Fifty percent of Dutch dairy farmers use surface water as the main source of drinking water for their cows during the grazing season. In many locations this surface water is in direct contact with a sewerage overflow. Belfroid and coworkers (1999) have demonstrated that this sewerage overflow surface water contains EDC, in particular xeno-oestrogens. The concentration of conjugated ethinyl-oestradiol, for example, in sewerage water was 0.02 mg/l. During the last decade the fertility of dairy cows has decreased dramatically. There is an increased incidence of cystic ovaries, an increase in the interval from calving to first insemination, an increase in the number of inseminations per pregnancy and more abortions have been recorded. These observations raise the possibility that EDC’s adversely affect reproduction in dairy cows. Meijer et al. (1999) compared the production and fertility of cows on 397 farms that used normal surface water with the production and fertility of cows on 60 farms that used water in direct contact with sewerage overflow. The results showed clearly that cows drinking water that was in direct contact with sewerage overflow produced less milk and had a greater age at first calving. Moreover they exhibited a tendency towards a longer interval between calving and first succesful insemination and tended to have a higher rate of abortions. Boerjan et al. (2001) have recently addressed the issues of concentrations of xeno-estrogens present in soil, in plants, in water and in cow tissues, milk and blood, in order to assess the potential risk to ruminants of xeno-estrogen exposure through soil and water ingestion. Although data are sparse and concentrations of EDC in feed and water of ruminant animals are low, under certain circumstances such as sewerage overflow and sludge-fertilized pasture, they concluded that rates of ingestion of certain xeno-oestrogens may exceed levels at which there is no effect. Since most EDC’s are lipophilic and become concentrated in adipose tissue, the mobilisation of fat during onset of lactation and pregnancy can expose animals to much higher concentrations of xeno-estrogens than are present normally in the environment. Important questions are:

1. 1) how much of the EDC’s stored in fat cells will enter the blood under certain circumstances

2. 2) how much of the EDC’s in soil, water and plants will pass the rumen and enter also the blood and

3. 3) how potent are the different EDC’s i.e. what is the dose response relationship? In order to answer the last question an in vivo animal-model is urgently needed.

We have developed an animal-model, based on the genital tract of an ovariectomized cow; the height and organisation of the endometrial lumen-epithelium, the rate of oedema in the stratum compactum and the electrical resistance of the cervical mucus are sensitive measures of oestrogenic activity.