It'll be under the hair, then, I would think. The Cattle Movement service won't be able to do anything with just the individual number - every 8th cattle farm will have [had] a 300006. (The first digit is a marker-type thing, the remaining 5 digits are the individual number of the animal. The first digit goes from 1 to 7 then back to 1 as the individual numbers go up.) Mind, not many farms still have #6 alive
(we're well into our 500s now, and we don't have a massive breeding herd; the dairy cross calves we buy are into the 1000s and 2000s)
Anyhoo, have a look at a typical cattle tag on the
Shearwell page, you will see the large individual number and then above it, smaller, the UK<6digits> herd number. The two together identify the animal specifically, and yes the Cattle Movement service would know who owns / is looking after that beast at the moment.