What to Feed a Pet When You Run Out of Food: The Two Directions Are Not the Same Risk

There is no published number of days that a cat can safely eat dog food, or a dog can safely eat cat food. Call your veterinarian or an emergency clinic and describe your animal, the food and how long it has been. Do not fill the bowl with a substitute first if your animal is on a prescription diet, is a puppy or kitten, is pregnant or nursing, is diabetic, has a food allergy, or is already showing signs of illness. Never substitute onions, garlic, grapes, raisins, chocolate or the other foods in the never-list below.

The bag is empty, the roads or the shelves are, and another animal’s food is still in the cupboard. The question is whether that food can go in this animal’s bowl tonight, and what the sources say happens if the answer is wrong.

The two swaps are not mirror images. A cat eating dog food and a dog eating cat food are described very differently in the veterinary literature, and only one direction has a named list of missing nutrients attached to it. The number everyone wants, the number of days, does not appear in the sources on this page.

Six households this page cannot help

Substitution guidance is only reasonable for a healthy adult dog or cat on an ordinary over-the-counter food. If any of the following describes your animal, call a veterinarian.

An animal on a therapeutic or prescription diet. Renal, hepatic, urinary, gastrointestinal, hydrolyzed or allergy, weight-management and cardiac diets are treatments, so a substitution changes the treatment. Tufts University’s Clinical Nutrition Service, in an article by Lisa M. Freeman, DVM, PhD, DACVIM (Nutrition) dated May 3, 2021, says:

An abrupt change in diet may also be harmful to your pet if they are on a therapeutic diet for a medical condition.

The same article advises checking with a veterinarian about any alternative a retailer suggests, because well-meant recommendations can sometimes be dangerous for your pet.

FDA’s Compliance Policy Guide Sec. 690.150 (April 2016; content current as of 11/06/2024) explains why these diets sit behind a veterinarian. One of the factors it says FDA will consider is whether the product is made available only through licensed veterinarians, or through retail or internet sales to people buying under a veterinarian’s direction. It says that because these products have not been evaluated for safety and efficacy, “veterinary oversight is especially important” for them. The document is marked “Contains Nonbinding Recommendations”, so it describes FDA’s thinking, not a rule you can cite at a store counter. No substitute can be named here for a prescription diet.

Puppies, kittens, and pregnant or nursing animals. These are separate nutrient profiles, not smaller versions of the adult one. AAFCO’s consumer page lists the recognized life stages as gestation and lactation, growth, maintenance, and all life stages, and says different quantities and ratios of nutrients, and different feeding rates, are ideal for different stages. Packing help is in our kitten evacuation go-bag, puppy emergency kit and pregnant or nursing pet evacuation guide.

Diabetic animals. For dogs, the 2026 AAHA diabetes guidelines for dogs (published August 31, 2026) say dogs with diabetes can do well on any diet that is complete and balanced, fed at consistent times and in appropriate portions, and palatable enough to support a consistent appetite. A substitution disturbs all three, which is why it belongs in a phone call. AAHA published separate guidelines for cats in 2026 as well (J Am Anim Hosp Assoc 62(3)).

Cats do not carry the same timing constraint. The 2026 feline guidelines’ dietary-management section says meal feeding is preferred but not essential, and that grazing over the day is acceptable. It asks instead for reliable intake of a complete and balanced diet, and for managing protein and carbohydrate intake to limit high blood sugar after meals. For a diabetic cat, a dog-food swap is a composition problem: it changes the protein and carbohydrate levels the cat’s diabetes management is built around. Call the prescribing veterinarian before you fill the bowl. For the medication side, see the insulin cooler and diabetic pet kit page.

An animal with a diagnosed food allergy or intolerance. The point of the diet is the ingredient list, and a substitution reopens it.

Any animal already showing signs. Vomiting, diarrhea, refusing food, lethargy, labored breathing, weakness, disorientation or a painful abdomen are not a feeding question. Call a veterinarian or an emergency clinic.

