Veterinarians Charlie Meynier and Jim Stortz write that spaying female dogs and cats reduces the incidence of mammary cancer, eliminates uterine and ovarian cancer risk and prevents pyometra, a potentially life-threatening infection of the uterus. Neutering male animals protects them from prostatic hypertrophy and infections, as well as testicular cancer and certain types of hernias. Drs. Meynier and Stortz also note that many less desirable animal behaviors are usually reduced by spaying or neutering, including roaming and territorial aggression.

There are many theories when it comes to the medical and behavioral effects of spaying and neutering dogs and cats. It is a controversial subject and there are numerous viewpoints out there among trainers, breeders, and within the veterinary profession.
The chief intent of this article is to state proven scientific facts. we’ll go through the medical benefits of neutering and spaying both dogs and cats, and finish with our personal beliefs on the behavioral changes that can occur.
The principal benefit of spaying female dogs and cats is the prevention of mammary cancer. A dog spayed before her first heat will have a near zero chance of developing mammary cancer later in life. After the first heat, this incidence climbs to 7 percent, and after the second heat the risk approaches 25 percent. Statistics are similar in cats.
The prevention of what is frequently a very difficult and potentially fatal form of cancer is reason enough to spay our dogs. Another potential condition in intact females is a bacterial infection of the uterus called pyometra. Treatment is surgery in a potentially unstable patient and can be very costly.
Less common conditions such as uterine and ovarian cancer are 100 percent prevented by spaying. Intact female dogs come into heat about every 8 months, resulting in bloody vaginal discharge and an unpleasant odor.
The major health benefits involved in neutering a dog involve the prostate gland. As dogs age, the prostate will gradually enlarge. This is known as benign prostate hyperplasia or BPH (think Flomax commercials). The prostate under the influence of testosterone is also predisposed to infection. This is an extremely painful and sometime life-threatening condition which is not likely to resolve without neutering and often invasive surgery.
Other medical conditions that are prevented include testicular cancer, along with certain types of hernias and perianal tumors. The effects of neutering male cats are more behavioral and are listed below.
There are no concrete facts when it comes to the behavioral changes seen in spayed and neutered dogs and cats. Neutering male dogs and cats can reduce urine marking in your house, aggression towards other dogs, and territorial aggression. It is important to realize that these behaviors can become a habit and continue after neutering.
Many experts say that once a pet is older than 1 year of age and still intact, undesirable behaviors are more likely to become permanent even if they are neutered at that time. The most dangerous behavior seen in intact males is roaming, i.e., running away to look for a mate, because it leads to animals running away as well as car accidents.
The reproductive tracts of the female dog and cat are dormant for most of the year. From a behavioral standpoint, the animals will “act spayed” most of the time and no personality changes should be noted with spaying. When in heat, females are more likely to be aggressive and can show erratic behavior such as howling and writhing on the ground. And an intact male can detect females in heat from miles away so it is not safe to leave them outside unsupervised.
The medical benefits resulting from spaying and neutering pets lead to longer and healthier lives. In addition, the majority of animals will be more relaxed and less prone to undesirable behavior. The Vail Valley Animal Hospital recommends spaying and neutering at six months of age. They are outpatient procedures and animals can go home the day of the surgery.
Dr. Charlie Meynier, DVM, has been a practicing vet for more than 12 years with a degree from the LSU School of Veterinary Medicine and Dr. Jim Stortz, DVM, has been a practicing vet since completing his Emergency and Critical Care Medicine internship in 2006. The Vail Valley Animal Hospital offers services at both Eagle Vail and Edwards locations. For more information and to make an appointment, call 970-949-4044 (Eagle-Vail) or 970-926-3496 (Edwards) or visit

59 responses to “How spaying and neutering benefits pets’ health and behavior”

  1. Ronda Dowdy says:

    I have a 1 yr old English mastiff. She has had 1 cycle. I was told that I should not have her spayed till she is 18 months old. True or false???

  2. RumpyDog! says:

    But if my vet said that to me, I’d get a second opinion.

  3. Buddy says:

    Just had my 3yr old male Pappillon neutered. My vet recommended it due to Prostatic Hypertrophy & indicated in about 65% of cases, it decreases their desire to “mark” in the house. It also decreases the possibility of testicular cancer.

    Will pick him up in about an hour – trusting it is the best thing 4 both of us & that it does not affect his personality.

    • Rosa says:

      I am not worry about the marking I hate the humping on other dog male r female it don’t matter and he want stop does it stop that

      • Katie says:

        Rosa, that is not a sexual thing. That has to do with dominance. While it may decrease it happening it probably won’t stop it.

