Embryo biopsies for genomic selection in tropical dairy cattle

Genomic selection has transformed the livestock industry, enabling early-life selection of animals. Biopsy sampling of pre-implantation embryos has been described since 1968. However, it was only after 2010, with the advancement of molecular biology techniques such as whole genomic amplification and SNP Chips, that next-generation sequencing became commercially available for bovine embryos. It is now possible to make decisions about which embryos to transfer not only based on recipients' availability or embryo morphology but also on genomic estimates. This technology can be implemented for a wide spectrum of applications in livestock. In this review, we discuss the use of embryo biopsy for genomic selection and share our experience with Gir and Girolando Brazilian breeding programs, as well as future goals for implementing it in Brazilian bovine in vitro embryo production practices.

Variations in bovine embryo production between individual donors for OPU-IVF are closely related to glutathione concentrations in oocytes during in vitro maturation

Variations in embryo production between individual oocyte donors represent a serious problem in cattle production, when implementing ovum pick-up (OPU) and in vitro maturation (IVM) of oocytes. However, the precise cause of this problem is unknown. Here, we aimed to investigate the relationship between the glutathione (GSH) concentration in IVM oocytes and embryo development to explore a potential cause of the variations between individual donors. First, we found a high positive correlation (r = 0.80) between the GSH concentration in IVM oocytes and the blastocyst development rate of oocytes collected in the same OPU session for each donor (N = 11). Second, we selected two donors with significantly different blastocyst development rates. In samples from these donors, we examined the dynamics of oocytes GSH concentrations, and the gene expression of the glutathione synthetase (GSS) and glutathione peroxidase (GPX) genes in cumulus-oocyte complexes (COCs) during IVM. At 0 and 24 h after IVM, oocytes from the donor with the highest blastocyst development rate (high donor) exhibited significantly higher oocyte GSH concentrations than oocytes from the donor with the lowest blastocyst development rate (low donor, P < 0.05). At 4 and 9 h after IVM, GSH concentrations gradually decreased in oocytes from both donors. The GSS expression levels at 0, 4, and 9 h after IVM were significantly higher in COCs from the high donor than in COCs from the low donor (P < 0.05). The expression levels of GPX, a marker of oxidative stress, at 4 and 9 h after IVM were significantly higher in COCs from the low donor than in COCs from the high donor. Finally, adding cysteine into the IVM medium of oocytes collected in the same OPU session from the low donor significantly increased oocytes GSH concentrations and blastocyst development rates (P < 0.05). In conclusion, we showed that oocyte GSH concentrations were related to the differences in embryo development between individual donors. Our results suggested that increasing the GSH concentration in IVM oocytes could reduce the individual differences in embryo production between donors.

Estradiol benzoate treatment before ovum pick-up increases the number of good quality oocytes retrieved and improves the production of transferable embryos in Japanese Black cattle

The aim of this study was to evaluate the efficacy of treatment with estradiol benzoate (EB) at luteal phase prior to the ovum pick-up (OPU) during in vitro production of transferable embryos in Japanese Black cattle. A total of 15 cows were used as oocyte donors for OPU. Of those, four donors were randomly allocated (three times) into each of two treatment groups as a crossover study, and OPU session was carried out six times per one donor. Another eleven donors were used in a paired difference test by one crossover trial. Donors in the control group received no hormonal treatment; whereas, donors in the EB group received 1 mg of EB as a single injection. First, we observed dynamics of ovarian follicles and emergence of follicular wave after EB injection using transrectal ultrasonography. The number and proportion of medium-sized follicles with 4 to 6 mm in diameter increased gradually and achieved a peak at 72 and 96 hours after EB injection. The OPU was performed 88 hours after EB injection. The EB-treated donors had a higher proportion of follicles with 4 to 6 mm in diameters at the time of OPU. The stimulation with EB significantly increased the numbers of follicles aspirated, and the good quality cumulus-oocyte complexes per OPU. Furthermore, in the EB group, the percentage of transferable blastocysts was significantly greater than that in the control group (P<0.05). In conclusion, a single EB injection before OPU increases the number of medium-sized follicles and can produce more transferable embryos.

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Efficacy of one-shot treatment with 1 mg of estradiol benzoate (EB) at luteal phase prior to the ovum pick-up (OPU) for in vitro production of transferable embryos in Japanese Black cattle was investigated.

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The donors had a higher proportion of follicles with 4 to 6 mm in diameter at 72 and 96 hours after EB i.m. injection.

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The stimulation with EB before OPU increased significantly the number of good quality cumulus-oocyte complexes, and the percentage of blastocysts or transferable embryos after in vitro fertilization.

Effective embryo production from Holstein cows treated with gonadotropin-releasing hormone during early lactation

The low efficiency of embryo production in Holstein cows during early lactation presents many challenges for animal production. To improve its efficiency, the outcomes of single GnRH injections 48 hours before each of three cycles of ovum pick up (OPU; weeks 2, 4, and 6) were compared with three cycles of unstimulated OPU (controls; weeks 1, 3, and 5) in 35 Holstein cows during 6 weeks of early lactation (40-80 days postpartum). More total follicle numbers (19.5 vs. 16.0; P < 0.05) but fewer dominant follicles (0.5 vs. 1.4; P < 0.01) were observed by ultrasound, and more cumulus-oocyte complexes were collected in a single OPU in the treatment cycles compared with controls (15.3 vs. 11.5; P < 0.05). The numbers of morphologically "good" cumulus-oocyte complexes graded A and B in the stimulated OPUs were significantly greater than in controls (2.8 vs. 1.7 and 5.8 vs. 4.2, respectively; P < 0.05). Significantly, more oocytes stained positively with brilliant cresyl blue after GnRH treatment compared with the control cycles (13.7 vs. 9.6; P < 0.05). After in vitro fertilization, embryos in the treatment cycles had improved development (P < 0.01) during each developmental stage compared with the controls (9.0 vs. 6.2 two-cell embryos; 4.7 vs. 3.0 four-cell embryos; 3.3 vs. 2.0 morulae; and 3.0 vs. 1.7 blastocysts, respectively). Moreover, there was no significant difference in pregnancy rate of the recipient cows after embryo transfer (57.1% vs. 42.1%; P > 0.05) no matter if the embryos came from the GnRH-treated cycles or not. Thus, GnRH-stimulated OPUs improved the efficiency of embryo production in Holstein cows during early lactation. This novel method for in vitro embryo production should benefit the dairy industry.