Castration

If I don't Castrate Zeke when hes old enough, will he fight with my other dog (Shihtzu 2 years old) who has not been castrated? Although they are best friends now.

That's a question nobody can answer.

Castration won't stop fighting if one or other of them wants to be 'top dog', but entire males can be a bit iffy with other entire males.

Personally I'd be more inclined to wait and see. Watch their interractions at all times & make sure you step in if you're not happy with the way they are playing.

Also, I would never leave two entire males of any breed alone together!

Thanks, I would never leave them alone together. Wouldn't risk it even if they are best friends now! Thanks for the advice.

It is def true that entire males can sometimes be a bit strange with other entire males, I have found so with Logan, however they are always dogs that are strange/unfamiliar to him.

Neutering won't prevent fighting and it is quite common for dogs to have the odd scrap even if they have been living together.

Agree with above never to leave two dogs together unsupervised, but for me it is the same for all breeds and not dependant on gender either.

I had two female dogs before Logan and they would fight from time to time, but there was normally a reason...over a toy, not getting enough exercise etc.

Both my females were spayed too.