Cytogenic analysis of preimplantation blastocysts from prepuberal gilts treated with gonadotropins.

Metaphase chromosomes were examined in 10-day-old embryos collected from prepuberal gilts that had been induced to ovulate, using a combination of 200 IU of human chorionic gonadotropin (HCG) and 400, 600, or 800 IU of pregnant mare serum gonadotropin (PMSG) followed 72 hours later by 500 IU of HCG. A repeatable, reliable method was developed for the processing of early porcine embryos in the hatched spherical blastocyst stage for cytogenetic analysis. Of 170 embryos recovered and processed from 21 gilts, 169 yielded analyzable metaphase cells for determination of somatic cell chromosome number for an overall success rate of 99.4%. All embryos were diploid (2n = 38) in chromosomal constitution, and although isolated tetraploid (4n = 76) and octaploid (8n = 152) cells were found, true triploid or other polyploid embryos were not present. The absence of these aberrations indicated that at the dosage levels tested, the hormone PMSG did not cause an increase in occurrence of polyploidy in porcine blastocysts present at day 10 of gestation. Analyses showed no significant (P less than 0.05) increase in numbers of corpora lutea or embryos at day 10 of gestation in gilts treated with these PMSG dosage levels.