Effects of Dietary Net Energy Density and Standardized Ileal Digestible Lysine: Net Energy Ratio on the Performance and Carcass Characteristic of Growing-Finishing Pigs Fed Low Crude Protein Supplemented with Crystalline Amino Acids Diets

Two 3×3 factorial design trials with 1 080 of Yorkshire×Landrace×Duroc barrows were conducted to investigate the effects of dietary net energy (NE) density and standardized ileal digestible (SID) lysine: NE ratio on the performance of growing-finishing pigs and carcass characteristic of finishing pigs fed low crude protein (CP) supplemented with crystalline amino acids (CAA) diets. Low CP corn-soybean meal basal diets (14% for Exp. 1 and 11% for Exp. 2) supplemented with crystalline lysine, methionine, threonine, and tryptophan were formulated. Nine treatments with increasing NE density and SID lysine:NE ratio were used in each trial (Exp. 1: 9.66, 9.87, and 10.08 MJ kg−1 NE, 0.89, 0.96, and 1.03 g MJ−1 SID lysine: NE; Exp. 2: 9.83, 10.04, and 10.25 MJ kg−1 NE, 0.69, 0.76, and 0.83 g MJ−1 SID lysine:NE). In Exp. 1, we observed that the average daily gain (ADG) for barrows that received the diet containing 9.87 MJ kg−1 NE was significantly higher than that of barrows fed a 9.66 MJ kg−1 NE diet (P<0.05), but no difference was observed when compared with barrows that received a diet containing 10.08 MJ kg−1 NE (P>0.05). The ADG was affected both linearly (P<0.05) and quadratically (P<0.05) as the SID lysine:NE ratio increased. The NE density or SID lysine:NE ratio and their interaction had no effect on the average daily feed intake (ADFI) and serum urea nitrogen (SUN) (P>0.05). The feed to gain ratio (F:G) decreased (linearly, P<0.05; quadratically, P<0.05) as the NE density or SID lysine:NE ratio increased, but no interaction of NE density and SID lysine: NE ratio on the F:G. In Exp. 2, the dietary NE density both linearly (P<0.05) and quadratically (P<0.05) affected the ADG and F:G. Barrows that received a diet containing 10.04 MJ kg−1 NE had a greater ADG (P<0.05) than barrows that received a 9.83 MJ kg−1 diet, but there was no difference (P>0.05) as compared with barrows that received a diet containing 10.25 MJ kg−1 NE. F:G was significantly higher (P<0.05) for barrows that received a 9.83 MJ kg−1 diet when compared with barrows that received the other two diets. The ADG was significantly decreased (P<0.05) for pigs that received a diet containing 0.69 g MJ−1 SID lysine:NE ratio when compared with pigs fed a diet containing 0.76 or 0.83 g MJ−1 SID lysine:NE ratio. The NE density or SID lysine:NE ratio and their interaction had no effect on the average daily feed intake, SUN, and carcass characteristic for finishing barrows (P>0.05). The overall results of the two experiments indicated that barrows that received the diet with the dietary CP level reduced 4 percentage units compared the NRC (1998) recommendations. Maximized the best performance with NE density and SID lysine: NE ratio were 9.87 MJ kg−1, 1.03 g MJ−1 NE for 20-50 kg pigs, and 10.04 MJ kg−1, 0.76 g MJ−1 NE for 60–100 kg pigs, respectively.