There's Been a Decline in the Quality of Dog Sperm—and It Might Be a Concern for Humans

Woman veterinarian listens dachshund
Photo Credit: Poprotskiy Alexey/Shutterstock

With overpopulation a major concern for sustainability and the environment, it might be argued that less fertility for humans may not be such a bad thing. But try telling that to a couple trying to get pregnant.

According to the world's largest study of human sperm quality and concentration of 26,000 men between 1989 and 2005, sperm counts fell by a third, significantly increasing the chance of infertility. The amount of healthy sperm was also reduced, by a similar proportion. There are many theories as to why this is happening, including the use of pesticides. While there is some disagreement about the cause, most scientists agree that male sperm count has been decreasing over the last century, and even more so over the past 25 years. 

A recent U.K.-based study published in journal Scientific Reports and conducted by researchers at the University of Nottingham, the James Hutton Institute and the National Breeding Center for the Guide Dogs for the Blind Association may hold the key to understanding the environmental issues that have been causing a drop in the sperm counts of men around the world. The study points the finger at chemicals found in dog food that may also be responsible to human male infertility.

The researchers studied dogs bred to be service animals for disabled people and covered several different breeds, including Labrador retrievers, golden retrievers, curly coat retrievers, border collies and German shepherds. Since the conditions at the breeding center have been the same for many years, it was the perfect opportunity for scientists, as the possibility of outside influences were minute and detailed records were kept on all the dogs.

“Over the past 70 years, there have been a number of reports suggesting that the quality of human sperm has declined," Richard Lea, a professor of veterinary medicine and science at the University of Nottingham and the chief researcher of this study, told AlterNet. "However, this decline remains a controversial issue since many have criticized the variability of the data of the studies on the basis of changes in laboratory methods, training of laboratory personnel and improved quality control over the years. Since the dog occupies the same environment as the human, we wondered if there might be any evidence for a similar decline in dog semen quality."

Dr. Lea and his colleagues collected 1,925 semen samples over a period of 26 years. Every year, they tested between 42 and 97 dogs, and every year, their sperm counts fell. Between 1989 and 1998, sperm counts dropped by 2.5 percent every year, and the counts dipped by 1.2 percent a year between 2002 and 2014. Overall, the sperm counts dropped around 35 percent over the course of the study.  

Some of the chemicals found in the dogs' food are alarming, and include diethylhexyl phthalate (DEHP) and polychlorinated bisphenol 153 (PCB153)—two environmental contaminants that cause fertility problems in other species. The food also contained phthalates and PCBs, chemicals used to make plastic that probably got into the food through its packaging. The dogs used in the study ate both wet and dry dog food. The brands of the food were not identified, but are sold all over the world.

Puppies who had fathers with lower quality semen were more prone to cryptorchidism, meaning their testes did not fully descend into the scrotum.

"Our studies showed that over the 26 years of the study, the quality of sperm declined in a similar way to some reports in the human," said Dr. Lea. "We also found that testes recovered from dogs undergoing routine castration, and sperm, contained chemicals at concentrations able to disrupt sperm motility and viability when tested. Although this suggests a possible link, we have not been able to show that the decline in sperm quality over time is due to exposure to such pollutants. Further research is needed to demonstrate this."

But is there truly reason to believe that these environmental issues could affect humans in similar ways?

Allan Pacey, a professor of andrology at the University of Sheffield, thinks there might be. He said the study "suggests that the sperm quality in a population of dogs enrolled in a breeding program in the U.K. may have declined over a 26-year period, in a manner which mimics what others have claimed may have happened in the human male over the last century."

Dr. Lea agrees. He said:

We believe that it is possible that whatever is causing the decline in sperm quality in the dog may be the same as what has been reported in the human. Indeed in the human it has been suggested that environmental contaminants may be involved, although this has not been demonstrated. Interestingly, an increased incidence of cryptorchidism, has been reported in the human and we found the same in male pups generated from the stud dogs with declining semen quality. This is also thought to be related to exposure to pollutants. When all of these pieces of information are put together, it does suggest that environmental chemicals may be responsible but as yet, a conclusive link has not been demonstrated.

The dogs we share our lives with are exposed to the same types of chemicals that we are. The chemicals researchers found in dog food are also common in paint, plastics and electrical transformers. While more studies are needed to conclusively prove that these types of environmental chemicals are affecting human fertility, it seems likely that they are. But one thing seems fairly certain: Exposure to harmful chemicals that impact the biological function of many species, including ours, will continue.