Male dog fertility has sharply declined over the past three decades, according to a new study that suggests some commonly available pet foods are contributing to the problem.
Environmental contaminants found in many dog foods, including some puppy chow formulations, appear to be the culprits. The findings, published in the journal Scientific Reports, link the contaminant-containing food to the drop in male dog sperm quality.
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"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," Richard Lea, a reproductive biology specialist at the University of Nottingham's School of Veterinary Medicine and Science, said in a press release.
Earlier studies found chemicals such as PFCs, PCBs and pesticides like DDT in foods, including pet foods. Many of these substances were banned some time ago, but because they don't break down well in the environment, they can persist.
Lea says dogs may serve as sentinels for humans who are exposed to these types of chemicals from different sources since a dog "shares the same environment, exhibits the same range of diseases, many with the same frequency and responds in a similar way to therapies."
The study, conducted over a period of 26 years, centered on five dog breeds: Labrador retriever, golden retriever, curly coat retriever, border collie and German shepherd. Semen was collected from between 42 to 97 dogs for each of these breeds every year over the course of the study. Lea and his colleagues analyzed the samples to assess the percentage of sperm that showed normal movement and that appeared healthy.
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Between 1988 and 1998, healthy sperm movement (motility) declined by 2.5 percent per year. Following a short period when the male breeding 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.
The researchers also discovered that male puppies fathered by the dogs in the study with declining semen quality had an increased incidence of cryptorchidism, a condition in which the testes of the pups fail to correctly descend into the scrotum.
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 health, according to Lea and his team. The scientists detected the same chemicals 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 (in reducing male dog fertility), for example, some genetic conditions do have an impact on fertility," Lea said. "However, we discounted that because 26 years is simply too rapid a decline to be associated with a genetic problem."
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