Life & Non-humans
Labrador retrievers are less vulnerable than golden retrievers to the long-term health effects of neutering, as evidenced by higher rates of certain joint disorders and devastating cancers, according to a new study by researchers at the University of California, Davis, School of Veterinary Medicine.
Results of the study now appear online in the open-access journal PLOS ONE at http://tiny.cc/tia0ix.
“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,” said lead investigator Benjamin Hart, a distinguished professor emeritus in the School of Veterinary Medicine.
“The data, however, showed that the incidence rates of both joint disorders and cancers at various neuter ages were much more pronounced in golden retrievers than in the Labrador retrievers,” he said.
He noted that the findings not only offer insights for researchers in both human and veterinary medicine, but are also important for breeders and dog owners contemplating when, and if, to neuter their dogs. Dog owners in the United States are overwhelmingly choosing to neuter their dogs, in large part to prevent pet overpopulation or avoid unwanted behaviors.
This new comparison of the two breeds was prompted by the research team’s earlier study, reported in February 2013, which found a marked increase in the incidence of two joint disorders and three cancers in golden retrievers that had been neutered.
Health records of goldens and Labradors examined
The golden retriever and the Labrador retriever were selected for this study because both are popular breeds that have been widely accepted as family pets and service dogs. The two breeds also are similar in body size, conformation and behavioral characteristics.
The study was based on 13 years of health records from the UC Davis School of Veterinary Medicine for neutered and non-neutered male and female Labrador retrievers and golden retrievers between the ages of 1 and 8 years of age. These records included 1,015 golden retriever cases and 1,500 Labrador retriever cases.
The researchers compared the two breeds according to the incidence of three cancers: lymphosarcoma, hemangiosarcoma and mast cell tumor. They also calculated the incidence for each breed of three joint disorders: hip dysplasia, cranial cruciate ligament tear and elbow dysplasia.
The researchers also noted in these cases whether the dogs had been neutered before the age of 6 months, between 6 and 11 months, between 12 and 24 months or between age 2 and 9 years of age.
Neutering and joint disorders
In terms of joint disorders, the researchers found that non-neutered males and females of both breeds experienced a five-percent rate of one or more joint disorders. Neutering before the age of 6 months was associated with a doubling of that rate to 10 percent in Labrador retrievers.
In golden retrievers, however, the impact of neutering appeared to be much more severe. Neutering before the age of 6 months in goldens increased the incidence of joint disorders to what Hart called an “alarming” four-to-five times that of non-neutered dogs of the same breed.
Male goldens experienced the greatest increase in joint disorders in the form of hip dysplasia and cranial cruciate ligament tear, while the increase for Labrador males occurred in the form of cranial cruciate ligament tear and elbow dysplasia.
“The effects of neutering during the first year of a dog’s life, especially in larger breeds, undoubtedly reflects the vulnerability of their joints to the delayed closure of long-bone growth plates, when neutering removes the gonadal, or sex, hormones,” Hart said.
Neutering and cancers
The data also revealed important differences between the breeds in relation to the occurrence of cancers. In non-neutered dogs of both breeds, the incidence of one or more cancers ranged from 3 to 5 percent, except in male goldens, where cancer occurred at an 11-percent rate.
Neutering appeared to have little effect on the cancer rate of male goldens. However, in female goldens, neutering at any point beyond 6 months elevated the risk of one or more cancers to three to four times the level of non-neutered females.
Neutering in female Labradors increased the cancer incidence rate only slightly.
“The striking effect of neutering in 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.
Funding for the study was provided by the American Kennel Club Canine Health Foundation and the Center for Companion Animal Health at UC Davis.
Other members of this UC Davis research team are Lynette Hart and Abigail Thigpen, both of the School of Veterinary Medicine, and Neil Willits of the Department of Statistics.