1 treatment might affect embryo survival post-transfer as early as Day 14 after ovulation. Further experimentation is warranted to verify this finding.     

Plasma progesterone profiles and factors affecting embryo-fetal mortality following embryo transfer in dairy cattle

The relationship between plasma progesterone (P4) levels and embryo survival, and the value of P4 profiles for the selection of cattle embryo transfer recipients is still a matter of controversy. This study reports a comparison between lactating cows and heifers (n = 407) from a single dairy herd, after transfer of either fresh or frozen-thawed good quality embryos, of their ability to sustain embryo-fetal development to term. Plasma P4 concentrations on the day of estrus (Day 0 = D0), Day 4, Day 7 and on Day 21 were measured and related to embryo survival. Plasma P4 levels on Days 0, 4 and 7 were similar in recipients later found pregnant or open. Plasma P4 levels on Day 7 were significantly higher (P < 0.01) in heifers than in cows, but they were similar in pregnant and nonpregnant heifers and in pregnant and nonpregnant cows. Pregnancy rates for fresh and frozen-thawed embryos were higher in heifers than in cows, but the differences did not reach significance. However, the overall late embryonic mortality was significantly higher (P < 0.01) and the calving rate for frozen-thawed embryos was significantly lower (P < 0.05) in cows than in heifers. As expected, plasma P4 on Day 21 was significantly higher (P < 0.001) in pregnant than in nonpregnant recipients, but there was no difference between pregnant cows and pregnant heifers. Plasma P4 levels on Day 7 of recipients presumed pregnant on Day 21 and later found pregnant or nonpregnant were similar, but plasma P4 levels on Day 21 were significantly higher (P < 0.001) in pregnant than in nonpregnant recipients. The results of this study suggest that plasma P4 levels until the day of transfer, except for the rejection of recipients with abnormal luteal function, are of limited practical use for embryo transfer recipient selection. However, in lactating cows low plasma P4 values on Day 7 might negatively affect embryo survival, while in heifers this effect is not noticeable. Lactating cows are more prone to embryo loss than heifers, especially in the case of frozen-thawed embryos; this is associated with a lower competence of the corpus luteum at Day 7.     

Fertility of Bos indicus and Bos indicus x Bos taurus crossbreed cattle after estrus synchronization

Ninety-five cows (79 Boran and 16 Boran-Brahman crossbreeds) and 107 heifers (55 Boran and 52 Boran x Friesian F1 crossbreeds) were used to determine estrus response, estrus response interval and pregnancy rate following synchronization with prostaglandin (PGF(2)alpha), a progesterone-releasing intravaginal device (PRID) and Synchro-mate B (SMB). The proportion of cattle responding to synchronization treatment was 62.5, 43.5 and 57.7% for cows and 85.7, 68.0 and 81.5% for heifers using PGF(2)alpha, PRID and SMB, respectively. The overall mean response was 59 and 81.8% for cows and heifers, respectively. The estrus response of the control animals over a 45-d breeding period was 72.7 and 90% for cows and heifers, respectively. The estrus response interval for cows was 31.8, 22.1 and 18.0 h and it was 51.1, 38.0 and 21.6 h for heifers with PGF(2)alpha, PRID and SMB treatment, respectively. Mean pregnancy rate for cows was 50.0, 34.8, 46.2 and 68.8% and for heifers it was 60.7, 40.0, 55.6 and 77.8% in the PGF(2)alpha, PRID, SMB and control groups, respectively. Based on these findings, it was concluded that both PGF(2)alpha and SMB produce a satisfactory estrus response and pregnancy rate in the cattle studied.     

Embryo production with sex-sorted semen in superovulated dairy heifers and cows

The aim of this study was to examine the effect of sex-sorted semen on the number and quality of embryos recovered from superovulated heifers and cows on commercial dairy farm conditions in Finland. The data consist of 1487 commercial embryo collections performed on 633 and 854 animals of Holstein and Finnish Ayrshire breeds, respectively. Superovulation was induced by eight intramuscular injections of follicle-stimulating hormone, at 12-hour intervals over 4 days, involving declining doses beginning on 9 to 12 days after the onset of standing estrus. The donors were inseminated at 9 to 15–hour intervals beginning 12 hours after the onset of estrus with 2 + 2 (+1) doses of sex-sorted frozen-thawed semen (N = 218) into the uterine horns or with 1 + 1 (+1) doses of conventional frozen-thawed semen (N = 1269) into the uterine corpus. Most conventional semen (222 bulls) straws contained 15 million sperm (total number 30–45 million per donor). Sex-sorted semen (61 bulls) straws contained 2 million sperm (total number 8–14 million per donor). Mean number of transferable embryos in recoveries from cows bred with sex-sorted semen was 4.9, which is significantly lower than 9.1 transferable embryos recovered when using conventional semen (P ≤ 0.001). In heifers, no significant difference was detected between mean number of transferable embryos in recoveries using sex-sorted semen and conventional semen (6.1 and 7.2, respectively). The number of unfertilized ova was higher when using sex-sorted semen than when using conventional semen in heifers (P < 0.01) and in cows (P < 0.05), and the number of degenerated embryos in cows (P < 0.01), but not in heifers. It was concluded that the insemination protocol used seemed to be adequate for heifers. In superovulated cows, an optimal protocol for using sex-sorted semen remains to be found.     

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.