Individual variation for in vitro fertilization success in dairy bulls

Sex-sorting of spermatozoa affects developmental competence of in vitro fertilized oocytes in a bull-dependent manner

The aim of the present study was to clarify if flow-cytometric sex-sorting of bovine sperm affected in vitro blastocyst production in different bulls, either in terms of its ability to fertilize the oocyte or by interfering with post-fertilization embryo development. We performed in vitro fertilization (IVF) using both commercially available frozen-thawed X-sorted and non-sorted sperm of 4 Holstein bulls at 3 concentrations (1 × 10⁶, 2 × 10⁶, and 5 × 10⁶ sperm/ml). When fertilization rates were compared, a variation in fertilization rates among different sperm concentrations was detected in 2 bulls, with similar results for X-sorted and non-sorted sperm. However, we found no evidence that the fertilization rates were affected by the sorting process. To investigate effects on embryo development, we determined the optimum sperm concentration for IVF in each bull, which resulted in similar fertilization rates among bulls. We next performed IVF using both X-sorted and non-sorted sperm of the 4 bulls at their optimum sperm concentration and compared in vitro embryo development. Cleavage rates with X-sorted sperm were similar to their non-sorted counterparts. However, significantly reduced blastocyst development was associated with the use of X-sorted sperm in one bull, whereas in the other three bulls, blastocyst development after IVF with X-sorted and non-sorted sperm was similar. In conclusion, in our system, X-sorting affects in vitro blastocyst production by reducing the developmental competence of fertilized oocytes rather than affecting the fertilization ability of the sperm. However, the occurrence of this phenomenon varies among bulls.

Potential use of ovum pick-up for embryo production and breeding in cattle

The efficacy of transvaginal ultrasound-guided puncturing of ovarian follicles for collecting immature oocytes in cattle was studied. Three experiments were conducted to examine the effects of puncturing on follicle recruitment and on the number of oocytes collected. Puncture sessions were executed twice weekly at regular intervals of 3 and 4 d respectively. The oocytes were matured, fertilized and allowed to develop in vitro and the number of transferable embryos was recorded. The health of the cows was checked daily. In Experiment 1, dairy cows (n=10) were punctured over a period of 5 mo, and the collected oocytes were fertilized with the semen of 1 bull. In Experiment 2, oocytes were collected from one 12 year old high pedigree dairy cow and an one month pregnant cow were punctured. The oocytes of the old cow were fertilized with semen of 8 different bulls. In Experiment 3, beef cows (n=6) were punctured over a 2 mo period and the semen of 2 different bulls of the same breed was used to fertilize the oocytes from 3 of these cows. In Experiment 1, 14.5 +/- 0.4 (mean +/- SEM) follicles were punctured per session, and 8.0 +/- 0.3 (mean +/- SEM) oocytes were recovered. A mean of 16% of the oocytes developed into transferable embryos with a pregnancy rate of 40%. The results did not differ between the months of the experiments, indicating that the transvaginal puncturing method can be used successfully over a 5 mo period. No detrimental effects were observed after clinical and post mortem examinations, nor did breed, age or reproductive status appear to affect the results. However, large differences were observed between individual cows and between cow/bull combinations.

Effects of oocyte quality, semen donor and embryo co-culture system on the efficiency of blastocyst production in goats

The aim of the study was to determine whether the selection of immature oocytes by a combination of cumulus-oocyte-complexes (COCs) morphology and staining with brilliant cresyl blue (BCB) would be helpful in selecting developmentally competent oocytes, and thereby increase the efficiency of blastocyst production from ovarian oocytes of FSH-primed, adult goats. In a second experiment the interaction between oocyte quality and semen donor was assessed. In a third experiment the usefulness of Vero cells for co-culture with goat embryos was investigated. In the pool of morphologically normal COCs recovered from ovaries following slicing (21.9+/-11.0), the mean rate of COCs classified as BCB+ was 85.6%, and the BCB- was approximately 11%. Oocytes classified as grade 1 and BCB+ exhibited the highest developmental competence (P<0.001) after in vitro maturation and fertilization compared with oocytes of grade 1 BCB- and grade 2 BCB+ or BCB-. There were no significant differences in developmental competence in grade 2 oocytes, regardless of BCB coloration. No significant differences in embryo cleavage and blastocyst formation rates among three bucks were observed when morphologically normal, BCB+ oocytes were used. For all tested bucks, differences in embryo production efficiency were related only to the oocyte quality. Similar blastocyst rates were developed from embryos co-cultured with goat oviduct epithelial cells (34.3%) and with Vero cells (33.3%). These results show that the most important criterion for selection of COCs before maturation is the visual assessment of morphological features. Staining with BCB of COCs recovered from adult goats does not enhance efficiency of selection of developmentally competent oocytes for IVF.

