Off their food since a change of diet

What this tends to look like

• Reduced enthusiasm since a change of brand, recipe, or wet to dry
• Softer stools, more gas, or louder gut noises alongside it
• Sometimes eats the first meal keenly and then goes off it by day three
• Occasionally picking out the old kibble and leaving the new, if you mixed them
• No other signs of illness, still active and bright
• Often follows a recipe reformulation rather than a deliberate switch

What is usually going on

The gut microbiome adapts to a consistent diet, and a fast change gives it more than it can absorb. The result is looser stools, gas, and reduced appetite for a few days, which is uncomfortable rather than dangerous. Nearly all of it is avoidable by changing over roughly seven to ten days, moving in steps of about a quarter of the ration every two or three days, and letting the stools tell you whether to move on or hold at the current step.

The common mistake at this point is to conclude the new food does not suit them and change again. That resets the clock and stacks a second disruption on top of the first, and it is how households end up with a cupboard of half-used bags and an animal with a permanently unsettled gut. Unless there is vomiting, blood, or real illness, the better move is almost always to slow down rather than switch again.

It is worth separating this from a genuine food intolerance, which is less common than it is blamed. A true intolerance tends to produce persistent signs on a food, over weeks, that reliably resolve when it is removed and return when it comes back. A few days of soft stools during a transition is not that. If you do suspect intolerance, it is worth doing properly with veterinary guidance, because informal elimination trials are usually confounded by treats nobody counted.

What people commonly use

Educational information only — not veterinary advice. Check with your vet before starting anything new.

Where to find them

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What you can do at home

• Slow the transition down. Go back to a mix that suited them and move in quarter steps every two to three days
• Hold at each step until the stools are firm before increasing the new food further
• Feed smaller portions more often during the changeover, and keep everything else in the diet constant
• Cut treats, chews and scraps to nothing while you transition, so you can actually tell what is causing what
• Do not switch to a third food. Two disruptions is worse than one, and it makes the cause impossible to identify
• A probiotic during and for a week after the switch is one of the more reasonable uses for one

What progress should look like

How long to give this before you conclude it is not working.

• Two to four daysStools should firm up once you step back to a mix that suited them.
• Seven to ten daysA properly paced transition completes on this clock, which is the point of doing it slowly.
• Two weeksAppetite and stools settled on the new food, treats reintroduced one at a time.
• If it does not settlePersistent soft stools two weeks after a completed switch is worth a conversation, and possibly a proper diet trial.

When to stop and call your vet

• Vomiting, or blood or mucus in the stool
• Diarrhea lasting beyond a few days, or any diarrhea with lethargy
• Weight loss during the transition
• Persistent signs on every food you try, which needs a proper investigation rather than more switching