The digestible lysine requirements for fattening pigs have not been established clearly. The objective of this trial was to determine a level of protected lysine in pig diets that was adequate for growth performance, carcass characteristics, and plasma urea nitrogen concentration. Fifty crossbred pigs (29.55 ± 1.80 kg initial bodyweight) were used in a completely randomized design with a 3 × 2 factorial arrangement of treatments. Treatments were 0.90%, 1.00% and 1.10% lysine in the growing phase, followed by diets with 0.75%, 0.85% and 0.95% lysine in finishing stage I, and 0.83%, 0.93% and 1.03% lysine in finishing stage II. The lysine was provided in its conventional form and as protected lysine. For growing pigs, the highest average daily feed intake (ADFI) and final bodyweight were obtained with 1.1% and 1.0% lysine, respectively. The average daily gain, ADFI, final bodyweight, fat free lean gain and longissimus muscle area (LMA) were reduced with protected lysine. In finishing I stage, pigs fed 0.95% lysine had greater final bodyweight, LMA, and lean meat percentage than pigs fed with 1% unprotected lysine. For finishing II pigs, ADFI and final bodyweight were the greatest when 1.03% lysine was provided, regardless the type of lysine that was fed. The plasma urea nitrogen increased with the 1.03% lysine diet and was reduced with protected lysine. Results indicate that the digestible lysine requirement for the fattening pig diets might be 0.10% higher than in current recommendations. The use of protected lysine affected growth negatively during the growing stage.
"Experientia docet" - Experience is the best teacher