My dog is 12, life expectancy for the breed is 10-12. Just under 1 month ago he passed his vet check and was prounounced in excellent all round condition for his age, the vet was very impressed. A few grey hairs on his face aside he could be 5-6. He has no heart respiratory problems, no lumps anywhere, his eyes are bright, no cataracts, his nose is always wet, his coat is shinny, he eats very well, no teeth problems/no tartar, he does not drinking excessively, and has no problems peeing and pooing. He walks 4-5 miles every day and literally skips round effortlessly with no signs of any joint problems, he's happy and out going as ever. His weight was spot on. But morning I noticed that he's lost weight in the last week but nothing has changed. He's only fed Arden Grange dog food no treats, bones, human food. He's an inveterate liar and sometimes when either my DH or I are at work he can persuade the other we have have forgotten to feed him and get an extra bowl of food!
Is it common for older dogs to struggle to maintain their weight?