A warning for dogs, and their best friends, in study of fertility
For decades, generations of dogs have been bred, raised and trained as service animals for disabled people at a center in England: Labrador retrievers, golden retrievers, curly coat retrievers, Border collies and German shepherds. Scientists at the University of Nottingham realized that they had an ideal opportunity to study dog fertility — five types of purebreds, uniform conditions, one location, systematic record-keeping. So in 1988, they started annually testing the sires’ sperm.
In a study published Tuesday in Scientific Reports, they found declining sperm quality and other effects that they believe could be related to environmental causes. Over 26 years, motility, the progressive forward movement of sperm, dropped 30 percent in all five breeds. Although it has not reached a critical point — the dogs are still successfully impregnating — further decline in motility could eventually harm their ability to reproduce.
“The dogs who share our homes are exposed to similar contaminants as we are,” said Richard G. Lea, an associate professor of reproductive biology at the School of Veterinary Medicine and Science at the University of Nottingham. “So the dog is a sentinel for human exposure,” added Dr. Lea, the study’s principal investigator.
German shepherd puppies. The researchers also found a small rise in the mortality rate of female puppies and a 10-fold increase in undescended testicles in male puppies. CreditAuscape/UIG, via Getty Images
From 1988 to 2014, researchers studied between 42 and 97 stud dogs annually. Between 1994 and 2014, they also noticed that the mortality rate of the female puppies, although small, showed a threefold increase. And the incidence of undescended testicles in male puppies, also small, had a 10-fold increase, to 1 percent from 0.1.
When the researchers tested testicular tissue for chemical content (in dogs retired from breeding or neutered for other reasons), they found concentrations of chemicals that had been common in electrical transformers and paint, and others still used in plastics. In additional analyses done in the last three years, researchers found concentrations of the same chemicals in the dogs’ semen. The chemicals include PCBs, which, though banned, have a long half-life, and diethylhexyl phthalate (DEHP).
The researchers also found traces of the same chemicals in the food that handlers gave the dogs. The brands were not named in the study (nor was the training center), but Dr. Lea said the food, both wet and dry, is sold worldwide — in other words, quite possibly what you serve your own dear beast.
The scientists cannot determine how the chemicals were introduced into the food supply; these are not additives. But Dr. Lea and his colleagues speculate that they could be in the packaging as well as in water that came into contact with any ingredients.
A border collie puppy. Tests of testicular tissue detected concentrations of chemicals that were common in electrical transformers and paint. CreditAuscape/UIG, via Getty Images
They cannot even conclusively say the dog food is a direct or even the only source of the chemicals found in the testes. But Dr. Lea said it was probably a major one.
The study, the authors said, may support other research findings about environmental exposure and human semen. For at least 70 years, studies have noted a decline in human sperm quality, and a gradual increase in rates of testicular cancer and genital tract abnormalities, like undescended testes. But there has been a debate in the scientific community about whether this trend is directly associated with industrial chemicals discharged in the environment. Critics have noted that lab conditions and standards for the many studies have varied widely. Establishing a cause-effect link over time, they say, is not reliable.
Peter J. Hansen, a professor of reproductive biology at the University of Florida, describes himself generally as a skeptic of many studies linking chemical exposure to declining sperm quality. Much research on the effect of environmental hazards on humans is typically done by administering doses of hazards to research animals in much greater concentrations than is typically found in water supplies, he said.
But the Nottingham study, he noted, detected the chemicals in the dogs’ tissue and also in their food. And researchers did so over decades, tracking a concurrent decline in reproductive markers.
“I think it was very rigorous,” he said. “It’s much more clear from their data that there was a decline over time, which agrees with the human data but doesn’t suffer from the same research problems.”
One question researchers had was whether the effects they saw were genetic rather than environmental. These are purebreds. Purebred dogs have genetic predispositions to health problems, which can be exacerbated by intentional inbreeding.
But because records were kept fastidiously, researchers could rule out inbreeding. And while undescended testes can have a genetic component, it occurred in all five breeds, suggesting another cause. Dr. Lea said that declining sperm motility, the most pronounced effect, does not have a strong heritable association.
The current study, of course, looks exclusively at male dogs. And so Dr. Lea’s team is now studying dissected ovarian tissue, to see whether females also show signs of reproductive problems and chemical concentrations.