EARLY-EMBRYO COLLOQUIUM, COMPTON
455
Physiological Factors and the Early Embryo R. NEWCOMB A.R.C. Unit of Reproductive Physiology and Biochemistry, 307 Huntingdon Road, Cambridge CB3 OJQ, U.K. (1) The uterine environment
Early embryos of farm animals enter the uterus some 3-4 days after ovulation, a process regulated by ovarian steroids. If embryos enter the uterus prematurely they may be ejected from it because of myometrial activity. The bovine uterus, for example, does not become quiescent until 4 or 5 days after oestrus (Ruckebusch & Bayard, 1975). The early cleavage stages are more susceptible to deleterious influences, including premature exposure to the uterine environment. Transfer to the uterus of synchronized recipients of day-3 (day 0 = oestrus) bovine embryos (which are normally resident within the oviduct) results in a very low pregnancy rate. However the transfer of day-4 embryos to the same uterine stage results in a significantly higher (Pc0.01) conception rate even though the transfers are asynchronous (Newcomb & Rowson, 1975). Several factors such as deleterious culture media and cooling have been shown to adversely affect bovine early cleavage stages, but not to affect embryos a few days older [see review by Newcomb (1976)l. When 48-84h sheep embryos are transferred either to the Fallopian tubes or to the uterus, there is a significant increase in the number of ewes which lamb (P
455
Physiological Factors and the Early Embryo R. NEWCOMB A.R.C. Unit of Reproductive Physiology and Biochemistry, 307 Huntingdon Road, Cambridge CB3 OJQ, U.K. (1) The uterine environment
Early embryos of farm animals enter the uterus some 3-4 days after ovulation, a process regulated by ovarian steroids. If embryos enter the uterus prematurely they may be ejected from it because of myometrial activity. The bovine uterus, for example, does not become quiescent until 4 or 5 days after oestrus (Ruckebusch & Bayard, 1975). The early cleavage stages are more susceptible to deleterious influences, including premature exposure to the uterine environment. Transfer to the uterus of synchronized recipients of day-3 (day 0 = oestrus) bovine embryos (which are normally resident within the oviduct) results in a very low pregnancy rate. However the transfer of day-4 embryos to the same uterine stage results in a significantly higher (Pc0.01) conception rate even though the transfers are asynchronous (Newcomb & Rowson, 1975). Several factors such as deleterious culture media and cooling have been shown to adversely affect bovine early cleavage stages, but not to affect embryos a few days older [see review by Newcomb (1976)l. When 48-84h sheep embryos are transferred either to the Fallopian tubes or to the uterus, there is a significant increase in the number of ewes which lamb (P
