This chapter deals with quantitative aspects of macronutrient metabolism and its regulation in maternal and conceptus tissues in vivo, emphasizing data and concepts generated or revised during the decade since publication of a similar chapter in the first edition of this book (see Bell, 1993) | 20 Pregnancy and Fetal Metabolism . Bell 1 . Ferrell2 and . Freetly2 1Department of Animal Science Cornell University Ithaca NY 14853 USA 2USDA ARS Meat Animal Research Center Clay Center NE 68933 USA Introduction This chapter deals with quantitative aspects of macronutrient metabolism and its regulation in maternal and conceptus tissues in vivo emphasizing data and concepts generated or revised during the decade since publication of a similar chapter in the first edition of this book see Bell 1993 . Recent findings on the regulation of nutrient partitioning among maternal tissues the placenta and fetus es are highlighted as is new information on placental transport mechanisms. Energy Cost of Pregnancy Practical considerations Meeting the nutrient requirements of pregnant females is important to ensure an adequate nutrient supply for proper growth and development of the fetus to ensure that the female is in an adequate body condition for birth lactation and rebreeding and to provide immature females with adequate nutrients for continued growth. Recognizing those needs most feeding systems currently in use for ruminants . AFRC 1990 CSIRO 1990 NRC 1996 2001 recommend a factorial approach such that estimates of nutrient requirements for maternal maintenance body weight gain and growth of gravid uterine or conceptus tissues are summed to derive total requirements for pregnant females. This approach implies that fetal nourishment will be adequate if maternal body weight condition and growth are maintained at suitable levels. Limited or no interaction among tissues or nutrient needs of the gravid uterus and maternal tissues is also implied by this approach. CAB International 2005. Quantitative Aspects of Ruminant Digestion and Metabolism 2nd edition eds J. Dijkstra . Forbes and J. France 523 524 . Bell et al. Recommended levels of feeding during late gestation range from about times maintenance in cows and ewes with single fetuses to to .
