Q: If I spay/neuter my pet, won’t it get fat?
If you do not decrease your pet’s food by 20-25%, it will get fat.
Respiratory calorimetry measurements in kittens, a definitive measure of calorie
requirements, have shown that energy requirements decrease about 20-25% after
the kitten is spay/neutered. It does not matter whether it is a female or a male,
the energy decrease is the same, nor does it matter whether you neuter them
early or late (Root et al. Am J Vet Res 57:371-374, 1996). What is different
between females and males is the effect of estrogen on food intake. Estrogen is
appetite suppressing, so loss of estrogen from spaying a female will cause them
to eat more if allowed food free-choice (Flynn et al. J AM Vet Med Assoc
174:1083-1085, 1979). This is one reason spayed females tend to be 4 times as
likely to be overweight than intact females, and castrated males may be only
twice as likely as intact males.
We have no calorimetry data from puppies like we have from kittens as of yet.
However, the same anecdotal observations apply for both dogs and cats about
spayed/neutered animals getting/being fatter. The epidemiological data from dogs is
consistent with the cat-calorie findings. In my experience, dogs maintain their
weight on 75% of what was prior fed to being spay/neutered. The estrogen effects
are from both cats (Flynn) and dogs (Houpt).
A: If you adjust your pet's diet appropriately, it will not get fat.
William J. Burkholder, DVM, PhD
Diplomate, American College of Veterinary Nutrition
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