At the heart of the research is not the dog, but the question of male human fertility.
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Is our environment damaging canine fertility?
Lea and his team are yet make any definitive conclusions about the cause, but they did confirm the presence of environmental chemicals called PCBs and phthalates in both the dogs’ semen and in testicles removed by vets during routine desexing procedures.
And scientists believe that because they can link the decline in fertility to chemicals in dogs’ food and living environment, the same chemicals could be behind a reduction in human fertility. The samples were taken over a period of 26 years.
Richard Lea, of Nottingham University’s school of veterinary medicine and science, and colleagues collected samples of semen from a carefully monitored population of labradors, border collies, German shepherds and golden retrievers used as stud to breed dogs meant to help the disabled.
The fertility levels of dogs may have suffered a decline over the past 30 years.
Motility refers to the ability of something to move spontaneously. Professor Gary England, Nottingham’s foundation dean of veterinary science, supervised all of the sampling, and each sample was handled by only three technicians over the course of the 26-year study. “And the incidence of undescended testicles [where testes fail to correctly descend into the scrotum] in male puppies, also small, had a 10-fold increase, to 1 percent from 0.1”.
The next generation of stud dogs saw a further reduction of sperm motility between 2002 and 2014, by 1.2 percent per year.
Tests revealed that the concentrations of these contaminants were high enough to interfere with sperm motility and viability.
The researchers also found traces of the same chemicals in the food that handlers gave the dogs. The foods included brands specifically sold for puppies.
They looked at other possible factors like genetic condition but ultimately ruled it out because the rate of the decline is too steep after a couple of decades. For the past 70 years, there has been a decline in human sperm quality, and a rise in testicular cancer cases as well as genital tract problems.
Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism, Scientific Reports (2016).
Meanwhile, Allan Pacey, spokesperson for the British Fertility Society, said the study could serve as a warning for humans.
“The Nottingham study presents a unique set of reliable data from a controlled population which is free from these factors”.
In a press release, Lea said it is for the first time ever when such a fall in male fertility has come into notice in the dogs and according to them this is because of environmental contaminants, some of which have been found in dog food and in the animal’s sperm and testes.
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Lea says dogs may serve as sentinels for humans who are exposed to these types of chemicals from different sources since a dog “shares the same environment, exhibits the same range of diseases, many with the same frequency and responds in a similar way to therapies”.
