New Report on Complication Rates for Neutering Surgery in Dogs and Cats

I have written extensively about the subject of neutering (spaying and castrating male and female dogs and cats). The bulk of the discussion and debate about this procedure centers on the health effects. It is generally recognized to be a pretty safe procedure, though of course no surgery is entirely without risk. The scientific literature has limited information on the specific risks of the neutering surgery procedure itself and how often they occur.

Total complication rates for routine castration or spaying have been reported from 2.6%-33% of cases.The majority of these complications are minor and require no treatment. Complication rates vary considerably from practice to practice and are generally reported to be higher in studies of surgeries performed by students in training. Reported death rates are less than 0.1%.1-5

A new source of data on this subject has recently become available which represents the type of “Big Data” so popular these days. The Royal College of Veterinary Surgeons (RCVS) charity arm RCVS Knowledge,  has a program in place that collects information from practices around the country in a central database. The goal is to encourage clinical audit, a quality improvement process in which veterinary practices can investigate the outcomes for their patients and compare these with those of other practices or with an established “gold standard.” This facilitates recognizing processes that aren’t working as well as they could and improvement in patient care.

The RCVS has recently released the results of data collection on complications of neutering. Though not the result of a controlled, prospective research process, this audit report is based on over 30,000 individual surgeries, so it at least represents a potentially powerful source of data. The specific variables that affect outcome of neutering surgery in individual animals can’t be identified, and there is the problem of patients who can’t be followed and whose outcome is unknown. However, this type of data complements the research evidence already available and gives us a general sense of the complication rates in the UK for these common procedures.

Routine Neuter Complication Rates

The outcomes measured were cases with no complications, those with minor complications not needing treatment, problems needing medical treatment, problems needing surgical treatment, and fatalities. About 8% of the cases in the database were not available for followup, and these were not included in the calculation of complication rates.

Total Overall Complications

Outcome Frequency Percent Cum Percent
Abnormal but no treatment necessary 2795 9.3% 9.3%
Abnormal requiring medical treatment 2254 7.5% 16.8%
Abnormal requiring surgical intervention 341 1.1% 17.9%
Fatality of animal 29 0.1% 18.0%
No abnormality present 24627 82.0% 100.0%
Total 30046 100.0% 100.0%


Complications for Male Cats

Outcome Frequency Percent Cum Percent
Abnormal but no treatment necessary 56 1.4% 1.4%
Abnormal requiring medical treatment 53 1.3% 2.7%
Abnormal requiring surgical intervention 23 0.6% 3.3%
Fatality of animal 3 0.1% 3.4%
No abnormality present 3885 96.6% 100.0%
Total 4020 100.0% 100.0%


Complications for Male Dogs

Outcome Frequency Percent Cum Percent
Abnormal but no treatment necessary 977 11.4% 11.4%
Abnormal requiring medical treatment 796 9.3% 20.6%
Abnormal requiring surgical intervention 61 0.7% 21.3%
Fatality of animal 6 0.1% 21.4%
No abnormality present 6763 78.6% 100.0%
Total 8603 100.0% 100.0%


Complications for Female Cats

Outcome Frequency Percent Cum Percent
Abnormal but no treatment necessary 616 7.0% 7.0%
Abnormal requiring medical treatment 385 4.4% 11.4%
Abnormal requiring surgical intervention 163 1.9% 13.3%
Fatality of animal 5 0.1% 13.3%
No abnormality present 7596 86.7% 100.0%
Total 8765 100.0% 100.0%


Complications for Female Dogs

Outcome Frequency Percent Cum Percent
Abnormal but no treatment necessary 1146 13.2% 13.2%
Abnormal requiring medical treatment 1020 11.8% 25.0%
Abnormal requiring surgical intervention 94 1.1% 26.1%
Fatality of animal 15 0.2% 26.3%
No abnormality present 6383 73.7% 100.0%
Total 8658 100.0% 100.0%


These results are broadly similar to previously reported numbers, though lower than sometimes seen in studies in which inexperienced veterinary students are performing the procedures. They confirm that the procedure is very safe, that most complications are minor and do not require much, if any, treatment, and that mortality rates are very low. Females experience more complications because the surgery is necessarily more invasive. These data don’t tell us anything about the differences between specific neutering procedures, breeds, ages of patients, and many other factors, so they don’t let us predict the precise risk for individual patients. But they provide a general background that help us in making decisions about neutering.



