Absorption and Distribution of ¹⁴C-Labeled Condensed Tannins and Related Sorghum Phenolics in Chickens

Condensed tannins from sorghum [Sorghum bicolor (L.) Moench.] seeds are the only type of tannins found in this plant and are commonly associated with toxic effects in animals fed diets based on hightannin sorghum grains. However, it is still not certain whether those polyphenolic polymers are absorbed from the digestive tract. Condensed tannin and other related phenolic fractions from sorghum seeds were metabolically radiolabeled with ¹⁴C and separately fed to Hubbard White Mountain chicks. Their tissues were examined to determine the absorption and distribution of the polyphenolic fractions. Immature high-tannin sorghum seeds (Dekalb BR-64) were radiolabeled with NaH¹⁴CO₃ or ¹⁴CO₂, and various phenolic compounds were purified according to the method of Reddy and Butler (J. Agric. Food Chem. 1989, 37, 383-384). Radiolabeled condensed tannin and non-tannin phenolic fractions were lyophilized and separately placed into starch capsules, and each capsule was placed into the crop of chicks. Eight hours later, blood samples were taken by cardiac puncture, the birds were killed by excess CO₂ inhalation, tissue samples were excised, and total excreta were collected. Analyses of ¹⁴C distribution in chick tissues and excreta suggest that radiolabeled condensed tannins from sorhum grain were not absorbed from the digestive tract of chickens. However, ¹⁴C from non-tannin fractions was absorbed and distributed in various tissues. It is proposed that low molecular weight polyphenols present in these fractions may be partially responsible for the toxic effects seen in chickens fed high-tannin sorghum diets.