Nitrogen retention and lysine oxidation were measured in growing pigs given diets which supplied 0,0-2 or 08 of the lysine requirement, with other amino acids in relative excess. Eight groups of three female littermate pigs were used: one of each group was given each of the three diets. In half the pigs (four groups) N retention was measured at body weights (W) of approximately 25,35 and 45 kg. The other four littermate 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 ~-[6-~H]lysine. Lysine oxidation was estimated from the production of tritiated water. Rates of both N retention and lysine oxidation increased significantly with lysine intake; mean values (g/kg W@75 per d) for the three diets respectively were for N retention, 0.00, 0.32 and 1.22, and for lysine oxidation 0051, 0.058 and 0.078. From the N balance results (assuming a constant lysine concentration in body protein) the efficiency of utilization of absorbed lysine was estimated to be 085; from the oxidation results (assuming lysine absorbed but not retained is oxidized) the estimate was 095.

Two feeding regimes were used for investigation into the effect of meal frequency on the lysine requirement in chickens estimated with metabolism-oriented determination. 1-day-old male broiler chickens were fed either twice a day for 1 hour (one group) or 6 times a day for 1/2 hour (other group). 7 to 21 days posthatching the birds received a wheat-wheat gluten diet which was L-lysine-supplemented at 6 levels. Using lysine deficient diets chickens fed twice a day eat more and grow faster than chickens fed 6 times a day. The N-balance was 6 to 7% higher in the case of the feeding regime 2 times a day. After feeding period 14C-U-L-lysine was injected intravenously and 14CO2-excretion measured. The estimated range for lysine requirement was 11.9-13.1 g lysine/kg DM and 13.1-14.3 g lysine/kg DM for chickens fed 2 times and 6 times a day, respectively. A feeding regime of 6 meals a day does not improve the utilization of diets contains crystalline lysine compared with feeding of 2 meals a day.