[Environment and secular sperm trend. Stallion's semen quality during the last two decades]

Several reports have suggested that human semen quality has declined throughout the world over the last few decades. Chemicals in the environment acting as endocrine disruptors have been implicated as a possible cause. If this is indeed the case, then similar effects may be observed in animals. We report data on secular trends in semen quality of stallions collected during the last two decades by French National Studs.

We analyzed 1489 ejaculates collected from 390 Breton draught stallions between 1981 and 1996 and 341 ejaculates from 86 anglo-arab thoroughbred stallions from 1985 and 1995. We employed a standardized semen collection and analysis protocol for evaluating the semen quality.

For both stallion breeds studied, we observed a decreased seminal volume (around 2% per year) whereas total sperm production remains unchanged.

Seminal fluid volume is controlled by accessory sex glands, which are regulated by androgens. Chemicals with anti-androgenic properties have been detected in the environment. By affecting the development or function of accessory sex glands, these chemicals may be at least partly responsible for the observed decrease in semen volume.