Absorption of methionine and 2-hydroxy-4-methylthiobutoanic acid in conventional and germ-free chickens

The apparent absorption of H-3-labeled L-Met and L-2-hydroxy-4-methylthiobutoanic acid (MHAFA) was compared in germ-free and conventional broiler chickens to determine the effect of intestinal bacteria on the absorption of Met and MHA-FA. The two diets contained 0.236% of added Met or MHA-FA. Nineteen germfree birds were maintained in two isolators and fed diets that had been sterilized by gamma irradiation (50 kilogreys). Nineteen conventional birds were reared in batteries and received nonirradiated feed. Diets were fed ad libitum for 3 wk. On d 21 of the experiment, the birds fasted overnight and were refed the experimental diets to which 1.11 x 10(7) Bq of 1-[methyl(3)H]MHA-FA or 1-[methyl(3)H]Met/kg of feed had been added. (CrCl3)-Cr-51 (1.11 x 10(7) Bq/kg of feed) was added as an indigestible marker. After 3 h the birds were euthanized, and their intestinal tracts were removed and partitioned into six sections. Residual Met and MHA-FA in digesta were calculated as the ratio of H-3: Cr-51 in each sample divided by the ratio of H-3: Cr-51 in the feed. The residual MHA-FA in the distal ileum of germ-free broilers was lower than in conventional birds (4.7 and 10.2% respectively; P < 0.05). In contrast the residual Met in the distal ileum of germ-free broilers was not different than in conventional birds (3.0 and 3.7% respectively; P > 0.05). This study demonstrates that intestinal bacteria significantly reduce the apparent absorption of MHA-FA from the intestinal tract of broiler chickens.