Male dog fertility on the decline, and their food might be to blame

Scientists tracked the sperm quality of five different breeds of dog over a 26-year period

By monitoring the sperm quality in dogs across the last few decades, scientists at the University of Nottingham have uncovered an alarming decline in the animal's fertility. Their study suggests that the sperm quality may have been impacted by contaminants in dog food, and the scientists say the findings could possibly have some parallels with human fertility as well.

Over a 26-year period, the scientists tracked the sperm quality of five different breeds of dog: labrador retrievers, golden retrievers, curly coat retrievers, border collies and German shepherds. The researchers studied between 42 and 97 dogs each year, collecting samples in order to measure the levels of healthy motile sperm, that is, sperm capable of reaching the egg.

Between 1988 and 1998, the team recorded a 2.5 percent decline in the amount of motile sperm per year. Then between 2002 and 2014, this trend continued at a rate of 1.2 percent each year. The researchers also found that male pups produced by dogs with declining sperm quality had an increased incidence of cryptorchidism, a condition where one or both of the testicles don't settle in the scrotum properly.

The samples collected throughout the study, along with testicles collected from dogs that had undergone castration, contained environmental contaminants in high enough concentrations to affect sperm motility. These same chemicals were also discovered in various commercially available dog foods.

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

The researchers say the findings raise the question of whether a purported decline in human semen quality over the last 70 years could also be a result of environmental factors. The veracity of this data has been called into question, however, with some questioning the consistency of the testing methods, but the team says the findings could help to shed more light on the debate.

"The Nottingham study presents a unique set of reliable data from a controlled population which is free from these factors," says Lea. "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."

The research was published in the journal Scientific Reports.

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