It's an old myth that neutering your dog or cat will make him fat, lazy and dumb. This isn't true. While altering a pet can cause metabolism issuesnote , it's not always a major enough difference as this trope makes it seem. Overfeeding and not enough exercise are other common reasons for a pet gaining excessive weight.
Also, the obesity and lethargy that neutering can cause in real life is not to confused to the inaccurate lazy portrayal of castrated or companion animals in fiction.
One of the metabolic issues that castration and spaying causes is lethargy, which is an unnatural sort of low energy. Lethargy should not be confused with laziness however. Obesity is another effect of this endocrine disrupting procedure. In cats, this gonadal divestation (what spaying and neutering is) not only lowers metabolism, it increases appetite, which can result in them either having a hard time regulating their appetite or having an insatiable appetite. However, being fat doesn't equate to being lazy.
In fiction, however, spayed and neutered animals (but especially neutered ones) will usually end up chubby, lethargic, and lazy after the surgery. A previously energetic pet will suddenly just want to sit around all day. This trope is one of the top reasons why Animals Fear Neutering; they don't want to become lazy, fat, dumb, and lethargic like the others they've seen.
- Tailchaser's Song:
- Cats mock lazy cats by comparing them to eunuchs (AKA, neutered toms).
- Hushpad was a playful Proper Lady kitten at the start the book. When Tailchaser reunites with her, he finds her much rounder than he remembers (but nonetheless pretty). Tailchaser soon finds that all Hushpad wants to do is nap all day. She isn't even remotely interested in having kittens anymore. The two cats part due to their conflicting interests.
- Almost all neutered toms in Warriors become lazy. Kittypets are already known for being plumper than their forest-dwelling brethren, but neutered ones are especially so.
- Mentioned in both the novel and film version of Stephen King's Pet Sematary. Louis gets Ellie's cat Church fixed because, as Jud puts it, "fixed cat don't tend to wander," and Louis wants to avoid Church being killed in the very busy road on which their new home is situated. It doesn't work.
- Pufftail from Stray makes mention of a few overweight Big Eater cats who have gotten "the Operation".
- The Unadulterated Cat by Terry Pratchett describes neutered toms as "fat and lazy and just want to kip all day", although the book is clear that they're not dumb (indeed, they may have more on their minds than the sex-obsessed Entire Tom), and that neutering is A Good Thing.
- One strip of Saturday Morning Breakfast Cereal comic consists of Charles Darwin screaming "Eat, fight, fuck!" at a cat, who does those things with relish and savagery... up until it gets neutered, at which point it declares itself free of evolution's influence. The final panel of the comic is the cat, now morbidly obese, sighing about how happy it is.
- One Cutaway Gag from the Family Guy episode "Screwed the Pooch" has Peter imagining what his dog Brian will be like after being neutered. There Brian is overweight and eating chocolate, lamenting that he knows it makes him fat, but doesn't care.
- The Fairly Oddparents episode "Dog's Day Afternoon" revolves around Timmy switching bodies with Vicky's dog Doidle, which leads to Vicky planning to have Doidle neutered. Her other pets have also been neutered (including those that normally aren't castrated, such as a fish), which has made them all lethargic to the point of nonresponsiveness—one spontaneously falls over without even blinking. Timmy obviously tries to avoid his fate, and Doidle is clearly displeased where he's headed when they switch back bodies, but he ultimately ends up neutered.