DL-Methionyl-DL-Methionine as a Methionine Source for Weaned and Growing Pigs

Methionine (Met) is often limiting in typical swine diets and balancing with supplemental Met sources to ensure optimal performance of pigs. Two studies were conducted to evaluate the relative bioavailability (RBV) of DL-Methionyl-DL-Methionine (DL-Met-Met) compared with DL-methionine (DL-Met) as Met sources in pigs. In Exp. 1, 42 barrows (PIC, initial BW of 21.0 ± 1.37 kg) were allotted to 7 experimental diets with 6 replicate pigs per treatment in a nitrogen balance study to evaluate the RBV of DL-Met-Met compared with DL-Met. A basal diet was formulated based on corn and soybean meal using analyzed ingredient AA contents to be deficient in Met [0.23% standardized ileal digestible (SID) Met; 0.47% SID Met+Cys; 1.15% SID Lys; diet 1] but adequate in all AA. Three graded levels of DL-Met (0.03, 0.06 and 0.09%) or DL-Met-Met (0.0306, 0.0612 and 0.0919%) were supplemented to the basal diet on top to create diets 2 to 7. In Exp. 2, 216 weaned pigs (PIC, initial BW of 10.2 ± 0.98 kg) were used. The dietary treatments consisted of a Met-deficient basal diet (0.24% SID Met; 0.53% SID Met+Cys; 1.30% SID Lys; diet 1) and the same supplemental levels of DL-Met and DL-Met-Met for Exp. 1 were used to produce diets 2 to 7. In Exp. 1, fecal and absorbed N were not different among the two Met sources. A linear increase (P < 0.05) in N retained (g/d), N retention (% of intake) and N retention (% of absorbed) were observed for supplementations with DL-Met or DL-Met-Met. The linear slope-ratio regression estimated the RBV of 109% [95% confidence intervals (CI): 57-160%] for N retention (% of intake), 111% (95% CI: 63-158%) for N retained (g/d) and 98% (95% CI: 43-154%) for N retention (% of absorbed), respectively on an equi-molar basis. In Exp. 2, the ADG and G:F increased linearly (P < 0.001) by additions of DL-Met or DL-Met-Met. Using a slope-ratio procedure, the RBV of DL-Met-Met to DL-Met were estimated to be 104% (95% confidence limits: 66-141%) and 117% (95% confidence limits: 61-174%) on an equimolar basis for ADG and G:F, respectively. In conclusion, the 95% CI for the RBV of DL-Met-Met cover 100% indicating DL-Met-Met is at least equally bioavailable as DL-Met as a Met source for pigs.