New research has discovered that the fertility of dogs may have fallen sharply over the past three decades, and the findings could have implications for human reproductive health.
The research, published in Scientific Reports, found that sperm quality in a population of stud dogs fell ‘significantly’ over a 26-year period.
The researchers say there is a potential link to environmental contaminants. They found chemicals linked to fertility issues and birth defects in the sperm and testes of the dogs and even in their food.
The chemicals observed were a type of phthalate and PCB. PCBs were once used in electrical equipment but were banned in the 1980s while phthalates have attracted controversy more recently.
The study’s lead author, Dr Richard Lea, said: ‘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.
‘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.’
This study, which followed dogs from 1988 to 2014, was based on the idea that, since dogs live among humans and experience a similar environment, they can shed light on the effects of this environment.
The trend being studied was men’s declining sperm count and quality over the last 70 years, and the increase in cryptorchidism (that is, testes not dropping to the scrotum in infants), which have been linked with the rise in industrialisation and the increase in some environmental chemicals which are thought to be hormone disrupters in developing adults.
The results were significant — canine sperm quality decreased steadily from around 90 per cent in terms of motility (ie, the ability to move) in 1988 to about 60 per cent in 2014. Morphology, or the size and shape of the sperm, was fairly consistent, as was the total output.
The problem with this study is that the observations were subjective and entirely dependent on the operator behind the microscope. People will perceive the same image differently — something that is hard to standardise. To an extent, this study accommodated for this by using computer assisted analysis.
The amount of cryptorchidism in the dogs made a slight trend upwards between 1994 and 2014, and the amount of male dogs born over the same time decreased slightly.
The second part of the study looked at the presence of environmental chemicals in dog food, testes and semen. The chemicals observed were DEHP (diethylhexylphthalate) and PCB153 (polychlorinated bisphenol 153). Detectable levels of the chemicals were found. Similar levels of these chemicals have been observed in men.
Interestingly, the dog food also tested positive for these chemicals, with one brand showing particularly high levels.
In summary, the study shows preliminary evidence that some environmental chemicals may have an effect on sperm quality in dogs, and by extension in humans, while having an effect on cryptorchidism too. What makes the findings more relevant is that the dogs with the least mobile sperm were removed to improve the quality of the study.