
I looked after a chubby young Yorkie (as long as a dachsi), and they brought a whole Tupperware container of cooked chicken breast as that is all that she would eat.
I told them straight that she would get a few bits on her food but would be fed a complete food here, as this was totally unsuitable as the only food.
First day I gave her 1 ounce of complete and similar volume of the chicken.
She ate the chicken.
Next day she got a few pieces of the chicken and about two ounces of dry which she left. So I picked it up and offered her it the next day with a few cubes of chicken, she ate about half.
The next day she ate a bit more dry. the last two days she tucked into her 2 ounces of dry no problem, and I suggested they continue to feed her this small amount of dry food a day and nothing else until she lost a little weight. I had frozen their large container of cooked chicken and returned it to them. :D
In Poland my dads cousin was a large animal vet. He was asked by his employers wife to help them over their toy poodle not eating.
He put him in a kennel with just water and no food for two days, and on the third day gave him some dinner :D