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Use of Bioassay Techniques with Rats to Measure the Antithyrotoxic Factor in Roughages and other Materials^1,2,3,

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691

Rat liver malic enzyme activity, blood serum protein-bound iodine, body weight gains and 24-hour uptake of ¹³¹I by the thyroids were determined to measure antithyrotoxic activity of roughages, cow feces, coumestrol and diethylstilbestrol. Hemoglobin was used as a standard source of antithyrotoxic factor (ATF). The response to graded levels of hemoglobin in the diet by rats made hyperthyroid by dietary thyroxine or iodinated casein was compared in six experiments. Feces were shown to have significantly more ATF activity than roughages when the reduction of thyroxine-increased malic enzyme activity was compared. Protein-bound iodine (PBI) responses did not show significant differences for feed and feces in all cases. When malic enzyme activity, serum PBI and body weight were incorporated in multiple regression equations, hemoglobin ATF was predictable in three experiments (R² = 0.78). The level of thyroxine or iodinated casein included in the diets was too high to use thyroidal uptake of ¹³¹I as an assay parameter.

² Approved for publication as Journal Article No. 46-70 by the Associate Director of the Ohio Agricultural Research and Development Center, Wooster.

³ A preliminary report was presented at the 63rd Annual Meeting of the American Dairy Science Association, Columbus, 1968.

⁴ Present address: Department of Animal Sciences, Washington State University, Pullman, Washington 99163.

⁵ Present address: Department of Animal Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802.

Manuscript received 29 May 1970.