Effect of fasting and of methionine deficiency on L-methionine, DL-methionine and DL-2-hydroxy-4-methylthiobutanoic acid metabolism in broiler chicks

Abstract

1. Metabolism of L-[1-14C]methionine, DL-[l-14C]methionine and DL-[ 1-14C]2-hydroxy-4-methylthiobutanoic acid (DL-HMB) by broiler chicks which had been fasted overnight or given a methionine-deficient diet was compared with fed (control) birds.2. The excretion of 14C-labelled material, total 14CO2 exhaled, 14C incorporation into tissue proteins and the 14C-labelled material in perchloric-acid-soluble tissue fractions were measured 6 h after injection of the 14C-labelled materials.3. The incorporation of 14C into tissue proteins and the relative rates of conversion of D-methionine and DL-HMB to L-methionine in tissues under different nutritional regimens were compared using protein-bound 14C:protein-free 14C values.4. Fasted birds exhaled more 14CO2 than control birds but excreted less 14C, while methionine-deficient birds behaved very similarly to the control animals in these respects.5. Fasted birds incorporated much less 14C into proteins of tissues other than liver and kidney from all three labelled tracers. The values for protein-bound 14C: protein-free 14C were lower in all tissues.6. Methionine-deficient birds had similar levels of 14C in tissue proteins but lower values for protein bound 14C: protein-free 14C.7. Examination of the values for protein-bound 14C:protein-free 14C suggest that brain and probably liver tissues from fasted and methionine-deficient birds showed improved rates of conversion of D-methionine and DL-HMB to L-methionine compared with control animals.

Bioavailability ofl-methionine relative todl-methionine in Broiler chickens

“…In the present study, supplementing L-Met to the diets elevated or tended to increase EW and BMW, LMW and LMY of broilers compared with DL-Met. One possible explanation for this would be that L-Met rather than D-Met was directly incorporated into protein biosynthesis, resulting in a greater efficiency of L-Met involved in body weight gain of broilers (Saunderson 1987). The respective RBA of L-Met to DL-Met for EW and BMW of birds were 122.9% and 116.8%, which, however, were not significantly different from 100%.…”

“…In the present study, L-Met addition resulted in higher ADG and FE of broilers compared with DL-Met, and the respective RBA of L-Met to DL-Met for ADG and FE of birds were 141.5% and 189.1%, the latter of which was different from 100%. These demonstrated that supplemental L-Met had an advantage over DL-Met for supporting the growth performance of broilers at an early age (1 to 21 d of age), which might be associated with the higher efficacy of L-Met than DL-Met utilised for protein synthesis in certain tissues such as skin and muscle in chickens (Saunderson 1987). In addition to the species of animals, the difference in the age of animals might also be responsible for the discrepancies in the bioefficacy of Met isomers (Cho et al 1980;Shen et al 2014), since research has indicated that that utilisation of Met isomers in animals was likely a function of age (Shen et al 2014).…”

Effect of arginine:lysine and methionine source on amino acid digestibility and response to dietary electrolytes in chronically or acutely heat-stressed broilers

“…These results perhaps imply that birds fed DLM are more susceptible to the negative effects of Arg:Lys ratio compared with those fed HMB. While differences in absorption, metabolism, organ distribution and/or clearance between HMB and DLM (Saunderson 1985(Saunderson , 1987Dibner 2003) may also play a role, changes in the efficacy of either source of Met to fulfill the birds' requirements for total sulfur amino acids during HS cannot be discounted. Dibner et al (1992) and Knight et al (1994) measured the absorption of DLM in vitro as affected by HS in broilers.…”

Bioavailability of different dietary supplemental methionine sources in animals

“…This process is up-regulated by HMTBA, but the transamination is not affected by HMTBA availability (26). Under fasting or methionine deficient conditions, brain and liver showed enhanced rates of DL-HMTBA and DL-Met conversion (30). In non-ruminants, oxidation is the major pathway for HMTBA catabolism.…”