Transport and hindlimb exchange of peptide and serum protein amino acids in calves fed soy- or urea-based purified diets.

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Holstein steer calves (130 kg) were used to monitor venoarterial concentration differences of plasma peptide and serum protein amino acids across the hindlimbs. Calves were fed purified diets containing soy protein or urea as the sole source of dietary N. Twenty-four hourly feedings per day were imposed to promote "steady-state" metabolism. Negative venoarterial differences of glutamic acid (P less than .10), valine (P less than .10), lysine (P less than .05) and histidine (P less than .01) were observed in soy-fed calves and isoleucine (P less than .10) in urea-fed calves from the peptide fraction. Negative venoarterial differences of amino acids from the peptide fraction were generally similar for the two dietary treatments, except for glutamic acid (P less than .01). A large negative venoarterial difference of glutamic acid was observed when soy protein was fed and, conversely, a large positive venoarterial difference was observed when urea was fed. Two groups of serum proteins were evaluated: fraction I (primarily globulins) and fraction II (primarily albumin). Hindlimb amino acid venoarterial concentration differences for soy-fed calves were inconsistent and nonsignificant for both fractions I and II. Conversely, hindlimb negative venoarterial concentration differences in urea-fed calves for both fractions I and II were large and statistically significant for many amino acids. Fraction II venoarterial differences were much greater than differences observed in fraction I. Soy and urea treatment differences were also much more pronounced in fraction II, being statistically significant for 8 of 17 amino acids. These data indicate venoarterial concentration differences of serum protein amino acids that react differently to varied nutritional regimens.(ABSTRACT TRUNCATED AT 250 WORDS)