Hi, hoping someone might have some thoughts on this - and hints gratefully received.
Our 1 year old Weim boy has fairly suddenly stopped eating his food. He's always been a bit of a problem, not appetite but his tummy - we've rejected a few things as they've upset him. We eventually settled him on Naturediet lamb and rice with Wainwrights puppy biscuits, morning and evening. Perhaps not ideal but the other dogs are on a combination of these brands and it seemed to be working for him.

Recently though (in the last couple of weeks), he's been slow to eat, barely having started by the time the others are done. No apparent ill-effects on his tummy but he's got more and more reluctant to eat and a couple of times just left his food. But he is hungry as he tries to eat the biscuits from the other dog (not good as they don't agree with him).
Initially we thought it was the biscuits he didn't like as we offered him his normal meal but separated the ND from the biscuits. He ate the ND but left the biscuits, just pushed them around the bowl. But yesterday we offered him ND on it's own and he didn't want that either.

He's otherwise healthy, full of energy and looks ok-ish weight-wise for an adolescent (ie I can see a little more rib than is ideal but he doesn't look like he's wasting away).

I guess we need to change his food but I'd like to know why he so suddenly took a dislike to his current offering. I don't want to make him a fuss-pot by keep changing but he needs to eat - he'll soon drop weight If he doesn't. I don't know where to start with changing it. We've had recommendations for Arden Grange, Burgess Supadog and Orijen on the grounds that he'll need to eat less of it...but I don't know where to begin. Also, if he won't eat his current food, how do I gradually introduce a new one? Do I still give it mixed in with the old? In which case how do I tell if he likes it?!

Also - do we have to change or is there another reason why he might be fussy? Like him being a pain in the neck teenager in the making?!
We have two other dogs who both eat pretty much whatever you put in front of them...so we've no experience with this at all.

So many questions...apologies...

Thanks

Firstly I would get him checked over at your vets to make sure it isnt something like toothache or something like that stopping him, once you have ruled that out I wouldnt be changing foods initially but leaving it down for 15 minutes and then taking it up - they normally get the idea fairly shortly as there are very few dogs that will actually starve themselves.  If you do carry on having a problem and the dog is refusing to eat then you may need to think about changing but for the moment I would try and avoid this. 

Thanks, he's been checked and no obvious issues. We've been leaving his food down for a short time (10 mins) and sometimes he eventually eats some or all of it, sometimes (fairly rarely) he won't touch it at all. We're trying to think of other reasons why he might not eat (someone strange in the house, distressed by the other dogs being around etc), but doesn't seem to be any real rhyme or reason to his pickiness. He is a little 'frantic' so not ruling out another influence...just trying to figure it all out!