Effects of Intestinal Modification by Antibiotics and Antibacterials on Utilization of Methionine Sources by Broiler Chickens

This is the authors' abstract. We don't add key points for this paper.

A study was conducted to determine if the response to different sources of Met was influenced by the presence or absence of antibiotics and antibacterials that might alter intestinal microflora. A Met-deficient diet (0.33% by analysis), based on corn and soybean meal, was fed with or without a mixture providing 200 g/ton of bacitracin methylene disalicylate, 200 g/ton of chlortetracycline, 100 g/ton of penicillin, and 100 g/ton of sulfaquinoxaline. Diets were fortified with DL-Met or the liquid form of 2-hydroxy-4-methylbutanoic acid (HMB) to provide supplemental levels of Met ranging from 0.0 to 0.20% in increments of 0.04%, based on 99% activity for DLDL-Met and 88% activity for HMB. The experimental treatments consisted of a 2 × 2 × 6 factorial arrangement of treatments with 2 diet types (medicated and unmedicated), 2 Met sources (DL-Met and HMB) at 6 levels of supplementation for a total of 24 dietary treatments. Each of these was fed to 6 replicate pens of 5 male chicks from 0 to 21 d, stratified across tiers in the battery. Feeding the medicated diets resulted in a significant reduction in intestinal bacterial as measured by total aerobic plate count of ileal contents, with significant improvements in BW and feed conversion. However, there were no significant interactions between the medications and the response to the 2 sources of Met. There was no difference in BW or feed conversion related to the 2 different sources of Met when fed to provide equimolar amounts of Met activity. Chicks responded to increasing levels of Met, but there was no interaction between source and level of Met for BW or feed conversion. Peak response appeared to occur at approximately 0.08% supplemental (0.41% total) Met, somewhat below current NRC recommendations. It does not appear that a difference in antibiotic content of test diets is responsible for the discrepancy in reported responses to the 2 sources of Met.