Animals can breed over distanced up to almost 8 blocks when only seperated by fences.
What I expected to happen:
Animals would have to go together to breed.
What actually happened:
My test-cows were breeding over a distance of 8 blocks (have to be close to the fence tho when it's 8 blocks)
This was already found and studied in MC-7426, there considered WAI. (Sheeps breeding over longer distances was found to be the reason for them getting babies of unexpected colors).