Commercial diets for tilapia juveniles contain high levels of plant protein sources. Soybean meal has been utilised due to its high protein content; however, soy-based diets are limited in methionine (Met) and require its supplementation to fulfil fish requirements. dl-Methinone (dl-Met) and Ca bis-methionine hydroxyl analogue (MHA-Ca) are synthetic Met sources supplemented in aquafeeds, which may differ in biological efficiency due to structural differences. The present study evaluated the effect of both methionine sources on metabolism and growth of Nile tilapia. A growth trial was performed using three isonitrogenous and isoenergetic diets, containing plant ingredients as protein sources: DLM and MHA diets were supplemented on equimolar levels of Met, while REF diet was not supplemented. Hepatic free Met and one-carbon metabolites were determined in fish fed for 57 d. Metabolism of dl-Met and MHA was analysed by an in vivo time-course trial using 14C-labelled tracers. Only dl-Met supplementation significantly increased final body weight and improved feed conversion and protein efficiency ratios compared with the REF diet. Our findings indicate that Met in DLM fed fish follows the transsulphuration pathway, while in fish fed MHA and REF diets it is remethylated. The in vivo trial revealed that 14C-dl-Met is absorbed faster and more retained than 14C-MHA, resulting in a greater availability of free Met in the tissues when fish is fed with DLM diet. Our study indicates that dietary dl-Met supplementation improves growth performance and N retention, and that Met absorption and utilisation are influenced by the dietary source in tilapia juveniles.

The aim of the present study was to evaluate the effects of heat stress (HS) and methionine supplementation on the markers of stress and on the gene expression levels of uncoupling proteins (UCP), betaine–homocysteine methyltransferase (BHMT), cystathionine β-synthase (CBS), glutathione synthetase (GSS) and glutathione peroxidase 7 (GPx7). Broilers from 1 to 21 d and from 22 to 42 d of age were divided into three treatment groups related to methionine supplementation: without methionine supplementation (MD); recommended level of methionine supplementation (DL1); excess methionine supplementation (DL2). The broilers were either kept at a comfortable thermal temperature or exposed to HS (38°C for 24 h). During the starter period, we observed the effects of the interaction between diet and environment on the gene expression levels of UCP, BHMT and GSS. Higher gene expression levels of UCP and BHMT were observed in broilers that were maintained at thermal comfort conditions and received the MD diet. HS broilers fed the DL1 and DL2 diets had the highest expression level of GSS. The expression levels of the CBS and GPx7 genes were influenced by both the environment and methionine supplementation. During the grower period, the gene expression levels of BHMT, CBS, GSS and GPx7 were affected by the diet × environment interaction. A higher expression level of BHMT was observed in broilers maintained at thermal comfort conditions and on the MD diet. HS induced higher expression levels of CBS, GSS and GPx7 in broilers that received the DL1 and DL2 diets. The present results suggest that under HS conditions, methionine supplementation could mitigate the effects of stress, since methionine contributed to the increased expression levels of genes related to antioxidant activity.

This report will cover studies of the metabolism of a supplemental source of L-methionine (L-met), Alimet® feed supplement. The goal of these studies was to gain an understanding of how this methionine precursor is converted to L-methionine and how it is used by the chick, in order to optimise the conditions for its use. The methionine precursor in Alimet is 2-hydroxy-4- (methylthio) butanoic acid (HMB). HMB differs from methionine by having a hydroxyl group on the alpha carbon rather than an amino group. Like synthetic DL-met, HMB has one asymmetrical carbon atom and therefore occurs as a mixture of 50% L-isomer and 50% D-isomer. Because HMB bears a hydroxyl group instead of an amino group, it is an organic acid. Until it is converted to L-met antimicrobial properties of HMB resemble those of organic acids such as lactic acid. Once inside the tissue of the animal, however, HMB is rapidly converted to L-met. Following conversion to L-met, HMB will have the same availability for methyl group transfer or cysteine synthesis as L-met from any other source. This report will cover the bioavailability of HMB polymers, the conversion of HMB to L-met and the role of HMB in normal L-met intermediary metabolism. It will also include a discussion of HMB absorption and incorporation into protein.