By Dr. Becker
A new study conducted at the University of California, Davis1 further supports a growing body of evidence that spaying or neutering, and the age at which it is done, may increase a dog's risk of certain cancers and joint diseases.
The UC Davis researchers point out that the U.S. takes a very different approach to spay/neuter compared to many European countries. In this country, not only are most dogs spayed or neutered, increasingly the preferred timing of the procedure is before the animal is a year old. The motivation is presumably pet population control, and owners are considered responsible only if their pet has been sterilized.
In contrast, in many European countries dogs remain intact and animal health experts do not promote spaying or neutering. In fact, a study of 461 dogs in Sweden reported 99 percent of the dogs were intact. In Hungary, 57 percent were intact, and in the U.K., 46 percent.
The UC Davis study was undertaken, according to the researchers, because "Given the importance of gonadal hormones in growth and development, this cultural contrast invites an analysis of the multiple organ systems that may be adversely affected by neutering."
Study Looked at the Impact of Spay/Neuter on One Breed, Both Genders, and Five Different Diseases
The UC Davis study looked at the health records of 759 Golden Retrievers. Goldens were chosen because they are one of the most popular breeds in the U.S. and Europe, are often used as service dogs, and are also susceptible to various cancers and joint disorders.
The intent of the study was to investigate the effects of neutering on the risks of several diseases in a single breed of dog, distinguishing between males and females, and between dogs that had been neutered or spayed early (before one year), late (after one year), or not at all.
The dogs ranged in age from 1 to 8 years and had been seen at UC Davis' William R. Pritchard Veterinary Medical Teaching Hospital for one or more of the following problems: hip dysplasia (HD), cranial cruciate ligament (CCL) tear, lymphosarcoma (LSA), hemangiosarcoma (HSA), and mast cell tumor (MCT).
The researchers focused on joint disorders and cancers because neutering or spaying removes the testes or ovaries and disrupts production of hormones that play important roles in body processes like bone growth plate closure.
Findings Reveal Significantly Higher Disease Rates in Spayed/Neutered Dogs
The study revealed that for all five diseases, the rates were significantly higher in both males and females that were neutered or spayed (before or after one year of age) compared with intact dogs.
Of special concern is that results showed a 100 percent increase in the rate of hip dysplasia in male Goldens neutered before 12 months of age. Ten percent were diagnosed with the condition, which was double the rate of occurrence in intact males. Past studies have reported a 17 percent increase among all neutered dogs compared to all intact dogs.
- There were no cases of CCL tears in intact male or female Goldens. In early neutered males there was a 5 percent occurrence, and in early spayed females, an 8 percent occurrence.
- Almost 10 percent of early-neutered males were diagnosed with lymphosarcoma, which was 3 times more than intact males.
- Hemangiosarcoma in late-spayed females was 8 percent -- 4 times more than intact and early-spayed females.
- No intact females had mast cell tumors, but 6 percent of late-spayed females did.
The UC Davis findings are in line with the results of earlier studies, however, it's the first study to identify a connection between late spaying and mast cell tumors and hemangiosarcoma in female dogs.
What These Results Mean for Dog Owners
The study authors consider their findings clinically relevant as follows:
"Specifically for Golden Retrievers, neutering males well beyond puberty should avoid the problems of increased rates of occurrence of HD, CCL, and LSA and should not bring on any major increase in the rates of HSA and MCT (at least before nine years of age). However, the possibility that age-related cognitive decline could be accelerated by neutering should be noted2.
For females, the timing of neutering is more problematical because early neutering significantly increases the incidence rate of CCL from near zero to almost 8 percent, and late neutering increases the rates of HSA to 4 times that of the 1.6 percent rate for intact females and to 5.7 percent for MCT, which was not diagnosed in intact females."
According to lead study investigator Benjamin Hart, professor emeritus at the UC Davis School of Veterinary Medicine, "The study results indicate that dog owners and service-dog trainers should carefully consider when to have their male or female dogs neutered."
Hart goes on to say it's important to keep in mind that different breeds have different vulnerabilities to various diseases, and the effects of spay/neuter and when it is done very likely vary from breed to breed. The Golden Retriever findings can't be generalized to other breeds, or dogs in general. However, in other breeds with a propensity for joint disorders and types of cancer different than those prevalent in Goldens, spaying and neutering may increase the risk for those breed-specific disease tendencies.
More breed-specific studies are needed for a full understanding of the disease conditions affected by spaying and neutering.