Is declining dog fertility a warning for people?

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New research finds that sperm quality in a population of stud dogs studied over a 26-year period had fallen significantly.

The work, published in Scientific Reports, highlights a potential link to environmental contaminants, after they were able to demonstrate that chemicals found in the sperm and testes of adult dogs—and in some commercially available pet foods—had a detrimental effect on sperm function at the concentrations detected.

Man’s best friend

Scientists are debating a reported significant decline in human semen quality and these results with our close companions may offer a new piece of the puzzle, say the researchers.

“This is the first time that such a decline in male fertility has been reported in the dog and we believe this is due to environmental contaminants, some of which we have detected in dog food and in the sperm and testes of the animals themselves,” says Richard Lea, reader in reproductive biology in the University’s of Nottingham’s School of Veterinary Medicine and Science, who led the research.

“While further research is needed to conclusively demonstrate a link, the dog may indeed be a 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.”

Fewer and fewer normal sperm

The study centered on samples taken from stud dogs at an assistance dogs breeding center over the course of 26 years. “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,” says Gary England, professor of comparative veterinary reproduction at the School of Veterinary Medicine and Science, who oversaw the collection of semen.

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The work included five specific breeds of dogs—Labrador retriever, golden retriever, curly coat retriever, border collie, and German shepherd—with between 42 and 97 dogs studied each year.

Semen was collected from the dogs and analyzed to assess the percentage of sperm that showed a normal forward progressive pattern of motility and that appeared normal under a microscope (morphology).

Over the 26 years of the study, they found a striking decrease in the percentage of normal motile sperm. Between 1988 and 1998, sperm motility declined by 2.5 percent 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 percent per year.

In addition, the team discovered that the male pups generated from the stud dogs with declining semen quality had an increased incidence of cryptorchidism, a condition in which the testes of pups fail to correctly descend into the scrotum.

‘A unique set of reliable data’

Sperm collected from the same breeding population of dogs, and testes recovered from dogs undergoing routine castration, were found to contain environmental contaminants at concentrations able to disrupt sperm motility and viability when tested.

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The same chemicals that disrupted sperm quality were also discovered in a range of commercially available dog foods—including brands specifically marketed for puppies.

“We looked at other factors which may also play a part, for example, some genetic conditions do have an impact on fertility. However, we discounted that because 26 years is simply too rapid a decline to be associated with a genetic problem,” says Lea.

Over the past 70 years, studies have suggested a significant decline in human semen quality and a cluster of issues called “testicular dysgenesis syndrome” that affect male fertility and include increased incidence of testicular cancer, the birth defect hypospadias, and undescended testes.

However, declining human semen quality remains a controversial issue—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.

“The Nottingham study presents a unique set of reliable data from a controlled population which is free from these factors,” adds Lea. “This raises the tantalising 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.”

Source: University of Nottingham