Ahh someone else with a thin Chihuahua. My Mums Theodore has only just started to put on weight now, he turned 2 years old in june. Before his second Birthday and even after he was neutered he was so thin and nothing we did would put weight on him.

Theo was just like Tony, very actice (Still is) and would sometimes eat all his dinner and at other times barely touch it (Still does), we tried putting him back onto puppy food and giving him extra but he just would not put the weight on.

I would keep an eye on Tony and if he becomes lethargic have the Vet check him out again, other than that he sounds like a very healthy little guy and hopefully he will gain a bit of weight as he gets older.

I would love to see new photos of the Chi's and Max, when you have the time that is.