UC Davis study shows negative effects of neutering

It comes as no surprise that the most common procedure done in veterinary medicine is sterilization in the form of castration. Animal science students are exposed to the procedure fairly early in their undergraduate career, and most likely will be performing the operation themselves after graduating from veterinary school.

It is also no surprise that many dogs escape their homes and breed without the owners’ knowledge. The American Society for the Prevention of Cruelty to Animals (ASPCA) is a huge proponent of neutering and spaying as a means of controlling the stray pet population, since some people will dump unwanted litters on the street or take them to a shelter where the animals have little chance of being adopted before they are euthanized.

While neutering and spaying are obviously beneficial for controlling stray pet populations, not much is known about how these operations affect the animals themselves. The UC Davis School of Veterinary Medicine did a recent study of the effects of neutering in an effort to get the full story.

“We started getting notices and emails from people wanting to know the adverse effects of neutering,” said lead investigator Benjamin Hart, a distinguished professor emeritus in the UC Davis School of Veterinary Medicine. Hart went on to describe the initiation of the study and the breed choice.

“We decided to narrow it down to golden retrievers…and divided [the subjects] into early and late neutering,” Hart said.

Golden retrievers were chosen as the first breed to examine for commonality, among other qualities.

“Golden retrievers were selected as the first breed in which to investigate this issue because they are one of the most popular breeds and therefore were numerous in the veterinary medical teaching hospital database,” said UC Davis researcher Gretel Torres de la Riva in an email interview. “Another reason for choosing this breed is that they are often service dogs for people with disabilities.”

The study used 759 records of golden retrievers, focusing on incidences of hip dysplasia and seven other diseases the breed is prone to develop later in life. They found that the incidence of hip dysplasia nearly doubled in the neutered and spayed groups as opposed to the intact groups.

“In young life … there is a growth plate,” Hart said. “When the time of puberty is reached and hormones start kicking in — testosterone in males [and] estrogen in females — you get a closure of these growth plates and effectively cause [them] to stop growing.”

If these hormones are absent due to the animal being spayed or neutered, the bones will not stop growing at the correct time and will become distorted. This distorted bone growth can lead to hip dysplasia and other ailments.

Another issue compounding improper joint development is weight gain. Neutered or spayed animals have a tendency to gain weight more easily as their metabolisms are impacted. With more weight, the joints experience increased pressure, which can exacerbate the animals’ condition. The discovery of the effects of neutering on hip dysplasia is not the worst news, however.

“With an early neuter, in males and females, you increase the chance of lymphoma by three to four times,” Hart said.

Lymphoma is a type of blood cancer often originating in the lymph nodes. Hart also discussed hemangiosarcoma (HSA) and mast cell tumors (MCT) in female retrievers, both cancers that can metastasize and become systemic. The mechanism behind the development of the cancers is not fully understood; however, there will be many more studies to come regarding this phenomena.

It would seem that pet owners are now up against a wall with such weighty pros and cons regarding neutering, but there are other options for companion animals that are less invasive and less expensive. A vasectomy is recommended for males and tube tying for females. Both procedures have reduced trauma and allow the animal to grow naturally.

Rachel Flatebo, a fourth-year animal science major with experience in vet clinics, commented that while vasectomies are possible, they are not common and it will take time before anything other than castration becomes the norm.

Hart recommended that animals be sterilized between 13 and 18 months of age. For females, spaying after this period can increase the risk of medical problems later in life.

“[It is important] that dog caregivers be informed of all the potential risks and benefits of neutering before deciding if and when to have this procedure performed,” said Torres de la Riva.

Torres de la Riva also stresses the factor of owner responsibility and noted that European countries have far lower rates of spaying and neutering, yet are also free from many of the pet overpopulation problems that plague the United States.

NICOLE NOGA can be reached at science@theaggie.org.

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