l-Lysine sulfate (Biolys), containing 54.6% l-Lys as well as other amino acids (AA) and phosphorus as fermentation co-products, is available as an alternative to l-lysine.HCl. A 21-d experiment was conducted to evaluate the relative bioavailability (RBV) on equimolar basis of Biolysrelative to l-Lys.HCl (set at 100% availability). A total of 135 barrows (PIC; initial BW of 12.46 ± 0.55kg) were assigned to 5 treatments with 9 pen replicates (3pigs/pen) for 21 d. A Lys-deficient basal diet (BD) was formulated to contain 0.57% standardized ileal digestible (SID) Lys but adequate in all other AA. The diets included (1) BD, (2) BD + 0.128% l-Lys.HCl, (3) BD + 0.256% l-Lys.HCl, (4) BD + 0.183% Biolys, and (5) BD + 0.366% Biolys. The final BW on d 21 and the overall ADG increased linearly (P < 0.01) by adding both Lys sources. Feed intake was not different but F:G improved (P < 0.01) linearly by supplementing both Lys sources. Performance responses (ADG, ADFI, F:G) of pigs fed diets supplemented with the same inclusion levels of l-Lys·HCl and Biolys were not different (P > 0.05). Using multiple linear regression and the slope ratio the RBV estimates were 104.1 and 113.3% for Biolys relative to l-Lys·HCl to optimize ADG and F:G, respectively. In conclusion, Biolysand l-Lys·HCl are equally bioavailable on equimolar basis as Lys sources for 12 to 25 kg pigs. Table 1. Performance and bioavailability (BV) of l-Lys sulfate for piglets from 12 to 25 kg¹

Item	BD	l-Lys HCl		Linear	Biolys			CV (%)
0.0%	0.128%	0.256%	0.183%	0.366%	Linear
BW, kg2	23.58B	24.35AB	25.23A	0.01	24.39AB	25.28A	0.03	5.1
ADG2	0.530A	0.566A	0.608A	0.01	0.568A	0.611A	0.03	10.4
F:G2	1.921A	1.730B	1.685B	0.01	1.721B	1.647B	0.01	7.1
BV of Biolys vs. l-Lys·HCl
Intercept	bLH	bBL	Bioavailability
ADG	0.634	0.392	0.408	104.1
F:G	1.938	–1.103	–1.250	113.3

^A,BMeans within a row with different letters differ (P < 0.05) by the SNK test. ¹Linear regression analysis; b^LH = l-Lys·HCl regression coefficients; b^BL = Biolys regression coefficients.