Golden retrievers are more likely than Labrador retrievers to be diagnosed with joint disorders or cancer after the animals have been spayed or neutered, according to the results of a study published Monday in the online journal PLOS ONE. Intact members of both breeds enjoy lower rates of joint disorders and cancer, researchers at the University of California, Davis, School of Veterinary Medicine added. The researchers did not take a stand on spaying and neutering, which is done to an estimated 83 percent of all U.S. dogs to control the pet population and prevent unwanted behaviors. Instead, they stated that the study served to measure the long-term health effects of sterilization and to educate breeders and dog owners who are deciding when, and if, to spay or neuter their animals. When a golden or Labrador retriever is sterilized can play a role in the onset of joint disorders and cancer, the researchers stated. A connection was found between early sterilization—before the animal is 6 months old—and the appearance of joint disorders. About 5 percent of intact golden and Labrador retrievers of both genders suffer from a joint disorder, the researchers determined. The rate in dogs sterilized before 6 months old jumped to 10 percent of Labs and 20 to 25 percent of goldens. The removal of hormone-producing organs during the first year of a dog’s life leaves the animals vulnerable to the delayed closure of long-bone growth plates, said lead investigator Benjamin Hart, DVM, Ph.D., a distinguished professor emeritus in the School of Veterinary Medicine. “We found in both breeds that neutering before the age of 6 months, which is common practice in the United States, significantly increased the occurrence of joint disorders, especially in the golden retrievers,” Dr. Hart said. “The data, however, showed that the incidence rates of both joint disorders and cancers at various [sterilization] ages were much more pronounced in golden retrievers than in Labrador retrievers,” he said. The findings were based on 13 years of health records accumulated by the UC Davis veterinary school. Some 1,015 golden retrievers and 1,500 Labrador retrievers—two popular breeds that share similar body size, conformation and behavioral characteristics—were included. The researchers looked at the incidence of hip dysplasia, cranial cruciate ligament tear and elbow dysplasia and three cancers: lymphosarcoma, hemangiosarcoma and mast cell tumor. Among the other results: • Male goldens neutered before age 1 experienced a marked rise in the occurrence of hip dysplasia and cranial cruciate ligament tears, while the incidence of cranial cruciate ligament tears and elbow dysplasia in male Labradors was greatest when sterilization occurred in the first 6 months. • Among intact goldens and Labs, the incidence of one or more cancers ranged from 3 to 5 percent. However, the cancer rate for intact male goldens was 11 percent. • Female goldens sterilized after age 6 months were three to four times more likely to develop cancer compared with intact females. Sterilized female labs had only a slightly higher risk of getting cancer. “The striking effect of [sterilizing] female golden retrievers, compared to male and female Labradors and male goldens, suggests that in female goldens the sex hormones have a protective effect against cancers throughout most of the dog’s life,” Hart said. The American Kennel Club Canine Health Foundation and the Center for Companion Animal Health at UC Davis funded the study. Besides Hart, the research team included Lynette Hart, MA, Ph.D.; population health and reproduction specialist Abigail Thigpen; and statistician Neil Willits.
