MEASURING LEUCINE FLUX AND PROTEIN-METABOLISM WITH C-13 ISOTOPE IN GROWING CATTLE

Leucine irreversible loss (ILR) and fractional leucine oxidation (FO) were estimated using primed infusions of L-[1-C-13]leucine and [C-13]b icarbonate. Feed restriction decreased (P < 0.05) ILR from 16.42 to 10 .82 mmol h(-1), but did not affect FO (0.172) in two young dairy heife rs. In six growing steers, ILR and FO averaged 30.03 +/- 5.09 mmol h(- 1) and 0.147 +/- 0.027, respectively. L-[1-C-13]leucine and [C-13]bica rbonate can be successfully used to measure the different components o f protein metabolism in cattle.