  1. Pollari FL, Bonnett BN, Bamsey SC, Meek AH, Allen DG.Postoperative complications of elective surgeries in dogs and cats determined by examining electronic and paper medical records. Journal of the American Veterinary Medical Association 1996;208(11):1882-6.
  2. Howe LM. Short-term results and complications of prepubertal gonadectomy in cats and dogs. Journal of the American Veterinary Medical Association 1997;211(1):57-62.
  3. Pollari FL, Bonnettt B.N. Evaluation of postoperative complications following elective surgeries of dogs and cats at private practices using computer records. Canadian Veterinary Journal 1996;37:672-8.
  4. Burrow R, Batchelor D, Cripps P. Complications observed during and after ovariohysterectomy of 142 bitches at a veterinary teaching hospital. Veterinary Record 2005;157(26):829-33.
  5. Root Kustritz MV. Effects of surgical sterilization on canine and feline health and on society. Reprod Domest Anim. 2012 Aug;47 Suppl 4:214-22.


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19 Responses to New Report on Complication Rates for Neutering Surgery in Dogs and Cats

  1. Jazzlet says:

    Than you for this. Could you explain what the categories “abnormal requiring no treatment”, “abnormal requiring medical tretment”, and “abnormal requiring surgical intervention” might mean, when you have some time? I’ve only ever had animals have entirely normal neuters, so have no idea what the possibilities might be. Thanks.

  2. Frances says:

    I would be interested to know why the complication rates are so much higher in dogs – approximately double that of cats across all the categories.

  3. Michael says:

    Dogs vs. cat castration; the procedure is anatomically different and dogs are typically larger, perhaps by an order of magnitude. In surgery, bigger is more likely to ooze, bleed, attract unwanted post-op attention from the patient. Dog vs. cat spay; similar surgeries, but cats are again very consistent in their proportions whereas dogs can vary tremendously from relatively easy to very difficult mobilization of the tract. Also, dogs put fat into their mesovarium and broad ligaments, which makes the isolation, handling, and ligation of the structures more challenging (fat breaks down under finger pressure and tension, makes your gloves fit badly, makes things a greasy, oozy mess). So dogs are more challenging surgically and it is not surprising that they have more peri- and post-operative complications.

  4. Maggie says:

    From a client perspective, this is anecdotal, but it’s based on years of experience running the vetting for a foster-based breed dog rescue, overseeing the successful speutering hundreds of large-breed dogs — including quite a few large-breed seniors that were 8+ — and working with a breed that is genetically prone to weird reactions to…life:

    We’ve never had a dog die from a speuter. NEVER. We have lost far too many to fatal diseases that earlier speutering would have prevented though (esp. mammary cancer in older females). Our population is the most vulnerable to complications too: many with heartworm disease, frequently underweight and stressed from shelter life, with run-down immune systems, at all ages (pediatric to geriatic) — and yet not one speuter death! However, we’ve had LOTS of complications over the years (from allergic reactions to sutures to pulling out sutures to infections), and I think our “not one death” result is a credit to a very good vet who handles post-op complications, when they happen.

    1. The worst complications have come from vet students. That makes some sense, but it’s worth putting out there for people thinking about low-cost “spay day” events at their local vet school. I know everyone needs to learn, but…if there’s going to be a catastrophic error, here’s where it’s most likely to occur. In one case, a vet student on rotation at a shelter nearly killed an older female dog that had full blown pyometra because the student simply didn’t recognize it AND left part of the uterus in by mistake — it was a bungled spay from start to finish (not recognizing the infection, screwing up the surgery itself, and then not putting it on post-surgery abx because she didn’t know there was pyo). The dog ended up with a massive abdominal infection, with organ adhesion, and nearly died. It was a big, expensive ordeal to save its life from student inexperience, and negligent supervision. Saving the dog not only required another (much more complicated) surgery by a highly skilled vet, but also a week-long clinic stay — very expensive. But the dog lived.

