A new study from University of California, Davis, suggests that neutering--and the age at which a dog is neutered--may affect the animal’s risk for developing certain cancers and joint diseases. The study examined the health records of 759 golden retrievers and found an unexpected doubling of hip dysplasia among male dogs who were neutered before one year of age.
The prevalence of neutering practices vary from country to country. In the United States neutering is commonplace and supported by veterinary and animal welfare groups. The practice is intended to prevent pet overpopulation or avoid unwanted behaviors, and is normally done when the dog is less than one year old. In Europe, however, neutering is generally avoided by owners and trainers and not promoted by animal health authorities.
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In recent years, studies have suggested that neutering can adversely affect the health of certain dog breeds. Since those studies examined individual diseases using data on one breed or pooled from several breeds, Hart and colleagues set out to examine the effects of neutering on the risks of several diseases in the same breed and using a data set from one hospital. They also distinguished between males and females and between early neutering, late neutering and non-neutering.
The researchers chose the golden retriever because it is one of the most popular breeds in the U.S. and Europe while also susceptible to various cancers and joint disorders.
The research team crunched data from the records of female and male golden retrievers ranging in age from 1 to 8 years, who were classified as intact (not neutered), neutered early (before 12 months age), or neutered late (at or after 12 months age). All dogs had been examined at UC Davis’ Veterinary Teaching Hospital for two joint disorders--hip dysplasia, cranial cruciate ligament tear--and three cancers--lymphosarcoma, hemangiosarcoma and mast cell tumor.
Results showed that, for all five diseases analyzed, the disease rates were significantly higher in both males and females that were neutered (either early or late) compared with intact (non-neutered) dogs. Males neutered early were more likely to develop hip dysplasia, cranial cruciate ligament tear and lymphosarcoma, while females were more prone to cranial cruciate ligament tear. Late neutering was associated with the development of mast cell tumors and hemangiosarcoma in females.
Previous studies have suggested similar increases in disease risks, but the new study is the first to specifically report an increased risk of late neutering for mast cell tumors and hemangiosarcoma. The study also revealed a doubling in the incidence of hip dysplasia among early-neutered males. Earlier studies did not differential between early and late neutering, resulting in a smaller reported increase (17%).
Joint disorders and cancers are particularly affected by neutering because the surgery removes organs that are essential to producing hormones that regulating growth, closure of bone growth plates, and the estrous cycle in female dogs.
While results of the new study are revealing, the researchers caution that the relationship between neutering and disease-risk is still a complex issue. The results are likely the combination of several factors, including the effect of the procedure on the young dog’s growth plates as well as the increase in weight on the joints that is commonly seen in neutered dogs.
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“The study results indicate that dog owners and service-dog trainers should carefully consider when to have their male or female dogs neutered,” said lead investigator Benjamin Hart, a distinguished professor emeritus in the UC Davis School of Veterinary Medicine.
“It is important to remember, however, that because different dog breeds have different vulnerabilities to various diseases, the effects of early and late neutering also may vary from breed to breed,” he said.
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