How to Feed My Pet

Changing your dog's food without missing illness

DogsAdult & senior·Sources checked September 13, 2026
This is general information, not veterinary advice, and it cannot diagnose your animal. Every figure here is a starting point to adjust against your own animal, not a prescription. Medical disclaimer

Most food-change advice stops at "mix it gradually over a week." That is fine as far as it goes. The part usually left out is more useful: a food change is also a window where real illness gets mistaken for adjustment.

How we label our evidence

  • Source-supportedStated directly in the cited institutional publication.
  • Our editorial guidanceA conservative reading of the evidence applied to a caregiver decision. Not a validated clinical protocol.
  • Evidence gapWe could not verify this in our approved sources, so we have not invented a number.

How long

Source-supported
WSAVA's Principles of Wellness recommends an ideal transition over 7–10 days, watching acceptance and tolerance. An older WSAVA FAQ (last updated January 2018) describes at least 3 days, with longer for dogs that are unwell. Neither represents one experimentally proven duration.
A practical 7-day schedule
DaysOld foodNew food
1–275%25%
3–450%50%
5–625%75%
7 onward, if tolerated0%100%

For a 10-day version, spend three days at each mixed stage. A dog with a history of stomach upset may need smaller steps or longer stages.

Our editorial guidance
This schedule is our implementation of "gradual" using the familiar 25-point steps. It is not a trial result showing these exact days prevent diarrhoea. And worsening signs should trigger a call, not automatic advancement because the calendar says so.

Percentages of what, exactly?

Here is a detail most handouts skip. If the two foods have different energy densities, mixing them by weight silently changes how many calories your dog gets. The percentages should be of calories.

With E as the daily allowance in kcal and p as the new food's share:

  • Old food (g/day) = E × (1 − p) ÷ old food kcal/g
  • New food (g/day) = E × p ÷ new food kcal/g

Convert with kcal/g = kcal/kg ÷ 1,000. If the label only gives kcal per cup, don't invent grams per cup — get the matching product data.

Our editorial guidance
Worked example. At 800 kcal/day, an old food at 4 kcal/g and a new one at 3.2 kcal/g, a 50/50 calorie split is 100 g old + 125 g new — not equal weights. Splitting by weight here would quietly underfeed. This calorie-based definition is our design choice; published handouts don't define it uniformly.

You'll need both foods' energy densities for this — see finding kcal/kg on the bag.

When gradual isn't an option

Situations that break the normal schedule
SituationWhat to do
The food is discontinued, or you've run outChoose an appropriate complete replacement and mix gradually only if safe old food remains. If it doesn't, switch and monitor closely — don't invent a fasting period. Similar packaging or ingredient names do not prove similar digestibility.
A recall, or suspected contaminationStop the affected food. Do not keep feeding it to complete a transition ratio. Keep the packaging and lot information and call your veterinarian about exposure.
A vet prescribes an urgent diet changeFollow the treatment plan, including whether mixing is appropriate at all.
A diagnostic elimination dietDifferent rules entirely — the trial only starts once excluded foods have stopped, and ordinary treats can invalidate it. See itching and food allergy.
Mild loose stool appearsPause rather than advancing. If the dog is otherwise well and the old food is still safe and appropriate, discuss going back a stage and restarting more slowly.

Softer stool, or a dog that needs seeing?

Cornell distinguishes mild loose stool in an otherwise well dog from diarrhoea with appetite loss, lethargy, vomiting, blood or tarry stool. Its own guidance varies between calling after one to two days and waiting roughly 48–72 hours.

What the action labels mean

Emergency now —
contact an emergency veterinary service and arrange immediate assessment. Do not wait for the next scheduled feed or weigh-in.
Call now for triage —
telephone the veterinary service when you notice the sign. The veterinarian decides how quickly the animal needs to be seen.
Contact today —
get in touch when you notice the issue to agree on a time. This does not mean waiting until evening.

Emergency now

Collapse, marked weakness, severe abdominal pain or distension, black tarry stool alongside illness, or substantial bleeding.

Call now for triage

Blood in the stool, repeated vomiting, inability to keep water down, or diarrhoea with reduced appetite or activity.

Contact today

Mild diarrhoea continuing beyond about 24 hours — sooner in a senior dog or one with existing disease.
Our editorial guidance
That 24-hour contact point is our choice within genuinely variable guidance, not a validated line between harmless and dangerous. We would rather people call early than apply a 72-hour wait to a dog that needed help on day one.

One slightly softer but still formed stool, with normal behaviour and appetite, is reasonable to note and watch — though that doesn't prove the food change caused it. Record stool appearance and frequency, vomiting, intake, activity, treats, medicines, and exactly which day and ratio you were on. Avoid human anti-diarrhoeal medicines unless your vet directs it.

Sources