    2. My complication rates are also higher when speutering is done at SOME shelters — I’m in the Deep South where our shelters are mostly in abysmal shape with poorly paid vets on staff who work under terrible conditions without all the equipment and meds they wish they had (typically, they are also recent graduates who only stay until they find better-paying positions). There are a few shelters that send me A LOT of surgical infections when we pull their dogs into rescue. I think it’s a combination of poor clinic sanitation, lack of experience, and operating on filthy dogs without pausing to bathe them first (dogs literally covered in feces…and sometimes with full-blown staph infections on their skin…that went right into surgery and then straight back into a dirty kennel post-surgery). When more infections come out of those conditions, it’s one of those “no duh” kind of results, but…it’s treatable.

    3. My infection rates have seemed higher with neuters when they use the technique where they do a small incision at the base of the scrotum and pull out the testicles, leaving the empty scrotal sack there to flap around vs. with the other more common technique. Some shelters tend to use that “empty sack” technique supposedly because it’s faster. Most adopters hate it though because it’s unsightly, especially on older dogs that were “low hanging” …the sack will shrink, but it takes a long time.

    4. In-heat spays seem to have a significantly higher complication rate — and that is logical. Many vets who practice conservatively prefer to wait til the dog is out of heat. Shelters and high-volume speuter clinics do them without hesitation though…often without much thought about complications.

    5. The low-cost speuter-only clinics doing $95 spays move dogs in and out of surgery quickly, without pre-op bloodwork, and without IV catheter (or fluids). I honestly don’t worry about high-volume procedures in most young, healthy dogs, but I’d prefer not to have senior dogs (or dogs with underlying chronic conditions) operated on under those conditions. Sometimes its worth paying more to minimize risk.

    6. We get better recoveries when dogs are recovered in foster homes that are compliant with post-care instructions: making the dog wear the hated “cone of shame,” restricting activity for 7-10 days, etc. Some of the most common complications are due to people letting the dogs lick the surgery site!!!

  5. L says:

    @ Maggie
    Thanks for your post. I have noticed the same thing. Some specialists allow vet techs and interns/students to perform delicate procedures under the supervision of the specialist. Some are worse than others.
    My dog’s dermatologist does not do this.
    I am sick of it. Paying $$$ for someone to learn on my dog? Not cool. No explanation of the findings but yet they have the time to explain them to their student in detail.

  6. L says:

    PS: Angell in Boston is excellent. Very professional.

  7. skeptvet says:

    “We’ve never had a dog die from a speuter. NEVER”
    That’s great. If the complication rates in the RCVS Knowledge survey are used, (0.1-0.2%), you would expect to see only 1-2 deaths per 1,000 surgeries, so these are pretty low rates. However, we can’t make any direct comparison between different facilities, especially based on anecdotal evidence, because there are all sorts of variables. The RCVS Knowledge data, for example, included elderly animals, females with pyometra, and other cases which are likely to have a higher mortality rate than young shelter populations. Overall, we can all agree that the mortality rate is extremely low, so it problem shouldn’t be a reason to avoid the procedure.

    “The worst complications have come from vet students.”
    Again, that may be your personal experience, but it doesn’t necessarily generalize. There is, in fact, some research looking at complications rates at shelters that found no difference between experienced vets and supervised students.

    Outcomes of elective gonadectomy procedures performed on dogs and cats by veterinary students and shelter veterinarians in a shelter environment
    Rachael E. Kreisler VMD, MSCE; Stephanie L. Shaver DVM; John H. Holmes PhD
    OBJECTIVE To determine complication rates for elective gonadectomy procedures performed by veterinary students on dogs and cats in an animal shelter, characterize these complications, and compare rates with those for shelter-employed veterinarians (SEVs).

    DESIGN Retrospective cohort study.

    ANIMALS 10,073 dogs and cats for which gonadectomy was performed by a veterinary student (n = 3,048 surgeries) or SEV (7,025 surgeries) at an urban animal shelter over a 16-month period.

    PROCEDURES Electronic medical records for included dogs and cats were reviewed and data collected regarding patient signalment, duration of gonadectomy, surgeon type (student or SEV), and types of surgical complications recorded (including death or euthanasia) during the period from anesthetic induction to 72 hours after surgery. Complication and mortality rates were compared between veterinary students and SEVs.

