Transport and Hindlimb Exchange of Plasma and Blood-Cell Amino Acids in Calves Fed Soy- or Urea-Based Purified Diets2

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  • KWK. E. Webb
    K. E. Webb
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Abstract
Plasma and blood-cell free amino acid concentrations and venoarterial differences across the hindlimbs via abdominal aorta and caudal vena cava cannulae were determined on Holstein steer calves (130 kg) fed purified diets containing soy protein or urea as the sole source of dietary N. Calves were fed 24 hourly feedings per day to promote “steady-state” metabolism. Trials lasted 30 d and consisted of four calves per treatment. Urea feeding resulted in reduced venous concentrations of plasma amino acids, namely, a 30% decrease in essential amino acids (P<.05) and a 16% decrease in nonessential amino acids (P<.10). Nonessential amino acid concentrations of blood cells were affected little in urea-fed calves; however, blood-cell essential amino acid concentrations were depressed due to significant decreases in threonine, valine, methionine, isoleucine and phenylalanine. A net negative concentration difference across the hindlimbs for plasma free amino acids was noted for soy-fed calves. Urea feeding resulted in a small positive amino acid concentration difference. The branched-chain amino acids (BCAA) changed (P<.01) from a large negative concentration difference in soy-fed calves to essentially a zero difference in calves fed urea. Blood-cell total amino acid change across hindlimbs showed no treatment differences, although BCAA changed from large outputs from the blood cells in soy-fed calves to essentially zero change in urea-fed calves. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science

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