I guess I missed it that they are dumping actual trash in your paddocks.
You said originally that they dumped buckets of crab apples.
That is kind of different than them dumping trash.
To me it is obvious that I do not go to my neighbors and start handing their dogs biscuits.
To other people it is not so obvious.
I personally do not take someone innocently wanting to give my horse treats as them not having respect.
Maybe a neighbor whose animals you do not give treats to thinks you are a prick for not caring enough to give their animals treats?
Now, if they are dumping actual trash that is different. But that is not how this thread started. If you want to change the story now so you can be angry with them, then fine.
I just firmly believe that neighbors are someone you have to live next to. If they have not proven their intentions are being a jerk it is best to assume they are clueless first.
My new neighbor drove his car through the middle of my hay field this spring when it was very wet. Got his car stuck even. You would call him a jerk. I call him city clueless. Much easier to not be angry all the time I say.