August 9, 2016

expert reaction to study looking at dog fertility and environmental contaminants

Publishing in the journal Scientific Reports a group of researchers have assessed fertility in a group of dogs and report a decline in sperm motility since 1988 and suggest a potential link to the presence of certain chemicals.

Prof. Richard Sharpe, Group Leader of Male Reproductive Health Research Team, University of Edinburgh, said:

“The interest in the present study in dogs is its potential relevance to men, for reasons that follow. The debate as to whether sperm counts in men have fallen from much higher values before ~1950 remains controversial and is unlikely to ever be resolved. What is beyond question is that, today, one out of every 6 young men across Northern Europe has a sperm count low enough to impact couple fertility, especially where the female partner is >35. The studies that provided evidence for ‘falling sperm counts’ in men did not look at changes in sperm motility.

“Intertwined with the sperm count issue is whether the ‘possible’ decrease in sperm counts is due to exposure to man-made environmental chemicals, a debate that is also deeply controversial. The limited available data is inconclusive/unconvincing, in part because of considerable difficulties in doing definitive studies in humans to address this. Studying what has happened to sperm counts in ‘man’s best friend’ is therefore an innovative piece of thinking, especially as dogs share much of our environment.

“The study is technically well done and the authors do not over-interpret their findings. At face value they provide convincing evidence that sperm motility in male dogs used for breeding (studs) has fallen progressively since ~1990. In contrast, total sperm output (=sperm count) did not change with time.  Although at face-value the latter does not fit with the human data, it’s not really possible to compare sperm counts in dogs and man because dogs store sperm and humans don’t. This difference is very important because, in men, sperm count reflects sperm production whereas in dogs it reflects production plus storage (storage enables animals to maintain a high sperm count over many ejaculations, whereas in a man sperm count will decline with repeated ejaculations because there is no storage). Does this difference mean that the dog study is not relevant to humans?

“What the study also shows is that the incidence of testis non-descent (cryptorchidism) in dogs has increased across the same timescale as the drop in dog sperm motility.  There is reasonable evidence that in man, incidence of cryptorchidism has increased over the timescale of the postulated fall in sperm counts.

“In conclusion, the study does not help to resolve the ‘falling sperm count’ debate in humans.  It adds to the circumstantial evidence that exposure to common environmental chemicals is associated with adverse changes in semen quality (and provides some evidence for cause and effect). However, it takes us no further in establishing if this is important in man (and if so how important), and despite the ingenuity of the study design, it ultimately fails to provide enough data that can be systematically compared to that in man to enable a truly informed assessment of what the implications of these findings are for men in the UK.”

Prof. Allan Pacey, Professor of Andrology, 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.

“These observations, combined with the fact that the authors can detect concentrations of some environmental chemicals in the dogs’ testicles as well as in commercial dog foods, is very interesting. Indeed, because dogs share the human home, this could suggest that they might be a useful model species to detect possible threats to male reproductive health.

“However, until more work is done, I think we need to interpret this data with caution and use it to guide further studies rather than have a knee jerk reaction about any impact it might have on human public health. Currently scientific opinion is very much divided about whether human male fertility and semen quality has declined in recent years, although there are several intriguing observations in the human there are also many (as yet unproven) theories to explain them.”

Prof. Darren Griffin, Professor of Genetics, University of Kent, said:

“Performing this study on dogs is a novel innovation as it allows for the study of an inbred population of animals that occupy the same space as humans. The association with environmental chemicals, while not causal at this stage (that was not part of the study) is certainly one to put on the watch list. The study certainly paves the way for human studies of a similar type and for experimental studies of model systems on the effects of these chemicals.”

Gudrun Ravetz, Junior Vice President, British Veterinary Association, said:

“The study released today has highlighted some interesting results; we would support further research to identify if environmental causes are having a significant impact on male dog fertility and, if so, to understand these effects in order that health risks can be eliminated.”

‘Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism’ by Richard G. Lea et al. published in Scientific Reports on Tuesday 9 August 2016. 

Declared interests

Prof. Richard Sharpe: “I have no conflicts to declare.”

Prof. Allan Pacey: “Chairman of the advisory committee of the UK National External Quality Assurance Schemes in Andrology, Editor in Chief of Human Fertility and Trustee of the Progress Educational Trust (all unpaid). Also, recent work for the World Health Organisation, British Broadcasting Corporation, Purple Orchid Pharma (paid consultancy with all monies going to University of Sheffield). Co-applicant on a research grant from the Medical Research Council (ref: MR/M010473/1).”

Prof. Darren Griffin: “Have a research council grant on cattle fertility with the University of Nottingham (different scientists).”

None others received.