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When to Spay & Neuter - Based on Research!

26 Mar 2022

Review compiled by Laurie Edge-Hughes, BScPT, MAnimSt (Animal Physio.), CAFCI, CCRT

I have posted this article elsewhere on Facebook, but wanted to dive into this paper here as well.  Here goes!

https://doi.org/10.3389/fvets.2020.00388 

Hart BL, Hart LA, Thigpen AP, Willits NH.  Assisting decision-making on age of neutering for 35 breeds of dogs: Associated joint disorders, cancers, and urinary incontinence.  Front. Vet. Sci., 07 July 2020.

The introduction discusses what is currently in the literature.

• In studies that did not focus on specific breeds or ages of neutering, one found that hip dysplasia and cranial cruciate ligament tears or ruptures were significantly more likely in neutered than intact males and females.
• Another study found that neutering was associated with a 3-fold increase in excessive tibial plateau angle, which is a risk factor for development of cranial cruciate ligament tears or rupture. 
• Neutering is reported to be a risk factor for canine intervertebral disc herniation in Dachshunds.
• The occurrence of lymphoma was found to be higher in spayed than intact females, as was the occurrence of mast cell tumors and hemangiosarcoma. 
• A study of over 40,000 dogs utilizing the Veterinary Medical Database found that neutered males and females were more likely to die of cancer than intact dogs. 
• A recent finding was that the absence of estrogen from spaying females was associated with accelerated brain aging. 
• Another recent report from the Golden Retriever Lifetime Project is that neutering at
• In the Labrador Retrievers, Golden Retrievers, and German Shepherd Dogs, there was an increase in the incidence of one or more of the joint disorders with neutering in the first year in males and females to 2–4 times >3–5% incidence in intact dogs. 
• In female Golden Retrievers, neutering at any age was associated with an occurrence of one or more of the cancers followed to 2–4 times higher than the 5 percent incidence in intact females. But in male Golden Retrievers, and in male and female Labrador Retrievers and German Shepherd Dogs, there was no evident increase in cancers above that of the dogs left intact. 
• Preliminary analyses from some small-dog breeds revealed no apparent increased risks of joint disorders with neutering.

What was done in this study?

In an attempt to address the absence of breed-specific information on joint disorders and cancers associated with neutering, the authors undertook a project focusing on various specific breeds using data collection and analyses with their extensive veterinary hospital database where the same diagnostic criteria could be applied to all breeds.

The joint disorders examined included cranial cruciate ligament tears or rupture (CCL), hip dysplasia (HD) and elbow dysplasia (ED). The cancers examined, which previous studies found could be affected by neutering, were lymphoma/lymphosarcoma (LSA), hemangiosarcoma (HSA), mast cell tumors (MCT), and osteosarcoma (OSA).

The final list of 35 (including three varieties of Poodle) represented in the present study are, alphabetically, the: Australian Cattle Dog, Australian Shepherd, Beagle, Bernese Mountain Dog, Border Collie, Boston Terrier, Boxer, Bulldog, Cavalier King Charles Spaniel, Chihuahua, Cocker Spaniel, Collie, Corgi (Pembroke and Cardigan combined), Dachshund, Doberman Pinscher, English Springer Spaniel, German Shepherd Dog, Golden Retriever, Great Dane, Irish Wolfhound, Jack Russell Terrier, Labrador Retriever, Maltese, Miniature Schnauzer, Pomeranian, Poodle-Miniature, Poodle-Standard, Poodle-Toy, Pug, Rottweiler, Saint Bernard, Shetland Sheepdog, Shih Tzu, West Highland White Terrier, and Yorkshire Terrier.

The original paper (click on the link, it’s free access) lists everything found for each breed.  Here’s a sample.

Shetland Sheepdog

“The study population was 31 intact males, 30 neutered males, 20 intact females, and 52 spayed females for a total sample of 133 cases. There were no joint disorders in intact males and just one in the intact females. In neutered males, the only joint disorder was in one of the males neutered at <6 mo. and in females there was no joint disorder associated with spaying. The occurrence of cancers in intact males was 6 percent and in intact females, zero. There were no evident increases in cancers in neutered males or females. There was no occurrence of MC (mammary cancer) in intact or spayed females and a 14 percent occurrence of PYO (pyometra) in intact females. Spaying at 6-11 mo. resulted in a 6 percent occurrence of UI (urinary incontinence), but at 1 year a 33 percent occurrence. Lacking a noticeable occurrence of increased joint disorders or cancers in neutered males, those wishing to neuter should decide on the appropriate age. However, to avoid the high level of UI occurrence in females, one could consider spaying females at, or beyond, 2 years.”

This table is a summary of recommendations for each breed in regards to spay / neuter.

As a conclusion, the author stated the following, “In conclusion, the data presented should provide to veterinarians and interested puppy caregivers data-based information for the best age for neutering to avoid increasing the risk of joint disorders and some cancers beyond that of leaving the dog intact. Readers can note that an elevated risk for a joint disorder or cancer occurs in relatively few of these breeds. In other words, with most breeds or sexes, neutering can apparently be done without referral to a particular age, at least with regard to the joint disorders or cancers covered in this study.”

Further research / data compilation is being conducted by the same researchers to look at mixed breed dogs as well.

So, there you go!  Some great guidelines in regards to advising or discussing spay and neutering with your puppy owners! 

Food for thought!