Male dog fertility has drastically decreased over the past 26 years, a University of Nottingham study finds 1.
A reduction in the overall sperm quality of a population of breeding studs has been linked to environmental contaminants accumulating in the semen and testes.
The environmental contaminants connected to the drop in fertility have also been found in commercial pet foods.
A 26 Year Fertility Study of Dog Semen Quality
The University of Nottingham study followed a population of breeding dogs at an assistance dog centre for a 26 year period. Semen samples were taken from stud dogs and analysed at a laboratory throughout the study.
The study focussed on five breeds including; Labrador retriever, golden retriever, curly coat retriever, border collie and German shepherd.
Semen samples were taken from between 42 and 97 dogs each year. A total of 232 dogs were used in the study.
The semen samples were analysed to show the percentage of sperm with normal motility and morphology. Sperm quality declined by up to 2.5% per year.
The study also found that male pups from stud dogs with reduced fertility had an increase in the incidence of cryptorchidism, a condition in which the testes of pups fail to correctly descend into the scrotum.
Which Environmental Contaminants are to Blame?
The contaminants identified in this study are all man-made chemicals. The implicated chemicals were diethylhexyl phthalate (DEHP), polychlorinated biphenyl (PCB) and various polybrominated diphenyl ethers (PBDE). These chemicals were found in high abundance in both the testes of breeding males and some commercial pet foods.
Dietary exposure to DEHP or PCB has been shown to alter semen quality in other animals. Sperm from PCB-treated goats showed a higher percentage of sperm with damaged DNA 2.
Mice treated with DEHP were found to have altered reproductive performance as well as a lowered body weight 3.
PBDEs have been previously linked to an increase in feline hyperthyroidism. See our article on PBDEs in fish-flavoured cat foods.
How Are These Contaminants Affecting Fertility?
The exact mechanism by which PCB and DEHP alter sperm motility and viability is still uncertain. Their ability to mimic certain hormones is suggested as the main route of disruption.
Dr Richard Lea, Reproductive Biologist at The University of Nottingham, ruled out a genetic cause for the reduced sperm quality. He suggests that 26 years is too short a time span for such a large decline to be linked to genetics.
The decrease in sperm quality is likely due to the presence of these chemicals in the testes. Eliminating the source of the contaminants could therefore prevent a decline in fertility.
The study puts forward the diet as the source of these contaminants, although the exact pet food brands examined were not revealed.
How these chemicals have entered the food is not entirely clear, although there are many theories. For example, the use of DEHA in plastic wrapping. Also, animal derivatives that have been contaminated e.g. fish.
Summary: Rapid Decline in Male Dog Fertility
- Study finds potential link between environmental contaminants and reduced male dog fertility.
- Semen quality of an isolated population of breeding dogs reduced over a 26 year period.
- An increase in cryptorchidism was also found in the population.
- DEHP, PCB and PBDEs (contaminants) were found in the testes and semen of the stud males.
- These contaminants have been linked to altered reproductive ability in other animals.
- Contaminants also found in commercial dog foods.
- Further work needed to confirm a potential link between the two.
Featured Image: Mattias Agar
References:
- Lea, R., Byers, A., Sumner, R., Rhind, S., Zhang, Z., Freeman, S., Moxon, R., Richardson, H., Green, M., Craigon, J. and England, G. (2016). Environmental chemicals impact dog semen quality in vitro and may be associated with a temporal decline in sperm motility and increased cryptorchidism. Sci. Rep., 6, p.31281. ↩
- Oskam, I. C. et al. Effects of long-term maternal exposure to low doses of PCB126 and PCB153 on the reproductive system and related hormones of young male goats. Reproduction 130, 731–742 (2005). ↩
- Pocar, P. et al. Exposure to di(2-ethyl-hexyl) phthalate (DEHP) in utero and during lactation causes long-term pituitary-gonadal axis disruption in male and female mouse offspring. Endocrinology 153, 937–948 (2012). ↩
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