Effects of epidural injections and transvaginal aspiration of ovarian follicles in heifers used repeatedly for ultrasound-guided retrieval of ova and embryo production.

Postmortem examinations of 13 Simmental heifers that had received between 16 and 28 injections to induce caudal epidural anaesthesia, the last not less than seven months before they were slaughtered, showed that none of them had any evidence of infection or inflammation at the injection site or in adjacent bone and soft tissues. Seven of them had minor damage to intercoccygeal discs, consisting of discospondylosis with neovascularisation and chondroid metaplasia, consistent with injuries caused by needles. The severity of the damage was not related to the number of epidural injections received, suggesting that the damage was probably caused by a discrete suboptimal injection procedure. In a second study, the ovaries from 22 Simmental heifers that had undergone between 13 and 16 transvaginal follicular aspirations were examined postmortem. Approximately one-third of them had a natural texture with little or no evidence of scar tissue, and less than one in five had extensive scarring and a toughened texture. There was no evidence of compromised ovarian function, as determined by the number and normality of corpora lutea and large follicles, in any of the animals.

Embryo production using defined oocyte maturation and zygote culture media following repeated ovum pick-up (OPU) from FSH-stimulated Simmental heifers.

To determine whether differences in ovarian follicle populations and endocrine status at ovum pick-up (OPU) influenced the quality and developmental competence of oocyte-cumulus complexes (OCC's) collected from follicle stimulating hormone (FSH)-stimulated donors, 24 Simmental heifers had their ovarian follicles aspirated via transvaginal ultrasound-guided OPU at both 15 (OPU1) and 21 (OPU2) days following a synchronised oestrus, on four consecutive occasions at 15-week intervals. More OCC's were collected during OPU1 than OPU2 (means +/- S.E.M. = 7.2 +/- 0.47 versus 5.7 +/- 0.44; P = 0.01), but the respective percentages that were of good quality (categories 1 and 2) did not differ significantly (55 +/- 3% versus 47 +/- 3%). The incidence of zygote cleavage following OCC maturation (Medium 199; protein-free), in vitro fertilization (mTALP; including 0.6% (w/v) albumin) and culture (modified SOF; protein-free) was not significantly different (mean +/- S.E.M. = 81 +/- 2% and 71 +/- 7% for OPU1 and OPU2, respectively). Corresponding blastocyst yields from good quality OCC's (24 +/- 3% and 26 +/- 4%) also did not differ. Although the same 3-day FSH regimen was used immediately prior to each OPU session, plasma FSH concentrations were consistently lower at OPU1 than OPU2 (1.3 +/- 0.28 ng/ml versus 2.5 +/- 0.45 ng/ml; P < 0.05). In contrast, plasma progesterone concentrations were higher at OPU1 (6.6 +/- 0.48 ng/ml versus 3.9 +/- 0.53 ng/ml; P < 0.001), with concentrations at OPU2 being consistent with the presence of luteal tissues, including both persistent corpora lutea and luteinised follicle remnants following OPU1. Failure of the significant differences in follicular and endocrine status between OPU1 and OPU2 to alter the developmental competence of OCC's suggests that, probably as a result of its stabilising influence on nutritionally-sensitive intraovarian regulators of oocyte competence, the constant feeding regimen had a more profound effect on oocyte quality than observed shifts in the peripheral concentrations of some reproductive hormones. Finally, the study demonstrates that it is possible to generate acceptable numbers of in vitro blastocyst-stage embryos from high genetic merit heifers using strategies which restrict reliance on protein to the in vitro fertilization stage of the production process.

Effect of frequency of follicle aspiration on oocyte yield and subsequent superovulatory response in cattle.