Every species that is not a dog or a cat. Every source here is about dogs and cats. Rabbits, guinea pigs, birds, reptiles, small mammals, chickens, horses and livestock have different digestive systems and failure modes, and nothing here transfers to them. The ASPCA Animal Poison Control Center makes one difference plain: it says avocado is primarily a problem for birds, rabbits, donkeys, horses and ruminants including sheep and goats, with cardiovascular damage and death in birds and rabbits as the biggest concern. The ASPCA still lists avocado among foods to avoid, and this page keeps it on the never-list. If you keep those animals, start at rabbit and small pet emergency prep, the guinea pig evacuation kit, bird and parrot emergency preparedness or horse and livestock evacuation basics, and call a veterinarian who treats that species.

Why the two directions differ

The Merck Veterinary Manual’s professional article on dog and cat foods (author Sherry Lynn Sanderson, DVM, PhD, DACVIM-SAIM, DACVIM-Nutrition; last reviewed November 2023, last modified June 2025) says dog foods are “generally not satisfactory for cats”. It gives the reasons: some dog foods are lower in protein, often lack assured concentrations of taurine, may lack other nutrients cats need and dogs do not (such as preformed vitamin A and arachidonic acid), and may not meet cats’ requirements for fat, vitamins and minerals. It adds that many feline diets are formulated to a target urinary pH to lessen the chance of forming crystals.

The hedges in that passage (generally, some, often, may) matter: it describes a category, not the bag in your hand. But the list of what can be missing is specific, and every item on it is a nutrient a cat needs and a dog does not need from its diet.

The same author’s article on nutritional requirements of small animals (last modified September 2024) makes the point from the other side. Cats can develop nutritional deficiencies on diets formulated for dogs. Unlike dogs, they need dietary sources of vitamin A, arachidonic acid and taurine, and they have higher requirements for some amino acids such as arginine and for the vitamins niacin and pyridoxine (B6).

AAFCO puts it in consumer language: “Because dogs and cats have different nutrient requirements, pet food must be formulated for the intended species.” Its example is that cats require nutrients such as taurine and preformed vitamin A that dogs do not.

AAFCO is not a federal regulator. Its FAQ says AAFCO does not approve, certify or otherwise endorse pet foods, and that most state feed laws and regulations reference its Official Publication. Its standards are model standards adopted state by state. The nutrient profiles themselves are in that annual publication. Where a number below is attributed to AAFCO, it reaches this page through the Merck Veterinary Manual, which cites AAFCO for it.

What cats need that dogs do not

The National Academies’ pamphlet Your Cat’s Nutritional Needs, based on the 2006 Nutrient Requirements of Dogs and Cats, names the amino acids that carry most of the risk:

• Arginine is critical to removing ammonia from the body through urine. Without enough in the diet, cats may suffer a toxic buildup of ammonia in the bloodstream.
• Taurine is a dietary essential for cats but not for dogs. The pamphlet lists the effects of deficiency as feline central retinal degeneration and blindness, deafness, cardiomyopathy and heart failure, inadequate immune response, poor neonatal growth, reproductive failure and congenital defects. Taurine is found abundantly in many fish, birds and small rodents, and is absent or present only in trace amounts in plants.
• Vitamin A and niacin must come directly from food. A vitamin A shortfall can affect the eyes, and adult cats deprived of niacin will lose weight and may die.

Merck explains the vitamin A chemistry: cats cannot convert beta-carotene to vitamin A, so they need a preformed source such as liver, fish oil or synthetic vitamin A. Merck also says cats have an additional requirement for arachidonic acid, which is absent in vegetable oils and fats but found in fat from meat, poultry and eggs, and that unlike dogs they cannot readily convert linoleic acid to it.

On protein, Merck gives these composition minimums for formulated foods: adult cats need at least 26% protein as dry matter, or 65 grams per 1,000 kcal ME (AAFCO guidelines), or 40 g per 1,000 kcal ME (NRC guidelines). Adult dogs need at least 18% protein as dry matter, or 45 grams per 1,000 kcal ME (AAFCO guidelines). These show the gap. They are not amounts to feed anything.

