Effect of sorghum grain flake density on site and extent of digestion in feedlot steers.

Experiments were conducted to determine the effects of sorghum grain flake density on site and extent of nutrient digestion in beef steers. Sorghum grain was steam-flaked to densities of .41, .36, .31 and .26 kg/L. Diet digestibility was determined during the growing and finishing periods of a feedlot performance trial with dietary grain levels of 50 and 80%, respectively. Starch digestion was increased from 92 to 98%, and from 98 to 99%, on growing and finishing diets, respectively, in response to decreased flake density. Digestion of dry matter and energy was increased in growing diets but decreased in finishing diets as flake density in the diets decreased. Fiber digestion was not influenced in growing diets but decreased in finishing diets. In an experiment using cannulated steers fed diets with 50% grain, flow of starch at the duodenum was reduced 50% (466 vs 232 g/d) as flake density was decreased from .41 to .26 kg/L. Starch digestion was increased in each segment of the digestive tract with the greatest response occurring in the rumen (83 vs 92%, for .41 and .26 kg/L, respectively). In another experiment using cannulated steers fed 80% grain diets, starch flow from the rumen was also reduced by 50% (694 vs 371 g/d) by decreasing flake density from .41 to .36 kg/I. Starch digestion was improved throughout the digestive tract. Ruminal, intestinal and total tract starch digestion was comparable when grain was flaked to .36 kg/s or less. In conclusion, flaking of sorghum grain over a range of flake densities primarily affected starch digestion. As flake density in the diet decreased, starch digestion increased in all three studies. The largest differences among treatments in ruminal, intestinal and total tract digestion occurred between the .41 and .36 kg/L treatments. Starch digestion was similar when sorghum grain was flaked to .36, .31 or .26 kg/L. Response pattern for protein digestion followed that for starch digestibility. Effect of flake density on digestion of other nutrients was not consistent among the three experiments