A total of 408 weaned pigs (19 d of age; 6.59 kg initial BW) were used in a 3-phase feeding program to evaluate effects of increasing levels of crystalline L- Lysine on performance of nursery pigs. Pigs were blocked by weaning BW and allotted to 44 pens which were assigned to one of 4 dietary treatments (9-10 pigs/pen; 11 pens/treatment), including the control diet supplemented with one of the four L-Lysine levels: 0.3% (L1), 0.5% (L2), 0.6% (L3), or 0.7% (L4). Diets were formulated to be isocaloric and contained 1.40, 1.32, and 1.25% Sid Lys for phase 1, 2, and 3, respectively. L-Val, L-His and L-Arg were included in the L2, L3, and L4 treatments in addition to DL-Met, L-Thr, L-Trp, and L-Ile which were offered in all diets. In Phase 1 (d 0-9), no effects of L-Lys levels on performance were observed (P > 0.10). In Phase 2 (d 9-21), increasing L-Lys from L2 to L4 Lys reduced ADG (Linear, P < 0.001), while L4 also reduced ADFI (Linear, P = 0.01) and feed efficiency (Linear, P < 0.001). In Phase 3 (d 21-42), L3 and L4 significantly improved feed efficiency (Linear, P = 0.001). Overall (d 0-42), feeding L-Lys at L4 tended to reduce ADG (Linear, P < 0.10) and ADFI (Linear, P < 0.10), while feeding L-Lys at L3 improved feed efficiency (Cubic, P < 0.05).
Data of this study suggest that responses to high levels of L-Lys are more profound on feed efficiency during phase 2 and 3. Inclusion level of L-Lys at 0.3% is best for gain but 0.6% is the best for optimal feed efficiency. Increasing L-Lys level to 0.7% enhanced feed efficiency in phase 3, but reduced all performance measures in Ph1, 2, and overall.