So, farmers are all large-scale landowners kept afloat by subsidies? You may live in the country, but it's a bit you don't have the nous of your namesake.
Grazing is about grass management - there are reasons that heifers, bullocks or whatever are in particular fields. And if you should find a bull in a field with a public right of way, yes, you have every right to report it. Otherwise, remember that you are walking across someone else's workplace, and show a little care. If a public footpath went through a foundry you'd exercise a little caution, so do the same in the countryside. It also behoves walkers to be aware of the risks and of how they can minimise their impact. Ignorance can kill.
And I can only assume you had your tongue in your cheek with the 'theme park' remark!