Why Do Dogs Gain Weight After Being Neutered?

Dogs gain weight after being neutered for the simple fact that the surgical procedure causes changes in the dog's body and his incentive to exercise. If you are noticing your dog pack up pounds after being neutered, you are likely not imagining things-statistics show that male dogs are three times more likely to be heavy or obese compared to intact, non-neutered dogs.

You might have heard about female dogs and cats gaining weight after being spayed, but did you know that male dogs can gain weight too after neutering? Knowledge is ultimately, power, if you are aware of the problem, you are at an advantage. Forewarned is forearmed, as the saying goes. 

*Please note: while the term neutering is often used to depict fixed dogs of any sex, in this article, the term neutering will be used to refer to male dogs who have undergone castration. 

An Insight into the Procedure 

Neutering in dogs, also known as castration, is a surgical procedure that involves the removal of the dog's testicles (orchiectomy) which is where sperm is produced.

The procedure is carried out mainly for the purpose of preventing the birth of unwanted litters, but sometimes it can also be suggested for behavior modification (although not proven to be effective other than for some hormone-related behaviors).

After being neutered, testosterone levels tend to gradually decline. In general, the "half life" of the hormone testosterone in dogs is approximately two weeks. This means that in two weeks testosterone hormone levels are expected to be 50 percent less than prior to castration. 

Afterwards, it's a downward spiral, with the levels gradually declining more and more until they reach the level of zero by the end of the two weeks (sometimes it may take longer). 

By this time, there should be a reduction in hormonally-driven behaviors such as roaming, mounting and urine marking. However, it's important to take into account the fact that behaviors have also a learning component, meaning that they can be habit-forming and sometimes may persist despite neutering. 

"The study shows that castrated male dogs have three times as high a risk of being heavy or obese compared to intact dogs."~University of Copenhagen

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You are not imagining things if your neutered dogs seems to be plumper

Lower Energy Requirements

While the study above provides data proving a strong correlation between neutering and weight gain, it fails to provide details as to the exact dynamics known for causing such weight gain in the first place. 

The study though mentions a possible correlation between decreased levels of circulating testosterone and an increased body condition scoring. This theory is based on a study (Mauras et al.) conducted in humans in 1998. 

 In the study, testosterone deficiency in young men was associated with increased weight gain. This lack of testosterone apparently triggered a lower metabolic rate and protein metabolism, resulting in a lower energy requirement.

Something similar is likely happening in neutered dogs, so much so, that it might be worthy of considering making slight changes to the diet so that neutered dogs don't consume as many calories as intact dogs. 

For example, the daily calorie requirement for a 20 kg border collie declines from 175kcal/kg to 97kcal/kg after spaying/neutering, explains veterinarian Dr. Ivana Crnec. Consult with your vet for specific dietary instructions, custom-tailored for your dog. 

Changes in Activity 

As mentioned, neutering often leads to substantial changes in a dog's propensity to roam, urine mark and mount. When these hormonally-induced behaviors reduce, up to the point of sometimes disappearing from the dog's behavioral repertoire, it can lead to increase weight.

With reduced hormonal drives, the drive to roam in search of mating partners decreases drastically, and with less activity along with lower energy requirements, you therefore have the perfect recipe for a rounded pup.

Did you know? The prevalence of obese dogs is more than twice as large among overweight/obese dog owners than owners who are slim or of a normal weight.

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Golden retrievers that are neutered are 50 to 100 percent more likely to become overweight or obese

Age is Not a Factor

Data gathered from the Morris Animal Foundation Golden Retriever Lifetime Study (GRLS) found that spayed or neutered golden retriever dogs were 50 to 100 percent more likely to become overweight or obese. This initial data also found that these risks were relatively constant, regardless of age at the time of spaying or neutering. 

In other words, data showed that whether the dog was neutered at 6 months or 6 years didn't matter-the risk of weight gain remained relatively constant regardless. Things though were radically different when it came to the development of orthopedic problems though, in which case, age surely mattered. 

While this study was conducted on golden retrievers, the yielded data and results can likely be virtually applied to any large- and giant-breed dogs, claims Melissa Simpson, the lead author of the study.

Now That You Know...

As seen, reduced activity and lower energy requirements can sure pack a punch when it comes to a dog's weight. Indeed, it is safe to say that obesity results from an imbalance between a dog's energy intake and energy expenditure. Fortunately, there are several things dog owners can do to prevent their neutered dogs from plumping up.

  • If you are debating on whether to neuter your dog or not, look carefully at data and consider individual factors (e.g sight hounds aren't very prone to obesity compared to the average beagle or Labrador retriever). There are lots of pros and cons of neutering dogs. And age does matter when it comes to the development of orthopedic problems. For instance, according to research, males neutered before 1 year of age were found to have a higher risk (10.2 percent) of developing hip dysplasia compared to intact dogs (5.1 percent) or those neutered after 1 year of age (3.1 percent).
  • Consider that, according to research, dogs were mostly found to be at risk for gaining weight during the first two years after the spaying/neutering procedure. However, this doesn't mean you should keep your guard down past the first two years. As animals age, they become more prone to getting lazy and overweight. 
  • Since spaying/neutering reduces a dog's metabolic rate, consider a proper feeding regimen. Ask your vet for specific recommendations. Your vet may also suggest particular weight-loss diets.
  • As well, make sure you keep your neutered dog on a good exercise program.
  • When training, consider using a portion of your dog's daily ration of food.
  • Keep in mind that overweight dogs are more prone to health problems such as orthopedic problems, heart disease and cancer. Also, consider that previous studies have shown, that generally, heavy dogs tend to live 1.3 years less than dogs who are placed on restrictive diets, so weight really matters!
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Adrienne F.
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Dr. Ivana Crnec
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