Feed Ingredient Insights
Efstratia Papanikou is a Kansas State (MSc) and University of Illinois (PhD) graduate working as a consultant in the interface between plant and animal science: the feed ingredients. Papanikou can be contacted at [email protected]
An important crop in arid areas, sorghum is a globally traded commodity.
Sorghum (Sorghum bicolor), also known as milo and kafir, is a grain crop, but there are significant varieties of grass sorghum. Modern genetic development through cross-breeding has created improved varieties, all termed under the name of sorghum, and thus, other terminology is quickly disappearing.
Sorghum is a major cereal crop for the semi-arid tropic zone, including areas in China, India, Africa, Australia, Argentina, and even the Midwest and southern United States. In general, sorghum thrives in areas that are not as suitable for corn as it can withstand high temperatures and lack of irrigation. Of course, sorghum cannot easily withstand the harsh conditions under which cold-resistant cereal crops can be raised. As a rule of thumb, at warm climates devoid of ample irrigation, sorghum outperforms corn, and the opposite is true when water is more freely available.
Sorghum grain is a small, round seed with a color that ranges from almost yellow to dark red to dark brown. Sorghum is an alternative cereal for corn in many countries worldwide as it is a commodity exported mainly from the U.S. and Latin America. Of course, everything depends on the price of corn and those of locally grown cereals.
The chemical composition and nutritive value of sorghum is quite similar to that of corn. Sorghum is composed mostly of starch and, like corn, waxy and non-waxy varieties exist. The waxy-starch (100% amylopectin) varieties appear to support better animal performance, compared with non-waxy or normal varieties (27% amylose and 73% amylopectin). Brown-seed varieties generally have lower nutritive value, mainly because they contain higher levels of anti-nutritional factors (tannins), but this is mostly determined by variety anymore.
The nutritive value of sorghum is usually taken at 90% to 100% compared with corn, with a value of 96% being most common. Sorghum contains slightly more protein than corn (9.5% vs. 8%), but its protein profile is equally deficient in lysine and threonine. However, the greatest problem in sorghum is the wider variation in protein concentration as it ranges from below 7% to above 13%. For this reason, it is important to know the protein content of a batch of sorghum before committing to it. In addition, the protein (amino acid) digestibility in sorghum is lower than that in corn. Total nitrogen digestibility is 75% and 81% in sorghum and corn, respectively. This difference is mainly due to the presence of tannins in sorghum.
Carcass firmness from sorghum-fed pigs is similar to that from corn-fed pigs, which in turn is rather soft compared to carcass from wheat/barley-fed pigs. Sorghum contains virtually no pigments that can be absorbed by the animal, and thus fat from sorghum-fed pigs will be whiter than fat from corn-fed pigs.
The palatability of sorghum can be affected by the presence of tannins (condensed) and other bitter substances which, in nature, serve as a deterrent against birds on the field. The concentration of tannins in yellow seed varieties ranges from 0.2% to 0.5%, whereas that of most brown-seed varieties can reach more than 3%. Although seed color is a good initial indicator of tannin concentration, the concentration of tannins in many modern brown-seed varieties (bird resistant) may be as low as that in yellow-seed varieties.
Tannins not only reduce palatability and subsequently feed intake and growth, but as indicated above, they reduce amino acid digestibility. The only practical solution to the problem of tannins is to use varieties low in tannins. Chemical treatment with 0.8N HCl or 0.8N NaOH (25% by weight) for two days decreases considerably the concentration of tannins and improves digestibility. Also, micronization and addition of polyethylene glycol can improve the feeding value of high-tannin sorghum. These measures, however, are rather impractical as they increase the final cost of feeding sorghum.
Low-tannin sorghum, containing less than 0.5% tannins, may be used freely in all feeds. Sorghum with 0.5% to 1% tannins may make up 50% of the total cereal concentration in a formula, whereas sorghum with more than 1% tannins should be used in gradually increasing amounts, or even better reserved only for feeds destined to older and more tolerant animals. When sorghum of unknown tannin concentration is used, it is best to be conservative, as always.
Extruding sorghum does not always yield superior performance as it does not destroy tannins, although starch digestibility due to gelatinization may be improved in young chicks, pigs, and calves. Fine grinding of sorghum is recommended to improve nutrient digestibility and consequently the efficiency of feed utilization. Grinding sorghum to 600 microns is considered an optimal compromise between animal performance, feed handling characteristics and grinding efficiency.