Effects of test weight and processing method on in vitro intestinal digestibility of barley grain
An in vitro study was conducted to investigate the effects of test weight and processing method on intestinal digestibility of barley grain following ruminal incubation. The study was designed as a 2×2×2 factorial arrangement with treatments: test weight (TW; low vs. high), precision processing (PP; control vs. PP), and processing index (PI; 75 vs. 85%). Ten barley samples with 5 low (574 g/L) and 5 high (632 g/L) TW were either dry-rolled with single roller setting (control) or sieved into small and large kernels, then dry-rolled based on kernel size of each fraction (i.e., PP). Each sample was dry-rolled moderately or coarsely with PI of 75 or 85%, respectively. Intestinal DM digestibility (iDMD; % of ruminal residue input) of barley grains was determined using the modified three-step in vitro procedure. Barley samples were incubated in the rumen for 12 h to produce ruminal residues using three beef heifers (650 ± 25 kg BW) fitted with rumen cannula and fed a diet consisting of 70% barley silage and 30% barley grain. Ruminal residues were incubated in 1 N HCl containing 1 g/L of pepsin for 1 h, and then in phosphate buffer (pH 7.8) containing pancreatin at 39°C for 24 h. An interaction between TW and PP (P < 0.02) and between PP and PI (P < 0.01) was detected but not between TW and PI (P > 0.05). The iDMD was greater (P < 0.01) with high (25.6%) than with low (23.1%) TW of barley grain for control barley, whereas the iDMD was not different between the low (20.2%) and high TW (20.4%) for PP barley. Compared to control processing, PP reduced (P < 0.01) the iDMD (PP vs. control; 13.5 vs. 21.2%) for processed barley with PI of 85% but not for barley with PI of 75% (27.3%). Decreasing PI from 85 to 75% increased (P< 0.01) iDMD from 17.3 to 27.4%. These results indicate that the intestinal digestibility of barley grain varied with TW, processing method, and extent of processing. It suggests that manipulating these factors may partly shift grain starch digestion from the rumen to the intestine, thereby potentially reduce rumen acidosis and improve feed efficiency in feedlot beef cattle fed high-grain diet.
Keywords: barley grain, precision processing, in vitro intestinal digestibility