Effectiveness and optimum level of protected methionine in fattening pig diets

39 Background: The methionine (Met) requirements have not been clearly established for fattening 40 pigs due to their metabolic interrelationships and its bioavailability for protein synthesis. 41 Objective: To determine the optimum level of regular crystalline or protected Met in fattening 42 pig diets. Methods: A total of 48 crossbred pigs (11.74±1.72 kg of initial body weight) were 43 used. The treatments consisted of four levels (0.00, 0.05, 0.10, 0.15% in addition to dietary 44 content) and two types of Met (regular and protected) in fattening pig diets. Results: Nursery, 45 finishing I and II pigs fed protected Met increased daily feed intake (DFI; p≤0.10). Protected Met 46 raised daily weight gain (DWG) in nursery pigs and increased backfat thickness (BT) in nursery 47 and growing pigs (p≤0.10). In finishing I pigs, protected Met increased DWG and improved 48 carcass characteristics (p≤0.10). In nursery and growing pigs, extra 0.15% of Met decreased 49 feed:gain ratio (FGR; p≤0.10). In growing and finishing II pigs fed extra 0.05% of Met improved 50 DWG and extra 0.10% of Met reduced plasma urea concentration (p≤0.10). Conclusions: 51 Protected Met in pig diets increase DWG, DFI and BT. Increasing 0.05-0.15% Met level 52 improves FGR, DWG; in addition, the excretion of nitrogen to the environment could be reduced. 53