Occurrence of endocrine disrupting compounds in tissues and body fluids of Belgian dairy cows and its implications for the use of the cow as a model to study endocrine disruption

The reproductive performance of high producing dairy cows has dropped severely throughout the last decades. It has already been suggested that the presence of endocrine disrupting compounds (EDCs) in the environment could be one of the reasons for this declining fertility. Reliable data concerning tissue and body fluid concentrations of these chemicals are thus crucial, but currently only scarcely available. Therefore, we selected dairy cows (≥ 6 years) from diverse locations in Belgium and analysed tissues (liver, adipose tissue, muscle, kidney, and ovaria) and body fluids (serum, follicular fluid, and milk) for their content of potential EDCs, such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs). Furthermore, we collected milk and serum samples from high producing dairy cows 2-3 weeks post-partum to verify if the massive lipolysis required to sustain milk production is accompanied with an increase in EDC concentrations in milk and serum.Overall, contamination was very low (median sum PCBs liver: 11.7 ng g⁻¹ lw), with follicular fluid samples showing no detectable contamination. CB 153 was present in each tissue sample. Strong correlations could be found between EDCs in the same tissue. The increased PCB concentrations observed in milk samples from high producing dairy cows could indicate that massive lipolysis can play a role in liberating and thereby increasing EDC concentrations in milk.Because concentrations of the most prevalent EDCs in dairy cow tissues and body fluids are very low, exposure to EDCs can hardly be considered as a major cause of declining fertility in high producing dairy cows in Belgium. As a result of this low contamination and the similarities between the female bovine and human reproductive physiology, in vitro studies based on Belgian dairy cow ovarian follicles can be considered as a valuable model to study the effects of EDCs on human reproduction.