Why men are in the doghouse when it comes to collapsing fertility levels

They say dogs are a man’s best friend. Turns out that was the vital clue in helping science understand why both are experiencing a dramatic decline in fertility.

We slip them a sausage — or three. We snuggle with them on the couch. We roll with them on the floor. We may even admit to letting them sleep on the bed.

Dogs, after all, are part of the family.

And that’s led science to some disturbing conclusions.

The collapse in human sperm quality has been dramatic in the past 80 years. Between then and now, sperm motility (the energy with which sperm swim) has been cut in half.

Nobody knows why.

Turns out, the same has been happening to our male domestic dog companions.

Studies carried out over the past quarter century have tracked a 30 per cent decline.

And that’s an important clue.

Many things are suspect when it comes to declining fertility.

Stress. Economic uncertainty. Diet. Fitness. Environment.

Dogs experience some — but not all — of these factors, and in different ways.

Because of this, a study published in the journal Nature: Scientific Reports has pinned down what is afflicting both dog and man.

It’s their shared household.

Blame the dog? Well … no. It’s actually everything we share.

DOGGED PROBLEM

It’s easier to examine animals, both for ethical and privacy reasons.

But, with the smoking gun provided by canine health, researchers were able to seek links with their male human counterparts.

“We now believe this is the same in pet dogs because they live in the same domestic environment and are exposed to the same household contaminants,” University of Nottingham researcher and study lead author Dr Rebecca Sumner says.

“The dog, therefore, seems to mirror what we see in the human and, a bit like a ‘canary in the coal mine,’ provides a way of monitoring chemical effects in humans,” co-author Dr Richard Lea added.

The research points a finger at two man-made chemicals found in the family home: Diethylhexyl phthalate (DEHP) and polychlorinated biphenyl 153 (PCB153).

DEHP is found in plastics as it helps determine how flexible they are.

As a result, it is everywhere in the house — from carpets, curtains and wiring through to clothes, containers and toys.

Its residue can be found in food and drink.

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PCB153 used to be used globally.

It was banned in 2001 as the chemical — often used in paints, coolant fluids and copy paper- was found to be a definite carcinogen.

But it is a long-lived chemical, and remains widespread through our environment — and food chain.

The researchers quickly found identifiable levels of both in domestic dogs, and dog food.

“It was important to test this idea by looking at the effects of the two chemicals on sperm,” Dr Lea says.

Dogs have turned out to be man’s best friend in more ways than expected.

TOXIC HOUSEHOLDS

To safely test the potential link, the University of Nottingham researchers took 11 samples of dog semen and nine from humans.

In the laboratory, they combined them with the same levels of DEHP and PCB153 as found in the environment of the dogs they had previously studied.

The outcome?

The exposed sperm from both man and dog produced significantly lower sperm motility and higher levels of DNA fragmentation. This means reduced fertility.

It’s a small sample. But it adds to a growing pool of scientific evidence linking these two chemicals to fertility issues.

The researchers say such household environmental pollutants feature heavily in the Western way of life, and could explain why our culture is affected the worst.

The team now wants to initiate a larger-scale study into the link between fertility, location, culture and exposure to these pollutants.

“This new study supports our theory that the domestic dog is indeed a ‘sentinel’ or mirror for human male reproductive decline,” Dr Lea says.

“Our findings suggest that man-made chemicals that have been widely used in the home and working environment may be responsible for the fall in sperm quality reported in both man and dog that share the same environment.”

And, in tackling the issue, dogs may once again prove to be man’s best friend: “Dogs may be an effective model for future research into the effects of pollutants on declining fertility, particularly because external influences such as diet are more easily controlled than in humans,” Dr Sumner says.