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The New 'Dog' Twist on a Vexing Human Problem

commercial dog food

Story at-a-glance -

  • A 26-year study suggests the quality of sperm in intact male dogs in the U.K. has decreased dramatically since 1988
  • The researchers discovered hormone-disrupting chemicals in the dogs’ testes and sperm at levels high enough to have a harmful effect on sperm function
  • The same chemicals were also found in certain dry and canned commercial dog foods
  • A previous study linked similar chemicals in fish-flavored cat foods to feline hyperthyroidism
  • It’s impossible to completely protect your pet from environmental chemicals, but feeding a fresh organic diet and following a detoxification protocol can reduce your dog’s or cat’s toxic load

By Dr. Becker

Researchers at the University of Nottingham School of Veterinary Medicine and Science in the U.K. have determined the fertility of dogs has decreased precipitously over the last 30 years.

Their study, which was published recently in the journal Scientific Reports, suggests the quality of sperm in a population of intact adult male dogs has fallen significantly over a 26-year period.1

The researchers discovered hormone-disrupting chemicals in the dogs’ testes and sperm — the same chemicals also found in some commercial dog foods — in concentrations high enough to have a harmful effect on sperm function.

The scientists suspect the presence of these chemicals may play a role in the reported significant decline in the quality of human sperm as well. According to lead researcher Dr. Richard Lea:

"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.

‘While further research is needed to conclusively demonstrate a link, the dog may indeed be a sentinel for humans — it shares the same environment, exhibits the same range of diseases, many with the same frequency and responds in a similar way to therapies.’"2

Dogs’ Sperm Motility Declined by 35 Percent Over 26 Years

The dogs involved over the 26-year study (1988 to 2014) were intact male assistance dogs. Five breeds were represented, including the Labrador Retriever, Golden Retriever, Curly Coated Retriever, Border Collie and German Shepherd. From 42 to 97 dogs were studied each year.

All semen samples were processed and analyzed by the same laboratory, using the same protocols. The sperm was assessed for normal forward movement patterns and normal appearance under a microscope.

Over the 26-year study, the researchers noted a conspicuous decrease in the number of normal sperm, with sperm motility falling by around 35 percent overall.

During a 10-year period from 1988 to 1998, sperm motility declined by 2.5 percent per year. From 2002 to 2014, and after dogs with decreased fertility were retired from the study, the decline was measured at a rate of 1.2 percent per year.

The slowing decline in the final years of the study could also be a result of stricter regulations on the use of certain hormone disrupting chemicals.

Another irregularity the researchers discovered was that male offspring of dogs with decreased sperm quality showed a greater tendency toward cryptorchidism, a condition in which the testicles don’t descend normally into the scrotum. In addition, they noted a decline in the number of male puppies born versus females.

Flame Retardants, Other Chemicals Found in Dogs’ Sperm Also Found in Commercial Dog Foods

The sperm collected from the dogs in the study, as well as the testes of neutered study dogs, were found to contain environmental contaminants at levels high enough to interfere with sperm motility and sustainability.

The same chemicals were also found in a range of commercial dog foods, including canned, dry and puppy formulas. From the study:

“ECs [environmental chemicals], 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.”3

These chemicals, which are used to make plastics more flexible or furniture flame-retardant, can end up in commercially processed pet food, leaching into the food from packaging and result in contamination of plants and livestock.

Exposure to Flame-Retardant Chemicals Also Linked to Feline Hyperthyroidism

Dogs aren’t the only animals being exposed to chemicals in commercial pet food.
The sudden appearance and rapid increase in cases of hyperthyroidism in cats has generated research into potential causes, one of which appears to be exposure to flame-retardant chemicals (polybrominated diphenyl ethers, or PBDEs). PBDEs are recognized endocrine and thyroid disruptors.

A recent study suggests fish-flavored cat food could be a culprit.4 A team of Japanese scientists evaluated cat food and feline blood samples and discovered that the type of polychlorinated biphenyl (PCB) and PBDE byproducts found in both the food and blood samples are derived from marine organisms.

The researchers were able to simulate the way in which the bodies of cats convert the type of chemical present in the food into the type of chemical seen in the cats’ blood samples.

Based on their results, the team concluded that the byproducts detected at high levels in cats' blood samples likely came from fish-flavored food and not other forms of exposure to PCBs or PBDEs. However, further work is needed to determine the link between the metabolites (byproducts) and hyperthyroidism.

Why Fish-Flavored Cat Foods Are a Special Problem

Dr. Jean Hofve of Little Big Cat explains the link between fish-based cat foods, PBDEs and feline hyperthyroidism:

“There is a link between the feeding of fish-based cat foods and the development of hyperthyroidism, which is now at epidemic levels. New research suggests that cats are especially sensitive to PBDEs … chemicals found at higher levels in both canned and dry cat foods than dog foods; and more in dry than canned cat foods.

Fish-based foods are even worse, because marine organisms produce PDBEs naturally and can bioaccumulate up the food chain to high levels in fish … Predatory fish at the top of the food chain, such as tuna and salmon, may contain very elevated levels of heavy metals (including mercury) as well as PCBs, pesticides and other toxins.

Tilefish (listed on pet food labels as 'ocean whitefish') are among the worst contaminated, along with king mackerel, shark and swordfish.

These fish are so toxic that the FDA advises women of child-bearing age and children to avoid them entirely; and recommends only one serving of albacore tuna per week due to its high mercury levels (yellow or 'light' tuna is far safer for us, but still inappropriate for cats). If these fish are dangerous to children, cats are at even higher risk!

PCBs (polychlorinated biphenyls) in particular are toxic industrial chemicals that were banned in the U.S. in 1979. However, they are used elsewhere in the world; and because they are stable in the environment, they are still a concern in ocean waters.

Recent research found high levels of PCBs in dry and canned pet foods. Scientists also found that cats retain PCB metabolites in their blood longer than dogs.”5

How to Cleanse Your Pet’s Body of Chemical Contaminants

The chemicals discussed above and others are pervasive in plant and sea life, and food animals as well. If you’re concerned about contaminants in commercial pet food, my advice is to make nutritionally balanced dog or cat meals at home using as many fresh, organic ingredients as you can afford. An alternative would be to purchase commercially available, human-grade, fresh or dehydrated or freeze-dried organic pet food.

It’s very difficult to avoid all environmental toxins these days, and there are many different ways our pets are exposed. If you're wondering if your own pet is carrying a toxin load, unfortunately there's no doubt about it. The truth is that virtually every pet has measurable amounts of chemicals in their body. That’s why I recommend periodic detoxification depending on your dog’s or cat’s level of exposure to toxins.