Culture medium and protein supplementation influence in vitro fertilization and embryo development in the domestic cat

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Abstract
The influence of culture medium and protein supplements on in vitro fertilization (IVF) and morula‐to‐blastocyst development in culture was examined in the domestic cat. In Study I, follicular oocytes were fertilized and cultured in 1) modified Krebs Ringer bicarbonate (mKRB); 2) modified Tyrode's solution (TALP) without phosphate or glucose; or 3) Ham's F10. All media contained bovine serum albumin (BSA). Fertilization rates were similar (P>.05) among mKRB (75.0%), TALP (70.6%), and Ham's F10 (80.0%) treatments. Compared to TALP (77.8%), more (P<.05) embryos in Ham's F10 (95.0%) developed to the morula stage; development of mKRB embryos (88.9%) was intermediate and not different (P>.05). Study II evaluated the effects of protein availability and type on IVF and embryo growth. Ham's F10 was supplemented with polyvinylalcohol (PVA, 2 mg/ml), BSA (4 mg/ml), fetal calf serum (FCS, 5%), or estrous cat serum (ECS, 5%) and used to fertilize and culture embryos. Fertilization was enhanced (P<.05) using either FCS (84.0%) or ECS (85.2%) compared to PVA (67.3%). Oocytes exposed to BSA fertilized at a rate (76.1%) similar (P>.05) to other treatments. Embryos exposed to all four treatment groups (PVA, 82.8%; BSA, 82.8%; FCS, 92.9%; or ECS, 97.8%) were equally capable (P>.05) of becoming morulae. However, more FCS‐ or ECS‐supplemented morulae continued to the early blastocyst stage (30.8%, 22.2%, respectively, P<.05) than PVA‐ (10.3%) or BSA‐ (13.8%) exposed morulae. In the domestic cat IVF system, the type of medium and protein supplement used appears to have a greater impact on embryo development in vitro than on fertilization. There also is a morula‐to‐blastocyst developmental block for cat embryos resulting from IVF which is partially circumvented by adding serum to the culture medium. Ham's F10 containing FCS or ECS produces the highest incidence of fertilization (∼85%), and ∼2‐fold more of these embryos develop in culture to blastocysts compared to embryos supplemented with PVA or BSA.