Relationships between Tannin Content and Forage Digestibility in Sorghum1

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Abstract
Two related sorghum [Sorghum bicolor (L.) Moench] hybrids, one bird‐resistant (high‐tannin grain, 10.5%) and one non‐bird‐resistant (low‐tannin grain, 4.2%), were harvested at the dough stage of grain maturity. In vitro dry matter digestibilities (IVDMD) and astringent tannin contents were determined on whole plant samples containing varying amounts of grain and on plant components from ensiled and non‐ensiled samples. IVDMD was correlated with percent grain in the non‐ensiled mixtures, but the rate of IVDMD increase was much less in the mixtures high in tannin (Y = 47.0 ‐f‐ 0.08X, r = 0.81) compared with the low‐tannin mixtures (Y = 43.7 + 0.21X, r = 0.99). Ensiling increased IVDMD, and this increase was greater in the high‐tannin hybrid (Y = 42.0 A + 0.23X, r = 0.98) than the low‐tannin hybrid (Y = 40.8 + 0.28X, r = 0.99). Loss of tannins from the grain of the high‐tannin hybrid on ensiling resulted in tannin contents equal to the low‐tannin hybrid. Tannin contents of the chaff, leaves, and stalks of the bird‐resistant hybrid were 9.7, 6.6, and 6.8%, respectively, and 7.8, 6.1, and 1.7% respectively in the non‐bird‐resistant hybrid. This tannin did not dissipate upon ensiling as did that in the grain of the high‐tannin hybrid. These results indicate that feed quality of silage made from bird‐resistant sorghums should be improved and closer to that of non‐bird‐resistant sorghum silage.

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