ELSEVIER FEED AND FORAGE TOXICANTS AFFECTING EMBRYO SURVIVAL AND FETAL DEVELOPMENT T.G. McEvoy’, J.J. Robinson, C.J. Ashworth, J.A. Rooke and K.D. Sinclair Scottish Agricultural College, Animal Biology Division, Craibstone Estate, Bucksburn Aberdeen A82 1 9YA, UK ABSTRACT Early embryonic and fetal development in mammals is sensitive to deficiencies and excesses of specific nutrients and toxicants. Operating directly and/or indirectly, these deficiencies and excesses can result in embryonic death or, in less severe circumstances, disruption of normal embryo and fetal growth. This paper explores the threats posed by feed and forage toxicants to the developing embryo and their impact on early programming of fetal development. Using significant examples, we consider the relevance of temporal sensitivities during early development in utero, and their implications for the morphology and functional competence of specific organs and tissues. 0 2000 by ElsevierScience Inc. Key words. development, embryo, fetus, nutrients, reproduction, toxins INTRODUCTION Nourished by oviductal and uterine endometrial secretions. early embryos have to effect major temporal changes in substrate utilisation and gene expression in order to survive (644, 54, 57). They also have to initiate and complete the cell, tissue and organ differentiation processes that ensure normality of early development. Feed toxicants and dietary imbalances of specific nutrients which adversely affect the composition of oviductal and uterine secretions, either directly or indirectly through shifts in maternal hormone concentrations, can disrupt these events. The end result is reduced embryo survival or, in less severe circumstances, disruption of growth and development. In some instances the time when the embryo or fetus is vulnerable to a specific toxin or nutrient imbalance is either poorly defined or is assumed to be over an extended period; in others the critical window has been identified and is as brief as 1 to 2 days. There is evidence also that the severity of the adverse effect may be influenced by other dietary constituents, and by whether the embryo has come from a spontaneous ovulation or has been generated following ovarian stimulation by exogenous hormones. Acknowledgments: SAC receives funding from the Scottish Executive Rural Affairs Department. Large Offspring studies referred to in this review were funded by the UK Ministry of Agriculture, Fisheries and Food, and conducted in collaboration with Professor I Wilmut and Dr LE Young, Roslin Institute, Edinburgh. ‘Correspondence: E-mail: t.mcevoy@ab.sac.ac.uk Theriogenology 55113-129, 2001 009~69lWOl/$-eee front matter (B 2000 Elsevier Science Inc. PII: !30093-691x(00)00450-7