EFFECT OF SORGHUM GRAIN PROCESSING ON SITE AND EXTENT OF DIGESTION OF STARCH IN LACTATING DAIRY-COWS

Four lactating Holstein cows, fitted with T-type cannulas in the proximal duodenum were used in a 4 x 4 Latin square design to study the effects of sorghum grain processing on site of digestion of nutrients. Diets were steam-rolled corn, dry-rolled sorghum, steam-flaked sorghum, and an equal mixture of steam-flaked and dry-rolled sorghum as 43% of DM in a TMR (35:65, ratio of forage to concentrate). Intake and duodenal starch for all diets averaged 6.8 and 2.1 kg/d. Apparent total tract and ruminal digestibilities of starch for the respective diets averaged 81, 60, 70, and 60 and 97, 85, 91, and 89%. Starch digestibilities in the intestine were higher for steam-flaked than for dry-rolled or mixed sorghum (83 vs. 63 and 61%). Consistent with less postruminal passage of starch, cows fed steam-flaked sorghum had higher fecal pH than did cows on other treatments. No effects of diet occurred on NDF or ADF digestibilities. Compared with dry rolling of sorghum, steam flaking increased the digestibility of starch in the rumen from 60 to 81% and in the small intestine from 63 to 83%, increasing digestible starch intake 9% (6.4 vs. 5.9 kg/d). Values for steam-rolled corn. were intermediate. Microbial protein in the rumen was not significantly altered by diet.