    • Lela Kurtz says:

      I just don’t believe all these scare tactics that are used to get people to fix their animals to early. It is important to allow you pets,especially you canine companions time to grow fully before fixing them. I have just not found the scientific research that proves this is true and most of these cancers possible could happen if you don’t take out any organ.. So they could get stomach ca, so why not take out their stomach.. There are no scientific studies showing that there is any reason dogs need to be fixed to prevent these cancers. I agree that we need to fix all animals that the owners cannot keep them from being in situations where they have accidental pregnacies. If you are a responsible guardian most all dogs will benefit from not being allowed to be full grown before fixing them. I feel they should not be fixed until they are at least 1 year up to 3 years of age. Some vets think that fixing our canine companions have a high risk of adrenal insufficiency after fixing them. If you read the golden retriever study done at UC Davies they have found early fixing, poor eating habits and over vaccination is a main cause of cancers in golden retriever. We lived most of our lives with intact dogs. Over population is a big concern.. But we need to make our decision on what is best for our animal. Not all humping is because a dog isn’t fixed. 99% of the dogs at the parks are fixed and they are humping each other all the time. I have a very mellow male dog who shows no aggression even though he has not been fixed. Although he is humped by fixed dogs even when he was only a few months old. This was dog behavior.. It had nothing to do with him not being fixed at 3 months old. We let the little girl go through her first cycle before having her
      fixed. She did fine. No pregnancy, no dogs banging on the door. My unfixed 11 month old could have cared less. My boy will be fixed sometime between 1 and 3 years. I am not even sure this is the right thing to do.. He could go his whole life without any problems with not being fixed. Just use common sense and do your research.. The Humane Society fixes everything they can fix just to prevent overpopulation. It has nothing to do with the health of the dog.. Of course if a dog doesn’t have a uterus it can’t get uterine ca. That doesn’t mean that not fixing it will cause it to get uterine ca.. please do you research, feed your dog real food, don’t over vaccinate, and make sure your dog really needs that heart worm medication before you give therm another poison.. some places literally have no heart worm..

  4. Lora Cox says:

    i have a male kitten – he is about 5 weeks old today – i am bottle feeding him….what is the best age – weeks wise – to start trying them on can food mixed with their milk? also what is the earliest age wise that i can get him neutered? i dont want him spraying in the house !!!!

    • We do not give out medical advice. You should contact your veterinarian for their recommendation.

      • Mike says:

        I have a 7 year old dog, he is the sweetest dog I know. My older dog (14) (spayed female) has always been the pack leader, however, she is getting older and he is dominating her at times. He marks from time to time (once every month or so). I was considering taking him to get neutered, however, I am worried it will change his personality. I know this would just be an opinion, but have you honestly seen it change good traits in a dog? I understand it may prevent him from marking and may prevent some dominance, however, Can they become depressed? anxious?

    • Melody Stevens says:

      Kittens can start eating solid kitten food about 4 weeks. Spay/Neuter most vets will not do this until they reach 5 lbs. For males, about 12 weeks their testicles have to drop first and for females up to 5 months old.

      • Gina Bass says:

        Melody, some cats never reach 5 lbs. Most vets like to wait until the kitten is 2 las-this is the standard in most states that we go by.

  5. cat says:

    If you are dishing out cows milk frequently then this could well be the reason your cat
    is being sick. It will also give you peace of mind about your cat as it ages.
    It talks about its range, habitat, hunting and preying,
    and reproduction habits.

  6. Trish Muchler says:

    If cats are spayed or neutered does it make a difference if you put males or females or male & female together

  7. Kelsea says:

    I have inherited a 10yr old chihuahua who is very aggressive towards strangers and children. We are considering having him neutered. At 10 is he to old for this procedure?

  8. christa says:

    I have a female cat and she had kittens. After she gave birth I had her spayed, and she kinda acts differently now. She keeps to herself and is not as loving as she was when she was a kitten. Is she acting this way because she had kittens and was spayed? Also i kept one of the kittens, and it is a Male, He is super friendly and so loving…. Im about to have him neutered, is he going to change?

  9. joyce says:

    I have a 4yr old mini dachshund(none spayed). she does not act “wanting” when she is in heat.She tends to just lie in bed all day and refuses to go outside. When she is around male dachshunds she always gets very defensive if they try anything with her. Should I still get her spayed?

  10. Brenda says:

    I understand that spaying early does not allow the hormones that help in proper growth of the animal. Does spaying early keep an animal from growing properly?

  11. tammy m says:

    I have a 5 yr old Bichon male that still pees over everything. Would neutering him fix that problem

  12. Beverly says:

    ok i have a three year old lab that got ran over and lost a leg that was like a month ago ever since then him (tye) and my 8 month old lab (Tank) have started fighting for dominace so im wondering would it help if i had one or both of then nuetered or should i just give up and find a good home for the 8 month old? its to the point that i have to keep them separated at all time. 🙁

  13. LynnAnn Thomas says:

    Our 8 month old male GSD is showing sexual aggression towards me. I’m well past menopause…so I don’t believe I’m giving off pheromones.

    I’d like to have my husband (this is dog primarily) have the dog neutered, however he is saying he’ll wait until the dog is more than a year old.

    I can’t abide the behavior (which my husband thinks is “in my mind”). I had this happen with another GSD many years ago and the behavior ended with neutering. (it was my dog before getting married).

