How to Transition Your Dog or Cat to a New Food

Changing your pet’s food may seem simple, but switching too quickly can sometimes upset their tummy. You might notice softer stools, diarrhoea or vomiting. Some pets just refuse to eat the new food.

Why should you change your pet’s food gradually? 

Your pet and their microbiome are used to their current diet. A new food may have different ingredients, nutrient levels, taste and texture. A gradual transition gives them time to adjust and can help reduce the risk of digestive upset.

How to transition your pet to a new food 

Most pets do well with a 7-day switch to a new food. Gradually introduce your pet’s new food over 7 days by mixing it with their usual food:

• Days 1–2: 75% usual food + 25% new food.

• Days 3–4: 50% usual food + 50% new food.

• Days 5–6: 25% usual food + 75% new food.

• Day 7 onwards: 100% new food.

The percentages refer to your pet’s total daily food allowance.

Some pets may need longer to adjust. Cats often benefit from a slower transition, as they can be more sensitive to changes in taste, smell or texture. A slower transition over 10–14 days may work better in cats. You can do this by keeping each feeding stage for a few extra days before gradually increasing the proportion of new food.

Practical tips for switching food

• Mix, don’t swap: Put the old and new food in the same bowl. This helps your pet adjust gradually. 

• Measure the portions: New foods can have different calorie levels. Check the feeding guide on the bag or ask your vet how much to feed your pet.

• Avoid extra treats: If something upsets your pet’s tummy, you want to know the cause. 

• Follow veterinary advice: This is particularly important for vet prescribed diets or pets with medical conditions. 

What if your pet gets diarrhoea or vomits after changing food?

Keep a close eye on your pet's stools, appetite and energy levels when switching their food. 

Stools that are a little softer are usually not a big concern if your pet is otherwise well. If this happens, go back to the last stage that went well. Stay there for a few days, then try again more slowly. 

Get urgent veterinary advice if you notice any of the following: 

• Persistent vomiting or diarrhoea

• Blood in the stool or vomit

• Lethargy or weakness

• Refusing to eat anything for over 24 hours (sooner for puppies, kittens, or elderly pets)

What if your pet refuses the new food?

Be patient if your pet is reluctant to try a new food. Some pets can be suspicious of anything new. Cats can be particularly sensitive to changes in smell, taste, and texture. 

• Start by offering a small amount alongside their usual food. 

• Some cats prefer food at room temperature or slightly warmed to make it more appealing. Don’t overheat it, always check the temperature before serving. 

If your cat completely refuses the mixed food, return to their usual food temporarily and try a slower transition. Contact your vet urgently if your cat completely stops eating for more than 24 hours, as this can lead to serious complications. 

Frequently asked questions about switching diets

Q: How long should it take to change pet food?

Most pets do well with a 7-day transition period. Cats may need longer. Take it slowly and be patient. 

Q: Can changing food cause diarrhoea?

Yes. A new food can cause tummy upset, leading to vomiting or diarrhoea. Seek urgent vet advice if the signs are severe, persistent or accompanied by other signs of illness. 

Q: Should I mix old and new pet food?

Yes, ideally mix the foods in the same bowl. Mixing them can help your pet adjust gradually. If your cat refuses the mixed food, try offering the new food separately alongside their usual food. 

Q: How do I transition my cat from wet food to dry food?

Introduce the dry food gradually, and offer small amounts alongside your cat’s usual wet food. Increase the dry food slowly if your cat accepts it. Make sure fresh water is always available. Some cats prefer to keep eating wet food, so be patient and avoid forcing the change. Cats with certain conditions, such as urinary problems, often do better on wet food, so check with your vet first.