    RESULTS No significant differences were identified between students and SEVs regarding rates of overall complications for both species, minor complications for both species, major complications for both species, and overall complications for dogs or cats specifically. The most common complications were self-limiting, with no long-term consequences, for both students and SEVs. Differences in mortality rates between students and SEVs could not be definitively determined owing to low numbers of nonsurviving patients.

    CONCLUSIONS AND CLINICAL RELEVANCE With judicious case selection and as a part of a surgical training program, complication rates for veterinary student–performed gonadectomy procedures for dogs and cats were no different from those for SEV-performed gonadectomy procedures. We believe such information regarding patient outcomes will allow shelter staff to make informed decisions and help them in discussions with stakeholders who may have concerns about student participation.

    As the veterinary profession and veterinary teaching institutions become increasingly specialized and the nature of evaluated patients becomes more complex, opportunities for practical clinical education of veterinary students have decreased. The use of purpose-bred animals for student surgical laboratories has become less acceptable to educators owing to controversy regarding terminal surgeries.1,2 Student surgical laboratories are also expensive to run, representing a considerable drawback for already financially strained veterinary colleges. In light of these pressures, veterinary educators have increasingly turned to animal shelters and service learning, which combines learning objectives with community service, to provide the caseload for student surgical experience.3–6

    The rates and types of surgical complications associated with procedures performed by veterinary students in shelter environments are important to determine so that specific concerns associated with such training can be identified and addressed. In a study7 of fully trained veterinarians performing various elective surgeries in private small animal practice, postoperative complication rates ranged from 1% to 24%, with major complication rates ranging from 1% to 4%.7 A similar major complication rate (3.3%) was identified in a study8 of third-year veterinary students performing ovariohysterectomy. However, to the authors’ knowledge, no studies have been reported regarding surgical complication rates for veterinary students in a shelter environment, nor have comparisons between students and fully trained veterinarians been reported. The purpose of the study reported here was to characterize and compare complication rates (including mortality rates) associated with gonadectomy procedures between veterinary student and SEV surgeons in an animal shelter environment.

    “My infection rates have seemed higher with neuters when they use the technique where they do a small incision at the base of the scrotum and pull out the testicles, leaving the empty scrotal sack there to flap around vs. with the other more common technique.”
    There is not much research comparing scrotal and prescrotal neuters, and what there is doesn’t show any difference in complication rates:
    Woodruff K. Rigdon-Brestle K. Bushby, PA. et al. Scrotal castration versus prescrotal castration in dogs. Vet Med. 2015;110(5):131-135.
    If you are talking about a scrotal ablation, where they remove the entire scrotum, that isn’t routinely done for neuters, even in old dogs, because it is a lot bloodier and creates a much larger and harder to close wound. No direct comparison of complication rates, but it’s hard to imagine the more aggressive procedure wouldn’t have more complications.

    My own experience tends to agree with the other points you make. I work at an expensive private hospital, so we don’t do all that many neuters since we are far more costly than the local humane society. I certainly see more complications in patients neutered at the shelter than at our practice, but then they do A LOT more neuters, so I wouldn’t hazard a guess as to the statistical difference, if any, in complication rates. Lots of variables involved, so a subject without many simple, universal answers.

  8. Diane M says:

    Hi Skeptvet, have you seen any studies on complication rates for sterilization via “Zeuterin” injection? It seems like it would be safer than surgery and a good way to preserve the health benefits of leaving male dogs intact without risk of reproduction. Just wondering what you think about it.

  9. skeptvet says:

    There are a number of research studies of chemical sterilization using zinc gluconate (which is currently available as Zeuterin but has been on and off the market under various names over the years). Complication rates are about the same or sometimes lower than for surgical castration, so not a dramatic difference. Most studies show the technique is effective at preventing breeding, though some dogs may still have some ability to produce sperm, so it may not be perfectly effective in all dogs. Testosterone. levels are typically r educed by about 50%, so dogs sterilized with Zeuterin may experience the same benefits and the same risks as dogs not neutered at all.

  10. Diane M says:

    Interesting–thank you!

  11. MeggieMoo says:

    I’d dearly love some further analysis by breed.
    The largest group of complications we have encountered has been delayed postoperative bleeding in greyhounds, and to some extent, lurchers and deerhounds. In the UK a large group of vets in general practice seem unaware of, or reluctant to use, tranexamic acid. Within our rescue group we saw complications at around 30%. This has now fallen to under 10% with the use of the drugs. All very interesting stuff!

