The effects of season (January–March = I; April–June = II; July–September = III; October–December = IV) and ovarian status (freshly ovulated, follicular, luteal, intermediate, or inactive) on the efficiency of the in vitro production of domestic cat embryos were evaluated. Ovaries and testes from cats with access to daylight were collected at local veterinary clinics. A total of 6843 cumulus-oocyte complexes (COCs) were recovered from 363 pairs of ovaries, matured in TCM 199 supplemented with BSA and gonadotropins (IVM), fertilized with epididymal sperm in a medium based on Tyrode albumin lactate pyruvate (IVF), and cultured in synthetic oviduct fluid (SOF) medium supplemented with 10% estrous cow serum (ECS) and essential and nonessential amino acids. The proportion of freshly ovulated, follicular, or luteal ovaries was higher (P < 0.05) in seasons II (64.4%) and III (60.5%) than in seasons I (42.0%) and IV (30.6%). The average number of COCs recovered per donor was not influenced by season. After IVM/IVF, cleavage rates (Day 2) were significantly higher (P < 0.05) in seasons II (mean ± SEM: 53.1% ± 1.9%) and III (54.6% ± 2.8%) than in seasons I (48.4% ± 1.4%) and IV (44.9% ± 3.0%). Blastocyst rates on Day 6 were similar in seasons I (25.3% ± 1.3%), II (28.2% ± 1.5%), and III (29.6% ± 2.3%) but were significantly lower (P < 0.01) in season IV (18.6% ± 2.4%). The corresponding blastocyst rates on Day 8 were 28.9% ± 1.3%, 33.7% ± 1.6%, 37.9% ± 2.3%, and 23.6% ± 2.6%. In addition, we found a significant effect (P < 0.05) of ovary type; luteal, follicular, and intermediate ovaries yielding a higher proportion of developmentally competent oocytes than did freshly ovulated and inactive ovaries. These data show that the culture system used in our study supports development of IVM/IVF cat oocytes to blastocysts at a higher rate than those obtained with other methods. Although embryos could be produced throughout the year, the efficiency was significantly affected by season and ovary type.
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