The Evaluation of the Bioavailability of L-Lysine Sulfate Relative to L-Lysine HCl for Growing-Finishing Pigs

The objective of this experiment was to evaluate the bioavailability of L-Lysine sulfate (Biolys; Evonik Industries AG, Kennesaw, GA) relative to L-Lysine HCl for pigs weighing 26 to 48 kg (Phase 1) and 68 to 98 kg (Phase 3). A total of 280 pigs were randomly assigned to 1 of 7 treatments utilizing 56 pens each housing 5 barrows (n=28) or 5 gilts (n=28). A basal diet based on corn and soybean meal was formulated on an SID lysine basis to achieve 65% of the Lys requirement; to this was added L-Lysine HCl (78.8% Lys) or L-Lysine sulfate (54.6% Lys) to meet 75%, 85% or 95% of the requirement for SID Lysine. Phase 2 was a common diet fed for 21 days to all pigs to eliminate the effects of treatment during phase 1; consequently, BW were not different across treatment at the beginning of phase 3 (P = 0.47). Body weights and feed intake were recorded for each phase. Performance data were analyzed as a completely randomized design utilizing pen as the experimental unit. To estimate relative bioavailability (RBV) of lysine, orthogonal-polynomial contrasts were used to determine linear and quadratic effects of increasing levels of lysine on ADG and G:F and the effect of lysine source. The bioavailability of L-Lysine sulfate was expressed relative to L-Lysine HCl, which was assumed to be 100%. There was no effect of source for any variable in either growth phase (P > 0.35). Based on daily lysine intake (g/d) and using ADG as the response criteria, the RBV of lysine from L-Lysine sulfate was not different from L-Lysine HCl (90% and 106% in phases 1 and 3, respectively; P > 0.10). Based on % lysine in the diet, in phase 1, the RVB of lysine from L-Lysine sulfate was 107% of L-Lysine HCl for ADG and 97% for G:F (P > 0.10). In phase 3, RBV was 106% based on ADG and 104% based on G:F (P > 0.10). Following phase 3, pigs remained on experimental treatments until they reached an average hot carcass weight of 85.0 kg; there was no effect of lysine source for dressing percent, backfat, loin depth or percent lean (P > 0.10). However, backfat depth declined as lysine level increased (P < 0.01). In conclusion, the RBV of lysine from L-Lysine sulfate is not different from that of L-Lysine HCl in growing-finishing pigs.