Dogs will be more affectionate—and they’ll live longer too. Cats won’t get cancer. Rabbits won’t get infections.

These are some of the things pet owners often hear prior to getting their companions spayed or neutered, and it’s true, most pets will go on to live a long, healthy life post the operation, including a lower risk of cancer and infection.

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However, there are still some risks to “fixing” some animals too early on as well as long term affects. One thing that concerns pet owners most is obesity in their pet following spay or neutering, which can lead to heart and other problems if weight is not maintained.

Spay and neutering does lower an animal’s metabolism, according to Dr. Roger Mahr, a veterinarian and former president of the American Veterinary Medical Association, based in St. Charles, Ill., so over time, less food and more exercise may be necessary. “Animals are overeating, and there’s not enough exercise—it’s a problem we see with people,” said Mahr.

Another concern of pet owners is spaying and neutering an animal when they are too young, particularly smaller animals like rabbits and ferrets. The American Veterinary Medical Association (AVMA) recommends cats and dogs be spay and neutered as early as 8 to 16 weeks of age or as soon as they enter into their reproductive cycle.

For smaller animals, like rabbits and ferrets, who are “fixed” as young as 5 weeks old, which is often done to pet store animals, may lead to other problems later on in life if they cannot develop the proper hormones required for full maturity. It is recommended that most small animals should wait at least 4 months before undergoing this procedure. Also, these animals are internally more sensitive, particularly to anesthesia, if surgery is done too early.

Bigger pets like dogs can also have reactions to anesthesia used during surgery, so it’s important to have a complete check up with a vet before any procedure is done.

Cancer-free

Mahr adds that from a veterinary and medical perspective, there has been a proven increase in mammary and breast tumors in female dogs and cats that have not been spayed. It also eliminates infection of reproductive organs in both males and females, as well as reduced the risks of uterine, ovarian and prostate cancers. He added that the benefits of spay and neutering has the same effect on smaller animals like ferrets and rabbits.

Behaviorally, animals also change post getting “fixed.” For example, in males, there is less of an urge for territorial marking or roaming when they sense a female in heat. There’s also a lessening of aggressive behavior.

Dr. Mahr believes the benefits of spay and neutering pets far outweigh the potential side effects, one being the over population of animals in shelters.

“The first, obvious reason is the fact that there’s an overpopulation of dogs and cats,” said Mahr. “The first reason is to eliminate unwanted pregnancies and lessen the impact of an overpopulation of dogs and cats who need homes around the country.”

According to the Humane Society of America, there are approximately 6 to 8 millions dogs and cats in shelters each year and 3 to 4 million of them are euthanized.

“There really aren’t any down sides to it, but it does require a major surgical procedure, involving anesthetic and it must be done by veterinarian using specific surgical techniques, the proper use of anesthetics and pain managements,” said Mahr. “As long as the particular owner takes the animal in and has it evaluated by a veterinarian with a full physical exam, blood test, to make sure all the internal organs are functioning properly, including the heart and lungs, the function of the kidneys, liver and various internal organs, spay and neutering is safe.”