Nice name, I have a poodle named Prada
Firstly I would have to say he needs to be seen to by a vet just to rule out any medical problems he may have.
However, mine do that quite often, usually it is when they have eaten the same food for more than a week.
Just like people some dogs can get sick of eating the same old thing day in, day out.
What I do is to make sure I always feed the same base food and then add a "flavour" to it every 2-3 days.
Either by mixing in half a can of moist food in different flavors or adding some sardines or even beef or chicken mince to the base ingredient.
Mine also flat out refuse to eat plain dry food unless I mix a little canned in with it just to make it a bit more tempting.