Meddor
Why switch foods gradually
Your dog’s or cat’s digestion gets used to what it eats. Switching foods overnight hits it with a whole new recipe at once, and that’s what causes loose stools, gas, sometimes vomiting, or a cat that walks away from the bowl.
Mixing the two foods, with a little more of the new one each day, gives the gut flora time to adapt. The total amount stays the same: only the proportions change.
The 7 or 14-day plan
Seven days is enough for most pets. Here is the plan the calculator follows:
| Days | Old food | New food |
|---|---|---|
| 1 and 2 | 75% | 25% |
| 3 and 4 | 50% | 50% |
| 5 and 6 | 25% | 75% |
| 7 | 0% | 100% |
Choose 14 days for a sensitive stomach, for a cat, since cats are wary of anything new, or when the two foods are very different. The steps are then smaller: the new food starts at 15% instead of 25%.
How the portion is calculated
The most reliable source is the feeding chart printed on the new food’s bag, because it’s measured on that product. The calculator starts from the portion on the line for your pet’s weight. The chart is written for moderate activity; for a pet with low or high activity, the calculator scales it by the activity factors below.
Without the bag, the calculator estimates the portion in three steps, using the formula vets use:
- Resting energy needs are 70 × weight0.75 calories a day, with the weight in kilograms. The exponent is why a 40 kg dog doesn’t eat four times what a 10 kg dog eats, but a little under three times.
- The day’s needs are that number multiplied by an activity factor: 1.4, 1.6, or 2 for a dog with low, moderate, or high activity, and 1, 1.2, or 1.4 for a cat, which burns far less at the same weight.
- The grams are those needs divided by the food’s calorie content. The calculator assumes 380 kcal per 100 g for dry food, 85 for wet food, which is three-quarters water, and 150 for raw food.
For example, for a 20 kg (44 lb) dog with moderate activity: 70 × 200.75 ≈ 662 kcal at rest, × 1.6 ≈ 1,059 kcal a day, which is 1,059 ÷ 380 × 100 ≈ 279 g of dry food.
The third step is the weakest. Depending on the range, dry food provides 330 to 450 kcal per 100 g, which moves the portion by about 15% either way, and more for wet food. That’s why the estimate is only used when you don’t have the bag.
This calculation is for a healthy adult. For a puppy, a kitten, a pregnant or nursing female, or an overweight or sick pet, follow the manufacturer’s chart and your vet’s advice.
Frequently asked questions
Can I switch foods overnight?
Better not, unless your vet asks you to, for a prescription diet for example. A sudden switch is the most common cause of digestive upset when changing food.
Loose stools during the transition: what should I do?
Go back to the previous step for two or three days, then continue more slowly, over 14 days. If diarrhea lasts more than two days, or if there’s vomiting, blood, or your pet seems listless, call your vet.
My cat won’t eat the new food
Many cats are wary of anything unfamiliar. Stay longer on each step and choose 14 days. A cat shouldn’t go without eating for more than a day or two: if yours stops eating, talk to your vet.
What about switching from wet food to dry food?
Grams don’t carry over from one type to the other: 100 g of wet food provides about 85 kcal, 100 g of dry food about 380. Run the calculator twice, once with each bag, and apply the plan’s percentages to each of the two portions.
Should the amount change during the transition?
Not between two foods of the same type: each day, the grams of old and new food add up to the daily portion. The proportions change, not the size of the meal.