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For 26 years, between 1988 and 2014, a team of researchers collected and analyzed sperm samples from five dog breeds, including the Labrador retriever, golden retriever, curly coat retriever, border collie and German shepherd. The results, detailed this week in the journal Scientific Reports, suggest canine fertility is rapidly declining.
Each year, scientists measured the motility of sperm samples collected from dozens of dogs — both from stud dogs and from the testicles of dogs prior to castration. Motility is the normal forward momentum of sperm in the semen sample.
Researchers measured a 2.5 percent decline in sperm motility between 1988 and 1998. Between 2002 and 2014, after several stud dogs with compromised semen were retired from the research program, scientists measured a 1.2 percent decline.
Among the same dog populations, researchers measured significant levels of several environmental contaminants linked with fertility problems.
“We looked at other factors which may also play a part, for example, some genetic conditions do have an impact on fertility,” lead researcher Richard Lea, a specialist in reproductive biology at the University of Nottingham, said in a news release. “However, we discounted that because 26 years is simply too rapid a decline to be associated with a genetic problem.”
Researchers also found the offspring of dogs with declining semen quality were at greater risk of cryptorchidism, a condition whereby one or both testicles fail to descend.
Studies have suggested similar decline in semen quality among humans, as well as an increase in cryptorchidism, but some studies question the reliability of epistemological data.
No causes of the decline of human male fertility have been confirmed, but the latest research suggests the same factors triggering a decline in canine fertility could explain poor motility among human sperm.
Researchers say their latest analysis is free of the variability issues that have plagued studies of human semen quality.
“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,” Lea concluded.