96 Hyaluronan in transfer medium: is it able to support growth of bovine embryos while transported for field embryo transfer?

Hyaluronic acid (hyaluronan) is crucial for embryo attachment and implantation (Stojkovic et al. 2002 Reproduction 124, 141–153). We hypothesized that supplementing embryo transfer medium with hyaluronan would improve pregnancy rates and reduce early embryonic mortality. However, to transfer the in vitro-produced embryos to the farms, it is often necessary to carry them far from the laboratory. Thus, the present study was conducted to check whether the hyaluronan-supplemented transfer medium could maintain the viability and growth of in vitro-produced bovine embryos during transportation from laboratory to farm. A total of 297 grade 1 in vitro-produced embryos (blastocysts and expanded blastocysts) were randomly allocated to five groups: commercial medium A (n = 77), commercial medium B (n = 66), in-house medium without hyaluronan (n = 53), and in-house medium with two different concentrations of hyaluronan (Hyl.-A, 0.5%, n = 51; Hyl.-B, 0.025%, n = 47). Day 7 embryos after IVF were loaded into 1.2-mL tubes containing 500 µL of the respective transfer medium overlaid with 300 µL of embryo-tested oil and incubated at 38.5°C for 24 h. The embryos produced in each in vitro embryo production cycle were randomly allocated to the different transfer media indicated above, and the experiment was conducted over 4 months. Post-incubation, embryo hatching rates were assessed. Descriptive statistics were calculated for hatching rates, and data are presented as mean ± s.e.m. Statistical analysis was performed using ANOVA followed by Tukey’s post-hoc test for pairwise comparisons to assess variance between group means. The Hyl.-A medium showed a higher hatching rate (70.3 ± 7.6%) compared with the commercial medium A (69.1 ± 6.5%), commercial medium B (46.0 ± 9.2%), in-house medium without hyaluronan (60.1 ± 10.6%), and Hyl.-B medium (56.3 ± 5.4%); P-values were 0.99, 0.29, 0.92, and 0.77, respectively. The hatching rate in the Hyl.-B medium was higher than commercial medium B (P = 0.99), but lower than in-house medium without Hyaluronan and commercial medium A (P-values were 0.74 and 0.89, respectively). The in-house medium without hyaluronan showed a higher hatching rate than commercial medium B (P = 0.92) but lower than commercial medium A (P = 0.29). The hatching rate in commercial medium A was higher than in commercial medium B (P = 0.29). These findings suggest that transfer medium supplemented with hyaluronan, particularly at a concentration of 0.5%, can support and maintain embryo viability and growth during transport, potentially enhancing the efficiency of using the medium for field embryo transfers.