Just been watching my bitch feed her puppy (a singleton) he seems to favour the upper teats rather than the full lower ones, but on watching them she is feeding from the back teats!

Is this normal when the litter is small?

On a positive note, if she is milking the back teats then she is drawing off the excess milk and hopefully preventing any problems

Maybe they are uncomfortably full of milk and she has discovered this is a way to relieve them....