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Baggs ewes adapt to maternal undernutrition and maintain conceptus growth by maintaining fetal plasma concentrations of amino acids¹

W. S. Jobgen^*, S. P. Ford, S. C. Jobgen^*, C. P. Feng^*,, B. W. Hess, P. W. Nathanielsz, P. Li^* and G. Wu^*,2

^* Department of Animal Science and Faculty of Nutrition, Texas A&M University, College Station 77843; and Department of Animal Science and Center for the Study of Fetal Programming, University of Wyoming, Laramie 82071; and Department of Obstetrics and Gynecology, China-Japan Friendship Hospital, Beijing, China 100029; and and Department of Obstetrics and Gynecology, University of Texas Health Sciences Center, San Antonio 78299

² Corresponding author: g-wu{at}tamu.edu

Adequate delivery of AA is essential for normal fetal growth and development. Recently, we reported that when ewes from the University of Wyoming flock (farm flock with adequate nutrition) were fed 50% (nutrient-restricted) or 100% (control-fed) of the NRC-recommended nutrient requirements between d 28 and 78 of gestation, fetal weights as well as concentrations of most AA in maternal and fetal blood were substantially reduced in nutrient-restricted vs. control-fed pregnancies. The current study utilized Baggs ewes, which were selected under a markedly different production system (range flock with limited nutrition), to test the hypothesis that adaptation of ewes to nutritional and environmental changes may alter placental efficiency and conceptus nutrient availability in the face of maternal nutrient restriction. Baggs ewes received 50 or 100% of the NRC nutrient requirements between d 28 and 78 of pregnancy. On d 78, maternal uterine arterial and fetal umbilical venous blood samples were obtained, and the ewes were euthanized. Amino acids and their metabolites (ammonia, urea, and polyamines) in plasma were analyzed using enzymatic and HPLC methods. The results showed that maternal plasma concentrations of 9 AA (Asp, Ile, Leu, Lys, Orn, Phe, Thr, Trp, and Val) as well as maternal and fetal plasma concentrations of ammonia and urea were reduced (P < 0.05) in nutrient-restricted compared with control-fed Baggs ewes. However, fetal plasma concentrations of all AA and polyamines did not differ (P = 0.842) between the 2 groups of ewes. Collectively, these findings suggest that Baggs ewes, by adapting to the harsh conditions and limited nutrition under which they were selected, were able to maintain fetal concentrations of AA in the face of a maternal nutrient restriction through augmenting placental efficiency.

Key Words: fetal growth • fetal programming • fetal intrauterine growth restriction • nutrition • pregnancy