Fermentability and degradability of sorghum grain following soaking, aerobic or anaerobic treatment

Abstract

This study determined the effect of soaking (steeping), aerobic (germination) and anaerobic (reconstitution) treatments on the solubility of carbohydrate and nitrogen, and on the in vitro fermentability and in sacco degradability of dry matter (DM) of sorghum grain ( Sorghum bicolor cv Western Red). Samples of grain were dry rolled (DR, control), soaked (SK), stored anaerobically for 21 d (reconstitution, AS21), stored aerobically for 5 d (germination, G5) or stored aerobically for 5 d and then anaerobically for 16 d (G5AS16). Compared to the DR treatment, only G5AS16 treatment reduced ( P < 0.05) starch content by 2% units. Free sugar and buffer-soluble nitrogen contents were higher ( P < 0.05) in G5 and G5AS16 sorghum (21 and 54 g kg −1 DM; 241 and 375 g kg −1 total nitrogen, respectively) than in DR sorghum (8 g kg −1 DM; 142 g kg −1 total nitrogen, respectively). Free sugar and buffer-soluble nitrogen contents were similar ( P > 0.05) for SK, AS21 and DR control sorghum. Following a 5-h incubation in buffered rumen liquor, G5 and G5AS21 treatments increased ( P < 0.05) the in vitro fermentability of sorghum compared to the DR control treatment. This was indicated by increases in gas production (121–215%), volatile fatty acid (VFA) production (98.6–210%) and the amount of starch fermented (22–47%), following a 5-h incubation with buffered rumen liquor. In sacco degradability of DM in sorghum after 48 h of incubation was higher for G5 and G5AS16 (0.44 and 0.45, respectively) treatment than for DR, SK and AS21 treatments (0.39, 0.36 and 0.34, respectively). SK and AS21 treatments did not increase the degradability of sorghum compared to the DR treatment. It was concluded that the germination process occurring during aerobic treatment improved the fermentability and degradability of sorghum compared to other treatments investigated in this study.