LYSINE UTILIZATION BY GROWING PIGS - SIMULTANEOUS MEASUREMENT OF PROTEIN ACCRETION AND LYSINE OXIDATION

Nitrogen retention and lysine oxidation were measured in growing pigs given diets which supplied 0, 0.2 or 0.8 of the lysine requirement, wi th other amino acids in relative excess, Eight groups of three female littermate pigs were used: one of each group was given each of the thr ee diets, In half the pigs (four groups) N retention was measured at b ody weights (W) of approximately 25, 35 and 45 kg, The other four litt ermate groups of three pigs were given the same three diets; when they reached 35 kg W they were given a continuous (6 h) primed infusion of L-[6-H-3]lysine. Lysine oxidation was estimated from the production o f tritiated water, Rates of both N retention and lysine oxidation incr eased significantly with lysine intake; mean values (g/kg W-0.75 per d ) for the three diets respectively were for N retention, 0.00, 0.32 an d 1.22, and for lysine oxidation 0.051, 0.058 and 0.078. From the N ba lance results (assuming a constant lysine concentration in body protei n) the efficiency of utilization of absorbed lysine was estimated to b e 0.85; from the oxidation results (assuming lysine absorbed but not r etained is oxidized) the estimate was 0.95.