Roundup is a powerful herbicide.  The active ingredient is glyphosate.

Virtually all feedlot animals have corn and/or soy as part of their feeding regiment.  As mentioned above, almost all corn and soy produced today is GMO.  Entire fields are liberally sprayed to kill weeds while leaving the crops unharmed. As a result, the soy and corn fed to animals is highly contaminated with glyphosate.

“Glyphosate enhances the damaging effects of other food borne chemical residues and environmental toxins. Negative impact on the body is insidious and manifests slowly over time as inflammation damages cellular systems throughout the body.”

( http://www.mdpi.com/1099-4300/15/4/1416 )
Samsel A, Seneff S. Glyphosate’s Suppression of Cytochrome P450 Enzymes and Amino Acid Biosynthesis by the Gut Microbiome: Pathways to Modern Diseases. Entropy. 2013; 15(4):1416-1463.