In years past, many poultry nutritionists would typically discount the nutritional value of grain sorghum when compared to corn or wheat. The nutritional value of sorghum was assumed to be 85 to 90 percent of the total feeding value of corn. For sorghum to replace corn in a least-cost feed formulation, this meant that sorghum had to trade at prices much lower than corn before it would be included in the formulation.
Poultry and tannin
Today's sorghum varieties compare more favorable to corn in least-cost feed formulations. Old varieties of grain sorghum contained relatively high amounts of an anti-nutritional compound called tannin. The presence of tannin in poultry feeds is known to suppress growth and performance of all types of poultry. Tannins bind to proteins and render them less available for metabolism. Although tannin reduces bird damage in fields of sorghum, poultry are birds, too, and also are affected by the anti-nutritional properties of tannin.
Over many decades of research, sorghum varieties that contained various levels of tannin were used to compile tables and other references for the feeding value of sorghum compared to corn. Unfortunately, many nutritionists who do not have experience with sorghum continue to think of it as a lesser grain compared to corn when, in fact, new varieties have been introduced with high relative nutrient values. In many places, varieties of grain sorghum that contain significant quantities of tannin are still grown. However, in the United States, varieties grown for animal feeding today are low tannin, or 99 percent free of tannin.
Nutrients in sorghum
The nutrient profile of sorghum is complementary to protein sources typically used in poultry rations anywhere in the world, and is very similar to corn. Amino acid digestibility compares favorably with corn, especially when considering newer sorghum varieties that are produced in the US today. The fat content of grain sorghum and the energy value for poultry is slightly lower when compared to corn. However, this difference is easily balanced in rations with other sources of energy, such as animal byproduct meals or oils.
Compared to corn, grain sorghum contains reduced quantities of yellow xanthophylls required for egg yolk pigmentation and skin coloration for broilers. In some cases where lighter meat products are preferred by the customer, sorghum may be used to reduce carcass pigmentation for marketing advantages. Where color is required for some products, such as egg yolks that require intense pigmentation, other sources of pigments like marigold oil, yeast products, synthetic compounds and even corn based DDGS often can be included in rations on a least-cost basis.
Enzymes for sorghum based diets
Most cereal grains and poultry benefit to some extent by the addition of enzymes that increase nutrient availability or decrease the impact of anti-nutritional factors. For example, the use of glucanase enzymes to mitigate the negative effect of viscosity in wheat and barley-based 3 are a good candidate for enzymes to improve feeding values.
A research group studied the effect of adding a commercial mixture of pectinases, a-glucanases and hemicellulases to sorghum-soy feed rations for broilers. The research found that ileal amino acid digestibility increased 3 percent while the ME was increased by more than 6 percent when used in rations that were marginal in nutrients.
This demonstrates that enzymes can be used to get more nutrients from sorghum. Cadogan, et al., tested phytase enzyme preps on sorghum based diets and determined that the enzyme improved weight gain, amino acid digestibility, starch digestibility and broiler performance. Limited studies do indicate that there are opportunities to use enzyme preparations to improve bird performance. However, the database is currently lagging behind similar studies for wheat, barley and corn.