133 EVALUATION OF OOCYTE DONOR SOURCE AND CULTURE MEDIUM ON DOMESTIC CAT EMBRYO DEVELOPMENT RATES

Abstract

The use of assisted reproductive technology (ART), including in vitro maturation (IVM) and embryo culture, is well established in several species, including canine and feline culture systems. Embryo production conditions tend to be specific for each species and prepared in unique formulations by laboratory. However, the increasing numbers of commercially available media allows for new comparisons in companion animal systems. Therefore, a goal of this study was to compare the development rates of feline parthenotes cultured in a commercially available bovine embryo culture medium with those cultured in a published 3-step domestic cat-specific system. In addition, the source of ovaries utilised for oocyte retrieval was evaluated as a factor in development rates. Ovaries from 2 locations (L1 and L2) were collected on the same day, and harvested oocytes were held in meiotic arrest medium containing 25 μM roscovitine for 14 to 18 h. Oocytes were incubated in maturation medium for 24 h before cumulus cell removal with vigorous pipetting in 0.4% hyaluronidase, and a subset of each group was fixed and stained to determine meiotic maturation rates (n = 76 and 55 for L1 and L2, respectively). Following activation (day 0) by a single course of three 50-μs electric pulses at 1.2 kV cm^–1 in 0.3 M mannitol, 0.1 mM CaCl₂, and 0.1 mM MgSO₄, parthenotes from each source were randomly divided to culture medium treatment of Bovine Evolve medium (Zenith Biotech, Guilford, CT, USA) with 4 mg mL^–1 BSA (n = 209) or IVC-1 medium n = 269; (Pope et al. 2009 Theriogenology 71, 864–871), each containing 10 μg mL^–1 cycloheximide and 7.5 μg mL^–1 cytochalasin B. After a 4-h activation treatment, parthenotes were moved to culture media without cycloheximide and cytochalasin B for embryo development. All parthenotes in IVC-1 medium were moved to IVC-1a medium on day 2. On day 5, both sets of parthenotes were moved to culture media containing 10% heat-inactivated FBS instead of BSA. On day 7, all parthenotes were fixed and stained with Hoechst to determine cell number. No differences were seen in maturation rates between L1 and L2 (56.3 ± 9.5 v. 54.7 ± 9.5, respectively). However, cleavage rates tended to differ, and proportion of embryos greater than 64 cells was different (60.7 ± 5.8 v. 78.3 ± 5.8, P = 0.056 and 3.0 ± 3.1 v. 19.7 ± 3.1, P < 0.005; respectively). We hypothesised that the physical condition of the ovary donors may have affected development rates because cats from L1 tended to be feral animals, whereas cats from L2 were mostly privately owned. Bovine Evolve was similar to IVC-1 medium for cleavage, 32-cell, and 64-cell development rates (74.2 ± 6.7 v. 64.8 ± 6.7; 24.0 ± 7.5 v. 31.8 ± 7.5; 10.7 ± 4.8 v. 12.0 ± 4.8, respectively; P > 0.05). These results indicate that commercially available culture medium can support in vitro development, even if the commercial medium is developed for a different species, but that source of cat ovaries should be considered in feline ART.