Strong support exists for the view that gonadectomy has a net health benefit
for female dogs and cats, but it is less clear that neutering benefits individual males. The risks of some diseases occurring are reduced or eliminated by neutering (for example, testicular neoplasia, benign prostatic hypertrophy), but other disease appear to be more common in neutered males, though risk varies by breed and age at neutering (e.g., cranial cruciate ligament disease, feline interstitial cystitis).1
The evidence is complex and often inconclusive, and there are no simple or one-size-fits-all answers to client questions about if and when to neuter their male dogs.2 There also are justifications for neutering males other than direct individual health benefits, such as population control and managing undesirable behaviors. However, given the uncertainties around the health effects of neutering on individuals, methods of sterilization that do not remove the gonads may be appropriate for some individuals.
Despite the uncertainties, surgical neutering is the most common approach to sterilizing male cats and dogs. For dogs, frequently used techniques include closed castration (removal of the testes without opening the vaginal tunic) and open castration (which involves opening the vaginal tunic prior to ligating the vessels and ductus deferens). Both procedures can be performed through a scrotal or prescrotal incision, and there are a number of variations of each.
There is much debate about the relative merits of open and closed castration in dogs, but it is based mostly on theoretical reasoning and anecdotal evidence. Some argue that closed castrations are safer because there is no direct communication with the abdomen, reducing the risk of ascending infections or herniation of abdominal contents. Others claim that open castrations are less likely to lead to hemorrhage or scrotal hematomas. Typically, closed castration is recommended for small dogs and cats, and open castration is recommended for larger dogs.
There is little research evidence to inform these debates. One prospective randomized trial did find more overall complications in dogs undergoing open castration.3 However, problems with recruitment of subjects for this study significantly limit the strength of this evidence. Overall, serious complications are few in dogs undergoing castration, and it is unclear if there is a consistent advantage to either technique.
The research evidence comparing scrotal and prescrotal approaches in dogs is also quite sparse. A randomized, prospective study comparing the two approaches found similar complication rates.4 The scrotal approach had the advantage of inducing less self-trauma and of being about 30 percent quicker to perform (though the absolute difference, from about 5 minutes to 3 minutes, is of doubtful clinical significance). Once again, both techniques are effective, and it is not clear that one is superior to the other.
Several techniques have been described for neutering male cats,5 but there is virtually no formal research comparing complication rates. A scrotal approach appears to be the most common, and methods for securing the ductus and vessels include suture ligation and various methods of tying the tissues on themselves. One comparative study of these ligation methods found no significant complications and no difference between methods.6
An uncommon surgical technique used for male dogs in some resource-poor countries is pinhole castration. The spermatic cord is ligated with suture percutaneously to induce necrosis of the testes.7 While this technique is less expensive than standard surgical castration and it does reduce functional testicular tissue volume, it is unclear how effective it is as a means of sterilization, and some reports suggest a higher rate of infection, pain, and other complications compared with standard techniques.8-9
Finally, surgical or laparoscopic vasectomy is sometimes recommended as a means of sterilizing male dogs and cats without neutering.5 Both approaches are effective at achieving this outcome. There have been no direct published comparisons between surgical and laparoscopic vasectomy. One small study comparing laparoscopic vasectomy with surgical castration in dogs found few differences except for a subjectively greater level of postoperative discomfort in the surgical patients.10
Making the case for surgical neutering
Traditionally, veterinarians in the U.S. have strongly advocated for surgical neutering of male dogs, and most dog owners follow this recommendation. The impetus for this primarily has been population control and a desire to reduce rates of euthanasia for unwanted dogs and cats resulting from unintended breeding. Many veterinarians also believe that neutering necessarily improves the health of individual dogs and cats, but the evidence is far less supportive of that, especially for males. There appears to be growing awareness and concern among pet owners about potential negative effects of neutering. Not all such concerns are justified by scientific evidence, but there are certainly some negative health effects are clearly associated with neutering.
