Worried that neutering will change your pet?

Published by Emma Milne
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When you hear people talk about neutering cats and dogs there are lots of things that can worry owners. You may have heard that neutering cats and dogs causes changes in behaviour, makes them fat, might change their fur or even cause incontinence. So let’s have a look at these things and see if they really are a problem or not.


I once had a client who was dragged into my consult room by her huge, un-castrated boxer. The dog sniffed my nether regions, urinated all over my room and was totally out of control. I asked her if she’d ever considered castration and she said, “Oh, but we wouldn’t want to change his character”! So what behaviour changes can we see?

  • Male and female cats and dogs are likely to be less aggressive after neutering.

  • Male animals in particular are much less likely to roam in search of a mate so are more homely. This also means they are less likely to get injured or, particularly in the case of cats, spread diseases.

  • Male cats and dogs that are not castrated will urinate in lots of places to mark their territory. This may be unwanted if it’s in your house or other people’s. 

I think you’ll agree that these changes in behaviour are probably all pretty welcome!

Weight gain and obesity

The change in hormone levels after neutering makes the metabolism slow down slightly. This means that bodies burn fewer calories so indeed pets can gain weight if we’re not careful. BUT, the great news is that this isn’t anything to worry about. Here are some tips for how to avoid it.

  • Regular weight checks. Neutering usually happens around 4-6 months of age. As your pets are growing it’s essential to have them weighed regularly. You can track their growth and also your vet can make sure they are a healthy, slim weight. Knowing they are their ideal weight before neutering puts you ahead of the game.

  • Remember your pet will gain weight after neutering if they are still growing. Ask your vet to show you how to check body condition score (BCS). This will help you see if their weight gain is healthy.

  • Be ready to change their food. It can be dangerous to simply reduce rations of food because you could underfeed protein, vitamins and minerals. Your pet will also feel hungry and be more likely to beg or steal food. Talk to your vet about a lower energy, bulkier food like a neutered cat or dog food. Don’t change without talking to a vet because if your pet is growing you need to make sure they have grown enough to change food. 

  • Splitting your pet’s ration into smaller, more frequent meals can help them feel fuller through the day. 3-4 meals for dogs and up to 6-8 meals for cats are ideal. Timer feeders are a great way to do this if you’re out at work. Wet food has a higher water content than dry food so may help your animal feel fuller. Try wet foods or see if your pet will eat their kibble with added water. This can help keep them satisfied.

Coat and fur changes

Some owners really worry about this. It’s actually pretty rare to see coat changes after neutering. Some spaniel breeds in particular seem to become a bit fluffier. Some light-coloured cats like the Siamese may grow dark fur in the patch where they are clipped for the operation. These changes are rare, are only aesthetic and pose no problem at all for the cat or dog. 


Female hormones help keep the bladder toned and working in dogs. Because neutering removes the hormones we sometimes see urinary incontinence later in life. This usually shows itself as leakage of urine when the dogs are asleep or as they change position. It only affects about 5% of female dogs and tends to be worse in larger, chubbier or older animals. There are medicines available that can really help and I feel that the decrease in cancer risk with neutering still makes it worthwhile.

As an owner myself as well as a vet, I feel that the health benefits of neutering far outweigh these minor worries. You can read more about those health benefits in our articles on dog and cat neutering.

Contributor Bio

Emma Milne

Emma Milne


Dr Emma Milne qualified as a vet in 1996. She worked in small animal practice for 12 years and as a clinical nutrition advisor for seven years. She is well known for her animal welfare work and has written ten books on pet animals.