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Impacts of amino acid nutrition on pregnancy outcome in pigs: mechanisms and implications for swine production

G. Wu^*, F. W. Bazer^*, R. C. Burghardt^*, G. A. Johnson^*, S. W. Kim, X. L. Li^*, M. C. Satterfield^* and T. E. Spencer^*

^* Departments of Animal Science and of Veterinary Integrative Biosciences, Texas A&M University, College Station 77843 Department of Animal Science, North Carolina State University, Raleigh 27695

g-wu{at}tamu.edu

Abstract

Pigs suffer up to 50% embryonic and fetal loss during gestation and exhibit the most severe naturally occurring intrauterine growth retardation among livestock species. Placental insufficiency is a major factor contributing to suboptimal reproductive performance and low birth weights of pigs. Enhancement of placental growth and function through nutritional management offers an effective solution to improving embryonic and fetal survival and growth. We discovered an unusual abundance of the arginine family of AA in porcine allantoic fluid (a reservoir of nutrients) during early gestation when placental growth is most rapid. Arginine is metabolized to ornithine, proline, and nitric oxide, and these compounds possess a plethora of physiological functions. Importantly, nitric oxide is a vasodilator and angiogenic factor, whereas both ornithine and proline are substrates for placental synthesis of polyamines that are key regulators of protein synthesis and angiogenesis. Additionally, arginine, leucine, glutamine, and proline activate the mammalian target of rapamycin cell signaling pathway to enhance protein synthesis and cell proliferation in placentae. To translate basic research on AA biochemistry and nutrition into application, dietary supplementation with 0.83% L-arginine to gilts on d 14 to 28 or d 30 to 114 of gestation increased the number and litter birth weight of live-born piglets. Also, supplementing the gestation diet with 0.4% L-arginine plus 0.6% L-glutamine enhanced efficiency of nutrient utilization, reduced variation in piglet birth weight, and increased litter birth weight. By regulating syntheses of nitric oxide, polyamines and proteins, functional AA stimulate placental growth and the transfer of nutrients from mother to embryo/fetus to promote conceptus survival, growth and development.

Key Words: arginine • fetal growth • glutamine • litter size • reproduction • swine