Decline in canine fertility linked to contaminants
Environmental contaminants were found in the sperm and testes of stud dogs, and in some commercial pet foods, at concentrations that could affect fertility.
The fertility of male dogs has fallen significantly over the past three decades, according to a new study which suggests environmental contaminants could be responsible.
Scientists from the University of Nottingham found chemicals in the sperm and testes of adult stud dogs that could disrupt the motility and viability of sperm at the concentrations detected. The same chemicals were also found in a range of commercially available pet foods.
The results could shed new light on declining fertility in human males, which scientists continue to debate.
Over a period of 26 years, the team from Nottingham collected and analysed semen from dogs at an assistance dog breeding centre. Between 42 and 97 dogs were studied every year, with a focus on five breeds - Labrador retrievers, golden retrievers, curly coated retrievers, border collies and German shepherd dogs.
The results have been published today in the academic journal Scientific Reports.
In just under three decades, a striking decline was seen in the percentage of normal motile sperm. From 1988-1998, sperm motility fell by 2.5 per cent a year and continued to decline at a rate of 1.2 per cent between 2002 and 2014, after a short period when dogs with compromised fertility were retired from the study.
Male puppies produced by dogs with declining sperm quality were also found to have a higher rate of cryptorchidism - a condition where the testes of the puppy fail to descend correctly into the scrotum.
Sperm from this breeding population and testes from dogs that had undergone routine castration contained environmental contaminants at a concentration that could have a detrimental effect on sperm quality. These contaminants were also found in some pet foods, including those made specifically for puppies.
Researchers say they considered other factors, such as genetics, that could play a part in fertility. But according to lead author, Dr Richard Lea, this was discarded, as the period of 26 years "is simply too rapid a decline to be associated with a genetic problem."
The team believe their work could have important implications for human fertility research. Studies over the past 70 years have indicated a significant decline in the quality of human semen, but it remains a controversial topic, with many criticising the variability of the data, as well as the changes to laboratory methods, training of laboratory personnel and improvements to quality control over the years.
However, Dr Lea added: "The Nottingham study presents a unique set of reliable data from a controlled population which is free from these factors. This raises the tantalising prospect that the decline in canine semen quality has an environmental cause and begs the question whether a similar effect could also be observed in human male fertility."
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