Bovine embryos were produced in vitro using a 2 x 2 design of modified medium (KSOM or SOF) and oxygen concentration (5% or 20%). Day 7 blastocysts were transferred in bulk (n = 11, on average) to recipient heifers and recovered non-surgically at Day 14. In two replications of a Latin square, eight heifers received embryos from each combination of factors. Recovered embryos were evaluated for trophoblast length and width, as well as the presence and diameter of an embryonic disc (ED). An ED was detected in a higher percentage of embryos that had been cultured in KSOM than SOF (72% v. 46%, respectively; P < 0.05). The aim of a second series of experiments was to associate Day 14 morphology with subsequent developmental capacity. In vitro-produced blastocysts were transferred (n = 17-20) on Day 7 to each of eight heifers and recovered at Day 14. Thirty-eight blastocysts were retransferred to heifers following morphological evaluation. Embryos in which an ED with no signs of degeneration had been detected maintained more pregnancies than other embryos in which an ED had either shown signs of degeneration or had not been detected (5/8 v. 2/30, respectively; P < 0.01). Further investigation into ED integrity at the elongating stage may contribute to our understanding of pregnancy establishment and maintenance.

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Bos indicus embryos have a lower survival rate compared with Bos taurus after cryopreservation. It has been hypothesized that the lower survival rate is due to higher intracellular lipid content. The objective of this study was to determine if there is a difference in intracellular lipid content of oocytes from mature purebred Brahman and Angus cows. Donor females used in the study were maintained on pasture prior to the onset of the experiment and on a grain-supplemented hay ration during the study. Oocytes were collected from cows at 30-day intervals (3 aspirations/donor) by transvaginal ultrasound-guided oocyte aspirations (TUGA). Mature oocytes were evaluated using a sucrose step gradient procedure and Nile Red staining. FSH (Folltropin-V®; Bioniche Animal Health, Beltsville, Ontario, Canada) administration began on Day 4 of the estrous cycle (estrus = Day 0) twice daily for 3 days in decreasing doses (Brahman 232 mg and Angus 280 mg total), and on Day 8 oocytes were recovered. The mean number of follicles aspirated/donor and oocytes recovered/donor were 20 and 16.61 oocytes for the Brahman donors (n = 6) and 12 follicles and 7.06 oocytes/donor for the Angus donors (n = 10). Oocytes (individual donor basis) were then incubated in TCM-199 supplemented with 10% fetal bovine serum + bLH and bFSH (0.01 U mL−1) at 38.5°C. After 20 h, mature oocytes were denuded by vortexing for 3 min in HEPS + BSA (4 mg mL−1). Buoyancy was tested for individual mature oocytes using a sucrose step density gradient column prepared with sucrose and Dulbecco's PBS. Results from the sucrose gradients ranged from 23% sucrose (indicating high lipids) to 35% sucrose (indicating lower lipids). Oocytes recovered from the sucrose were fixed for 24 h in paraformaldehyde for evaluation with Nile Red stain. Oocytes were stained for 24 h, and then placed in Prolong® Gold (Invitrogen, Carlsbad, CA, USA) and evaluated under fluorescence. Oocytes images were evaluated using a Scion Image camera (Scion Corp., Frederick, MD, USA) to calculate mean (± SE) Nile Red units (NRU) (higher NRU = higher lipid content). Treatment groups were analyzed using one-way ANOVA. In summary, Brahman M-II oocytes had significantly lower (P ≤ 0.05) buoyant density, with a significantly higher mean NRU score, when compared with oocytes harvested from Angus donors (Table 1). Based on these results, Brahman oocytes have a higher intracellular lipid content then Angus oocytes. Table 1.Percent sucrose levels and Nile Red units for bovine oocytes from three replicates per donor