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Decline in dog sperm quality 'could be a concern for humans'

Wednesday 10 August 2016

"Study showing decline in dog fertility may have human implications," The Guardian reports. The study in question found a decline in the quality of British dogs' sperm since 1988.

The worry is that this is being caused by environmental factors that may also affect human sperm quality and count.

The study aimed to assess changes in sperm quality in dogs over time. Within this, the researchers also looked at whether chemicals in the environment may play a role.

Researchers reported a decline in sperm quality in canines over the 26-year study period, as well as an increase in the incidence of cryptorchidism, the absence of one or both testes from the scrotum.

In humans this is often referred to as having undescended testicles, and has been linked to male infertility and an increased risk of testicular cancer in later life.

The researchers also detected the presence of several environmental chemicals in the canine adult testis and semen.

Media interest revolved around the idea that the decline in dogs' sperm quality is linked to the decline in fertility that has also been observed in men.

But because of the design of this study it's not possible to extrapolate the trends seen in canines to humans.

The study does, however, highlight the potentially detrimental effect of chemicals in the environment on both humans and animals.

Possible risk factors for a low sperm count include smoking, poor diet, excessive alcohol consumption and drug use.

Where did the story come from?

The study was carried out by UK researchers from the University of Nottingham, Nottingham Trent University, the James Hutton Institute, and the Guide Dogs for the Blind Association.

It was funded by the Guide Dogs for the Blind Association and the University of Nottingham.

The study was published in the peer-reviewed journal, Scientific Reports. It is available on an open access basis and is free to read online.

Generally, the media headlines – and, to be fair, our own headline – centred on the notion that declines in dog fertility would have implications in humans.

But the study only looked at trends in canines – the link to humans is merely speculation that requires further research.

What kind of research was this?

This animal study aimed to assess changes in sperm quality in dogs over time. Within this, the researchers looked at whether chemicals in the environment may play a role in the observed trends.

Previous research found the incidence of testicular cancer in dogs has increased in parallel with rates observed in humans.

A similar pattern has been seen with undescended testicles. It has been suggested that this is because dogs and humans share the same environment.

Animal studies like this one are useful research for getting an indication of biological processes and how things may work in humans, but it's important to remember that we aren't identical to animals and findings can't necessarily be extrapolated.

What did the research involve?

Researchers collected semen samples annually over a span of 26 years between 1988 and 2014 from stud dogs bred to help the disabled as part of an assistance dog breeding programme.

The study involved five breeds of dog: Labradors, Border Collies, German Shepherds, Curly Coated Retrievers and Golden Retrievers.

The researchers tested a total of 1,925 ejaculates from 232 different dogs. The samples were assessed for trends in sperm motility, volume (ml), sperm concentration, total sperm output and total number of live sperm.

Ejaculates were assessed from 14 stud dogs to measure chemicals in their sperm, and a decline in sperm quality was observed.

The effects of environmental chemicals on sperm quality (sperm function and viability) were also tested for. And the chemical content in dog food (dry dog biscuit and wet meat) was also measured.

The data was analysed to evaluate changes in sperm quality over time. Confounding effects, such as the age of the dog and body weight, were controlled for.

In addition, the incidence of cryptorchidism in male offspring was evaluated from 1995 to 2014 using records from the National Breeding Centre database.

What were the basic results?

Overall, a decline in sperm quality in canines was observed over the 26-year study period, as well as an increase in the incidence of cryptorchidism in their male offspring during an overlapping timeframe.

A decrease in the percentage of sperm with normal motility was seen at a rate of 2.5% per year from 1988 to 1998.

After the removal of dogs with the poorest semen quality from the study, a further decrease of 1.2% per year was observed from 2007 to 2014.

Alongside this, the percentage of live sperm declined and the output of total sperm increased.

The incidence of cryptorchidism in puppies increased from 1995 to 2014. Over the same period, the number of male puppies born per litter declined.

However, the decrease was no longer observed when postnatal mortalities and stillbirths were excluded from the analysis.

The environmental chemicals polychlorinated bisphenol (PCB) congeners, 5-polybrominated diphenyl ether (PBDE) congeners and diethylhexyl phthalate (DEHP) were detected in the adult testis and semen.

How did the researchers interpret the results?

The researchers concluded that, "This study demonstrates that in a population of stud dogs, sperm motility has declined over a 26-year period.

"Although the mechanism remains to be determined, we have shown that chemicals present in testis and ejaculate directly affect sperm function and viability." 

Conclusion

This animal study aimed to assess changes in sperm quality in dogs over time. Within this, the researchers looked at whether chemicals in the environment may play a role in the observed trends.

The study reported a decline in sperm quality in canines over the 26-year study period, as well as an increase in the incidence of cryptorchidism in the dogs' male offspring during an overlapping timeframe.

The media interest in this study revolves around the idea that the decline in dogs' sperm quality can be linked to the decline in fertility also observed in men.

Further research would need to be conducted in humans to investigate the reasons behind the suspected decline.

The researchers also detected the chemicals PCB congeners, PBDE congeners and DEHP in the canine adult testis and semen.

But although these findings are interesting, the study did not aim to – and is not able to – confirm a link between environmental chemicals and sperm quality.

Professor Allan Pacey, Professor of Andrology at the University of Sheffield, said: "This is an interesting study which suggests that the sperm quality in a population of dogs enrolled in a breeding programme in the UK may have declined over a 26-year period, in a manner which mimics what others have claimed may have happened in the human male over the last century.

"Whilst I am not a strong supporter of the idea that sperm quality in humans has declined significantly – we have changed too much about how we make these measurements to be certain that the decline is real – what is interesting about this study in dogs is that the authors also see an increase in problems of the dogs' testicles (cryptorchidism) and a decline in the number of female dogs born over the study period."

Ways to possibly increase the quality and quantity of your sperm include moderating your alcohol consumption, stopping smoking, staying in good shapeexercising regularly and having a healthy, balanced diet.  

Analysis by Bazian
Edited by NHS Website