Labrador retrievers are less vulnerable than golden retrievers to the long-term health effects of neutering, according to a study by researchers.
But lead investigator Benjamin Hart, a professor emeritus in the School of Veterinary Medicine, said the data showed the incidence rates of both joint disorders and cancers at various neuter ages were much more pronounced in golden retrievers than in Labrador retrievers.
He said the findings offered insights for researchers in both human and veterinary medicine and were also important for breeders and dog owners contemplating when, and if, to neuter their dogs.
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.
The golden retriever and the Labrador retriever were selected for the 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 12 months and eight years. These records included 1,015 golden retriever cases and 1,500 Labrador retriever.
The researchers compared the two breeds according to the incidence of three cancers – lymphosarcoma, hemangiosarcoma and mast cell tumour. They also calculated the incidence for each breed of three joint disorders – hip dysplasia, cranial cruciate ligament tear and elbow dysplasia.
The team noted whether the dogs had been neutered before the age of six months, between six and 11 months, between 12 and 24 months or between two and nine years of age.
Researchers found non-neutered males and females of both breeds experienced a 5% rate of one or more joint disorders. Neutering before the age of six months was associated with doubling the rate to 10% in Labrador retrievers.
In golden retrievers the impact of neutering appeared to be much more severe. Neutering before the age of six months in golden retrievers increased the incidence of joint disorders to what Prof Hart called an “alarming” four to five times that of non-neutered dogs of the same breed.
Male golden retrievers 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,” Prof Hart said.
The data also revealed important differences between the breeds in occurrence of cancers. In non-neutered dogs of both breeds, incidence of one or more cancers ranged from 3% to 5%, except in male golden retrievers, where cancer occurred at an 11% rate.
Neutering appeared to have little effect on the cancer rate of male golden retrievers. However, in female golden retrievers, neutering at any point beyond six 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,” Prof Hart said.
The study results are available in the open access journal PLOS ONE.