    Please give any advice you can to resolve this situation. thanks…lynnann

  14. Tom Moffett says:


  15. B. Fontaine says:

    There is definitely more to the story then presented in this article! Here is a summary of 50 studies on the subject it is best to get unbiased information before you make a decision on when to spay or neuter an animal.

  16. Ana says:

    I want to have my 2-year old jack Russel chihuahua mix neutered. My husband on the other hand is very against the idea, because he “understands the pain Akiko would go through” I need some ideas on how to convince him. I just feel like it would be healthier in the long run for him to be fixed.

  17. Laryl says:

    I think dogs should…

  18. PAUL says:

    I have a 15 year old diabetic female that has not been spayed. Is it possible to have her spayed at this time?

  19. Audrey says:

    I have a one and a half year old american bully pitbull. He is very calm naturally except when seeing other dogs (mind you, i walk him three times a day for an hour). He is completely friendly to dogs that are fixed, but when we run into other males that are not he gets agressive. Is that something that will go away once he is fixed? Im hesitant to put him in a training class with other dogs if that doesn’t fix my potential night mare from happening.

    • Lela Kurtz says:

      This could be one of the few reasons for fixing this dog? If you wait much longer it might not improve his behavior. Male aggression at an early age is one of the incidents that I would see fixing male dogs. I think you answered your own question when you said he was not aggressive with fixed dogs.

  20. Maelyn says:

    My cat recently got spayed, and she has a decent size knot in the incision. Is that normal?

  21. Robert harris says:

    my male cat pissing marking his terroity,makng load meow sound. Will nuetering him stop that

  22. sally says:

    I have just got a male puppy that was neutered. I have noticed sometimes when rubbing his tummy that he has two lumps that look like his ( balls) under the skin at the base of his penis. Should they be there. I tried to take picture to send to vet, and then they are gone.

  23. London Mcmillan says:

    I have a 7 month old chocolate lab fox hound mix. Our neighbors dog is going through her first cycle and our little boy keeps escaping his kennel. Would now be a good time to get hi neutered?

  24. Patti says:

    I have a two month old male kitten and was recently told by my vet that he needs to be 6 months old before being neutered. Is that not to old? My cousins male kitten was neutered at 3 months so I am very confused. Does it depend on the vet as to when they will neuter a kitten? I have a 12 year old male as well that was neutered before I rescued him at 2 years old so I am hoping once I get Oliver neutered, my other cat will go a little easier on him.

  25. Robin says:

    I have a questions regarding my male 6 month Rottie/Ridgeback mix. My husband is on the fence regarding having our pup neutered. He has become very aggressive toward me and bites me now. The first time he want after me was when I was planting flowers and was on my knees – he came over and went after my arm. I pushed him away and said no. He kept going after me as if he was mad. I am the only female in the house and he goes after me and nips at me.

    If we get him neutered will this clam him down? Because he is 6 months old, will there be more resentment toward me? Is there any health side effects in having males neutered? I do not want to hurt my pup, I just want a happy healthy puppy that I can enjoy and not be scared of him.

    Please advise on the health issues of getting my Rottie/Ridgeback neutered

  26. Thank you for the terrific blog. You mentioned in this blog that pet neutering is essential, and that you should make sure to do it before they are a year old. My brother just adopted a cute puppy and I was wondering when he should get it neutered. We’ll have to find a vet that could neuter his puppy when the time is right, so that he can avoid those issues that occur when you don’t neuter.

  27. Jon Spidle says:

    I highly disagree with spaying and neutering pets because it can cause certain defects in pets and it prevents pets from reproduction of offspring which means that it we pet owners will cause future pet owners from owning pets in the first place

    • Nic Terry says:

      Millions of pets ate euthanized every year from that way of thinking–there are more than enough to go around. Obviously this is geared towards the average pet owner who has no intentions or desire to breed and raise. RESPONSIBLE breeders of both dogs and cats advocate the spaying or neutering of pets not used for breeding and showing.

  28. Sherry Barrett says:

    why does my Shuzu continue to have some bloody discharge when she pepes?

  29. Emily says:

    will a low cost spay/neuter company like FACE neuter a six week old male kitten?

  30. Hector Uba says:

    Thank you for the information on how desexing an animal can be beneficial to your pet’s health and behavior, it was very helpful. I had no idea that neutering your animal could lead to a longer and more healthy life, I always thought it was for behavioral benefits. My sister just got a new puppy and she has been wondering if she should desex her puppy, I’ll share these benefits with her.

  31. It’s interesting how you said that pet neutering is best done when your pet is young so they don’t have bad behaviors. My wife and I just bought a new puppy and we want him to be well behaved. We’ll have to look into a doctor to ensure that it gets done well and so we don’t have to worry about him being naughty.

  32. mike says:

    No dog should be neutered at 6 months. Any vet suggesting that really needs to update their education and do a little research of the matter.

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