Don't know where your getting your information from but don't be too quick to dismiss something until you have tried it. My cattle respond very well to kelp.
Any plant can only take up what is avaiable to it in the soil and water. If a plant is grown in soil lacking in a particular mineral it also will be lacking. Kelp grows in an environment rich with both major minerals and trace minerals and takes up many of them.
I did a quick search and found this on the web;
"An excellent general mineral supplement. Kelp is well known as an excellent source of most of the important trace minerals. There are few such sources anywhere on earth. Besides the well-known trace elements such as copper, zinc, manganese, chromium and others, kelp supplies many of the ultra-trace minerals such as germanium, iridium, rubidium and others of which we know much less. However, they may be very important for health, especially today when the food and the soils have become very depleted.
Kelp versus other mineral supplements. Kelp is rich in iron, calcium, magnesium, with some zinc and selenium, but low in copper. This is quite a good blend of minerals and the main reason why we prefer kelp to other "mineral supplements", that are sold. Other mineral supplements that are available either do not contain the ultra-trace minerals or they contain many more toxic metals without containing substances to counteract or bind and remove the toxins."
Look, I don't care if you use kelp or not but please do not mislead other people on this site making statements like "Miniscule amounts, Very expensive for what you get" I'm not saying to feed large amounts of kelp. I am saying it is a very good idea make it part of your feeding program. I have seen good results from using kelp.