PSIII-11 Effect of grain type and processing method on in situ ruminal dry matter digestibility.

Abstract Cereal grains are the main source of energy in finishing feedlot diets. Sorghum is a more water-efficient alternative to corn, but sorghum starch is less ruminally digestible. Processing methods can increase grain digestibility, improving animal efficiency. The objective was to determine the effects of grain type and processing methods on in-situ dry matter (DM) degradability (DMD). Five ruminally cannulated Angus crossbred steers (body weight [BW] = 730 ± 119 kg) were pen-fed a starter ration twice daily at 2% of BW during the experiment. Fresh steam-flaked corn (SFC) and steam-flaked sorghum (SFS) samples were collected, air equilibrated for 240 minutes, then densities were measured (410 g/L SFC and 494 g/L SFS). Fresh cracked corn (CC) samples were collected after the roller mill process (4 to 6 pieces per kernel). High-moisture rolled sorghum (HMRS) was harvested at physiological maturity with 28% humidity, processed through a roller mill bagger and stored for 300 d. After opening, samples of HMRS were collected from 3 different areas of the silo. Nylon bags (10 × 20 cm, 50-µm pores) were filled with 20.5g (± 0.5g) of each grain and incubated in duplicate in the ventral sac of the rumen of each steer for 0, 3, 5, 12, 24, 48, 72 and 96h. The 0h bags were incubated for 10 seconds and then retrieved. Bags were immersed in cold water, rinsed 5 times using a washing machine, and dried to evaluate in-situ DMD. The kinetics of rumen degradability including soluble fraction [a], potentially degradable fraction [b], and degradation rate of the b fraction (c; %/hour) were estimated by a first-order asymptotic model using the NLIM procedure of SAS. The effective degradability (isRD) was determined considering a 6%/hour ruminal passage rate. Data was analyzed using the MIXED procedure of SAS, using steer as experimental unit and the random effect of steer (treatment). Differences were set at P ≤ 0.05 using Tukey test. Fraction a was greater for SFC than SFS, that was greater than HMDRS, that was greater than CC (P ≤ 0.01). Fraction b was greater for CC compared to HMDRS (P < 0.001), with no differences between HMDRS and SFS (P = 0.12), and both HMRS and SFS greater than SFC (P ≤ 0.001). Fraction c was greater for SFC compared to CC (P < 0.001), which was greater than SFS (P < 0.001). Fraction c of SFS and HMDRS were similar (P = 0.23). The isRD of SFC was greater than SFS (P < 0.001). No differences in isRD between SFS and CC were detected (P = 0.96), but isRD of SFS and CC were greater than HMDRS (P < 0.001). Steam flaking appears to improve DMD rates relative to other processing methods.