The direct answer for a Doberman and other pets' food
A Doberman should not eat food made for other kinds of pets, because his size turns a small mismatch into a large absolute amount. A cat's portion looks trivial next to a Doberman, yet he can eat the cat's breakfast, the leftover wet food, and the kibble in the storage scoop in under a minute. Cat food is deliberately concentrated, with more fat and protein per bite than dog food, and a Doberman-sized serving of it is a heavy load for any stomach. The result is usually digestive rather than dramatic: vomiting, loose stool, and a dog who is off his own food for the rest of the day.
Eating fast, eating plenty: the Doberman pattern
A Doberman eats with speed and commitment, and that style matters when the food is wrong. Rich food swallowed quickly and followed by water and activity is a combination owners of deep-chested breeds are wise to avoid, so a Doberman who raids should be kept calm afterward and watched rather than sent straight out for a run. His lean, muscular build also hides weight change poorly in the other direction: if he fills up on bird seed, rabbit pellets, or another dog's leftovers, he may eat less of his own balanced food and lose condition while appearing well fed. Either direction, food designed for another animal distorts the careful portions a large breed needs.
Which other foods cause which problems
Cat food, wet or dry, is the main offender in a Doberman's home because its richness scales badly with the amount he can steal. Ferret food is more concentrated still, and even a cup of it is a serious fat load for one stomach. Pellets for herbivores such as rabbits pass through a Doberman largely undigested, causing gas, discomfort, and large, soft stools without giving him anything he needs. Fish food and bird seed are usually eaten in smaller amounts, but a Doberman who tips a container can eat far more than a sprinkle, so store those in cupboards he cannot open with a paw or nose.
Keeping a tall dog out of everyone else's dinner
Height alone will not protect other pets' food from a Doberman, because counters and shelves that stop smaller dogs are at his natural head level. Use closed doors or a gate he respects, feed the cat in a room he does not enter, and never leave food bags on the floor of a pantry he can push into. If small pets live in cages, site the cages where the Doberman is not left unsupervised, and clean spilled pellets promptly. Give the Doberman his own meal in his usual place at the same time, in the slow, settled routine that suits a big dog, so other pets eat in peace and he is not rehearsing the raid.
Veterinary thresholds after a Doberman raids the wrong food
Call your veterinarian if a Doberman who ate another pet's food vomits repeatedly, has ongoing diarrhoea, drools, paces, or seems uncomfortable and unable to settle. For a deep-chested breed, treat a swollen-looking belly, unproductive retching, or sudden restlessness as urgent and contact a clinic or emergency service immediately rather than waiting to see. Also call if a puppy Doberman ate a large amount of rich food, because young large-breed stomachs react strongly and his growth diet should not be disrupted for days. Note what he ate, how much is missing, and when it happened, so the clinic can judge quickly. Logging the Doberman's genuine meals in KinsLe Care Teams leaves that timeline ready when you need it.