Sterilization is the most common surgical procedure performed on pets in the United States. The main benefit of sterilization is population control and the reduction in euthanasia of unwanted dogs. The most common method of sterilizing female dogs is the traditional spay; however, there are other methods which may be more beneficial to your female dog. This blog outlines the four methods I recommend, along with a summary of the benefits and risks associated with each. The pros and cons of each method should be discussed with your veterinarian before proceeding with a sterilization.
- An Ovariohysterectomy, OVH, or “traditional spay” is the most common sterilization procedure in the US. In this procedure, the ovaries (gonads) and uterus are removed. In female dogs, OVH eliminates the risk of pyometra and pregnancy and heat cycles are eliminated. Removing the ovaries and uterus also eliminates the risk of a false pregnancy. False pregnancies mimic true pregnancies resulting in abnormal behaviors, as well as an increased risk of mastitis (mammary infection).
- The Ovariectomy, OVE, or “laparoscopic spay” procedure involves removal of the ovaries, but the uterus remains intact. This sterilization method eliminates the risk of pyometra and pregnancy. Behavioral changes associated with “heat” are avoided. The advantages of an OVE over an OVH are less postoperative pain, complications, and recovery time.
Removal of the ovaries may protect the female dog against mammary tumors, uterine infections and tumors (for OVH), mastitis (breast infection), transmissible venereal sarcoma, ovarian diseases (cancer, cysts, and infections), and chronic endometritis (inflammation of the uterine wall). However, a literature review on the connection between spaying and mammary tumors showed most studies had a high risk of bias. Of the four studies with only a moderate risk of bias, two found neutering to protect against mammary cancer and two found no association.
A Swedish study showed breed predisposition for mammary cancer and pyometra. Most dogs in Sweden are not spayed or neutered. Of 260,000 dogs, 20,423 were diagnosed with pyometra and 11,758 were diagnosed with mammary tumors. The top ten breeds diagnosed were the Leonberger, Irish Wolfhound, Bernese Mountain Dog, Great Dane, Staffordshire Bull Terrier, Rottweiler, Bullterrier, Doberman, Bouvier, and Airdale. Breed variations in incidence rate suggests genetic components in disease development.
A Norwegian study (where dogs are largely left intact) showed varying rates of mammary cancer development based on breed: 35.47 per 1,000 Boxer dogs, 3.87 per 1,000 in Bernese Mountain dogs, and 17.69 per 1,000 Bichon Frise` dogs. The mean age of mammary cancer development was 7 to 8 years.
Another Swedish study looked at the incidence of pyometra in five breeds with a high incidence of pyometra (Rottweiler, Collie, Golden Retriever, Labrador Retriever, and German Shepherd). In the Rottweiler, Collie, and Labrador Retriever, previous pregnancy showed protection against developing pyometra later in life. There was no protective effect found in Golden Retrievers and intermediate protection in the German Shepherd.
Any surgery that removes the gonads (ovaries in females) changes the animal in both positive and negative ways. There is mounting evidence supporting long-term health complications associated with surgical sterilization that includes gonad (ovaries) removal. Gonads are not just sex/reproductive organs; they are necessary endocrine glands for normal metabolic, behavioral, musculoskeletal, and anti-neoplastic (tumor/cancer) health.
The risks/disadvantages associated with OVH and OVE include:
- Higher risk of joint disorders – Female dogs that receive a traditional spay have a greater risk of joint disorders. For example, a study showed that spayed/neutered dogs had a 3.1 times higher incidence of patellar luxation. In females, neutering within the first year is also associated with a highly significant threefold risk of acquiring at least one joint disorder. – up to 17% compared with 5% in females left intact or neutered beyond one year.
- Higher risk of cancer – A study of Golden Retrievers found that neutering at any time through 8 years of age increased the risk of osteosarcoma, hemangiosarcoma, lymphoma and mast cell tumors by 3-4 times. A threefold increase in transitional cell carcinoma of the urinary bladder for both sexes when neutered has been reported. In another study, cardiac hemangiosarcoma in spayed females was reported to be 4 times greater than that of intact dogs.
- Higher risk of developing autoimmune diseases – Studies suggest that ovary removal is associated with an increased risk for certain autoimmune disorders. The reproductive system and the immune system are highly interdependent. Female dogs are particularly at risk for atopic dermatitis, irritable bowel disease (IBD), and canine immune-mediated thrombocytopenia (ITP). Sterilized female dogs have a significantly greater risk of lupus (LUP) than their intact counterparts.3
- Higher risk of urinary incontinence – Studies show that sterilized female dogs have a 5% to 20% higher risk of urinary incontinence.
