Nutritional value and toxins in various noxious weeds

Why don’t livestock eat most noxious weeds? Often weeds contain some level of toxins but most weeds are not so toxic that they cause health problems or death provided livestock have access to a variety of plant species. Novelty may be a better answer as to why livestock don’t eat many weedy species. When a weed invades a pasture, it is likely a new or novel food meaning livestock grazing the pasture have never eaten the new weed. Animals learn what to eat and avoid by grazing with their mothers and through individual experience. Once animals establish a preferred diet of familiar foods, adequate in nutrients, and low in toxins, most animals simply avoid eating new foods. In no time, weeds take over because plants that are not grazed have a competitive advantage over grazed plants