Endocrine disruptors and ovine reproductive development

Summary. Declining fertility and perturbations in reproductive development in a variety of species have been linked to exposure to endocrine disrupting chemicals (EDCs), which are ubiquitous in the environment. Ruminants are largely exposed to such chemicals in sewage sludge fertiliser widely used in animal production systems. This has been investigated experimentally through the deliberate exposure of pregnant ewes to sewage sludge fertilised pastures or control pastures treated with inorganic fertiliser containing no detectable EDCs. Perturbations in the developing fetal hypothalamic–pituitary–gonadal axis have been observed in both male and female fetuses. A sub-population of rams exposed both pre- and post-natally exhibited adversely altered testis development. Periods of developmental sensitivity to EDCs have also been identified. An in vitro culture system for ovine fetal ovaries has shown that mixtures have a greater effect than individual chemicals. The dog provides a sentinel model of human dietary exposure to chemicals in ruminant-derived food products. Evidence of altered fertility and testicular cancer, along with EDC detection in dog testes and pet foods, support this concept. Established rodent models of EDC exposure provide a means to investigate mechanisms and transgenerational effects. Overall, monitoring and in vitro studies carried out in sentinel species and on human tissues, combined with in vivo mechanistic studies carried out in ruminants and rodents, provides a clear picture of the global impact of EDCs on reproductive development. In particular, the ovine model of sewage sludge exposure provides the only currently available "real life" model of exposure to a cocktail of EDCs.