Most herbicides (weed killers) have restrictions on labels relative to cattle. Often, however, there are no specifications for horses and most herbicides are safe for horses. Most herbicide labels will have a restriction period for certain types of cattle. For the horse's safety, follow the label precautions before grazing after application of an approved herbicide. Remember, spraying should be done as the directions dictate. Be careful that there is no puddling of the herbicide.