How to switch your cat's or dog's food without upsetting the stomach

Your dog would eat the new food out of your hand on day one. Your cat might not touch it until day four. Either way, the stomach usually wants the same thing: time.

A digestive system gets used to what it receives every day. Change the food overnight and it has to adapt all at once, which is when soft stools, wind or a refused bowl appear. Change it over a week and most animals barely notice. Here is how.

The 7-day plan

Mix the new food into the old, increasing the share every couple of days:

Days	Old food	New food
1–2	¾	¼
3–4	½	½
5–6	¼	¾
7	none	all

Mix the two well, so your pet cannot pick out only the familiar part. Cats in particular are very good at that.

If everything looks normal, carry on. If it does not, go back one step and stay there a few days longer. There is no prize for finishing in exactly seven days.

What is normal along the way

• Slightly softer stools for a day or two are common, especially when moving from dry food to more wet food, which contains much more water.
• Different amounts in the litter or on the walk. A food with different fibre or more digestible protein can change the volume. That alone is not a problem.
• A bit of hesitation in the first days, especially in cats. Smell and texture are new.

What is not normal: diarrhoea lasting more than a day, vomiting, blood in the stools, a pet that stops eating, or one that seems tired and unwell. In those cases, stop the change and call your vet. Kittens, puppies and older animals deserve a call sooner rather than later.

Cats: patience, not pressure

Cats are creatures of habit, and food is part of the habit. A few things help:

• Go slower if you need to. Ten or fourteen days is fine for a cautious cat.
• Serve wet food at room temperature. It smells stronger and more appealing than fridge-cold food.
• Do not let a cat go without eating to "make it accept" a new food. Cats should not fast. If your cat refuses the mix, go back to a step it accepted.

If your cat is fussy in general, our article on picky cats covers the other usual suspects: freshness, bowl, place and routine.

Dogs: enthusiasm is not the same as tolerance

Most dogs will happily eat anything new, all at once. Their stomach may disagree a few hours later. Follow the plan even if your dog clearly approves of the new food from the first bite.

Dogs that change food often (holidays, a new bag in a hurry, leftovers from visitors) tend to have more sensitive digestion. Once you have found a food that suits, keep it steady.

Switching between kibble and wet food

Moving between dry and wet is a bigger change than switching between two kibbles, for two reasons:

1. Water. Wet food is mostly water. Our cat fillets, for example, are 76% moisture. More water in the bowl often means more water in the stools at first, and less drinking from the water bowl. Both are normal.
2. Calories. By weight, wet food contains far fewer calories than kibble, because so much of it is water. A gram of wet food does not replace a gram of kibble. If you combine the two, reduce the kibble so the total stays right; our feeding calculator works out the split.

Many owners never fully switch, and keep both: kibble as the base, wet food on top or as one meal of the day. That works well for cats and dogs, and it makes future changes easier because the stomach is already used to both.

Kittens, puppies and seniors

• Kittens and puppies: keep the food they had before coming home for the first week, then switch slowly. Our guide to feeding a kitten in the first months has the details.
• Older animals: take more time, and watch appetite and weight closely. Older digestive systems are often less flexible.

Testing new recipes

Changing recipe within the same range (one fillet for another, for example) is usually easier than changing brand, because the base stays similar. If you want to find out which recipes your cat prefers, a small mixed box such as our Discovery set lets you test several over a couple of weeks, alongside the usual food, without committing to 24 tins of the same.

In short

1. Switch over about a week: a quarter, half, three quarters, then all.
2. Mix well, and go back a step if the stools turn soft.
3. Diarrhoea for more than a day, vomiting or a pet that stops eating: call your vet.
4. From kibble to wet food, expect softer stools and less drinking at first, and adjust the amounts.
5. Once you find a food that suits, keep it steady.

Your pet will not thank you for the careful seven days. It will simply not be sick on the carpet, which, for everyone involved, is the better outcome.