IN-VIVO EMBRYOGENESIS, EMBRYO MIGRATION, AND EMBRYONIC MORTALITY IN THE DOMESTIC CAT

In vivo embryogenesis, embryo migration, and survival were studied in the domestic cat. Queens were naturally mated (three times daily) on t he second and third days of behavioral estrus and, if ovulation occurr ed, ovariohysterectomized at 64 (n = 8), 76 (n = 11), 100 (n = 8), 124 (n = 7), 148 (n = 6), and 480 h (n = 8) after first copulation. Of 52 cats mated, 48 (92.3%) ovulated (as evidenced by the presence of ovar ian CL), and of these, 38 (79.2%) either produced good-quality embryos or had implantation sites. From the remaining cats, only unfertilized oocytes (n = 5), degenerating embryos (n = 4), or no oocytes/ embryos (n = 1) were recovered. Embryos at 64, 76, 100, and 124 h after the f irst copulation typically were 1 to 4 cells (17 of 20; 85.0%), 5 to 8 cells (18 of 28; 64.3%), 9 to 16 cells (14 of 24; 58.3%), and morulae (15 of 21; 71.4%), respectively; all were within the oviducts. At 148 h, embryos primarily were compact morulae or early blastocysts (15 of 18; 83.3%), and all were within the uterus. For the preimplantation gr oups, the overall recovery of embryos plus oocytes per CL was 80.6%, a nd the mean (+/- SEM) numbers of CL and embryos were 64 h, 4.8 +/- 0.3 , 3.1 +/- 0.8; 76 h, 4.7 +/- 0.3; 3.9 +/- 0.6; 100 h, 5.8 +/- 0.5, 3.3 +/- 0.8; 124 h, 4.4 +/- 0.5, 4.0 +/- 0.6; and 148 h, 6.5 +/- 1.1, 3.7 +/- 0.7, respectively. Cats in the 480-h group produced a mean of 5.6 +/- 0.5 CL and 3.9 +/- 0.5 implantation sites. In six of eight cats i n this group, there was a disparity between CL number on a given ovary and number of implantation sites in the ipsilateral horn, supporting the concept of transuterine embryo migration. In summary, results indi cated that 1) more than 90% of cats ovulated following this multiple m ating regimen, but similar to 21% of these failed to produce any ferti lized or viable embryos; 2) embryo developmental rate in vivo was biph asic, with a rapid cleavage rate to the 5- to 8-cell stage followed by a slower cleavage rate to the morula stage; 3) cat embryos entered th e uterus as compact morulae or early blastocysts similar to 5.5 days a fter the first copulation; and 4) on the basis of implantation/CL rati o, similar to 30% of all ovulated cat oocytes underwent either fertili zation failure or preimplantation embryonic mortality.