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Feeding after spaying or neutering

After spaying or neutering, dogs and cats need less energy. If you don’t adjust the amount, it often shows on the scale a few months later.

The short answer

Using the factors in the Merck Veterinary Manual, spayed or neutered dogs need about 11% less energy than intact dogs, and cats about 14% less. Other sources say more: 20–30% less for cats (Tufts, PDSA) and about 30% for dogs (PDSA). Portiopet uses the Merck factors and lets the scale decide: a neutered 20 lb dog needs about 585 instead of 659 kcal, a spayed 9 lb cat about 241 instead of 281 kcal.

How much less?

The Merck Veterinary Manual multiplies resting energy by a factor: dogs intact 1.8, neutered 1.6; cats intact 1.4, neutered 1.2. That’s about 11% and 14% less.

PetIntactSpayed/neuteredLess
Dog 20 lb659 kcal585 kcal74 kcal
Dog 45 lb1,210 kcal1,076 kcal134 kcal
Dog 65 lb1,594 kcal1,417 kcal177 kcal
Cat 7 lb233 kcal200 kcal33 kcal
Cat 9 lb281 kcal241 kcal40 kcal
Cat 11 lb327 kcal280 kcal47 kcal

kcal per day for pets with normal activity, factors from the Merck Veterinary Manual.

Some sources say more

  • PDSA (UK animal charity): cats need about 25% fewer calories, dogs about 30% fewer.
  • Tufts University: cut calories by 20–30% for cats at spay or neuter.
  • International Cat Care: a neutered cat’s metabolic rate drops by about 20%.
  • In a study of female cats, food intake had to drop by 30% after spaying to keep their weight the same.

Portiopet starts with the Merck factors because all of its calculators use them. If your pet still gains weight, cut the amount in 10% steps.

Why?

The sources don’t fully agree. International Cat Care says a neutered cat’s metabolic rate drops by about 20%. A study of cats, on the other hand, found mainly that they ate more after neutering. In one study of dogs, the risk of becoming overweight was higher only in the first 2 years after neutering.

What to do

  • Adult pets: from the day of surgery, use the amount for spayed or neutered pets, for example in the food calculator.
  • Young pets: keep using the puppy or kitten food calculator and weigh more often. According to PDSA, a kitten neutered at 4 months stays on kitten food until 6 months.
  • Weigh every two weeks, especially in the first months.
  • Weigh the food instead of guessing, and count treats.
  • Feed cats in meals instead of leaving food out all day.

Your vet clinic will tell you what to feed on the day of surgery.

Questions

How much less should I feed after spaying or neutering?

Using the Merck factors, about 11% less for dogs and 14% less for cats. Other sources say 20–30%. Start with the amount for spayed or neutered pets and check with the scale that the weight holds.

When should I start feeding less?

From spaying or neutering. Energy needs go down afterwards, and without an adjustment, weight often goes up. Your vet clinic will tell you what to feed on the day of surgery.

Do I need a special food for neutered pets?

Not necessarily. The amount is what matters. If the new food has fewer calories per cup, work out the amount again.

Sources

Last checked: October 2026