Changes in sperm motility and damage to the DNA in the sperm are issues for males of both the human and the canine species. Over roughly the last 75 years (from 1938 to 2011), researchers have documented a 50-percent reduction in sperm quality in humans and the trend occurs worldwide. Similarly, dogs that live in homes with people have exhibited a sperm quality decline of about 30 percent over a 26-year period. These changes over time suggest that the declines are due to environmental factors.
The recent study “Independent and combined effects of diethylhexyl phthalate and polychlorinated biphenyl 153 on sperm quality in the human and dog”, in the journal Nature provides evidence that the same anthropogenic chemicals (pollutants caused by human activity) are responsible. Many such chemicals interfere with endocrine systems in mammals. This study examined the effects of diethyl phthalate (DEHP) and polychlorinated biphenyl (PCB153) on DNA fragmentation and motility in both human and dog sperm.
These pollutants are found in a variety of dog foods as well as a variety of tissues and body fluids, including human breast milk. Both chemicals are considered risk factors that negatively affect reproductive function, and have previously been found to be a factor in human infertility and reduced fertility.
Researchers exposed sperm from human donors and from stud dogs to the two chemicals and observed the effects on sperm. Samples were exposed to the chemicals alone and in combination since exposure to both chemicals simultaneously occurs in real life. The impact of various concentrations of the pollutants were studied to determine if the effects are dose-dependent.
Sperm from both dogs and people was affected by the chemicals. There was an interactive aspect of the two pollutants, meaning that the effect of each chemical were not independent of the other. As in real life, the way that the pollutants acted was complex. In humans, sperm motility was only affected when both chemicals were present, but in the dog, PCB153 alone lowered sperm motility, with the effect being more pronounced at higher doses.
DNA fragmentation in both species followed the pattern. In humans and in dogs, either chemical alone caused damage to the DNA in the sperm. Additionally, there were interactive effects in which the presence of the other chemical affected the degree of fragmentation in a manner that is more complicated than simply adding the effects together.
Dogs and men share so many similarities, including, unfortunately, a decline in sperm quantity and quality over the decades. On the bright side, this means that studies of the phenomenon in each species are likely to benefit the other. After all, what are best friends for?