Performance and mineral status of weaning pigs fed diets with different levels of glyphosate and tryptophan

Abstract

Glyphosate-based herbicides (GBH), like Roundup, are used worldwide for weed control in genetically modified feed crops and pre-harvest desiccation of conventional crops, leaving glyphosate residues in feed made from these sources. Glyphosate possesses herbicidal and antimicrobial properties due to inhibition of the shikimate pathway, involved in aromatic amino acid synthesis in plants and microorganisms, including animal gut bacteria. Furthermore, glyphosate possesses mineral chelating properties. The objective of the present study was to investigate potential effects of dietary glyphosate residues (here glyphosate-amended feed) on livestock, focusing on performance and mineral status of weaning pigs. Two experiments were conducted with pigs from 20 litters (4 females and 4 males per litter), weaned on day 28 of age. In experiment I, 104 pigs from 13 litters were assigned to one of four treatments on the weaning day and fed a standard weaning diet amended with glyphosate as follows: no glyphosate (CON), 20 mg glyphosate/kg as Glyphomax HL (GM20) (Albaugh UK,Ltd., London, UK), 20 mg glyphosate/kg as IPA salt (IPA20) (Monsanto Company, St. Louis, MO, USA) and 200 mg glyphosate/kg as IPA salt (IPA200). The EU maximum residue level (MRL) of glyphosate is 20 mg/kg for a range of common feed ingredients. In experiment II, 56 pigs from seven litters were assigned to one of two treatments on the weaning day and fed a weaning diet similar to that used in experiment I, but without supplementation of crystalline tryptophan. The glyphosate amendments were: no glyphosate (CON-II) and 200 mg glyphosate/kg as IPA salt (IPA200-II). In both experiments, half of the pigs were euthanised on day 9/10 (referred to as day 9) and the other half on day 35 after commencement of the treatments. Individual weight, feed intake and faeces score were registered during the experiment, and small intestine digesta, blood and urine were sampled immediately after euthanising. Analysed levels of glyphosate in the diets were close to the intended levels; only, the glyphosate level in the control diets was not zero, indicating that glyphosate-free diets are difficult to obtain. The concentration of glyphosate in small intestine digesta, serum and urine reflected the treatment levels, e.g. at day 9, serum concentrations were 0.06, 10.9, 11.7 and 68.2 µg/L for CON, GM20, IPA20 and IPA200, respectively. Neither feed intake, growth rate, serum mineral concentrations nor faeces score were significantly affected by level or source (pure glyphosate salt or GBH) of the dietary glyphosate.