Identifying physical, chemical and biological characteristics to assess grain processing responses of barley as a trait for the selection of feed varieties for cattle

Abstract

This study was conducted to evaluate the effects of barley hull type (hulled vs. hulless) and head type (two- vs. six-row) on kernel characteristics, particle size distribution (PSD), gas production (GP) kinetics and in vitro dry matter disappearance (DMD) in batch cultures. All barley grain was dry-rolled to a processing index (PI) of 0.80 and barley types were evenly distributed within each in vitro run. Kernel uniformity and PSD on 3.35-, 2.36-, 1.18-, 0.85-mm sieves, GP kinetics and DMD at 6 and 48 h of incubation were measured. For both hulless and hulled barley, two-row types tended to exhibit higher test weight, plumpness, ether extract, starch and β-glucan contents than six-row types. A hull type × head type interaction (P < 0.01) was noted for kernel uniformity and particles retained on 3.35- and 2.36 mm sieves. For both hulled and hulless barley, more (P < 0.05) kernels were retained on the 3.35 mm sieve for two- vs. six-row, but this pattern was the opposite on the 2.36-mm sieve, where six-row exceeded two-row. For rolled-hulled barley, more particles (P < 0.05) were captured on 3.35-mm sieve for two- vs. six row, whereas the opposite response was observed for the 2.36-mm sieve. In contrast, for rolled- hulless barley, more (P < 0.01) particles were captured on the 1.18 and 2.36 mm sieves, with a similar distribution between head types. The accumulative gas volume (GV, mL/g OM), GP rate, and average gas production rate (AGPR) were higher (P < 0.01) for hulless than hulled barley. However, the time when half of GV occurred (T1/2) was higher (P < 0.01) for hulled than hulless varieties. The DMD at 6 and 48 h of incubation were also higher (P < 0.01) for hulless than hulled barley. In general, GP kinetics and DMD at 6 and 48 h were lower (P < 0.01) for six- than two-row types, with the exception of T1/2 which was greater (P < 0.01) for six-row. The GP and DMD at 6 and 48 h were strongly correlated with finer particles. The results suggest that hull and head types can have a significant impact on the rate and extent of barley grain digestion. Differences in PSD of rolled barley along with the positive correlation between fine particles and rumen fermentation, presents an opportunity to select barley varieties that could enhance rumen function responses in addition to agronomic traits.