RESUMO
The average number of oocytes collected by ovum pick up (OPU) from Bos taurus cattle is <8 per live donor. The objective was to determine whether development of small numbers of cattle embryos (produced by OPU and IVF), was enhanced by including "helper" embryos, produced from abbatoir-derived oocytes and embedded in agarose. Oocytes were from abbatoir-derived ovaries (Experiments 1 and 2) or OPU of elite donors (Experiment 3). In Experiment 1, cleaved embryos (2-8 cells), were randomly allocated. Controls were groups of 1, 3, 5, 10, and 20 cleaved embryos cultured in 50 µL serum-free SOF, whereas treatments were groups of 1, 3, and 5 embryos freely cultured along with helpers in groups of either 9, 7 or 5 embedded in agarose per droplet. Therefore, there were 10 cleaved embryos per droplet in combinations of 1 + 9, 3 + 7 or 5 + 5 (free + helper), respectively. There was an increase in the progression to blastocyst for 1-5 embryos per droplet, compared to 10 and 20 (6.6-24.2% vs. 39.2-43.3%, P < 0.05). For the tested free embryos, those cultured with helpers had increased blastocyst development over their control counterparts (39.3-49.5% vs. 6.6-24.2%, P < 0.05). When the number of embryos per droplet was 10 or 20, blastocyst percentage was similar (39.2-49.5%, P > 0.05). In Experiment 2, addition of an agarose chip to the culture medium did not significantly affect development to the blastocyst stage. In Experiment 3, after fertilizing OPU oocytes with sorted X-sperm, a group of three cleaved embryos were cultured in a droplet with either seven helpers (3 + 7) or alone (3 + 0). Blastocyst development of OPU oocytes in the 3 + 7 group was 37.1%, higher than that in the 3 + 0 group (11.8%, P < 0.05). In conclusion, limited numbers of OPU/IVF oocytes had competent development when cultured with helpers (embedded in agarose to provide physical separation).
