Comparative study on the site and digestion rate of N and starch fractions of four steam-flaked cereals in finishing diets for feedlot steers

Abstract

FOUR HOLSTEIN STEERS (157 KG) WITH CANNULAS IN THE RUMEN AND PROXIMAL DUODENUM WERE USED TO COMPARE CHARACTERISTICS OF DIGESTION OF STEAM-FLAKED CORN, WHEAT, BARLEY AND SORGHUM. THE BASAL DIET CONTAINED (DM BASIS) 81% OF GRAIN. RUMINAL ORGANIC MATTER (OM) DIGESTIBILITY WAS LOWER (P < 0.05) FOR SORGHUM THAN FOR WHEAT, AND BARLEY (57 VS. 71 AND 67%, RESPECTIVELY). GREATER (P < 0.05) RUMINAL STARCH DIGESTIBILITY WAS OBSERVED FOR WHEAT AND BARLEY (92%) THAN FOR CORN AND SORGHUM (83%). EVEN IF THERE WERE NO DIFFERENCES IN POSTRUMINAL DIGESTION OF STARCH (P > 0.10), POSTRUMINAL DIGESTIBILITY OF OM WAS LOWER (P < 0.05) FOR BARLEY (61%) THAN FOR WHEAT (67%). RUMINAL DIGESTION OF N WAS GREATER (P < 0.05) FOR WHEAT (80%) AND BARLEY (72%) THAN FOR CORN (60%) AND SORGHUM (46%). POSTRUMINAL DIGESTION OF N WAS GREATER (P < 0.05) FOR WHEAT (79%) THAN FOR BARLEY (76%), CORN (74%) AND SORGHUM (71%). TOTAL TRACT DIGESTION OF OM WAS GREATER (P < 0. 05) FOR WHEAT (85%) THAN FOR CORN (82%), BARLEY (80%), AND SORGHUM (79%). TOTAL TRACT DIGESTION OF STARCH FOR ALL GRAIN WAS GREATER THAN 98%. DIETARY DIGESTIBLE ENERGY (DE,MCAL/KG) WAS GREATER (P < 0.05) WITH CORN (3.52) AND WHEAT (3.59) THAN WITH BARLEY (3.35) AND SORGHUM (3.34). GIVEN THAT THE DE AND RUMINAL UNDEGRADABLE INTAKE PROTEIN (UIP) VALUES THAT THE NRC (1996) ASSIGNS TO STEAM-FLAKED CORN ARE 4.10 MCAL/KG AND 57%, THEN THE CORRESPONDING REPLACEMENT DE AND UIP VALUES FOR STEAM-FLAKED WHEAT, BARLEY, AND SORGHUM OBTAINED IN THE PRESENT STUDY WERE 4.19 AND 21.5 MCAL/KG, 3.89 AND 34.8 MCAL/KG, AND 3.88 MCAL/KG AND 63.4%, RESPECTIVELY. IT IS CONCLUDED THAT CURRENT STANDARDS OF THE NRC SIGNIFICANTLY UNDERESTIMATE THE NET ENERGY AND RUMINAL ESCAPE PROTEIN VALUES OF STEAM-FLAKED BARLEY, WHEAT AND SORGHUM.