I had my cat, "Darien" (1 yr 3 months, Persian) neutered this last Sunday. He is doing okay, he's sleeping nicely, he is eating well as usual, and we are always monitoring him. It has been 4 days since the castration, and he has not meowed constantly to mate like he used to and seems like he is not much interested to run outside like he used to.

During the day of the appointment, when the doctor was shaving his bottom, she called me out and showed me that Darien has only one testicle. And that it is known as "Feline cryptorchidism". The doctor told me not to panic and that if the other testicle is inside, it will be very small and not worry about it. In the rare case scenario, it may form cancer. Or the inside testicle may descend on its own later on, and if that happens, bring him for castration again.

Further, she told me to perform an ultrasound to check the condition of the problem. Since where I am living there is none for the animals, I am planning to go to another city to perform an ultrasound later when Darien is fully healed.

What I would like to know is in such case, where one of his testicles is retained and is sterile, while the other is neutered:

  1. Will he be wanting to mate? My doctor told me he probably won't like he used to. But I think since hormones are secreted by the testicles, the retained/sterile testicle will produce the hormones.
  2. Can you guys share some of your stories if you have a cat with this problem?
  3. Does the retained testicle really descend on its own?

1 Answer 1


It is likely that there is another testicle inside. It is strongly encouraged to have this other testicle removed – the surgery is a bit like a spay in a female, going into the abdomen to hunt for it. Sometimes they can be difficult to find.

The retained testicle will still produce testosterone, and you will still therefore likely see many of the unwanted behaviours which we neuter cats for. He may still display mating behaviour, urine spraying, aggression, have an unkempt coat, etc.

However, he will probably (but not definitely) be sterile.

It is extremely unlikely a retained testicle will descend at this age.

Ultrasound is not a bad idea to try to identify the testicle. Unfortunately not finding it on ultrasound does not mean it's not there, so usually a surgical explore is the way to go.

To assess whether your cat is still producing testosterone (therefore still has a retained testicle), a few weeks after the partial castration your vet can check his penis to see whether there are penile spines (barbs) present. After a neuter (removal of both testicles), these spines will gradually disappear, but if there is a retained testicle producing testosterone they will not. There are blood tests to assess testosterone levels as well, for confirmation.

Also, this raises the importance of the pre-neuter exam. Before sedating the cat, it is important to make sure they are the right sex, and that there are two descended testicles. As a vet, if there is only one testicle I do not part neuter them, for two reasons. First, it can make it more challenging to find the missing testicle if you are not sure which side the descended one was. Second, if a second surgery is not performed to find the other testicle, then it will appear to future vets that the cat is neutered when he is not.

  • @HarryV. Sorry if this is a little off topic, but the "internal testicles cause cancer" argument gained some (un)popularity due to the intersex community speaking up more publicly about their treatment by medical professionals. Were you as a vet taught that information as well? Have you read any statistics or publications concerning the matter?
    – Elmy
    Dec 19, 2020 at 19:47
  • @Elmy Yes, abdominal testes in pets are more susceptible to cancer. One study found that intra-abdominal testes are 13.6 times more likely than scrotal testes to develop cancer in dogs (see Liao et. al. 2009). However there are no such studies in cats to my knowledge. Testicular tumors in cats are very rare, perhaps because of high rates of neutering in pet cats. Honestly, I rarely bring up cancer in the discussion of treatment of cryptorchid cats – it's usually the tomcat behaviour/smell that gets owners to pursue surgery.
    – Harry V.
    Dec 20, 2020 at 5:26

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