Nitrogen utilization and lean growth performance of 20- to 50-kilogram pigs fed diets balanced for lysine:energy ratio.

Two experiments were conducted to determine the lysine:DE ratio that would maximize nitrogen retention and lean growth in growing pigs. Diets were formulated to contain 2.5, 3.0, 3.5, or 4.0 g of lysine/Mcal of DE at 3.5 and 3.75 Mcal of DE/kg of diet arranged in a 4 x 2 factorial. Experiment 1 used 48, 20-kg crossbred barrows in a nitrogen balance study. Feeding diets containing 3.75 Mcal of DE/kg of diet resulted in higher (P < .01) nitrogen digestibility and retention as well as higher energy and DM digestibility. In diets containing 3.5 Mcal of DE/kg, increasing the lysine:DE ratio had no effect on nitrogen retention, but an increase up to 3.0 g of lysine/Mcal of DE was observed at the 3.75 Mcal of DE level. In Exp. 2, 96 individually housed growing crossbred barrows and gilts were used to determine lean and growth performance to the diets fed in Exp. 1 in a 4 x 2 x 2 factorial arrangement of treatments. Weight gain was unaffected by dietary treatment. A reduction (P < .01) in feed intake and an improvement (P < .05) in feed efficiency was observed as the DE level increased. Increasing the lysine:DE ratio to 3.0 to 3.5 g of lysine/Mcal of DE increased (P < .05) the rate of fat-free lean and empty body protein gain and the weight of fat-free lean at 50.9 kg increased (P < .01) with increasing lysine:DE ratio regardless of sex or energy level.(ABSTRACT TRUNCATED AT 250 WORDS)