And possibly in their best friends.
Dog sperm quality has been gradually declining over the past 26 years — a trend that mirrors reported declines in human sperm quality in the last several decades.
In a study published in the journal Scientific Reports, a research team monitored the semen quality of dogs in a breeding program between 1988 and 2014. Anywhere from 42 to 97 dogs, consisting of Labrador retrievers, golden retrievers, German shepherds, curly coat retrievers, and border collies, were studied each year.
Over the study period, sperm became less motile (even after the dogs with the worst sperm were removed from the study), and this coincided with a decline in the proportion of male pups being born. A birth defect called cryptorchidism, in which one or both testes do not descend, also became more prominent through the years.
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After the sperm quality trends were firmly established, the researchers looked back the dogs’ medical records to find out what was going on. It turned out that most of their sperm and testes contained environmental chemicals called PCBs and phthalates.
In a separate experiment, the researchers established that exposure to these chemicals reduced sperm motility and viability, implicating them as a potential reason why male fertility has been falling.
The source of these chemicals was traced back to the food the dogs were eating. As the researchers report, “the same chemicals were detected in a range of commercially available dog foods.”
These same chemicals are also present in human food, which may partly explain the worrying trends of declining human sperm quality and quantity over the past several decades.