Quote: We also now have a 1 year old male (entire) who we have had since a pup, generally they are fine with each other - we have had a couple of incidents were pup has gotten out of line and Os (older one) has told him off (growling, putting mouth on neck/snout) but done no harm.
Quote: Os has been getting worse and worse will other dogs over the last year or so
Since this seems to have started about the time the young male joined the pack, maybe your older male is afraid of losing his position.Quote: We had a complete (everything) thyroid panel done a month or so ago which came back fine and he has no obvious pain or physical problems.
I would reinforce the older male's position as alpha so that he doesn't feel as if he has to defend it so strongly. Always feed him first, let him go out first, etc, and I would be very careful leaving them together for play.
Just my opinion.