The direction nobody publishes a deficiency list for

None of the Merck Veterinary Manual, the National Academies pamphlets, AAFCO’s consumer pages, FDA’s pet food pages, WSAVA’s guidelines or Cornell’s feline health pages states that a dog eating cat food develops a named nutrient deficiency. No source here describes a concern for that direction. What Merck publishes is composition: it says most commercial adult dog foods typically contain 5% to 15% fat on a dry-matter basis, while as much as 60% of the calories in a cat’s diet may come from fat, though diets with 8% to 40% fat (dry-matter basis) have also been fed successfully. Add the higher protein minimum above. Neither Merck nor the other sources link these figures to a dog eating cat food, so treating the gap as a reason for caution is our inference.

So the risk we infer for a dog on cat food is a mismatch, mainly in fat and protein density, in a food never formulated to the dog’s profile. Separately, Merck’s pancreatitis article (author Jörg M. Steiner, last modified September 2025) says dietary indiscretion is believed to be a common risk factor for pancreatitis in dogs; it does not mention cat food. Merck’s general framing covers both directions: dog or cat foods and homemade diets built from a limited number of food items are often inadequate.

The summary is not that cat food is fine for dogs. Each direction carries a different kind of risk, only one has a published deficiency list, and neither has a published permission slip. If your dog has eaten a large quantity of cat food, or has a history of pancreatitis or any other medical condition, call your veterinarian.

No published source gives a number of days

This is what every version of the search is really asking: how long, and what is the ceiling? No source cited on this page publishes a duration, in either direction, or a general ceiling for feeding an animal a food not formulated for its species. That covers the FDA pet food pages, AAFCO’s consumer pages, the National Academies’ cat nutrition pamphlet, the WSAVA Guidelines on Selecting Pet Foods, the Merck Veterinary Manual articles listed under Sources, Cornell Feline Health Center’s Feeding Your Cat, and the Tufts Clinical Nutrition Service article on out-of-stock pet food. If you find a day count elsewhere, check that you can open the document it came from and read the sentence in place.

What is published, and what it measures. Three studies are quoted in this territory, and all three are easy to misread as countdowns.

• Arginine, hours. Morris and Rogers (Science, 1978) gave near-adult cats, fasted overnight, a single meal of a complete amino acid diet with no arginine at all. The cats developed hyperammonemia and showed clinical signs of ammonia toxicity within 2 hours, and one 2.7-kilogram cat died 4.5 hours after eating only 8 grams of the diet. That was a purified diet with no arginine. It was not dog food. Merck lists arginine among the ten amino acids essential in dogs’ diets, and says cats have higher requirements for it. A higher requirement is not a total absence, so this result is not a two-hour clock for a cat eating dog food.
• Taurine, months and years. Pion and colleagues (Science, 1987) linked low plasma taurine to myocardial failure, observed in 21 cats fed commercial cat foods and in 2 of 11 cats fed a purified diet with marginally low taurine for 4 years. Taurine supplementation was associated with normalization of left ventricular function in both groups.
• Taurine, a trial. Novotny and colleagues (Canadian Journal of Veterinary Research, January 1994) ran feeding trials of 6 to 15 months on an experimental taurine-deficient diet. The greatest rate of change in echocardiographic variables came in the first four months. Response was not uniform: a small number of taurine-deficient cats showed no diminution of myocardial function, while others declined to levels characteristic of dilated cardiomyopathy.

The taurine work runs on a scale of months and years on purpose-built deficient diets. The arginine work runs on a scale of hours on a diet engineered to contain none. None of the three studied cats eating commercial dog food. Anyone who blends them into one countdown has produced a number no study supports.

With no number, use the mechanism and the phone. The mechanism tells a veterinarian which nutrients are in question. What they need from you is how long it has been, which product, whether there are any signs, and what else is available. A day count from a stranger online is not an answer for your animal.

Read the bag you are holding

When the choice is between two products you did not plan to use, the nutritional adequacy statement decides more than the brand name. It is usually in small print on the back or side.

FDA’s Complete and Balanced Pet Food page (content current as of 02/28/2020) says a product with the phrase “complete and balanced” is intended as a pet’s sole diet, while treats, snacks and supplements typically are not. A food gets that claim by meeting one of the AAFCO Dog or Cat Food Nutrient Profiles or by passing a feeding trial using AAFCO procedures.

