New biological and economic data from the University of Missouri suggests the sulfur amino acid:lysine ratio for pigs weighing 15-38 lb. is approximately 60%.

Lysine is generally the first-limiting amino acid in typical swine diets. Depending on the diet composition, methionine is considered the second- or third-limiting amino acid. As a result, commercial diets for young pigs are normally supplemented with a methionine source.

Supplemental methionine is available as DL-methionine in a 99% powder or 40% liquid, and as an 88% aqueous solution of 2-hydroxy-4- (methylthio) butanoic acid, which is the Alimet® feed supplement from Novus International.

Research has shown that the early weaned pig can utilize Alimet® and DL-methionine with the same efficiency as long as both are based on the same molar equivalency. Therefore, the optimum sulfur amino acid:lysine ratio can be determined using either source.

Evaluating Ideal Ratios

The objective of the University of Missouri research was to evaluate the ideal ratio of sulfur amino acid:lysine ratio for young nursery pigs using both DL-methionine and Alimet® as supplemental methionine sources.

Experiment 1 randomly allotted 1,050 nursery pigs to one of five dietary treatments at a weight of 15.5 lb. The dietary treatments included five different sulfur amino acid:lysine ratios of 48.9, 53.5, 58.1, 62.6 and 67.2% of total lysine, respectively.

In Experiment 2, 1,549 nursery pigs were allotted to one of nine dietary treatments at an average weight of 18.2 lb. Diet 1, the control diet, was formulated to contain 1.32% true ileal digestible lysine with no supplemental Alimet® or DL-methionine (47.7% sulfur amino acid:lysine ratio). Diets 2 through 9 consisted of the control diet supplemented with four levels of DL-methionine or Alimet® that corresponded to sulfur amino acid:lysine ratios of 52.7, 57.7, 62.7 and 67.7%, respectively.

Growth performance data was collected for 21 days in Experiment 1, and for 14 days in Experiment 2. Body weights and feed intakes were recorded at the beginning and end of the trials.

Statistical analysis indicated no differences in growth performance traits between the methionine sources evaluated in Experiment 2. Thus, final data are presented by dietary treatment, evaluating only the effect of increasing sulfur amino:lysine ratio.

Growth performance data for Experiments 1 and 2 are presented in Tables 1 and 2, respectively.

Based on the results of the two experiments, the ideal ratio of sulfur amino acid:lysine was estimated to be 61.3% on a total basis, or 55.9% on a true digestible basis. However, using the combination of biological and economic data, the optimal sulfur amino acid:lysine ratio was estimated to be 62.6% on a total basis, or 57.7% on a true digestible basis.

As the Missouri researchers demonstrated in previous studies, an estimation of the sulfur amino acid requirement can be determined with either Alimet® or DL-methionine, as long as both are based on the same molar equivalency.

Researchers: Aaron Gaines, Brent Ratliff, Pairat Srichana, Gary Allee, University of Missouri-Columbia; and Ganfeng Yi and Chris Knight, Novus International, St. Louis, MO. Contact Gary Allee at (573) 882-7726.

Table 1. Effect of Sulfur Amino Acid (SAA) Lysine Ratio (Total Basis) on Nursery Pig Performance (Experiment 1)a
DL-Methionineb
SAA: Lysine Level 48.9 53.5 58.1 62.6 67.2
Body weight, Day 0 (lb.) 15.5 15.6 15.5 15.6 15.5
Body weight, Day 21 (lb.) 37.1 37.2 37.9 38.2 37.7
Average daily gain (lb.) 1.02 1.03 1.06 1.08 1.06
Average daily feed intake (lb.) 1.44 1.41 1.44 1.44 1.47
Feed:Gain 1.41 1.37 1.35 1.34 1.39
Return over feed $/pigc 6.65 6.78 6.98 7.15 6.88
aMeans calculated from six replicate pens/dietary treatment. Growth performance was evaluated for 21 days.
bLinear and quadratic comparisons were used for diets containing DL-methionine (48.9% - 67.2% sulfur amino acid- to-lysine ratio).
cReturn over feed $/pig takes into account income over feed cost and is a combination of biological and economic data.


Table 2. Effect of Sulfur Amino Acid (SAA) Lysine Ratio (True Digestible Basis) on Nursery Pig Performance (Experiment 2)a
DL-Methionineb
SAA: Lysine Level 47.7 52.7 57.7 62.7 67.7
Body weight, Day 0 (lb.) 18.2 18.3 18.3 18.3 18.2
Body weight, Day 14 (lb.) 32.0 32.3 32.5 32.6 32.2
Average daily gain (lb.) 0.99 1.00 1.02 1.02 1.00
Average daily feed intake (lb.) 1.35 1.33 1.33 1.34 1.31
Feed:Gainc 1.37 1.33 1.31 1.31 1.32
Return over feed $/pigd 4.42 4.51 4.61 4.59 4.46
aMeans calculated from eight replicate pens/dietary treatment. Growth performance was evaluated for 14 days.
bLinear and quadratic comparisons were used for diets containing an added source of methionine (47.7%- 67.7% sulfer amino acid- to-lysine ratio).
cMeans within a row without a common superscript differ (P < 0.05).
dReturn over feed $/pig takes into account income over feed cost and is a combination of biological and economic data.