ESTROGENIC ACTIVITY IN FORAGES - DIAGNOSTIC USE OF THE CLASSICAL MOUSE UTERINE BIOASSAY

The classical mouse uterine bioassay was evaluated and adapted for rou tine diagnostic use in response to requests for evaluation of forages suspected of being estrogenic. Forages were extracted in acetone or 10 % ethanol in acetone (v/v). Extracts were mixed with ground corn-based mouse feed. immature female mice (n = 3/group) were fed a total of 10 0 g of the ground feed for 5 days. Body weights were monitored before and after the trial. After 6 days, the mice were euthanized and uterin e weights were determined. Mean uterine weights were compared using 1- way analysis of variance with preselected contrasts for individual mea ns. Selected uteruses were fixed in 10% neutral buffered formalin for histologic examination. Control feeds, diethylstilbestrol (DES), estra diol, coumestrol, feeds with no reported estrogenic properties, and a feed that caused hyperestrogenism in cattle were tested. Moderate leve ls of estrogenic compounds resulted in dose-responsive uterine enlarge ments (10-270 ppm coumestrol over 5 days). Extremely high levels of es trogen frequently resulted in feed refusal and lack of uterine enlarge ment (10 ppm DES, 100 ppm estradiol). Diagnostically significant estro genic activity was recovered from the feed known to have been estrogen ic in cattle. The classical mouse uterine bioassay was relatively inex pensive, quick, repeatable, and capable of detecting clinically releva nt coumestrol levels in hay.