Merck explains the statement you least want to find on the only can left. “This product is intended for intermittent or supplemental feeding only” is required when a product does not meet the requirements for a complete and balanced diet and is suitable only for limited, intermittent or supplemental feeding.

That is where the one quantitative rule lands. The WSAVA Global Nutrition Committee (document stamped Updated on 10 March 2021) says foods labeled for short-term, intermittent or complementary feeding “should only be fed as a small portion of the diet (10% or less)”, or under veterinary supervision if the food is a therapeutic diet. This is a proportion of the diet for a labeled class of product. It is not a duration or a portion size for your animal. A stack of pouches labeled that way is not a week of food.

Read four things in order when you are standing in an aisle or a garage with two unfamiliar products:

1. Species. Does the label say dog food or cat food? Merck notes the intended species must appear on the label, and AAFCO’s consumer guidance is to choose a food labeled for the pet’s species, life stage and condition.
2. Nutritional adequacy statement. Does it say complete and balanced, or intermittent or supplemental feeding only?
3. Life stage. Growth, gestation and lactation, maintenance, or all life stages. Merck notes that all life stages means the product has been formulated or tested for gestation and lactation, growth and adult maintenance.
4. Anything that reads like a medical claim. If it is a therapeutic diet, go back to the first section. The decision belongs to the prescriber.

The never-list, from one named source

Every entry below is from the ASPCA Animal Poison Control Center’s People Foods to Avoid Feeding Your Pets page. The page says that if you suspect your pet has eaten any of these foods, note the amount ingested and contact your veterinarian or poison control.

• Alcohol and yeast dough. Alcohol can cause vomiting, diarrhea, incoordination, depression, difficulty breathing, tremors, changes in blood pH, coma and even death. It is rapidly absorbed, so ASPCA says to seek veterinary attention promptly after any exposure. Yeast dough can rise and cause gas to build up in the digestive system. That can be painful and cause the stomach to bloat and potentially twist, a life-threatening emergency.
• Chocolate, coffee and caffeine. Methylxanthines can cause vomiting and diarrhea, panting, excessive thirst and urination, hyperactivity, abnormal heart rhythm, tremors, seizures and even death. The darker the chocolate (higher cacao percentage), or the higher the caffeine content, the greater the risk.
• Grapes and raisins. ASPCA hedges here and so does this page: the toxic component is “speculated” to be tartaric acid, and because dogs cannot process it, exposure can lead to kidney damage. Treat the mechanism as proposed and the caution as firm.
• Onion, garlic and chives. Allium species can cause gastrointestinal irritation and red blood cell damage that can lead to anemia. Cats are more susceptible, but dogs are also at risk depending on the amount. Pet Poison Helpline’s onion page says onion, chives, garlic and leeks are all Allium species, poisonous to dogs, cats and livestock, and that cats and Japanese dog breeds such as the Akita and Shiba Inu are more sensitive. This entry matters most in a disaster pantry, because Allium turns up as seasoning in canned soups, stocks, gravies, seasoned meats and many jarred foods. Read the ingredient list on anything before it goes near an animal.
• Macadamia nuts and other nuts. Macadamias can cause weakness, incoordination, depression, vomiting, tremors and hyperthermia in dogs. Nuts generally, including almonds, pecans and walnuts, contain high amounts of oils and fats that can cause vomiting and diarrhea and potentially pancreatitis in some pets.
• Xylitol. It can cause low blood sugar and potentially liver damage depending on the amount. Early signs are vomiting, lethargy and loss of coordination, which can progress to seizures. ASPCA says liver damage can occur within 12 to 24 hours and can cause abnormal bleeding. Xylitol appears in sugar-free products; ASPCA names gum, candy, baked goods and toothpaste.
• Excessively salty foods. Excess salt can produce increased thirst and urination and sometimes abnormal blood electrolytes. Signs of salt toxicity include vomiting, diarrhea, depression, tremors, seizures and even death.
• Milk and dairy. Pets do not have significant amounts of lactase, so milk and dairy can cause diarrhea or other digestive upset. A bowl of milk is not a fallback, and digestive upset is the last thing to add to a shortage.
• Raw or undercooked meat, eggs and bones. Raw meat and eggs can carry bacteria such as Salmonella and E. coli, harmful to pets and people. Raw eggs contain an enzyme that can interfere with absorption of certain vitamins and lead to skin and coat problems. Bones can injure or obstruct the gastrointestinal tract, which could be serious and require surgery. Merck adds the biochemistry: avidin in raw eggs destroys biotin, and thiaminases in raw fish destroy thiamine.
• Avocado, citrus and coconut. ASPCA scopes avocado to birds, rabbits, donkeys, horses and ruminants, as above. It says citrus stems, leaves, peels, fruit and seeds contain citric acid and essential oils that can cause irritation and possibly depression in significant quantities, while small ingestions such as eating the fruit are not likely to cause problems beyond minor stomach upset. Small amounts of coconut are not likely to cause serious harm, but its oils may cause stomach upset, loose stools and diarrhea.

