Stephen J. Birchard DVM, MS, Diplomate ACVS

Friday, July 17, 2015

Does Spay or Neuter Make Dogs Overweight?

Effect of age at gonadectomy on the probability of dogs becoming overweight.

J Am Vet Med Assoc. 2013 Jul 15;243(2):236-43.


The authors of the above study compared 1,930 dogs that were spayed or neutered (gonadectomy) to 1,669 sexually in tact dogs to evaluate the tendency of the spayed or neutered dogs to become overweight.  They also looked at the effect of age at the time of gonadectomy to see if that had an effect on becoming overweight. All dogs were patients at Banfield Pet Hospitals, giving the authors a consistent data retrieval system. Follow-up on all animals was for a period of greater than or equal to 10 years.

The authors found that spayed or neutered dogs were statistically more likely to become overweight compared to sexually in tact dogs.  However, this was found only for the first 2 years after the spay or neuter. Age at gonadectomy and sex of the dog did not affect the tendency to become overweight.

An additional interesting finding in the study was that both groups of dogs (gonadectomy vs. sexually in tact) had a surprisingly high percentage of overweight individuals. In the sexually in tact dogs, 37% became overweight over time, and in the gonadectomized dogs, 66% became overweight. Also, large breed dogs were more likely to become overweight in this study.


This was a well-designed and executed study of a large population of dogs. The diagnosis of being overweight seemed arbitrary since no objective criteria were used other than body condition scores, but veterinarians performing routine examinations of the dogs were the ones making the overweight diagnosis.

Looking at the entire group of dogs (3,599), over half of them were diagnosed as being overweight. Beyond the effect of gonadectomy, this study illustrates the larger problem of obesity in pets. Whether being fed too much, or exercising too little, a high proportion of pets in the US are at an unhealthy weight which is likely affecting their quality of life and resulting in secondary health problems. More research is needed to investigate the causes of obesity in pets and how it can be effectively managed.

What are your thoughts about this study and about the more global problem of pet obesity? Post comments either here or on facebook (Dr. Stephen Birchard, Veterinary Continuing Education).

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