Submitted to: Applied Poultry Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2000
Publication Date: N/A
Interpretive Summary: The addition of certain antibiotics to animal feed at sub- therapeutic levels for an extended period of time is a common practice in animal production. The practice provides benefit by increasing weight gain, improving feed efficiency, and/or modification of other production parameters. The use of growth-promoting antibiotics in animal feeds is controversial due to the potential for disruption of the enteric flora in food animals. Indigenous enteric bacteria are thought to act as a barrier to colonization/infection by bacterial pathogens. Another concern is the development of antibiotic-resistant bacteria resulting in reduced effectiveness of antibiotics in treating animal or human disease. This study was conducted to detect changes in populations of the "normal" intestinal bacteria of commercial turkeys following a change from feed containing a coccidiostat to feed containing one of the antibiotics: bacitracin, virginiamycin, or Flavomycin. For the first two weeks, changes in intestinal bacterial populations were transient and limited. Four weeks after feed change, bacterial cells of the lactobacilli and clostridia groups were higher in number compared to numbers of these bacteria before the feed change. Bacitracin, virginiamycin, and Flavomycin had similar effects on intestinal bacterial populations. The consistency and implications of changes in populations of lactobacilli and clostridia after the change in feed antimicrobials remains to be determined.
Technical Abstract: Two trials were conducted to detect changes in the populations of intestinal bacteria of commercial turkeys after changing from a feed containing the coccidiostat, monesin, to a feed containing one of the growth-promoting antibiotics, virginiamycin, Flavomycin, or bacitracin. The first trial involved sampling turkeys from a commercial operation that replaced feed containing monensin with one containing bacitracin when the flocks were 11 weeks old. The second trial involved transporting, at five weeks of age, turkeys obtained from a commercial operation to a research facility with isolator floor pens and controlled environmental conditions and housing them for another three weeks. After this period, the feed which contained monensin was removed and replaced with one of five feed treatments: (1) no antimicrobial, (2) monensin as before, (3) virginiamycin (4) Flavomycin, or (5) bacitracin. At various times in both trials, before and after the change in feed antimicrobials, birds were sacrificed and their intestinal contents sampled for numbers of total aerobic, bacteria, Enterobacteriaceae, lactobacilli, total anaerobic bacteria, and clostridia. In the first trial, the counts for each bacterial group were similar at flock ages of 4, 8 and 12 wks. At 16 wks the numbers of lactobacilli & clostridia, but not of the other bacterial groups, were significantly higher at 16 wks compared to numbers at 4-12 wks. The population changes in the second trial were transient and not widespread, i.e., not observed for more than one day or one of two intestinal sampling sites. The numbers for each of the bacterial groups were similar in birds treated with virginiamycin, Flavomycin, or bactracin.