The micronutrient essential to the production of thyroid hormone is the halogen Iodine.
It will "hurt" (or kill, rather) cows and dogs if they are exposed to a lot of it, but otherwise it is a good fertilizer, micromineral supplement, topical/oral treatment for certain ailments, and an insecticide and fungicide.
What sort of things are poisonous to cows depends on where they live (especially in terms of plants) and what is present on the farm. A list of poisonous plants and other things are:Wild NightshadeWater HemlockWhite OakLocoweedLarkspurHairy VetchLead (metal)Any micromineral fed in excess are toxic to cattlePurple cockleOilMercury
No. This is a myth that has been passed along by drug addicts that have been trying to find unique ways of getting the necessary ingredients for illegal drugs like methamphetamine, also commonly known as crystal meth.
ZnOZinc oxide, ZnO, is a large band gap semiconductor. It is commonly found in things like sunscreen because it absorbs UV light (preventing the harmful rays from reaching your skin). For more information, see the Web Links below this answer.