I've been discussing this lately in connection with my 6+ month-old mixed-breed dog. She's about 50 pounds, so a much bigger dog--and some say that matters, that it's more important to wait for older dogs. Also, Ella is female.
The following is from a veterinarian. He laid out the issues pretty clearly, based on his reading of available research.
This is a good question. Unfortunately, the research out there is not fool proof to say either way. The research shows that spaying and neutering in dogs does allow for longevity to increase by approximately 27%. This is based upon a retrospective study performed in 2015. The disease processes that were looked at are multi-factorial in nature. That means that spaying early alone is not the only cause and good genetics are of utmost importance. For example:
"A study of 1,500 Labrador retrievers identified no difference in the risk of hip dysplasia in males at any neuter period compared to intact dogs. In females, however, the risk of developing hip dysplasia was higher for those spayed at <6 months (5.4%), 6–11 months (5.1%), and 12–23 months (4.3%) compared to intact females (1.7%). The risk of hip dysplasia for those dogs spayed between 2 and 8 years was 0." This is directly from the article that is being referenced everywhere.
At the same time, the following is also referenced in the article regarding osteosarcoma in Rottweilers:
"No attempt was made to correlate increased body weight with neuter status (gonadectomized dogs tend to gain weight following gonadectomy).No attempt was made to correlate increased body weight with neuter status (gonadectomized dogs tend to gain weight following gonadectomy)."
In short, I have not personally read anything specifically linking the development of disease to these procedures other than a study that looks back at old veterinary records. The only thing that is well established is the risk of testicular cancer and pyometras in animals as they age. Keep in mind that you can choose to weight if you wish as well. ... However, if you choose to wait, the procedure does become a bit more difficult and you would have to monitor Ella during and after each heat cycle to make sure she does well.
