Traditionally, many retriever owners who weren't interested in breeding their dogs opted to have them spayed or neutered. These procedures were typically performed before the dog reached six months of agethe accepted standard in the veterinary profession.

The decision was never risk free, of course. By eliminating the dog's reproductive capacity you're also shutting down the production of hormones that affect metabolismthe reason spayed and neutered dogs are at higher risk for becoming obese. Still, the long-term health implications were believed to be overwhelmingly positive.

In recent years, however, this picture has begun to change. "You have to look at the breed and gender of the dog in order to make an informed decision regarding spaying and neutering," says Dr. Benjamin L. Hart, distinguished professor emeritus at the University of California, Davis, School of Veterinary Medicine. "You can't apply the same standard to all breeds."

With funding from the American Kennel Club's Canine Health Foundation, Hart and his colleagues tracked the health histories of over 1,900 Labrador retrievers and more than 1,200 golden retrievers, including males and females that were spayed, neutered, or intact. They tracked the histories of numerous other breeds as well. Specifically, they looked at the incidence of three joint disorders (hip dysplasia, elbow dysplasia, and cruciate ligament injury) and four cancers (hemangiosarcoma, osteosarcoma, lymphoma, and mast cell tumors). They also looked at the incidence of mammary cancer in females.

What they discovered was surprising. "In golden retrievers," Hart explains, "the incidence of joint disorders in the intact population is just 3 percent. In males neutered before six months of age, however, the incidence of joint disorders jumps to 23 percent, and in males neutered between six months and one year to 11 percent. The percentage of joint disorders for female goldens spayed in those time frames is about the same."

Noting that goldens are known for developing cancers, Hart adds, "When you look at cancers in goldens, intact males have a 10 percent risk. The risk increases to 13 percent for males neutered before six months and to 12 percent for males neutered between six months and their first birthday. Based on these findings, the suggested guideline for golden retriever males is to delay neutering until they're beyond one year of age."

With respect to cancers in female goldens, Hart and his colleagues discovered something he describes as "really troubling and almost unique to the golden retriever." While the incidence of cancers in intact females is only 3 percent, spaying at any age elevates the risk to 12 percenta fourfold increase. Given these findings, Hart strongly recommends leaving female goldens intact or, if that's not possible, delaying spaying until after the one-year threshold and, in his words, "remaining vigilant for cancers."

Another option, notes Hart, is an ovary-sparing spay, in which only the uterus is removed. This preserves the hormonal "factory" while eliminating the possibility of pregnancy and the discharge associated with estrus. However, fewer veterinarians are qualified to perform this procedure than are qualified to perform a traditional spay.

For Labs, there is good news in one respect. Hart and his team found no correlation between spaying or neutering and increased risk of cancers, regardless of when the procedures are performed. But while intact Labs of either sex have a 6 percent risk for joint disorders, the risk for males neutered before six months jumps to 9 percent and for females spayed any time before their first birthday to 11 percent. The obvious conclusion is to delay neutering until after six months, and spaying until after one year.

And what of the conventional wisdom that spaying sharply reduces the risk of mammary cancer? "We were surprised," Hart acknowledges, "to find that the evidence for that in Labs and goldens is weak. The incidence of mammary cancers in intact females of both breeds is only about 1 percent."

Hart concludes, "We all want the best for our dogs. The hope is that our research will help to extend the working lives of Labs and goldens and promote their basic comfort. Still, every owner should make the decision to spay or neuter not only in light of our findings but in consultation with his or her veterinarian."