- Changes in behavior – One of the most stated reasons to spay a dog is to reduce aggression. In practice, I have seen it go both ways. I have seen dogs "calm down" after spay; I have also seen dogs become more reactive and aggressive after being spayed. A survey conducted of over 13,000 dog parents (both neutered and intact) concluded that there was no association between neutering and aggression towards familiar people. The study also found there was a low but significant increase in the risk of aggression towards strangers for neutered dogs compared to intact dogs. This data was driven, though, by dogs neutered at 7-12 months of age. That age group showed they were 26% more likely to show aggression with strangers.
To reduce the risks associated with removing the ovaries, there are two recommended ovary-sparing sterilization procedures. As with any method, there are pros and cons.1. Ovary Sparing Spay (OSS), also referred to as hysterectomy, removes the uterus and cervix, leaving one or both ovaries intact. This procedure eliminates the risk of pyometra and pregnancy, and it protects against some of the more serious cancers and immune-mediated diseases. This sterilization option is a wonderful option for those that want to eliminate the risk of pyometra, sterilize their pet, and keep hormones intact.
The risks/disadvantages associated with OSS include:
- “Heat” cycles continue – leaving the ovaries means the hormones are still intact so females will still be attractive to males. As such, she may show behavioral changes while in heat. However, removal of the entire uterus eliminates bleeding.
Higher incidence of mammary tumors and cancer – The degree of risk depends on the breed. For example, a higher incidence of mammary tumors has been reported in poodles, English cocker spaniels and dachshunds. However, many of the studies are biased, as published by the British Small Animal Veterinary Association:
"A commonly-stated advantage of neutering bitches is a significant reduction in the risk of mammary tumours, however the evidence for this has not previously been assessed by systematic review. The objectives of this study were to estimate the magnitude and strength of evidence for any effect of neutering, or age of neutering, on the risk of mammary tumours in bitches. A systematic review was conducted based on Cochrane guidelines. Peer-reviewed analytic journal articles in English were eligible and were assessed for risk of bias by two reviewers independently. Of 11,149 search results, 13 reports in English-language peer-reviewed journals addressed the association between neutering/age at neutering and mammary tumours. Nine were judged to have a high risk of bias. The remaining four were classified as having a moderate risk of bias. One study found an association between neutering and a reduced risk of mammary tumours. Two studies found no evidence of an association. One reported "some protective effect" of neutering on the risk of mammary tumours, but no numbers were presented. Due to the limited evidence available and the risk of bias in the published results, the evidence that neutering reduces the risk of mammary neoplasia, and the evidence that age at neutering has an effect, are judged to be weak and are not a sound basis for firm recommendations."
© 2012 British Small Animal Veterinary Association.
- Potential decrease in brain function - The uterus is thought to only be active during reproduction, but a fascinating rat model showed removing the uterus (hysterectomy) impacted brain functioning. The uterus is an organ that is part of the endocrine system. Removing it does not go without impact.
The risks/disadvantages associated with tubal ligation include:
- “Heat” cycles continue – As with OSS, leaving the ovaries means the potential for behavioral changes since the hormones are still intact. Regular heat cycles (including bleeding) will continue.
- Higher incidence of mammary tumors and cancer – The risks are the same for OSS, however there is controversy as to whether the incidence is higher for mammary cancer.
- Pyometra – Pyometra is a secondary infection that occurs because of hormonal changes in the female's reproductive tract. Pyometra can be fatal; the risk depends primarily on breed and age. However, the survivability of pyometra in a retrospective study was 97% in a non-specialized veterinary hospital setting.
Should I leave my female dog intact?
There is always the option to leave a pet intact. I respect that this decision is the best choice for some dogs. When it comes to spay and neuter, there is no one-size-fits-all solution. Pet owners need to look at the pet and their lifestyle when making the decision. The goal is always to eliminate the chance of unwanted pregnancy while mitigating the risks and disadvantages of a particular sterilization method. For example, if your female dog is a breed that is at higher risk for mammary cancer, removing the ovaries (OVE) may be the best choice. It is important for you and your veterinarian to discuss the risks and benefits for your dog, as well as proper management, to decide on the best plan for lifelong well-being.