Direct radioimmunoassay of 17β-estradiol in ether extracts of bovine

Anabolic estrogens such as 17β-estradiol or 17β-estradiol benzoate are used to promote growth and increase feed efficiency in food-producing cattle. This paper describes a technique to produce a more specific antibody to 17β-estradiol by intradermal immunization using microquantities of 6-(carboxymethyl)-17β-estradiol oxime bovine serum albumin and the development of a radioimmunoassay (RIA) procedure to measure directly the amounts of 17β-estradiol in ether extracts of bovine serum without using cleanup procedures. Results demonstrated that a specific and sensitive antibody was produced, and a titer of 1:10,000 was used in the RIA procedure. Antibody cross-reactivity with β-estradiol metabolites and other anabolic estrogens was negligible. The untreated bovine sera showed 0-24 pg of apparent 17β-estradiol/mL, while 0-31 pg/mL total estrogens had been reported in the literature. This assay can measure 5-100 pg in 20-250μL/sample. This method can be used before or immediately after slaughter to monitor the residual amounts of estradiol used in the treatment of cattle