Contamination of animal feeds with weed seeds is a major problem worldwide. The impact of weed seeds arises from the toxins they contain and from their diluent effects on nutrient density of feeds. The toxins include many of those cited in the previous section, particularly alkaloids, saponins, amino acids and proteinase inhibitors. Examples of weed seeds that are controlled by legislation in various countries include those of Datura spp., common vetch, castor-oil plant and Crotalaria spp.