A sudden change of food is the most common reason for soft stool in an otherwise healthy pet. The gut needs time to adjust, so vets advise moving to a new food gradually over 7–10 days: a quarter new, then half, then three quarters, then all new. Below is the plan day by day, what to watch for, and when to slow down. This is general information; if your vet prescribed a diet, follow their instructions.
The plan, day by day
Mix the two foods in each meal and keep the total amount the same. Ten days is the gentler choice for sensitive stomachs; seven days works for most healthy adults.
10 days: days 1–3 ¾ old + ¼ new · days 4–6 half and half · days 7–9 ¼ old + ¾ new · day 10 all new
7 days: days 1–2 ¾ old + ¼ new · days 3–4 half and half · days 5–6 ¼ old + ¾ new · day 7 all new
Keep treats and extras the same during the switch, so you know what caused any change
Everyone who feeds needs the same plan; one person’s “just a bit extra of the new one” undoes it
What to expect in the litter box and on the lawn
Stool can get a little softer for a day or two, especially at a step up. That on its own is common. Vets score stool on a 1–7 chart where 2 is ideal and 3 still normal; a day at 4 during a switch is a reason to go slower, not to panic.
If stool turns soft, go back to the last mix that was fine and stay there for two or three days before stepping up again. Slowing down is the whole trick.
Call your vet if…
Stop the switch and ring your vet when the signs go beyond a softer day or two.
diarrhoea lasts longer than 48 hours, or comes with vomiting, tiredness or no appetite
there is blood in the stool, or the stool is black and tarry: call today
a puppy has watery stool: puppies dehydrate much faster than adult dogs, so call today
a cat refuses the food and eats nothing for more than a day
Cats are pickier
Cats often turn down a new food outright. Go slower rather than waiting them out: a cat should never be left to go hungry until it gives in. Warming wet food slightly, or offering the new food in a separate bowl next to the old one, often helps.
Keeping the whole household on the same step
A switch fails most often at the handover: the morning person is on day 5, the evening person is still on day 2. In DidWeFeed, the pet file holds the plan, and each meal task shows today’s mix, such as “½ old + ½ new · Day 4 of 10”, to whoever feeds next. If stool gets soft, Slow down adds three days for everyone at once, and the digestion chart marks the day the food changed.
Food switch
Printable checklist
Pick a start date when the household is home and routines are normal
Choose 10 days for sensitive stomachs, 7 for healthy adults
Keep the total amount per meal the same; only the mix changes
Tell everyone who feeds which day it is (or let the app do it)
Log every stool during the switch; softer for a day or two is common
Soft stool: step back to the last good mix for 2–3 days
Blood, black stool, a watery puppy, or diarrhoea past 48 hours: call the vet
Common questions
Can I switch dog food all at once?+
Many dogs cope, but a sudden change is the most common cause of soft stool. Unless your vet tells you to switch directly (for example to a prescription diet), a 7–10 day transition is the safer choice.
My dog’s stool got soft on day 4. What now?+
Go back to the previous mix (¾ old + ¼ new) and stay there for two or three days before stepping up again. Call your vet if it becomes diarrhoea lasting beyond 48 hours, or sooner with vomiting, tiredness, no appetite or blood.
Does the same plan work for cats?+
The same steps work, but cats often need longer and may refuse the new food. Never let a cat go without eating to force the change; a cat that eats nothing for more than a day needs a vet.