133 Test of minimum-intervention protocols for optimizing in vitro embryo production in bison

Abstract

The study was done to determine whether minimal handling protocols for ovarian synchronization and ovarian superstimulation may be used to increase in vitro embryo production in bison. Ultrasound-guided cumulus-oocyte complex (COC) collection was done in a group of bison (n = 23; random start) during the anovulatory season to synchronize new follicular wave emergence. The COC were classified morphologically (compact-good and -regular, expanded, denuded, degenerate) but not processed further. At the time of COC collection (Day 0), bison were assigned randomly to 3 groups and given 5 mL of saline IM (non-superstimulated controls; n = 11), 10 Armour units of pFSH (Antrin R10, Kyoritsu Seiyaku Corp., Tokyo, Japan) in 5 mL of saline IM once per day from Day 0 to 2 (regular FSH; n = 5), or 30 armour units of a sustained-release form of pFSH (Antrin R10Al, Kyoritsu Seiyaku Corp.) in 5 mL of saline SC on Day 0 (long-acting FSH; n = 7). On Day 4, a second COC collection was performed. Only compact COC were processed. The COC were matured in vitro for 25 to 28 h at 38.8°C, fertilized (2 × 10⁶ sperm mL⁻¹) and co-incubated at 38.8°C in 5% CO₂ for 18 h. Presumptive zygotes were denuded and cultured at 38.8°C in 5% O₂, 5% CO₂ and 90% N₂. Nominal data were compared by t-test and analysis of variance. Binomial data were compared among groups by chi-squared. There was no difference between the first (random) COC collection (n = 23) and second collection (n = 11 non-superstimulated controls) in the total number of follicles detected, but the distribution among size categories (3-4, 4-8, and >8 mm) differed, i.e. fewer in the 3 to 4 mm category at the time of the second COC collection (12.2 ± 1.0 v. 8.1 ± 1.4; P < 0.05). In the nonstimulated control group, there were no differences between the first and second COC collections in the number of follicles aspirated (12.7 ± 1.0 v. 10.4 ± 1.5), number of COC collected (7.7 ± 0.9 v. 5.3 ± 1.3), or in the categorical distribution of COC. At the second COC collection, the number of follicles in the >8 mm category was greater in the regular FSH group than in the control or long-acting FSH groups (2.8 ± 0.5 v. 1.1 ± 0.3, and 1.9 ± 0.4, respectively; P < 0.05), but no differences were detected in the number of follicles aspirated, COC collected, or in the categorical distribution of COC. The cleavage rate (of total oocytes submitted to in vitro maturation), recorded 2 days after IVF, was higher in the control group than in either the regular FSH or long-acting FSH groups [25/35 (71.4%), 7/28 (25.0%), 8/35 (22.8%); P < 0.0001]. The freezable embryo production rate, recorded 7 days after IVF, was greater in the control group than in the regular FSH or long-acting FSH groups [19/35 (54.3%), 5/28 (17.9%), 5/35 (14.3%); P < 0.01]. In conclusion, minimal-handling interventions used in the present study to increase embryo production in bison were not effective, likely as a result of the timing, frequency, and duration of superstimulation. A random start resulted in greater COC collection than collection 4 days after ovarian synchronization, and embryo production rates were greater in non-superstimulated bison.

This work was supported by Parks Canada and Saskatchewan ADF. Antrin products donated by Kyoritsu Seiyaku Corp., Japan.