PRODUCTION OF SHEEP EMBRYOS IN-VITRO AND DEVELOPMENT OF PROGENY FOLLOWING SINGLE AND TWIN EMBRYO TRANSFERS

An in vitro culture system for producing ovine embryos is described, i n which heat inactivated sheep serum was used as a protein source for maturation, fertilization and 7-d culture phases. Ovaries obtained fro m a commercial abattoir were used as the source of mature ewe (285) an d lamb oocytes (356), which were subsequently cultured in this system to yield similar mean cleavage rates of 91 and 92%, respectively, but significantly different (P<0.025) proportions for blastocysts/cleaved oocytes (46 and 18%). At Days 7 or 8 of culture, embryos from each sou rce were transferred, either singly (ewe-derived) or in pairs (ewe- an d lamb-derived), to hormonally synchronized recipient ewes, resulting in the birth of lambs ranging in weight from 2.5 to 8.8 kg for singlet ons and 2.6 to 8.0 kg for twins. Mean gestation length of 153.4 +/- 0. 5 d (range 151 to 160) was slightly longer than the expected norm of a bout 150 d. The pregnancy rate was significantly higher after the tran sfer of embryo pairs (64%) than single (39%) embryos, while survival o f lambs to weaning was greater for singleton (80%) than for twin lambs (43%). Some factor(s) in the culture media, such as growth factors in the sera, may have a mitogenic effect on embryonic cells, or it may a lter the distribution of cells to the trophectoderm and inner cell mas s, resulting in enhanced body growth rates. (C) 1998 by Elsevier Scien ce Inc.