If your pet has already eaten something on this list, call your veterinarian, an emergency clinic or an animal poison control service with the amount noted, instead of watching to see what happens. As of September 29, 2026, the ASPCA Animal Poison Control Center listed (888) 426-4435 and Pet Poison Helpline listed (855) 764-7661. Both are staffed lines that may charge a consultation fee. Confirm the number on the organization’s own site.

Why cooking a substitute is the wrong instinct

The Merck Veterinary Manual’s article on nutritional requirements of small animals says “feeding predominantly meat or even an exclusive hamburger and rice diet to dogs or cats can induce calcium deficiency and secondary nutritional hyperparathyroidism.” It continues: “Feeding only liver can induce vitamin A toxicity in both dogs and cats.”

That passage takes out the two most common improvised menus. Meat and rice, the thing everyone reaches for, is named. Liver, chosen because it seems nutrient-dense, is named as a toxicity route. Merck’s article on dog and cat foods adds that it is most difficult to formulate a nutritionally complete and balanced diet for cats with enough nutrient density in a small volume of palatable food. It says owners who choose a home-cooked diet should use a recipe formulated by a boarded veterinary nutritionist, not one found on the internet or in a book.

Tufts’ Clinical Nutrition Service says the same for owners: cook for your pet only if you are “willing to work with a Board Certified Veterinary Nutritionist to get a nutritionally balanced recipe”, and follow that recipe exactly.

So this page publishes no recipe, portion, feeding frequency or supplement amount, including for taurine. Getting it right for a specific animal is a veterinary act, and getting it wrong is how the deficiencies above happen. The decision on what goes in the bowl belongs to a veterinarian.

The order of operations when you actually run out

Each step below is a routing step, not a substitution instruction. The steps draw on the Tufts Clinical Nutrition Service article on out-of-stock pet food; the order is ours.

1. Exhaust the same product first. Tufts says it may be a single bag size that is out of stock, and a larger or smaller bag of the identical product may still be available. That is not a diet change at all.
2. Then the same product in a different flavor, once you have checked who your animal is. Tufts says that for healthy pets a different flavor, or for dogs a different dog size (small breed versus large breed) of the same product, is usually a good alternative. For pets with medical issues, check first, because flavors or dog sizes of the same product can have very different nutritional profiles.
3. Call the manufacturer. Tufts suggests checking availability on several retailers’ sites or contacting the manufacturer, who can sometimes direct you to a retailer or veterinarian with the food in stock. WSAVA says company representatives should be easily accessible for questions such as the level of specific nutrients not on the label.
4. Call your veterinary clinic, and describe the actual situation. Tufts says to talk to your veterinarian about an alternate diet that meets your pet’s specific needs, especially if your pet has medical issues. In a disaster, add whether you are displaced, how long you expect to be, and what you can actually reach.
5. Ask about local pet food assistance. Ask your clinic, your shelter or your county animal services whether a pet food pantry or disaster food distribution is operating. No source cited here says what any given area offers.
6. Only then, with a veterinarian on the phone, talk about a substitution. By now the conversation is specific: this animal, this condition, this product, this many days, these options.

