Researchers have found that dogs in the United Kingdom are becoming less fertile after studying canine sperm quality over 26 years.
The team of scientists believe that environmental chemicals are partly responsible, raising fears that male humans could be affected in the same way. The study was carried out by Richard Lea, of Nottingham University’s school of veterinary medicine and science, along with his colleagues, writes Tim Radford for The Guardian.
Stud dogs studied over 26 years
Semen samples were collected from Labradors, border collies, German shepherds and golden retrievers which were carefully controlled studs used to breed dogs that help the disabled. A total of 1,925 samples from 232 dogs were tested over the course of the study.
Research showed that sperm mobility, or the ability to swim in a straight line, declined by 2.4% per year from 1988 to 1998. Some dogs were later excluded from the study due to doubts over their fertility, but from 2002 to 2014 a decline of 1.2% per year was still observed.
Traces of environmental chemicals like PCBs and phthalates were found in the samples as well as in the testicles of dogs castrated by veterinarians. These ubiquitous chemicals have been linked to fertility problems and birth defects.
Is human fertility also declining?
While it is worrying to see fertility declining in dogs, the main question is how the findings could be linked to male human fertility. A downward trend in male fertility has been found over the course of research from the past 70 years, however the accuracy of the findings have always been subject to question.
“Why the dog?” said Dr Lea. “Apart from the fact that it is a great population of animals to work with, dogs live in our homes, they sometimes eat the same food, they are exposed to the same environmental contaminants that we are, so the underlying hypothesis is that the dog is really a type of sentinel for human exposure.”
The different research techniques used in 60 separate studies of human male fertility over 50 years mean that it is difficult to compare results. However it is less disputed that rates of testicular cancer have been rising in recent decades, as have rates of a condition known as cryptorchidism, which prevents the testicles from descending to the scrotum in the usual way.
Dog study displays consistency
Problems of consistency were not a worry in the canine study, which used only healthy dogs that were well looked after. 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. Researchers also took into account the food given to the dogs and the chemicals it contained.
As it stands declining fertility does not mean that dogs are going to die out. “It’s very unlikely” Dr Lea said. “It’s very difficult to say at what point this becomes a problem.”
The offspring of the dogs involved in the study displayed higher incidences of cryptorchidism over the years, and researchers demonstrated a link between environmental chemicals and falling fertility.
“If you think about it, we are exposed to a cocktail. Who knows how many chemicals are out there and what they are doing? It gets even more complicated when you start to look at the effects of mixtures of chemicals,” Dr Lea said.
“What we have been able to do here is just to pull out ones that we know are present, and we have tested those in terms of their effects and it does suggest there is an impact. The next stage – and it is a big next stage – is trying to tease out what else is there and how those chemicals are interacting.”
