Two dogs (clearly not guide dogs) on my recent AA flight from MXP to MIA, think they travelled in the rear J cabin so only noticed them on disembarking. One was a large dog and as he exited the plane his rear legs gave way beneath him and he was struggling to walk, so he clearly hadn't coped well with being couped up so long. The other was a tiny thing and wearing a nappy, which was completely pointless as in the immigration hall he stopped and peed and left a giant puddle on the floor (the Italian owner just carried on and completely ignored it). I would therefore suggest that unless they are specially trained, dogs really aren't suited to long haul travel.