The effect of frequency of transvaginal follicular aspiration on oocyte yield and subsequent superovulatory response was studied in 2 experiments. In Experiment 1, 32 primiparous Hereford x Friesian cows were assigned to 4 treatments (n = 8 per treatment). Oocyte recovery was carried out once a week for 12, 8, 4 or 0 (control) wk. Embryo recovery for all animals was 7 wk after the completion of the aspiration schedules. In Experiment 2, the effects of oocyte recovery once or twice a week (n = 8 per treatment; control n = 18) for 12 wk and response to superovulation 4 wk after the last aspiration were compared using nulliparous purebred Simmental heifers. Increasing the period of once weekly aspirations from 4 to 12 wk (Experiment 1) did not affect the number of follicles observed per session (mean +/- SEM; 10.0 +/- 0.82) or aspirated (7.8 +/- 0.71), but the recovery rate of oocytes from follicles aspirated was greater for donors aspirated for either 4 or 8 wk than for 12 wk (32.3 +/- 3.73 vs 28.4 +/- 2.61 vs 20.1 +/- 2.13 %; P < 0.05). Following the last aspiration and prior to commencing superovulatory procedures, estrus or estrous activity was observed in 7 8 , 8 8 , 7 8 and 6 8 of the animals aspirated over 12, 8, 4 or 0 wk, respectively. Subsequent superovulatory responses and in vivo embryo recoveries were similar for all aspiration treatments and for control animals. Changing the frequency of oocyte recovery from once to twice weekly (Experiment 2) did not affect the numbers of follicles observed (9.1 +/- 0.63 vs 8.3 +/- 0.85), follicles aspirated (5.9 +/- 0.56 vs 6.2 +/- 0.69), oocytes recovered (1.7 +/- 0.27 vs 1.9 +/- 2.0) per session or the oocyte recovery rate (29.4 +/- 2.4 vs 30.4 +/- 2.4 %); nor was there any effect of frequency of aspiration on subsequent superovulatory response and embryo recovery. In conclusion, increasing the period of aspiration from 4 to 12 wk and the frequency from once to twice a week over 12 wk did not reduce the number of follicles observed or aspirated, or number of oocytes recovered per donor per session. Subsequent estrous cyclicity and responses to superovulation were unaffected by the periods or frequencies of oocyte recovery examined here.

Norgestomet implants, plasma progesterone concentrations and embryo transfer pregnancy rates in cattle.

A study was undertaken to test the hypothesis that supplementation with exogenous progestagen at the time of embryo transfer would enhance pregnancy rates in recipients. Two-hundred-and-seventy-two oestrus-synchronised crossbred heifer and cow recipients received 200 grade 1 and 72 grade 2 Simmental embryos transferred non-surgically. Heparinised blood samples were taken on day 6 and day 7 (oestrus = day 0) for the assessment of the endogenous plasma progesterone concentration. Half the recipients received an ear implant impregnated with 3 mg norgestomet on the day of embryo transfer. The pregnancy rates were 51.9 and 49.6 per cent for the norgestomet-treated and control groups, respectively. The pregnancy rate for grade 1 embryos was 56.0 per cent and for grade 2 embryos 36.1 per cent (P < 0.01). The breed of recipient, weekday of transfer, operator and condition score had no effect on pregnancy rate. The maiden heifers had a higher pregnancy rate (54.2 per cent) than the cows (46.2 per cent). The mean plasma progesterone concentrations of the pregnant and non-pregnant groups on day 6 were 6.7 ng/ml and 6.6 ng/ml, respectively, and 7.6 ng/ml in both groups on day 7.

Evaluation of Crestar, a synthetic progestogen regime, for synchronising oestrus in maiden heifers used as recipients of embryo transfers.

Crestar consists of an ear implant containing 3 mg norgestomet combined with an intramuscular injection of 3 mg norgestomet and 5 mg oestradiol valerate. Its effectiveness for synchronising oestrus in embryo transfer recipients was evaluated in comparison with a progesterone-releasing intravaginal device (PRID) and prostaglandin regimen, using 334 maiden heifers. The treatment devices were inserted on day 1, prostaglandin was administered to the PRID-treated heifers on day 8 and the devices were removed on day 10. High proportions of the heifers were seen in oestrus within five days of the removal of the devices after both the PRID prostaglandin (90.4 per cent) and Crestar (86.2 per cent) treatments. The interval from the removal of the device to the onset of oestrus was significantly shorter for Crestar than for PRID prostaglandin-treated heifers (45 vs 51 hours, P < 0.001), and the duration of oestrus was significantly longer (13 vs 10 hours, P < 0.01). The PRID prostaglandin treatment resulted in a higher degree of synchrony than the Crestar treatment (74.1 per cent vs 61.8 per cent, P < 0.05). There were no significant differences between the treatments in the proportions of the heifers selected as embryo transfer recipients or in the proportions which became pregnant after embryo transfer.

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.