In Situ Ruminal Disappearance Among Corn Grains in Holstein and Angus Steers

Objectives were to compare DM, NDF, and starch in situ disappearance in Angus and Holstein steers using 3 corn grains: a floury corn (FC), steam flaked corn (SFC), and a standard yellow dent number 2 corn (YDC). Holstein (n=4) and Angus (n=4) steers (average BW = 400 ± 30 kg; age = 14 ± 1 mo), fitted with rumen cannula, were used. Whole grains (FC and YDC) were ground using a Wiley mill with no screen, to mimic cattle mastication of the grain. Corn grain (15 ± 0.2 g) was weighed into dacron bags with 4 replicate bags per treatment in each time point (3, 6, 12, 24, 48, and 72 h incubation). Bags were tied shut with nylon string, grouped by hour within steer, and placed in larger mesh sacs. Weights were inserted in the mesh sacs, and mesh sacs were placed in the rumen of steers to achieve 72, 48, 24, 12, 6, and 3 h of incubation. All bags were removed at the same time (0700) and immediately place in cold (~4˚C) water. Samples were dried in a 55⁰ C oven for 3 d. Bags were composited by steer and hour, ground using a Wiley mill (1 mm), and analyzed for DM, NDF, and starch. Data were analyzed using the MIXED procedures in SAS (SAS Inst. Inc., Cary, NC) with repeated measures. A single degree of freedom contrast was used to compare FC to YDC. There were no effect (P ≥ 0.16) of breed, no interactions of breed and treatment (P ≥ 0.15), nor were there 3-way interactions with breed, treatment, and hour (P ≥ 0.28). However, there was an interaction of treatment and hour for DM (P < 0.01) and starch (P < 0.01) disappearance. The in situ rate of DM disappearance was increased in SFC when compared to FC and YDC, and DM disappearance of FC and YDC were not different (P = 0.13) from one another. The in situ rate of starch disappearance was increased in SFC when compared to FC and YDC; and, rate of starch digestion was increased (P < 0.01) by 20% for the first 24 h after ruminal incubation in FC when compared to YDC. In conclusion, SFC had greater in situ ruminal disappearance of DM and starch than YDC or FC. However, the rate of in situ ruminal starch disappearance increased 20% in FC when compared to YDC corn.