190 Effect of TCM-199 and synthetic oviductal fluid medium supplemented with varying hormone concentrations on in vitro maturation of canine oocytes

Abstract

In vitro oocyte maturation (IVM) in the domestic canine is yet to be optimized, with low rates of cumulus-oocyte complexes (COCs) reaching MII. This limits the progression of assisted reproductive technologies, which could benefit breeding programs for assistance dogs and endangered Canidae. Canine oocyte maturation differs from that in other mammals, with the ovulation of a COC in the germinal vesicle stage and nuclear maturation occurring in the oviduct. Because of this, the environment in which a canine COC matures is unlike that of other mammals, meaning that IVM protocols cannot be readily adapted. The aim of the current work was to determine (1) the effects of varying concentrations of FSH, human chorionic gonadotrophin (hCG), and oestradiol (E2) during IVM on meiotic resumption and nuclear maturation of canine COCs; and (2) the optimal medium base, either synthetic oviductal fluid (SOF) or tissue culture medium-199 (TCM). Reproductive tracts of bitches (6 months to 7 years of age) were collected from veterinary clinics within 2 h of routine spaying. Ovaries were sliced using a scalpel blade, releasing the COCs into aspiration medium. The COCs were randomly allocated to a maturation medium consisting of one of the hormones at two concentrations (FSH: 5 or 10 µg mL⁻¹; hCG: 5 or 10 IU mL⁻¹; E2: 1 or 5 µg mL⁻¹) and for both SOF and TCM base. Each hormone was tested individually for a replicate of eight animals per hormone (total of 12 experimental groups; 24 animals). The COCs were cultured for 72 h in their allocated medium and then denuded and stained with Hoechst 33258. Fluorescence microscopy was used to determine nuclear maturation stage. Nuclear maturation rates to MII were analysed using a general linear model with pairwise comparison (SPSS version 25; SPSS Inc./IBM Corp.) with each individual animal acting as a replicate. Canine COCs matured in a SOF-based media had higher rates of meiotic resumption (MI and MII) (SOF: 38.68%, n = 515; TCM: 25.78%, n = 542; P < 0.05) and number reaching MII (SOF: 7.54%; TCM: 4.39%; P < 0.05) compared with TCM-based medium. Resumption of meiosis and nuclear maturation to MII did not differ between media with differing E2 or hCG concentrations. The use of FSH at 10 µg mL⁻¹ in SOF medium decreased resumption of meiosis (8.57%) and MII rates (0%) compared with 5 µg mL⁻¹ FSH in SOF (29.41% and 3.92%, respectively; P < 0.05). In summary, our data indicated that higher concentrations of FSH during IVM have a negative effect on meiotic resumption and maturation to MII, whereas canine COCs resume meiosis and mature to MII in higher rates in a SOF-based medium compared with a TCM base. An IVM medium that replicates the in vivo environment in which canine COCs mature is beneficial. However, rates of IVM canine oocytes reaching maturity are low, signifying that future research must investigate a greater range of hormone concentrations and combinations to better mimic in vivo conditions to assess the possible benefits for canine IVM.