It was just last month that I wrote a blog here about the pros and cons of the decision on whether or not to spay/castrate your dog. This seems to be an area which is coming under increasing scrutiny by researchers, perhaps because it is relatively easy to analyse stored data to discover differences between spayed/neutered and entire populations. After all, the contrast between two study groups doesn’t get much more black and white than that: spayed/neutered or entire.

In one of the most recent studies (published online in April 2013), the historical records of over 80,000 sterilized and reproductively intact dogs were examined from a database of dogs presented to North American veterinary teaching hospitals over a period between 1984 and 2004. The cause of death and the lifespan of each animal was noted. To make the data as “clean” and unbiased as possible, the researchers removed around half of the records. First, they took out all young dogs, and all those where the spay/neuter status had not been recorded. Then they took out all those dogs that had died from congenital disease (i.e. disease which the animal had been born with, which obviously could not be influenced by neutering). Finally, they removed all of those dogs where no specific cause of death could be categorised. This left them with 40,139 dogs for analysis of the relationship between the effect of spay/neuter on age and cause of death.

The findings of the study are fascinating, and if you have an interest in reading scientific papers, you should read the report in full yourself. For those who don’t wish to, there were two main findings.

First, spaying/neutering caused dogs to live significantly longer lives. Females lived for 26.3% longer if they were spayed, and the life expectancy of males was increased by 13.8% after castration.

Second, there was a striking effect of spaying/neutering on the cause of death. Spayed/neutered dogs were dramatically less likely to die of infectious disease, trauma, vascular disease and degenerative disease. In contrast, sterilized dogs died more commonly from neoplasia and immune-mediated disease. This difference was similar for both males and females.

So what does this mean for pet owners? The study results could be taken to be broadly supportive of spaying and neutering both males and females, if length of life is taken as the most important outcome. It also suggests that owners of spayed/neutered dogs should be aware of the fact that their pets will be more likely to suffer from neoplasia or immune-mediated disease, and it would make sense to discuss with their vet what sort of signs they should look out for, so that if these diseases do develop, they will be well briefed in advance.


I still stand by my recommendations in the previous blog: all pet owners should discuss spaying and neutering with their vet. It may not be the right decision for every pet, but on average, this study demonstrates that it’s the most likely choice to lead to a longer life for your much loved pet.