The protein and starch in sorghum grain are usually not as digestible as that in corn. Sorghum grain tends to vary more than corn in protein content and feed value because of cultural practices, soil fertility, and variety. As seed hardness increased, digestibility decreased. Bird-resistant varieties of sorghum grain, especially, have been lower in feed value than corn or other sorghum varieties for cattle. Bird-resistant varieties have a high tannin content, which helps keep birds from eating the ripe grain in the field.
Tannin appears to lower the digestibility of the protein and starch.
It is doubtful, however, if bird-resistant varieties are less palatable for cattle than other grain sorghum. In some trials the bird-resistant sorghum grain was consumed in smaller amounts than corn or other sorghum varieties. In contrast, bird-resistant varieties were eaten in larger amounts by cattle in other comparisons. Evidently, cattle were trying to compensate for the lower energy level of the grain by eating more. In an average of 10 trials from 1963 to 1973, cattle fed finishing rations gained 5 percent faster on 11 percent less feed when the grain was corn in comparison to sorghum grain.