Bobco...all mammals have the same basic process to extract as many minerals and vitamins from our body. This includes the kidney..loop of henle (acsending and descending) and also misc. tubuoles that our "waste" goes through so that any needed minerals, salts or h20 can be xtracted for our use. Once we take out all we can then it goes out of our body as urea....so the only differences in us and deer are any other minerals we may have eaten and that our body doesn't need so we get ride of it in waste. again this is a small percentage of our waste. something to think of is that urine coming out of our body is sterile. Now for mating there are other chemicals in females or males during the mating season ie estrogen or testosterone that are in mass quanitities and become removed from the body viaurine,this is to let the buckknow that the femaleis ready to be mated with..
Please let me know if that helps or if you have other questions...