    Epsilon aminocaproic acid for the prevention of delayed postoperative bleeding in retired racing greyhounds undergoing gonadectomy.
    Marín LM1, Iazbik MC, Zaldivar-Lopez S, Guillaumin J, McLoughlin MA, Couto CG.
    Author information
    Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA.

  12. skeptvet says:

    Yes, there are breed-specific issues. which aren’t addressed in this study. Breeds with a predisposition to von. Willibrand’s disease, for example, as well as the concern you raise about Greyhounds. More data is always desirable!

  13. Kerri Charles says:

    I have often wondered why a hysterectomy but leaving ovaries intact or vasectomy is not done? It seems there is talk about removing risk of malignancy in these organs but many dogs seem to have issues metabolically and preserving anabolic hormones like testosterone would help improve lean muscle mass development. I’m a human physician and posed this question to my vet when my dog was getting neutered and my reply was simply that it isn’t done and no one does that. It seems simple to investigate amd compare long term outcomes of obesity versus malignancy rates in these organs in both types of procedures. If we removed the gonads in a young human they would have decreased muscle, bone density, increased fat and lipids and sugars, and effects on mood and cognition. Obviously humans and animals are different but I have a friend who has two dogs same breeder and they were robust and enthusiastic bird dogs, one got neutered because of growth on tail so they decided not to breed. In six months the difference in the two dogs is shocking. The neutered one has become much more sedate almost lazy at times and he has lost a lot of muscle to the point people kept asking if he was sick. Has this been studied? Just curious if “partial hysterectomy” and vasectomy is ever done?

  14. skeptvet says:

    The short answer is that so-called “ovary-sparing spay” (which is just a hysterectomy) and vasectomy are sometimes performed in dogs and cats. They are essentially procedures that prevent reproduction without any of the health effects, positive or negative, or gonadectomy. They are essentially equivalent to not neutering at all in terms of health.

    The question that then arises is are the health effects of neutering net positive or negative, and there is no simple answer to that. The risk of some adverse health outcomes increase with neutering while the risks of others decrease, and the effects vary with sex, breed, age at neutering, and many other variables we don’t fully understand. It is generally believed that the net effects on males are pretty closely balanced, with neutered and intact males being roughly equally health overall (though, again, breed is a major factor). If you perform a vasectomy instead of gonadectomy, you will still have any roaming, fighting, urine marking, and mating behaviors you would have with no surgery at all, so if managing these is your goal then the procedure will be ineffective. If the only goal is to prevent reproduction, and these other issues aren’t a concern, then it may be appropriate.

    With females, the health outcomes are pretty consistently worse in intact females, due primarily to mammary cancer and pyometra (uterine infections). Some conditions in some breeds may be less common if females are left intact, but the idea that females are overall healthier if not neutered is not nearly as clear or supported by research evidence as opponents of neutering often claim. A hysterectomy serves only to prevent reproduction and pyometra, ut the risk of mammary cancer will still be much higher than in neutered females.

    Here are some more detailed articles that might interest you:

    Pros, cons of surgical sterilization, neutering options for females

    Surgical sterilization, neutering options for male cats, dogs

    Benefits and Risks of Neutering–An Evidence-Based Approach

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  16. Rain Havok says:

    Hi. I just wanted to let you all know that I took my 1 year old female cat Nova in to get spayed g they killed her. She was perfectly healthy as the autopsy proves…idk what to do,idk how to go about getting answers. The vets won’t tell me shit. They won’t even tell me why she died. They called me g said come get her she’s fine then 3 minutes later called me back & said she died…These percentages don’t give me any answers. I want to know WHY THEY DIE…..please help if you can. I miss her so much. She passed on the 1st this month
    ..she was my emotional supportive animal…now I’m alone again. I swear I can’t trust anybody.

  17. skeptvet says:

    I’m so sorry this happened. I also understand the need for some concrete answer to explain such a loss. But ass a scientist and a clinician for twenty years, I can tell you that medicine is full of uncertainty and the unexpected, and the specific reason (or more commonly combination of reasons) for a particular adverse even often just isn’t knowable. The universe is complex and never completely predictable, which is scary and frustrating. I hope you find some answer that helps, or some comfort.

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