A long-term study conducted in Britain has found that male dogs are losing fertility, and that exposure to environmental chemicals (ECs) that have leached into the environment may be to blame.
The dogs—Labradors, Border Collies, German Shepherds and Golden Retrievers bred to aid the disabled—made an ideal group to explore the larger question of a decline in human semen quality that has been occurring since long before this study.
This twenty-six year long study, 1998-2014, was conducted by Richard Lea and colleagues at Nottingham University’s school of veterinary medicine. They collected annual samples of semen from dozens of dogs, all from the same breeding program, all healthy and well cared for. Each year, the same problem recurred; a 2.4 percent dip in sperm motility, that is the ability to swim in a straight line. In addition to monitoring semen quality, they analyzed health records, finding an increase in cryptorchidism, a condition in which the testicles fail to extend normally to the scrotum. Over the same years, fewer male pups were born than females, also there was an increase in fetal and prenatal female mortality.
And, lurking in the samples of semen and testicles of dogs obtained from neutering, it found ECs—chemicals that tamper with hormones. The chemicals include polychlorinated bisphenol (PCB), a compound banned in 1977, and diethylhexyl phthalate (DEHP). PCBs don’t readily break down while phthalates are common in a wide number of products, from cosmetics to detergent. Both chemicals are associated with fertility issues and birth defects.
In human babies, exposure to chemicals has been linked to faulty development of semen quality and cryptorchidism. According to the study, such reproductive problems often cluster in geographical areas, and so are suspected of having a common cause; exposure to hormone-disrupting chemicals is “thought to be the initiator.” To explore the same possibility in dogs, chemicals were measured in canine testes and semen taken from the same geographical area where the study took place.
Both chemicals “perturbed sperm viability, motility and DNA integrity in vitro.” The researchers concluded that the direct effects of chemicals on sperm “may contribute to the decline in canine semen quality” that parallels that in humans.
“Why the dog?” said Dr. Lea. “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.”
The same ECs were found in a range of commercially available dog foods. DEHP and PCB153, “were detected in adult dog testes and commercial dog foods at concentrations reported to perturb reproductive function in other species.”
While the brands were not named, they are reported to be both wet and dry forms sold worldwide. The scientists don’t know how the chemicals made it into the food, but since they are not deliberate additives, they may have leached from the packaging or processing sources.
These overall findings are troubling, but they also noted that: “Amongst the dry dog food samples, one sample designed for puppies (1 to 24 months of age) had higher concentrations … relative to the other samples tested.”
Plus, while the researchers cannot say the dog food is a direct source of the ECs, the New York Times reports that "Dr. Lea said it was probably a major one."
What is known is that the chemicals wound up in dog’s testicles, where they messed with sperm motility and viability. “This may be a way by which environmental chemicals directly affect male fertility.”
While the dogs in the study were still able to reproduce, it’s hardly reassuring that, once more, the dogs who share our homes also share our diseases, unwittingly, acting as the “canary in the mine” for us.