Relationship between embryo development in vitro and 56-day nonreturn rates of cows inseminated with frozen-thawed semen from dairy bulls

Frozen-thawed bull semen with > 50% post-thaw motility from 40 batches (21 bulls, 2 consecutive ejaculates per batch) was used for fertilization (IVF) and embryo development in vitro to assess the relationship between field and laboratory fertility using a retrospective approach. Each frozen batch was tested in 3 or 4 replicates with 30 oocytes per replicate. Field fertility, quantified as the 56-d nonreturn rate and based on 89 to 441 artificial inseminations per frozen batch, ranged between 46.2 and 74.8%. The cleavage and blastocyst rates after IVF varied from 29.0 to 81.9% and from 1.8 to 32.0%, respectively, with significant differences among frozen batches. Rates of cleavage and blastocyst formation were significantly related to the nonreturn rate (r = 0.59, P < 0.001; r = 0.35, P < 0.05, respectively). The interaction between cleavage and blastocyst rate was 0.69 (P < 0.001). Significant variations (P < 0.05) among frozen semen batches within 15 bulls with >/= 2 different semen batches were found for the nonreturn rate (13.3%) of 2 bulls, for cleavage rates (26.7%) in 4 bulls and for blastocyst rates (20.0%) in 3 bulls. Significant differences (P < 0.05) among replicates within the 40 frozen semen batches were only found in 3 batches (7.5%) for the cleavage rate and in 7 batches (17.5%) for blastocyst rate. Overall, bull and frozen semen batch were the greatest sources of variation in the cleavage rate (30.6 and 29.4%, respectively), while testing date was the greatest source of variation in the blastocyst development rate (21.7%). The results indicated that in vitro fertilization and, to a lesser extent, culture to the blastocyst stage could be useful in estimating the potential fertilizing ability of frozen-thawed semen from dairy bulls.

Development of bovine embryos after in vitro fertilization of oocytes with flow cytometrically sorted, stained and unsorted sperm from different bulls

The objective of this study was to determine the effect of staining bovine sperm, with or without flow cytometry, on in vitro fertilization of bovine oocytes and blastocyst development. Bovine oocytes (n=4273) were fertilized with frozen-thawed sperm from three bulls that was: stained with Hoechst 33342 and sorted (into X- or Y-chromosome-bearing sperm) with flow cytometry; stained but not sorted; and not stained or sorted (Control). Oocytes, aspirated from slaughterhouse ovaries, were matured in TCM199 (supplemented with 10% fetal calf serum and 15 ng FSH, 1.0 microg LH, 1.0 microg E2/ml) for 22-24h at 39 degrees C in 5% CO(2) in air with maximum humidity. Presumptive zygotes were removed from culture and placed in chemically defined medium (CDM-1) 6-7h after insemination and cultured for 65-66h. Embryos that had cleaved by 72h post-insemination were cultured an additional 96h in CDM-2 containing 0.12 IU insulin/ml. Cleavage and blastocyst rates per oocyte inseminated were recorded on Day 3 and Days 7-8 after insemination, respectively. There was no significant difference in blastocyst rate among the three types of sperm; however, cleavage rates with stained and sorted sperm (53.1%) and unsorted, stained sperm (59.9%) were lower (P<0.05) than Control sperm (69.7%). Furthermore, there were significant differences due to semen from different bulls in cleavage and blastocyst rates.