China continues to import larger than ever loads of sorghum from the U.S. in an effort to satisfy its growing need for cereals. But, sorghum is rather unknown to China, like tapioca is rarely used in Europe. Sorghum, which is hardly a new ingredient, is new in many territories that import it when the price to value ratio make it attractive over maize or wheat. So, the first question to ask when it comes to formulate sorghum-based diets is how to use it efficiently to reduce feed cost.
In general terms, the chemical composition and nutritive value of sorghum is similar to that of maize. The nutritive value (energy) of feed-grade sorghum is usually taken at 90 to 100 percent compared to maize, with a value of 96 percent being most common. It contains slightly more protein (11-13 percent) than maize, but its protein profile is comparably deficient in lysine and threonine. Carcass firmness from sorghum-fed pigs is similar to that from maize-fed pigs (indicating a similar fatty acid profile), which in turn is rather softer compared to wheat/barley-fed pigs. Sorghum contains no carotenes, and thus fat from sorghum-fed pigs will be whiter compared to fat from maize-fed pigs. This becomes especially important in sausage making, where firm and white fat is preferred.
Tannins
The palatability of sorghum is affected by the presence of tannins and other bitter substances, which in nature serve as a deterrent against birds on the field, but in feed they depress intake. The concentration of tannins in yellow-seed varieties ranges from 0.2 to 0.5 percent, whereas that of most brown-seed varieties from 0.5 to over 3 percent. Although seed color is a good initial indicator of tannin concentration, the concentration of tannins in many modern brown-seed varieties may be as low as that in older yellow-seed varieties.
Tannins not only reduce palatability and subsequently feed intake and growth, but they also reduce amino acid digestibility in the gastrointestinal tract, further impairing animal performance. Currently, the only practical solution to the problem of tannins is to use varieties low in tannins, as the alternative (chemical treatment with HCl) is largely impractical under commercial conditions. Lately, it has been shown that micronization and addition of polyethynolglycol may improve the feeding value of high-tannin sorghum, but these technologies are rather unexplored.
Sorghum in pig, poultry diets
As a rule of thumb, low-tannin sorghum, containing less than 0.5 percent tannins, may be used freely in all pig diets. Sorghum with 0.5 to 1 percent tannins may make up 50 percent of the total cereal concentration in a diet, whereas sorghum with over 1 percent tannins should be used in gradual amounts, starting from 5 percent in piglets and lactating sows, and reaching up to 20 percent in the later stages of finishing and for gestating sows. For piglets below 10 kg body weight it is best to use only low-tannin sorghum and never exceed 50 percent of total cereal concentration in creep feed and the first diet post-weaning.
In poultry, low-tannin sorghum of modern varieties has been shown to be able to replace 100 percent of maize in broiler diets. For layer diets, up to 50 percent of cereals in diets can be made up of sorghum. In addition, it should be noted that sorghum contains less pigments than maize. Thus, broiler skin and egg yolk pigmentation are reduced as sorghum concentration increases. This can be fixed by used synthetic pigments or other natural xanthophyll-rich ingredients.
