Declining Fertility in Dogs: A Boon for Human Research

A study* conducted by the University of Nottingham highlights a rapid decline in fertility among dogs due to an overall decrease in canine sperm quality over the past three decades. The causes cited could also explain the many cases of infertility in humans, which are linked to environmental contamination.   British researchers collected sperm samples from 42 to 97 dogs each year over a total period of 26 years, between 1988 and 2014. The sample consisted of five dog breeds: Labrador, Golden Retriever, Curly-Coated Retriever, Border Collie, and German Shepherd. According to the analysis of the collected data, the decline in canine sperm quality appears significant and abrupt, effectively ruling out a genetic cause. The analysis focused on sperm count and motility. Over the study period, the percentage of normally motile sperm showed a sharp decline. Over a decade, from 1988 to 1998, sperm motility declined by 2.5% each year. From 2002 to 2014, the decline continued at a rate of 1.2% per year. In addition to this decline, researchers observed an increased incidence of cryptorchidism in male puppies sired by breeding dogs in which a decline in sperm quality had been noted. The study points to an environmental cause. According to the findings, there is a link between declining fertility in dogs and the presence of certain environmental contaminants detected in the semen and testicles of adult males, as well as in some commercially available foods for pets—including those specifically formulated for puppies! And the concentrations of these substances were found to be high enough to impair sperm motility and viability in the tests. However, as the researchers pointed out, dogs are pets so closely integrated into human daily life that the findings can be extrapolated to men, who, in parallel, have also been facing a decline in sperm quality over the past seventy years. Dogs thus become not only a preferred animal model for researching the causes of declining male fertility, but also a sentinel for humans: “They share the same environment, exhibit a range of similar diseases—often with the same frequency—and respond similarly to treatments.” ” Thus, “the decline in canine sperm quality raises the question of whether a similar effect might also be observed in humans.” The major strength of this study is that the entire protocol—from semen collection to sample processing and analysis—was carried out over a period of twenty-six years within the same laboratory. In humans, the decline in sperm quality is a controversial topic within the scientific community, which continues to debate it because the samples collected do not follow the same analysis protocols and are not processed by a single research institution. But the fact remains: the quality of human sperm has indeed been declining significantly for several decades. Its impacts on fertility—collectively known as testicular dysgenesis syndrome—have been demonstrated and are associated with a rising incidence of testicular cancer, hypospadias, and undescended testicles. These abnormalities are on the rise among the global male population… just as they are in dogs.   * Richard G. Lea et al.: Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism, Scientific Reports, August 9, 2016, http://www.nature.com/articles/srep31281