Year of Publication


Degree Name

Master of Science (MS)

Document Type

Master's Thesis


Agriculture, Food and Environment


Animal and Food Sciences

First Advisor

Dr. Merlin D. Lindemann


DL-Methionine (Met) has been conventionally used in swine diets with assumption of similar bioefficacy with L-Met. However, because L-Met is the form that is utilized by animals for protein synthesis, L-Met could, theoretically, be more available. Four experiments were conducted to evaluate L-Met bioavailability in nursery pigs with 21-day growth trials. A total of 105,105,112 and 84 crossbred pigs were used in Exp. 1, 2, 3 and 4, respectively. Each experiment had a low Met basal diet and 3 levels of the Met sources (DL-Met and L-Met). In addition to the basal diet, supplementation levels were 0.053%, 0.107% and 0.160% in Exp. 1, 0.040%, 0.080% and 0.120% in Exp. 2, 0.033%, 0.067% and 0.100% in Exp.3, 0.040%, 0.080% and 0.120% in Exp. 4. Body weight (BW), average daily gain (ADG), average daily feed intake (ADFI), gain: feed (G:F) were measured and plasma urea nitrogen (PUN) was analyzed in blood samples weekly. In Exp. 3 and 4, preference studies were conducted with the basal diet and the second highest level of each Met source. When additional DL-Met or L-Met were supplemented to the basal diet, BW, ADG, ADFI, and G:F ratio increased (P < 0.05). In the comparison between the DL-Met and L-Met diets in Exp. 1, pigs in the L-Met group had greater ADG and G:F ratios in the d 0-7 (P < 0.05) period than those in the DL-Met group. However, there were no differences for the overall experimental period. In Exp. 2, pigs in the DL-Met group had greater BW (P < 0.05), ADG (P < 0.05) and ADFI (P < 0.05) than those in the L-Met group for the overall period whereas no differences were observed in G:F ratios and PUN concentrations. In Exp. 3 and 4, there were no differences in BW, ADG, ADFI, G:F ratios or PUN concentrations between L-Met and DL-Met groups for the overall period. There was no preference exhibited for either the DL-Met or L-Met diet. In the results of relative bioavailability of L-Met to DL-Met, the values was 111.1% for d 0-14 based on the estimation by ADG in Exp. 1; L-Met bioavailability was lower than DL-Met based on all response measures in Exp. 2. However, in Exp. 3, relative bioavailability of L-Met to DL-Met was 100.4, 147.3, and 104.1% for d 0-14 ADG, G:F ratio and PUN concentrations. In Exp 4, the relative bioavailability of L-Met was 92.9, 139.4 and 70.4% for d 0-14 ADG, G:F ratio and PUN concentrations. In conclusion, using L-Met in the nursery diet demonstrated no consistent beneficial effect on ADG, G:F ratio or relative bioavailability compared to conventional DL-Met.