Doomsday for Dogs? Are Declines in Fertility Due to Food?

Males of 5 purebreds show declining sperm quality and increasing cryptorchidism

Posted Aug 12, 2016

Are dogs "canaries in the coal mine" indicating serious environmental effects on reproduction?

A recent study by Richard Lea and his colleagues in Scientific Reports called "Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism" has raised warning flags about what's happening to males of five purebreds. The abstract for this essay, which is available online, reads:

Adverse temporal trends in human semen quality and cryptorchidism in infants have been associated with exposure to environmental chemicals (ECs) during development. Here we report that a population of breeding dogs exhibit a 26 year (1988–2014) decline in sperm quality and a concurrent increased incidence of cryptorchidism in male offspring (1995–2014). A decline in the number of males born relative to the number of females was also observed. ECs, including diethylhexyl phthalate (DEHP) and polychlorinated bisphenol 153 (PCB153), were detected in adult dog testes and commercial dog foods at concentrations reported to perturb reproductive function in other species. Testicular concentrations of DEHP and PCB153 perturbed sperm viability, motility and DNA integrity in vitro but did not affect LH stimulated testosterone secretion from adult testis explants. The direct effects of chemicals on sperm may therefore contribute to the decline in canine semen quality that parallels that reported in the human.

This study has received global attention and a good review can be found in Jan Hoffman's essay in the New York Times called "A Warning for Dogs, and Their Best Friends, in Study of Fertility." This essay begins:

For decades, generations of dogs have been bred, raised and trained as service animals for disabled people at a center in England: Labrador retrievers, golden retrievers, curly coat retrievers, Border collies and German shepherds. Scientists at the University of Nottingham realized that they had an ideal opportunity to study dog fertility — five types of purebreds, uniform conditions, one location, systematic record-keeping. So in 1988, they started annually testing the sires’ sperm.

In a study published Tuesday in Scientific Reports, they found declining sperm quality and other effects that they believe could be related to environmental causes. Over 26 years, motility, the progressive forward movement of sperm, dropped 30 percent in all five breeds. Although it has not reached a critical point — the dogs are still successfully impregnating — further decline in motility could eventually harm their ability to reproduce.

The principal investigator of this study, Richard G. Lea, who works at the School of Veterinary Medicine and Science at the University of Nottingham, notes, "The dogs who share our homes are exposed to similar contaminants as we are ... So the dog is a sentinel for human exposure." They are, in a way, "canaries in the coal mine" indicating serious environmental effects on reproduction. 

The researchers were able to rule effects of inbreeding and also "noticed that the mortality rate of the female puppies, although small, showed a threefold increase. And the incidence of undescended testicles in male puppies, also small, had a 10-fold increase, to 1 percent from 0.1."

Food is likely a major source of the deleterious chemicals

Of course, anyone who lives with a dog wants to know the role of food in these declines in fertility and increased cryptorchidism, and while the researchers can't say food is a direct or sole source of the chemicals found in the dog's testes, Dr. Lea notes, "it was probably a major one."

Even a skeptic of such studies, Peter Hansen, a professor of reproductive biology at the University of Florida, notes this study was very rigorous. He notes, "It’s much more clear from their data that there was a decline over time, which agrees with the human data but doesn’t suffer from the same research problems.”

I knew that many dog researchers and people who choose to share their home with dogs were paying close attention to this study, so I reached out to dog expert Dr. Michael W. Fox to ask him his opinion about this research. He kindly sent me this statement titled "Commercial Dog Foods Affect Fertility and Sexual Development" to appear in his Animal Doctor syndicated newspaper column. Dr. Fox writes:

Researchers Richard G. Lea and associates published on Aug 9th, 2016, a report entitled Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism. ... Against the background of declining semen quality and rising incidence of undescended testes (cryptorchidism) in humans associated with exposure to environmental chemicals (ECs) during development they report that “a population of breeding dogs exhibit a 26 year (1988–2014) decline in sperm quality and a concurrent increased incidence of cryptorchidism in male offspring (1995–2014). A decline in the number of males born relative to the number of females was also observed. ECs, including diethylhexyl phthalate (DEHP) and polychlorinated bisphenol 153 (PCB153), were detected in adult dog testes and commercial dog foods at concentrations reported to perturb reproductive function in other species”.

Estrogen-mimicking, endocrine-disrupting chemicals have become virtually ubiquitous in many of the foods we consume, some of which, along with their byproducts, are included in most manufactured pet foods; in the can-linings of moist, and in plastic bagging and wrapping of dry and semi-moist foods. Plastic may also be processed into the manufactured food along with discarded meats, packaging and all.

Food wrappers and other industrial and commercial products from firefighting foam to water-repellant clothing contain poly-and perfluoroalkyl substances, or PFAS, detected in drinking water, have endocrine disrupting and carcinogenic properties.

Dioxins, predominantly released as byproducts of human activities such as incineration and fuel combustion, are a most potent class of carcinogens and endocrine disruptors. They are ubiquitous in the environment, and from the soil and vegetation undergo bioaccumulation in the fat (tallow) of cattle, and sea foods, especially farmed salmon, which are common pet food ingredients. Their adverse impact on wildlife reproduction and sexual development in several aquatic and terrestrial species has been well documented.

Other estrogen-mimicking and endocrine disrupting contaminants of pet (and human) foods include glyphosate and other herbicide residues in corn and other cereals along with phytoestrogens in soy products especially in GMO soy, a widely used pet food ingredient.

Aflatoxin B1—yet another endocrine disruptor-from the mold on corn and other cereals, is often found in dry dog foods which are recalled too late to save many dogs from acute toxicity and death. Aflatoxins, dioxins and other endocrine disruptors, estrogen mimics, carcinogens and obesogens have harmful consequences in extremely low concentrations in the diet over an extended time period with possible synergism operating where one contaminant increases the toxicity of one or more others; and prenatal, epigenetic, developmental effects on the offspring of exposed parents. (For additional details visit www.drfoxvet.net and see "Chemical-related human diseases in companion animals.") 

Drs. Lea and Fox agree that food is central to what is happening to male dogs. Dr. Lea's study, along with Dr. Fox's review, raise numerous questions about what is happening to dogs and, of course, to numerous other species including humans. Dr. Lea's study focused on males and similar research is being undertaken on females. 

Dogs may well be "a sentinel for human exposure" and serve as "canaries in the coal mine" indicating serious and widespread environmental effects on reproduction that cut across different species.