On transitions, Tufts says some pets can switch diets “cold turkey” with no problem, while others need a much more gradual transition over 7 to 10 days. That describes two kinds of animal, not a schedule for yours. Having a cushion of food is what buys you the option to go slowly.

Build the reserve so this page is not needed

The version of this problem that bites a multi-species household is usually not that the family ran out of food. It is that one animal’s food ran out. Reserves are often sized in household days, then the shelf runs down unevenly because the animals eat different amounts of different products. The cat food goes first, or the special bag for the older dog does, and now you are holding a substitution question you never meant to ask.

Three habits fix it.

Count the reserve per animal, not per household. Each animal’s food is its own countdown. A shelf that holds a fortnight for one animal and four days for another holds four days. Our long-term pet food and water storage page has the published day-count standards, with the disagreements between agencies laid out, and our emergency food and water storage guide covers containers and water.

Rotate against the constraint animal. The animal with the least flexible diet sets the schedule for the household. Tufts frames it from the veterinarian’s side, describing one of her own dogs, whose medical issues make his requirements very specific, as the one she keeps a bigger cushion for. The pet emergency kit rotation checklist is the recurring version of that job, and when to buy pet emergency supplies before hurricane season sets the calendar.

Decide the back-up before you need it, and write it down. Tufts recommends this: ask your veterinarian for a good back-up food with a similar nutritional profile to the diet you feed, or, if your pet’s medical and nutritional needs are complex, consider working with a Board Certified Veterinary Nutritionist. Tufts says it is better to think about it ahead of time than in a panicked scramble over the last bites in a bag or can. For a multi-species household, that means one named back-up per animal, agreed with your clinic and kept with the vaccination records. The pet emergency binder is where that line goes, multi-pet emergency planning works the household arithmetic, and multi-pet go-bag math covers what you carry.

To choose the formats that make up the reserve, see freeze-dried versus canned versus kibble for emergency storage, which compares shelf life, weight, water dependency and heat tolerance.

Ran-out checklist

• Confirm whether your animal is on a therapeutic or prescription diet. If yes, call the prescribing veterinarian before substituting anything.
• Same for a puppy, kitten, pregnant or nursing animal, a diabetic animal, or an animal with a diagnosed food allergy. Each is a phone call, not a judgment call.
• If your animal is not a dog or a cat, none of this page applies. Call a veterinarian who treats that species.
• Check whether the identical product exists in another bag size or flavor before considering a different food at all.
• Call the manufacturer’s consumer line on the bag. They can sometimes route you to stock you cannot see online.
• Call your veterinary clinic with the specifics: which animal, which product, how long, any signs, and what you can actually reach.
• Ask your clinic, local shelter or county animal services whether a pet food pantry or disaster food distribution is operating.
• Read the nutritional adequacy statement on anything you are considering. Complete and balanced is a different product from one labeled for intermittent or supplemental feeding only.
• Read the ingredient list on any human food before it goes near an animal, because onion and garlic are ordinary seasonings and both are on the ASPCA’s list.
• Do not improvise a cooked diet, a recipe or a supplement, including taurine. That belongs to a veterinarian or a board-certified veterinary nutritionist.
• Watch for vomiting, diarrhea, refusal to eat, lethargy, weakness or a painful abdomen after any diet change, and call instead of waiting.
• Afterward, when it is calm, choose a named back-up food per animal with your veterinarian, write it in your records, and re-size the reserve per animal.

Where to go next

This page sits in our pet evacuation kits pillar.

Building the stock. Freeze-dried versus canned versus kibble picks the formats, long-term pet food and water storage sets the shelter-in-place standard against published agency figures, and the pet emergency kit rotation checklist keeps it from quietly expiring.

The water half. How much water per dog in an emergency and water purification for pets cover the other half.

The household. Multi-pet emergency planning covers the grab order and per-animal documents, multi-pet go-bag math covers what leaves the house with you, and returning home with pets after a disaster covers what to check when you get back.

Then do the one thing that makes this page unnecessary. On an ordinary day, ask your veterinarian what the back-up food is for each animal in your house, and write the answer down.