In vitro fertilization in domestic and non-domestic cats including sequences of early nuclear events, development in vitro, cryopreservation and successful intra- and interspecies embryo transfer.

The domestic cat may be used as a model for developing assisted reproduction techniques including in vitro fertilization (IVF), embryo culture, cryopreservation and embryo transfer (ET) for application to threatened and endangered species of non-domestic cats. Interoestrous domestic cats were injected with a total of 1.0-6.0 mg follicle-stimulating hormone (FSH) daily for 4 days and with 100 iu human chorionic gonadotrophin (hCG) on day 5. Follicular oocytes recovered at 26 +/- 1 h after hCG were co-incubated for 4-6 h at 38 degrees C in 5% CO2 with spermatozoa (1-2 x 10(5) motile spermatozoa ml-1) collected by artificial vagina. To determine the timing of sperm penetration and early fertilization events in vitro, oocytes were fixed and examined at intervals from 0.5 to 10 h after sperm exposure. The penetration rate of metaphase II (MII) oocytes at 0.5-3 h was equivalent to that at 3-6 h (95 versus 96%). Second polar body extrusion, pronuclear formation and apposition were observed at 2, 6-8 and 10 h, respectively. Simple (Tyrode's) and complex (F-10, M-199 and CMRL-1066) culture media with 10% fetal calf serum were compared for their ability to support development to the morula or blastocyst stage during culture periods of 96-168 h after IVF. The average number of cells per embryo was similar (P > 0.05) in the various media at each interval except that CMRL-1066 reduced (P < 0.05) development at 96 h if it was used before the two-cell stage. In F-10, neither the presence of intact cumulus cells nor changing to fresh F-10 medium at 48 h affected development at 96 h. Blastocyst development at 168 h was similar in both F-10 (18%) and Tyrode's (26%). To determine developmental ability in vivo, IVF-derived embryos (n = 586) were transferred at 96 or 120 h to recipients (n = 49) that had undergone synchronous oocyte recovery as donors. The percentage of recipients producing kittens after transfer of embryos cultured for 96 or 120 h in F-10 was 31 and 25, respectively, compared with 55% of 120 h recipients receiving embryos cultured in M-199 or Tyrode's. Overall, more pregnancies occurred following transfer of > or = 12 embryos (11/26) than if < 12 embryos were transferred (6/23).(ABSTRACT TRUNCATED AT 400 WORDS)