It is critical for veterinarians to be able to respond to owner concerns with an informed understanding of the issues and the current best evidence. We are more likely to be successful in educating our clients and supporting good healthcare choices if we are knowledgeable about their concerns, the relevant evidence supporting or challenging them, and the options available.
My own views have evolved in the years I have been in practice. I now routinely discuss the risks and benefits or neutering, and the significant uncertainty about these, with my clients, rather than simply making a standard, one-size-fits-all recommendation to neuter everybody at 6 months of age. I generally recommend neutering all female dogs, because I believe the best evidence supports this is better for the individual health of the dogs as well as in terms of population control. I am not as conclusive in my recommendations for male dogs, but I emphasize that if an owner wishes to keep their male dog intact, they are taking on the added responsibility of preventing unintended reproduction and dealing with any associated behavioral problems. For some of these owners, sterilization procedures that do not involve neutering, such as vasectomy, may be worthwhile.
I also recommend routine neutering for both male and female cats, though I admit to clients that there is a dearth of strong scientific evidence elucidating the relative risks and benefits of neutering and the advantages and disadvantages of specific techniques in this species.
These are simply my current views based on extensive consideration of a complex body of literature rife with gaps and inconsistencies. I do not intend to present these conclusions as imperative guidelines for others, and the same research evidence can reasonably support different views. However, I do encourage all of my colleagues to be familiar with the literature and with the most common questions and concerns arising from it so that we can make informed choices and recommendations and so we can avoid inappropriately simplistic and rigid practices.
Dr. McKenzie discovered evidence-based veterinary medicine after attending the University of Pennsylvania School of Veterinary Medicine and working as a small animal general practice veterinarian. He has served as president of the Evidence-Based Veterinary Medicine Association and reaches out to the public through his SkeptVet blog, the Science-Based Medicine blog, and more. He is certified in medical acupuncture for veterinarians.
- McKenzie B. “Evaluating the benefits and risks of neutering dogs and cats.” CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources. 2010; 5(45):1-18. Updated version available atgl/pWCKYl.
- Kustritz MV, Slater MR, Weedon GR, et al. “Determining optimal age for gonadectomy in the dog: a critical review of the literature to guide decision making.” Clin Therio. 2017; 9(2):167-211.
- Hamilton KH, Henderson ER, Toscano M, et al. “Comparison of postoperative complications in healthy dogs undergoing open and closed orchidectomy.” J Small Anim Pract. 2014; Oct; 55(10):521-6.
- Woodruff K, Rigdon-Brestle K, Bushby, PA, et al. “Scrotal castration versus prescrotal castration in dogs.” Vet Med. 2015; 110(5):131-135.
- Howe LM. “Surgical methods of contraception and sterilization.” Theriogenology. 2006 Aug; 66(3):500-9. Epub 2006 May 23.
- Karen Maciel de Oliveira, Leonardo Augusto Lopes Muzzi, Bruno Benetti Junta Torres, et al. “A comparative study among three open orchiectomy techniques in cats.” Acta Scientiae Veterinariae. 2010; 38(2):177-183.
- Okwee-Acai J, Omara R, Onyait JS, et al. “An evaluation of pinhole castration as an alternative technique for dog population control in resource-poor communities.” Bulletin of Animal Health and Production in Africa. 2013; 61(3):337-345.
- Baba MA, Fazili MR, Athar H, et al. “Pinhole castration technique: an alternative to orchiectomy in stray dogs.” Anim Reprod Sci. 2013; 137(1-2):113-8.
- Abd-el-Wahed RE, Korritum AS, Abu-Ahmed HM, et al. “Evaluation of pinhole castration technique compared with traditional method for castration in dogs.” Alexandria Journal of Veterinary Sciences. 2014; 42:90-98.
- Anburaja Mahalingam; Naveen Kumar; Maiti SK, et al. “Laparoscopic sterilization vs. open method sterilization in dogs: a comparison of two techniques.” Turkish Journal of Veterinary & Animal Sciences. 2009; 33(5):427-436.