Performance and mineral status of laying hens fed diets with different levels of glyphosate

Abstract

Concern has been raised about the potential influence of glyphosate on livestock health and performance due to its antimicrobial and mineral-chelating properties. The present study investigated potential effects of feeding diets amended with glyphosate (as a commercial product, Glyphomax HL, or as pure isopropylamine salt, IPA) to laying hens (layers). At the age of 22 weeks, a total of 320 Lohmann LSL-Lite layers started on one of four treatment diets: Control (CON), 20 mg glyphosate/kg as Glyphomax HL (GM20), 20 mg glyphosate/kg as IPA (IPA20) and 200 mg glyphosate/kg as IPA (IPA200). The EU-defined maximum residue level (MRL) of glyphosate for several feed crops is 20 mg/kg. The layers were housed in 32 enriched cages for 27 weeks. Glyphosate levels in the diets (mg/kg feed) were analysed to 0.03 for CON, 19.3 for GM20, 18.5 for IPA20 and 191.7 for IPA200. Using preselected contrasts, there were no clear effects of diet glyphosate amendment on average egg weight, egg mass, feed intake, feed conversion ratio and rate of lay, while post hoc contrasts suggested that diet glyphosate concentrations above 20 mg/kg may reduce rate of lay by 0.9%-point. Mineral levels of Mg, Ca, Mn, Fe, Cu and Zn in blood as well as indicators of welfare measured by plumage scoring and by a novel object test were not significantly affected by treatment. Glyphosate levels in blood serum (µg/L) were 0.29 for CON, 22.5 for GM20, 25.0 for IPA20 and 128.9 for IPA200. Glyphosate levels in egg yolk and egg white (ng/g) were respectively 0.26 and 0.01 for CON, 20.1 and 0.20 for GM20, 21.4 and 0.25 for IPA20 and 223.3 and 3.09 for IPA200. Glyphosate concentrations in blood serum, egg yolk and egg white reflected diet concentrations. The glyphosate degradation product, AMPA, followed the same trend as glyphosate in all analysed compartments. In conclusion, there were no clear adverse effects of glyphosate-amended diets on performance, welfare indicators and mineral status of Lohmann LSL-Lite layers even at a level approximately 10x higher than the MRL for soybeans and other common feed crops (20 mg glyphosate per kg feed). However, post hoc contrasts suggested that diet glyphosate concentrations above 20 mg/kg may reduce rate of lay by 0.9%-point. Moreover, the layers exposed down to 0.03 mg of glyphosate per kg feed produced eggs with residues of this pesticide.