Effects of Dietary Methionine Deficiency on the Growth Performance and Plasma Concentrations of Selected Metabolites in Growing Pigs

Methionine (Met) is the second or third limiting AA in a typical grain-based swine diet, and plays a very important role in promoting growth performance, especially, the muscle growth of pigs. This study was conducted to evaluate the effects of a dietary Met deficiency on the growth performance and blood plasma concentrations of selected metabolites that include total protein, albumin, urea nitrogen, glucose, triglycerides, and cholesterol in growing pigs. Twenty individually penned crossbred barrows (Yorkshire × Landrace; initial BW 23.6 ± 2.41 kg) were assigned to 2 dietary treatments according to a completely randomized design. A basal corn-soybean meal diet (Diet 1; Met-deficient ) was formulated using analyzed ingredient AA contents and published standardized ileal digestible (SID) coefficients to contain 0.22% SID Met and 0.52% SID Met + Cys, but to meet or exceed the NRC (2012) recommendations for other essential AA (e.g., 1.08% SID Lys), energy (2,545 kcal/kg NE), minerals, and vitamins. Crystalline DL-Met was supplemented to the basal diet at the expense of corn (0.15%) to create Diet 2 adequate in Met (0.37% SID Met; 0.67% SID Met + Cys). During the 4 weeks of ad libitum feeding trial, the BW and feed intake were measured weekly, and the ADG, ADFI and G:F were calculated weekly, as well as for the overall feeding period. Immediately before and after the feeding trial, jugular vein blood was collected for plasma sample analyses. The plasma concentrations of the selected metabolites were determined using an ACE Clinical Chemistry System (Alfa Wassermann, Inc.). Data were analyzed using Student’s T-test. After the 4 week trial, pigs fed Diet 1 had a lower (P < 0.001) ADG (870 vs. 980 g/d) and G:F (0.45 vs. 0.50) than the pigs fed Diet 2. Pigs fed Diet 1 had a higher (P < 0.001) plasma concentration of urea nitrogen than those fed Diet 2 (6.6 vs. 4.2 mg/dL). Pigs fed Diet 1 tended to have a higher (P = 0.085) plasma albumin concentration. There were no differences (P > 0.10) between the two treatments in all other parameters measured. These findings indicated that dietary Met deficiency can reduce the rate of body protein synthesis or growth performance as suggested by the plasma urea nitrogen level. Increasing plasma urea nitrogen concentration will lead to increased nitrogen excretion to the environment. However, what mechanisms at the cell signaling level responsible for the AA utilization warrants further investigation.