Researchers from the University of Nottingham’s school of veterinary medicine just released an epic, 26-year study on the fertility of British pooches. And it doesn't contain good news.
According to Tim Radford at The Guardian, the researchers collected 1,925 sperm samples from a 232 different dogs—Labradors, border collies, German shepherds and golden retrievers. The results, published recently in Scientific Reports, show that between 1988 and 1998 sperm motility—its ability to move down the female reproductive tract—dropped by 2.4 percent each year. Between 2002 and 2014, motility rates dropped by 1.2 percent per year. Over the entire study period, it was roughly a 30 percent decline. Male pups that came from papas with low sperm motility were also ten times more likely to experience cryptorchidism, a condition in which their testes don’t properly descend into the scrotum.
That’s not great news for dogs or purebred lovers, but lead author of the study, Richard Lea tells Radford there's no reason to start cloning puppies just yet. It will probably take further declines before the problem impacts puppy making.
But the study isn’t just about canine fertility—it serves as a stand-in for human fertility rates. “Why the dog?” Lea asks Radford. “Apart from the fact that it is a great population of animals to work with, dogs live in our homes, they sometimes eat the same food, they are exposed to the same environmental contaminants that we are, so the underlying hypothesis is that the dog is really a type of sentinel for human exposure.”
Researchers have noticed a decline in human sperm counts for over 70 years, as well increases in problems like testicular cancer and cryptochidism, reports Jan Hoffman for The New York Times. While there have been many, many studies looking at problems with human fertility, varying research protocols and lab standards have made it difficult to come up with reliable conclusions.
This latest dog study, however, was conducted by the same three researchers over almost three decades, using the same procedures and protocols. “I think it was very rigorous,” Peter J. Hansen, a professor of reproductive biology at the University of Florida tells Hoffman. “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.”
So why is the decline happening? Lea and his colleagues say their research points toward an environmental cause. Radford reports the study found the banned chemicals polychlorinated biphenyls (PCBs) and diethylhexyl phthalates, a class of chemicals used in plastic manufacturing, in the dogs’ semen. The chemicals, which are found widely in the environment, were also present in the testicles of neutered dogs. Hoffman says the researchers also found the chemicals in certain brands of dog food.
Reproductive problems related to chemical exposure are not just limited to dogs and people. Researchers are finding that these chemicals and many others effect a range of wildlife. Studies have shown that chemical pollution in rivers and lakes interrupts the ability of fish to breed, and artificial estrogens can cause male fish to turn female. Another study shows that atrazine, one of the most commonly used herbicides in the world, chemically castrates 75 percent of frogs that encounter it in the wild and causes one in ten male frogs to become female.
Lea and his colleagues are now working on a follow-up study dissecting the ovaries of female dogs to test chemical concentrations and look for reproductive abnormalities.