Effects of supplementation of graded level of glutamic acid to crude protein reduced diets on the performance of growing pigs

A total of 150 growing pigs ([Landrace × Yorkshire] × Duroc) with an initial average body weight (BW) of 24.45 kg were used in a 6‐week trial to estimate the optimum lysine to glutamic acid ratio in pigs fed low‐protein diets supplemented with increasing level of synthetic glutamic acid (Glu). Pigs were randomly allotted to 5 dietary treatments consisting of either control diet (CON) formulated to have 157 g crude protein (CP) or negative control diets (NC, NC1, NC2 and NC3) with 20 g CP reduction and addition of Glu (1.1, 3.9, 6.8 and 9.6 g/kg feed respectively). Supplementing the increasing level of Glu to low CP diets did not exert any linear or quadratic responses in the growth performance parameters as well as nutrient digestibility. The serum creatinine concentration in pigs receiving CON diet showed trends (p = 0.063) in increment compared with pigs receiving NC diet. However, with the increase in the supplementation of Glu, there were no linear or quadratic responses on serum blood urea nitrogen (BUN) and creatinine concentrations. There was a tendency in the reduction (p = 0.088, p = 0.064) of backfat thickness and lean percentage, respectively, at week 3 and a trend in the reduction (p = 0.092) in lean percentage at week 6 in pigs fed NC diet compared with those fed CON diet. The increase in the supplemental level of Glu tended to show quadratic responses in the backfat thickness and lean percentage at week 3 and 6. In conclusion, the growth performance parameters as well as carcass traits with Lys: Glu ratio 1: 2.71 were very close with the mean values of CON diet indicating that 6.8 g Glu when supplemented to 2% CP reduced diet could achieve the comparable growth performance and carcass trait as that of standard basal diet.