Effect of sub-therapeutic levels of antimicrobials in feed on the intestinal carriage of Campylobacter and Salmonella in turkeys

Since the 1950s, antimicrobials have been added to poultry feed at sub-therapeutic levels to minimize illness and promote growth. Despite the benefits to the agricultural industry and domestic animals, there are fierce debates worldwide on whether or not this practice carries a consequence in terms of human health. Turkeys and broilers provided these additives have increased weight gain, muscle yield, and feed conversion-in part due to decreases in diseases such as coccidiosis and necrotic enteritis. Benefits achieved by adding these compounds to animal feeds are attributed in part to a shift in the gut microflora. However, studies have been published in which it was determined that competitive exclusion cultures, administered to birds to control colonization by human pathogens such as Salmonella, can be negatively affected by antimicrobials commonly used in poultry rations. Other published studies have reported an increase in Salmonella levels when experimentally challenged birds were fed diets containing low levels of antimicrobials. This study demonstrated that although naturally occurring populations of Campylobacter were virtually unaffected by antimicrobial feed additives, Salmonella populations were significantly decreased when commercial turkeys were fed rations containing flavomycin, virginiamycin, or monensin.