What’s the Best Age to Neuter a Dog?

Does the surgery at 6 months limit the growth of large breeds?


[From Tufts March 2010 Issue]

Q: What is the medically recommended time to neuter a large breed?

We have had Great Danes for several years. Most have been males neutered at about 6 months. Recently, we have heard breeders and others say this age is too young for large-breed dogs. They say neutering them this early causes them to grow taller and not fill out. Our male is 18 months old and was neutered at 6 months. He now is 36 inches tall at the shoulders and barely tips the scale at 140 pounds. [The Great Dane Club of America includes no weight requirements in its standard, but other sources list weight for males at 135 to 170 pounds and height of 33 to 36 inches.]

Charlie Cadman
Enfield, Connecticut

A: Several studies have looked at the effects of neutering at 8 to16 weeks versus 6 months. They indicate early neutering is not associated with increased mortality, or serious health or behavioral problems when compared to neutering at the conventional age of 6 months.

But the studies do not answer your questions: What is the effect of neutering at 18 versus 6 months of age, and what is the difference in conformation – the look of the dog – when neutered at different ages?

Unfortunately, no studies answer these questions, and my recommendations are subjective and unconfirmed. It is true intact male dogs look different than neutered males. The effects of testosterone on increased muscling – and behavior – are usually obvious. However, testosterone levels drop after neutering and the muscling effects disappear.

From a health standpoint, I cannot make a strong recommendation whether neutering at 6 or 18 months is superior. Dogs of both ages should be able to safely undergo anesthesia, and the long-term effects of being exposed to testosterone for only one year are likely minimal. The effects of castration on cancer are controversial. Two studies so far have shown an increased risk of prostatic cancer when dogs are neutered at a young age. This is contrary to what is commonly believed.

If a dog develops aggression and/or territorial defensiveness, will these disappear after neutering? In many cases they are improved after castration, but I wonder if early neuter may prevent their development in the first place.

So my opinion is that you may neuter at any age when your dog can be safely anesthetized. Until newer information becomes available, my standard recommendation for owners of both small and large-breed dogs is the same: Neuter at 6 months.

Michael Stone, DVM,
ACVIM(Small animal internal medicine)
Cummings School


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