Effects of barley type and processing method on rumen fermentation, dry matter disappearance and fermentation characteristics in batch cultures

The objective of this study was to investigate the effects of barley type (two-row versus six-row) and processing method (grinding, dry-rolling and temper-rolling) on processing quality, dry matter (DM) disappearance (DMD), and fermentation characteristics in batch culture. The study was a completely randomized design with 2 barley types × 3 processing methods in a factorial arrangement. Thirty barley cultivars/lines were selected from a set of 85 cultivars/lines that were previously screened for in vitro DMD. The mean DMD values (g/kg) were 328 (low), 520 (medium), and 688 (high) after 48 of incubation. Ten representative samples of each DMD group (low, medium and high) of two- and six-row barley were selected. Barley samples were ground (1-mm screen), and dry- or temper-rolled to a processing index (PI) of 0.80. Particle size distribution (PSD) of rolled barley across 4.00-, 3.35-, 2.36-, 1.18-, 0.85-mm sieves, gas production (GP) kinetics, DMD and fermentation traits at 6, 24 and 48 h of incubation were measured. Two-row had higher kernel weight, test weight, plumpness, starch and ether extract content, and lower fibre content than six-row barley (P < 0.01).The PSD of rolled barley was affected by barley type, processing and their interaction (P < 0.01). More (P < 0.01) coarse particles were retained on the 3.35-mm sieve for two-row versus six-row barley (dry-rolled, 0.44 versus 0.34; and temper-rolled, 0.91 versus 0.85). Compared to six-row, two-row barley had greater (P < 0.01) DMD after 6 and 48 h and greater (P = 0.02) crude protein disappearance (CPD) after 48 h. Ground barley had higher DMD, CPD, microbial N production and molar proportion of propionate and total VFA production than rolled barley (P < 0.01); whereas these variables did not differ between dry- and temper-rolled barley. A barley type × processing interaction for DMD, CPD and GP kinetics was identified (P < 0.01). Coarse particles were negatively, while fine particle were positively correlated with DMD (P < 0.01). These results indicate that although PSD of dry- and temper-rolled barley differed, impacts on GP and DMD were small, particularly for two-row barley. The differences in DMD at 6 or 48 h between two- and six-row barley suggest that barley type can impact both the rate and extent of barley digestion in the rumen. These differences suggest that there is considerable opportunity to select barley varieties based on responses to processing and ultimately their feed value for ruminants.