Decline in Fertility in Dogs Can Be Linked to Environmental Contaminants

In a study conducted over the course of 26 years, researchers at The University of Nottingham have found that there has been a notable decline in the fertility of dogs, a decline that can be linked back to environmental contaminants found in a variety of pet foods, some marketed specifically to target puppies. Researchers state that these results both parallel and offer additional insight into the decline of human semen quality that has been noted in the past 70 years, according to a press release.

Richard Lea, PhD, Reader in Reproductive Biology in The University of Nottingham’s School of Veterinary Medicine and Science, said, “While further research is needed to conclusively demonstrate a link, the dog may indeed be sentinel for humans—it shares the same environment, exhibits the same range of diseases, many with the same frequency and responds in a similar way to therapies.”

According to the study, a significant decline in human semen has been reported over the course of 70 years, however, it remains a controversial issue. Due to different laboratory methodologies and standards, the reliability of the studies conducted is often questioned, according to the study. Regardless, the authors of the study go on to note that declining sperm counts are linked with epidemiological data showing an increase in abnormal genital tracts as well as testicular cancer which would further suggest that environmental factors are influential when it comes to male reproduction.

Testicular dysgenesis syndrome or reproductive issues are believed to collectively occur in areas that have a common etiology or common set of causes. The authors of the study link these causes back to environmental chemicals (ECs) that produce endocrine problems early on in life. Therefore, if puppies are exposed to commercially available foods that contain harmful environmental chemicals, that could attest for the decline in sperm mobility later on in life.

The study consisted of samples that were taken from stud dogs, focusing on five specific breeds (Labrador retriever, curly coat retriever, golden retriever, border collie, and German shepherd) in a controlled breeding program for the duration of 26 years, according to the press release. Between 42 and 97 dogs were studied each year of the 26 years.

In speaking about the collection of the semen samples, Gary England, professor and foundation dean of the School of Veterinary Medicine and Science and professor of Comparative Veterinary Reproduction, said, “The strength of the study is that all samples were processed and analysed by the same laboratory using the same protocols during that time and consequently the data generated is robust.”

Researchers collected semen from the dogs and calculated the percentage of sperm that appeared normal under a microscope and showed a normal pattern of motility. During the course of the study, they found that there was a significant decline in normal sperm motility.

According to the press release, “Between 1988 and 1998m sperm motility declined by 2.5 per[cent] per year and following a short period when stud dogs of compromised fertility were retired from the study, sperm motility from 2002 to 2014 continued to decline at a rate of 1.2% per year.”

The researchers also noted an increase in cryptorchidism, where puppies’ testes failed to descend correctly from the abdomen into the scrotum.

Additionally, environmental contaminants, specifically diethylhexyl phthalate (DEHP) and polychlorinated bisphenol 153 (PCB153), were found in the testes that were taken from dogs who underwent routine castration as well as sperm samples collected by the same dog breed populations. The levels of these contaminants were found to be at levels high enough to negatively impact sperm motility and viability.

According to Lea, the researchers also looked at other factors, such as genetic conditions, that may also serve to impact fertility. Ultimately, the team discounted genetic conditions playing an influential role with the rationale being that “26 [years] is simply too rapid a decline to be associated with a genetic problem,” according to Lea.

When speaking on the parallel between these results in dogs and what that might mean for humans, Lea said, “The Nottingham study presents a unique set of reliable data from a controlled population which is free from [outside] factors. This raises the tantalizing prospect that the decline in canine semen quality has an environmental cause and begs the question whether a similar effect could also be observed in human male fertility.”