The dog is standing over a full bowl, looking at you. You are standing over the dog, looking at the bowl. This is a daily event in a lot of houses and it generates more questions at our counter than almost anything else.
First, the unwelcome part. Rule out the boring explanations before you buy anything. A dog who gets a biscuit at the back door, a crust at lunch, and a chew in the afternoon is not picky, they are full. A dog whose portion was set when they were two and is still the same at nine is being offered more than they need. And a dog who stops eating suddenly, having always eaten well, is a dog for your veterinarian rather than for a new topper. Appetite change is information.
Once the boring explanations are out, toppers genuinely work. We carry a lot of them at 1288 Highway 33 and we would rather point you at the right one than the most expensive one.
Here is the ladder we actually suggest, cheapest effort first.
Warm water over the food. Costs nothing. For a lot of dogs the smell is the whole problem and a little moisture and warmth releases it. Try this for three days before spending money, because when it works it works immediately.
Next rung, a flavor topper. Something like Dinner Dust is built for exactly this: a shaker of meat you sprinkle over the bowl, labeled supplemental feeding only, around eleven kilocalories per tablespoon. It changes how the bowl smells without changing the diet underneath it. If the issue is enthusiasm rather than nutrition, that is the honest tool for the job.
Next rung, a freeze-dried mixer. A Duck Duck Goose Meal Mixer and the others in that line are richer, and the richest ones carry noticeably more calories per scoop. Duck runs 5,370 kilocalories per kilogram against 4,440 for the chicken, so if your dog is a touch heavy already, start at the lean end of the line rather than the rich end.
One caution on duck specifically, since it comes up. Despite the name, turkey, turkey liver, turkey heart and goose all appear in that recipe ahead of the vegetables. If you are avoiding poultry or specifically turkey, the name on the front will not tell you that. Read the list.
Keep Stella's ten percent ceiling in mind through all of this. Treats and toppers under ten percent of daily calories is their own guidance, and the easiest way to turn a picky eater into an overweight one is to top the bowl generously every night without taking anything out of it.
Our opinion, and it is a mild one. Rotating toppers constantly to keep a dog interested usually teaches the dog to hold out for the next thing. We would rather see one topper used consistently, or none, than a new jar every three weeks. Dogs are quick learners and some of what gets called pickiness is just a dog who has correctly worked out that waiting produces better food.
Try warm water tonight before you buy anything. If the bowl comes back empty, you have your answer and it was free.