THE EFFECTS OF EXCESSIVE AMOUNTS OF PROTEIN ON LYSINE UTILIZATION IN GROWING PIGS

Two experiments were conducted to investigate whether the utilization of lysine in growing pigs is affected by the level of excess protein i n the diet. Nine lysine-deficient diets containing 100, 200 or 300 g c rude protein/kg and between 1.2 and 6.8 g ileal digestible lysine/kg w ere prepared. In the first experiment the apparent heal digestibility of lysine in three of the nine diets was determined using pigs with si mple T-cannulas and Cr2O3 as an indigestible marker. Peal digestibilit y of lysine in the other diets was calculated by interpolation. In the second experiment N retention, as a measure of lysine utilization, wa s determined in all nine diets using growing pigs over the weight rang e 30-50 kg. The effect of excess protein on lysine utilization was ass essed by comparing the regression of N retention v. lysine (ileal dige stible) intake at the three levels of protein. Increasing heal digesti ble lysine in the diets resulted in a linear increase in N retention w ith all three protein levels and there was no significant difference a mongst the three regressions, indicating that lysine utilization was n ot affected by the level of protein. Therefore, all data were pooled t ogether to calculate a single regression for all treatments. An increa se of 1.0 g heal digestible lysine led to an increase of 1.43 g N or 8 .96 g protein (N x 6.25) retained. Assuming a lysine concentration in the retained body protein of 65-72 mg/g, lysine was utilized with an e fficiency of 0.58-0.65.