Experimental Production of Triploid Bovine Embryos by Microinjection of Two Sperm and Their Develoment

Abstract

To clarify the effect of triploidy on the development of bovine embryos, one or 2 sperm were injected into mature bovine oocytes and subsequent development and chromosome composi-tion were investigated. The cleavage rates of oocytes injected with one or 2 sperm using oocytes matured in vitro for 24 h were 36.3% (69/190) and 39.0% (53/136), respectively. Most of the embryos injected with 2 sperm had arrested development before the 8-cell stage and none devel-oped to the morula stage, although three (1.6%) embryos injected with one sperm developed to the blastocyst stage. The incidence of triploid embryos derived from 2-sperm injection was 12.9%, and the incidences of diploid and haploid embryos were 48.4% and 12.9%, respectively. About half (44.9%) of the uncleaved oocytes injected with one sperm and one-third (32.1%) of those injected with 2 sperm stopped developing at the second anaphase just after activation by ionophore treat-ment. Three pronuclei (10.7%) and one-cell metaphase (28.6%) with chromosome sets spread in 3 directions were observed only in uncleaved oocytes after 2-sperm injection. These facts suggested that triploidy is not the sole cause of arrested development before the 8-cell stage in cleaved embryos, although 2-sperm penetration and pronuclei formation strongly influenced oocyte cleav-age.