Methionine hydroxy analogue (DL-HMTBA) and DL-Methionine can be replaced with 67 % and 90.5 % of L-Methionine By Dr. Behnam Saremi, Head of Technical Center, CJ Europe GmbH
Methionine isomers and precursors and their conversion to L-Methionine Methionine is the first limiting amino acid in poultry and one of the first limiting amino acids in other species. Usual corn-soy diets are limited in methionine. Thus, supplementing methionine to feed in order to balance amino acids has a long history in animal nutrition. The first methionine sources which became commercially
available were DL-Methionine and its hydroxy analogue (DL-HMTBA or MHA-FA or MHA-Ca). These methionine sources are produced from nonrenewable resources through chemical synthesis, consequently D-Met and DL-HMTBA are not natural sources of methionine. Thus D-Met and DL-HMTBA need to be transformed to L-Methionine by the animal itself which costs energy, enzyme activities, amino acids (for amination of Keto-Methionine) and cellular capacities (Fig 1).
Figure 2. FCR of chickens at 37 days of age feeding different levels of DL and L-Met.
DL-HMTBA has a lower bioavailability compared with DL-Met
varying from 45 to 88 % for MHA-FA (MHA-FA contains 12 % water) depending on parameter (body weight, FCR, or breast muscle yield), starting level of sulfur amino acid and the applied estimation model (Sauer et al. 2008). On average, commercially accepted levels of bioavailability are 77 % for DL-HMTBA compared with DL-Met.
Figure 1. Metabolism of different dietary methionine (Met) sources. Met isomer D-Met and Met precursor DL-2-hydroxy-4- (methylthio) butanoic acid (DL-HMTBA) must be converted to L-Met for utilization. Different enzymes and cofactors play roles in this process (Zhang et al. 2018). D-AAOX: D-amino acid oxidase; L-HAOX: L-2-hydroxy acid oxidase; D-HADH: D-2-hydroxy acid dehydrogenase; KMB: 2-keto-4 methylthio butanoic acid.
However, nowadays L-Methionine which is produced from
renewable resources is also commercially available (in high volumes). Crystalline L-Methionine provides the opportunity of relieving farm animals from the extra unnecessary job of converting these isomers and precursors to L-Methionine.
Bioavailability of methionine sources End-users are always confronted with the question of bioavailability of methionine sources because of commercial and nutritional interests. Professor Baker is the major cited scientist when it comes to bioavailability of methionine sources (Katz and Baker, 1975). “L-Methionine is a better source of sulfur amino acids than D-methionine” Baker wrote and reported a bioavailability of 90 % for D-Met in chicken (Baker, 1994). More recent publications from Shen
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Radio-labeled methionine sources To better understand why the differences between methionine sources, Saunderson publications are very useful (Saunderson, 1985 and 1987). Saunderson (1985) published a paper using radio-labeled methionine sources. DL-Met was excreted at 10 % of the given dosage. DL-HMTBA was excreted at 21 % of given dosage while L-Met was excreted only at 2 % of the given dosage (Fig 3).
et al. (2015) as well as Esteve-Garcia and Khan (2018) found a lower bioavailability for DL-Methionine compared with L-Methionine (71 and 77% vs. L-Met 100%) in modern broilers (Fig 2).
Figure 3. Excretion of 14 from Saunderson, 1985).
C labelled DL-Met, L-Met and HMB (adapted Moreover, DL-Met had the highest oxidation rate (5.5 % of the
given dosage). DL-HMTBA was oxidized at 3-7 % of given dosage (5.0 ± 1.8 %) while L-Met oxidation was limited to 4.2 % of the dosage given (Fig 4).
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