Journal or Publishing Institution: Aarhus University
Author(s): Katholm, C.L.
Article Type: Study
Record ID: 1208
Abstract: Glyphosate, is a broad-spectrum, nonselective, systemic herbicide, existing in the form of the acid itself or formulated as a salt. Roundup consists of the glyphosate isopropylamine (IPA) salt, water and a surfactant, often a polyethoxylated tallowamine, POEA. Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the shikimate pathway, which leads to formation of aromatic amino acids. As the shikimate-pathway is present in plants, fungi and bacteria, and not in animals, usually glyphosate has been considered as non-toxic to animals. However, recent studies have raised concerns about the effects of glyphosate on gut microbiota, indirectly affecting farm animals, when fed feed, containing residues of glyphosate. It has been proposed that glyphosate has a potential inhibiting effect on growth of commensal bacteria, normally occupying the gut of farm animals, whereas potential pathogens in general, should be more tolerant. The present study was conducted to investigate effects of glyphosate on growth of selected commensals and potential pathogens, in lab media. In addition, effects on the overall activity of microbiota in stomach, cecum and colon contents from pigs, as well as in rumen contents from cows, were investigated. Glyphosate acid, glyphosate IPA salt, Roundup and POEA, were included to differentiate eventual effects between different compounds, included in commercial glyphosate formulations. We were able to show that glyphosate suppressed growth of both commensals and potential pathogens, and that inhibition differed between gram-positive and gram-negative bacteria; gram-negative being more tolerant towards all treatments. In addition, glyphosate changed fermentation pattern in the gut of pigs and
cows and overall, the effect of glyphosate depended on the chemical formulation (acid, salt, mixture and surfactant) used. In general, glyphosate acid were the least toxic of the treatments, whereas toxicity levels of glyphosate IPA salt, Roundup and POEA were higher and more similar. The concentrations, at which we observed an effect on gut content, were much higher than the concentrations affecting individual bacteria, indicating that gut microbiota is complex. As pigs and cows are not fed glyphosate directly, feeding trials should be performed, to give a better indication of how, and if, the animals are affected by residues of glyphosate in feed.
Keywords: Glyphosate, Roundup, gut microorganisms, farm animals, polyethoxylated tallowamine, POEA, pigs, cows, pig, cow, bacteria, microbiota
Citation: Katholm, C.L., 2016. Effects of Roundup (glyphosate) on gut microorganisms of farm animals. Doctoral dissertation, MSc Thesis. Aarhus University, Department of Animal Science.