Experimental chimaerism in sheep

Abstract

Composite sheep embryos (n = 110) were produdced by aggregation of blastomeres from 2-, 4- or 8-cell embryos. Each composite embryo consisted of equal numbers of blastomeres from 2-8 parent embryos, the total cell number ranging from one quarter of the normal cell number to 8 times the normal cell number. The embryos were embedded in agar and transferred to ligated sheep oviducts to allow development up to the early blastocyst stage. Of the 101 embryos subsequently recovered, 77 had formed normally organized blastocysts and 74 of these were transferred to 51 recipients. A total of 38 recipients went to full term, producing a total of 53 lambs. Of the 48 lambs which survived to be blood typed at 60 days of age, 36 were judged to be chimeric on the basis of their blood type and/or on the basis of external features. The proportion of chimeras was larger amongst the lambs produced from composite embryos of the normal number of cells or more (25/26) than among lambs produced from composite embryos of less than the normal number (11/22).