Quick answer: Change your dog's food gradually over about 7 to 10 days, mixing a little more of the new food into the old food every couple of days. A sudden switch is one of the most common causes of diarrhoea, wind and vomiting. Go slower if your dog has a sensitive stomach, and call your vet if they're unwell, have blood in their stool or are a puppy or older dog with diarrhoea.
Why a slow switch matters
Your dog's digestive system, including the bacteria in their gut, gets used to the food they eat. A sudden change can upset that balance and lead to loose stools, gas or sickness. Introducing the new food slowly gives their gut time to adjust.
A simple 7 to 10 day plan
| Days | Old food | New food |
|---|---|---|
| 1 to 2 | 75% | 25% |
| 3 to 4 | 50% | 50% |
| 5 to 6 | 25% | 75% |
| 7 onwards | 0% | 100% |
Keep the total amount the same and follow the feeding guide on the new food. If your dog's stools become loose at any stage, stay at that step for a few more days before moving on. Sensitive dogs may need two weeks or more.
Tips for a smoother change
- Change one thing at a time. Avoid introducing lots of new treats or chews during the switch, so you can tell what's agreeing with them.
- Keep mealtimes regular. Familiar routines help.
- Mix well. Picky eaters may try to eat around the new food.
- Keep fresh water available.
- Keep an eye on their stools. Slightly softer stools for a day or two can happen. Persistent diarrhoea isn't something to wait out.
What's normal, and what isn't
Mild, short-lived changes such as a bit more wind or slightly softer stools can happen as your dog adjusts. These should settle within a few days.
Call your vet if your dog:
- Has diarrhoea lasting more than a day or two, or very watery diarrhoea
- Has blood or a lot of mucus in their stool, or black, tarry stool
- Is vomiting repeatedly, or can't keep water down
- Seems lethargic, in pain or off their food
- Is a young puppy, an older dog or has a health condition, as they can become dehydrated more quickly
Frequently asked questions
Can I switch dog food straight away?
Sometimes a sudden switch is unavoidable, for example if a food is discontinued or your vet advises it. If so, watch closely for tummy upsets and speak to your vet. Otherwise, a gradual change is kinder to their stomach.
Do I need to transition between flavours of the same brand?
Even different recipes from the same brand can contain different proteins and ingredients, so a shorter gradual change is still sensible for sensitive dogs.
How long does diarrhoea last after changing food?
Mild loose stools from a food change usually settle within a few days once you slow the transition down. If it lasts longer, is severe or comes with other symptoms, call your vet.
Should I give anything for my dog's gut during a food change?
Some owners add a gut health supplement to their dog's routine. If you do, introduce it gradually too, follow the feeding guide, and ask your vet if your dog has ongoing digestive problems.
Supporting everyday digestion
Our Gut Health Chews are a daily soft chew made to support healthy digestion and a happy tummy, in Chicken, Duck or Beef. They're a complementary feed for adult dogs and not a substitute for veterinary advice. See all our gut health supplements.