A research study evaluated temporal changes in sperm quality and cryptorchidism incidence, and the effects of environmental chemicals on sperm quality, in a canine breeding program.
A study published in Nature’s Scientific Reports reported temporal decreases in canine sperm quality as well as increases in cryptorchidism incidence and identified environmental chemicals (ECs) in canine adult testes and semen. Results suggest that, as the authors note, “the direct effects of chemicals on sperm may therefore contribute to the decline in canine semen quality that parallels that reported in the human.”
In men, sperm quality has declined over the past 70 years. In addition, incidences of testicular cancer and reproductive tract abnormalities, collectively known as “testicular dysgenesis syndrome” (TDS), have increased. Such findings indicate the disruptive impact of ECs on human reproductive endocrine function.
The close companionship between dogs and humans makes it likely that ECs also negatively affect canine reproductive endocrine function. For example, canine testicular cancer rates have increased in close parallel to those of humans. Also, canine reproductive tract abnormalities are histologically similar to those seen with human TDS.
For 26 years, from 1988 to 2014, the authors studied dogs from a controlled breeding program in the United Kingdom. Sperm from stud dogs was collected annually to evaluate temporal changes in sperm quality and measure seminal EC concentrations. Data from 1999 to 2001 were not included in the analysis because dogs with the poorest semen quality during these years were removed from the breeding program.
Testis samples from healthy adult dogs undergoing routine castration were collected to evaluate luteinizing hormone—stimulated testosterone secretion and measure EC concentrations. Samples of commercial dry and canned dog foods were also tested for ECs.
Cryptorchidism incidence in puppies and the male:female birth ratio from 1995 to 2014 were analyzed. The puppies were offspring of the breeding program’s stud dogs.
Sperm motility decreased steadily between 1988 and 2014. The percentage of sperm with normal morphology dropped 8.1% per year from 1988 to 1994, increased from 1994 to 1998, then plateaued until 2014. Total sperm output increased between 1988 and 2005, then decreased and plateaued from 2006 to 2014. Significant changes were observed at different time points for each sperm quality measure.
Cryptorchidism incidence increased significantly. The male:female ratio of births significantly decreased, but only when including stillbirths and neonate deaths in the data analysis. In addition, male mortality significantly decreased and female mortality significantly increased. The authors believe the increased cryptorchidism incidence and female morality rates occurred through separate mechanisms.
Testis samples contained diethylhexyl phthalate (DEHP) and congeners of polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE). Pooled semen samples also contained several PCB and PBDE congeners. Notably, PCB153 was detected in testis and semen samples. The authors selected PCB153 and DEHP for in vitro studies of sperm cultures and testis explants.
PCB153 and DEHP at 2, 10, and 100 times their mean testis concentrations were used to evaluate in vitro sperm movement, sperm vitality, DNA fragmentation, and testosterone secretion. Several sperm movement parameters significantly increased with PCB153 (straight line velocity, percent motility, percent linearity) and decreased with DEHP (percent straightness, percent linearity, straight line velocity). PCB153 and PBDE significantly reduced sperm vitality and increased DNA fragmentation. However, neither PCB153 nor DEHP significantly affected testosterone secretion from testis explants.
Commercial dry and canned dog foods also contained PCB, PBDE, and DEHP. Concentrations of PCB and PBDE congeners varied between dog food samples. Notably, DEHP and predominant PCB and PBDE congeners in the testis samples were also detected in the dog foods.
Although the study’s findings demonstrate the effect of ECs on sperm quality, the authors acknowledge that the mechanism behind these effects remains unknown.
Dr. Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.