Characterization of various wheat types and processing methods using in vitro ruminal batch cultures

This study investigated the effect of kernel hardness, processing method, and their interaction on particle size, dry matter (DM) disappearance (DMD), and fermentation characteristics of wheat grain in batch cultures. The study was a completely randomized design with 3 wheat classifications (soft, medium, hard) × 3 processing methods (grinding, dry- and temper-rolling). Fifty-five wheat samples were characterized for chemical traits and classified for kernel hardness. Samples were either ground through 1-mm screen, dry-rolled or temper-rolled to a constant processing index (PI) of 0.80. In vitro gas production (GP) kinetics, fermentation characteristics and DMD at 6, 24 and 48 h of incubation were measured. Crude protein (CP) (g/kg) was lower and starch (g/kg) was higher for soft than medium and hard wheat. The PSD of rolled wheat was affected (P < 0.01) by a wheat hardness × processing interaction. With dry-rolling, soft wheat had more particles retained on the 2.36-mm sieve and less on the 1.18-mm sieve, while, with temper-rolling, soft wheat had more particles retained on the 3.35-mm sieve and less on the 2.36-mm sieve than those for dry- or temper-rolled medium and hard wheat. Kernel hardness × processing was observed (P < 0.01) for DMD and CPD after 24 h and 48 h of incubation; the DMD and CPD were higher (P < 0.01) with dry- than temper-rolled hard or medium wheat, but no differences in DMD and CPD were observed between dry- and temper-rolled soft wheat. A kernel hardness × processing interaction was also noted for total VFA production and molar proportions of propionate after 24 h of incubation (P < 0.05). Dry-rolled soft wheat had a higher (P = 0.04) total VFA concentration and molar proportion of propionate after 24 h of incubation as compared to dry-rolled hard wheat. Compared to grinding, VFA concentrations and proportion of propionate were all reduced by both dry- and temper rolling with the magnitude of these differences generally being greater for soft as compared to medium and hard wheat. In conclusion, regardless of kernel hardness, PSD of dry- and temper-rolled wheat had a significant impact on DMD. Tempering was more effective at reducing the generation of fine particles than dry-rolling, particularly with hard wheat, a factor that may reduce the risk of digestive disturbances in ruminants fed wheat.