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Carbohydrate and Amino Acid Metabolism in Lambs Fed Purified Diets Containing Urea or Isolated Soy Protein¹

Department of Animal Science, Cornell University, Ithaca, New York 14850

A purified basal diet was pair-fed to five sets of twin lambs for comparing the effects of soybean protein (SP) or urea (U) on liver, heart, kidney, plasma and urinary concentrations of amino acids, metabolic intermediates and other constituents. Feed was available from 8 to 10 AM and 1 to 3 PM daily during the entire feeding period of 76 days. Blood samples were drawn at 10 AM once each week except on day 34 when samples were taken immediately before the morning feeding and at frequent intervals thereafter. NH₃-N in peripheral blood following the AM feeding was higher and blood glucose was lower in the U-fed lambs with blood urea being the same in both groups. Plasma lactate and succinate declined and blood glucose increased following feeding in both treatment groups. Plasma citrate increased after feeding in the U-fed lambs. During 6 hours after the morning feeding total urinary excretion of citrate, -ketoglutarate and malate increased by factors of 12.2, 3.5 and 1.9, respectively, for U-fed lambs while their cis-aconitate excretion decreased. Plasma glutamate was higher at 1 PM than at 9 AM, 11 AM or 3 PM for both treatment groups. Plasma alanine, threonine, valine, leucine, isoleucine, lysine, ornithine and arginine were significantly lower in U-fed lambs but serine and glutamate were higher. Liver threonine, valine, leucine, isoleucine, lysine, histidine and ornithine concentrations were lower in U-fed lambs. Concentrations of valine and leucine were lower in the kidney and heart, isoleucine was lower in the heart, and lysine was lower in the kidney of U-fed lambs. Plasma Ca²⁺, Mg²⁺ and phosphate were the same for both dietary treatments.

KEY WORDS: • citrate • amino acids • organic acids • urea feeding

¹ Presented in part at FASEB meetings. Prior, R. L., J. A. Milner and W. J. Visek 1971 Metabolism of Krebs cycle organic acids in soy and urea fed lambs. Federation Proc. 30: 296 (abstr.), Financial support was provided in part by a grant from The Nutrition Foundation, New York, N. Y. This work was completed during tenure of a National Science Foundation Predoctoral Fellowship awarded to R. L. Prior.

Manuscript received 8 February 1972.