Effect of different dietary methionine sources on intestinal microbial populations in broiler chickens.

Two experiments were conducted to study the effect of various levels of DL-Met or 2-hydroxy-4-methylthiobutanoic acid (MHA-FA) on Clostridium perfringens and other intestinal bacteria in broiler chickens. In each experiment, 2 cages of 6 birds (14 d posthatch) were assigned to 1 of 7 different diets in a 2 x 4 factorial arrangement. The main effects were Met source (either DL-Met or MHA-FA) and Met level (0, 0.2, 0.4, or 0.8% dl-Met or 0, 0.227, 0.454, and 0.908% MHA-FA, thus providing 4 corresponding equimolar levels of each Met source). All birds were orally gavaged with a C. perfringens type A broth culture on d 1 and on d 14 to 20 and killed on d 28. Intestinal populations of C. perfringens, lactobacilli, Streptococcus group D, and coliforms were enumerated in the ileum and cecum, and necrotic enteritis intestinal lesions were scored. There was a significant reduction (P < 0.05) in C. perfringens populations in birds fed either Met source in the cecum (experiment 1) or the ileum and cecum (experiment 2). In experiment 2, the lactobacillus populations were significantly higher (P < 0.05) in the ceca of birds receiving 0.8% Met than in the birds given diets with the other levels of Met tested. Significantly lower populations (P < 0.05) of coliforms and Streptococcus group D were enumerated in the ileum of birds fed the 0.8% Met-supplemented diet than in the other dietary treatments. The effect of Met source on intestinal bacteria was not significant, suggesting that both DL-Met and MHA-FA have similar antibacterial properties. Last, there were no significant differences in intestinal lesion scores or the performance of birds fed different Met sources and concentrations. The results suggest that both DL-Met and MHA-FA may reduce intestinal populations of C. perfringens in broiler chickens when used in relatively high concentrations, and may reduce the risk of necrotic enteritis. Thus, feeding low-protein diets supplemented with crystalline amino acids might be beneficial in terms of the growth of various enteric pathogens.