PSV-11 - Effects of standardized ileal digestible lysine: Crude protein ratio in diets with or without distiller’s dried grains with solubles on growth performance of 11- to 20-kg pigs

Abstract: The NRC (2012) suggests a minimum of 2.56% standardized ileal digestible (SID) nitrogen for 11- to 20-kg pigs, which equates to a SID Lys:crude protein (CP) ratio of 6.5 when comparing to the NRC (2012) SID Lys requirement estimate. Validation of this ratio will help determine the range of feed-grade amino acids that can be fed to balance economic outcomes while avoiding performance losses. Further research is warranted to determine the SID Lys:CP ratio required in diets containing different sources of CP such as DDGS. A total of 5,059 pigs (PIC 800 × Camborough and DNA 600 × 241; initially 11.0 ± 0.90 kg) were used in an 18-d trial to evaluate the effects on growth performance of 11- to 20-kg pigs fed different SID Lys:CP ratios in diets with and without DDGS. Pigs were weaned at approximately 21 d of age and housed in mixed-sex pens with approximately 35 pigs per pen. A pelleted early nursery diet was fed to all pigs from weaning until the beginning of the experiment. When pigs reached approximately 11 kg, pens were assigned to 1 of 12 treatments in a completely randomized design. A total of 143 pens were used with pen serving as the experimental unit, resulting in 11 or 12 replications per dietary treatment. Experimental treatments were arranged in a 2 × 6 factorial with main effects of DDGS (0 or 15%) and SID Lys:CP ratio (6.01, 6.22, 6.45, 6.70, 6.97, and 7.26). Pigs were weighed at the beginning of the study and at the end on d 18. Overall (d 0 to 18), a SID Lys:CP × DDGS interaction was observed (linear, P < 0.001) where G:F was improved (quadratic, P < 0.001) in diets without DDGS, with the poorest G:F at the lowest and highest Lys:CP ratios; whereas in the diets with DDGS, G:F decreased (linear and quadratic, P ≤ 0.002) as the SID Lys:CP ratio increased above 6.45. For the main effects, ADG increased quadratically (P = 0.021) as the SID Lys:CP ratio increased, with the greatest ADG with ratios of 6.45 to 6.97. Conversely, ADFI increased (linear, P = 0.018) as SID Lys:CP increased. A tendency was observed for pigs fed diets containing DDGS having decreased (P = 0.071) ADG and G:F. In conclusion, formulating diets to a SID Lys:CP ratio of 6.70 without DDGS and 6.45 in diets with DDGS increased G:F, and further increasing the ratio leads to a decrease in G:F, possibly due to nitrogen becoming the limiting factor as CP is decreased. Additionally, feeding diets without DDGS can lead to an increase in ADG and G:F.