Living in the UK I grew up on the belief that oats made a horse ' nuts'
In 1994 I moved to Germany for 18 months and the yard there fed Oats to everything ( including a european champion ) with no effect at all , our TB started to eat oats there and nothing changed in her manners at all but there was a real change in her condition , her coat bloomed and a growth line appeared in her hooves ( prior to the oats she had poor feet )
I now feed oats to all my neds ( mini to 16h sportshorse ) and none of them have any manners issues but they all have good condition . ( my sportshorse is uncontrolable if fed sugarbeet ) and my vet says that all you really need to feed is grass, hay , alfalfa and oats.
Just like to start a thread on other peoples experiances with oats.