Ruminal fermentation and degradability of sorghum cultivar whole crop, and grains, using an in vitro gas production technique

The purpose of the study was to determine fermentation and degradability of eight sorghum cultivars, being 8050-Agromen, 8118-Pioneer, 8419-Pioneer, BR306, BR700, BRS305, BRS701, Saara-Monsanto at different stages of growth, and to determine effects of condensed tannins (CT) in sorghum grain using a bio-assay. Cultivars were planted in 5 m×4.5 m plots in a randomized block design. Whole plants were harvested 30, 60, 90 and 120 days post-sowing, but grains (cobs) were harvested only at 120 days from plants other than those harvested as whole plant. Samples were analyzed for ash, acid detergent fibre and crude protein. In vitro gas production determinations of whole plant samples and grains were completed on oven dried (40 °C for 48 h) samples ground to pass a 1 mm screen. Grain samples assayed for CT, and their interference in gas production, was determined with addition of polyethylene glycol. Differences (P<0.05) in chemical composition occurred among cultivars at and after 60 days. Grains of cultivars with low CT levels had higher apparent dry matter degradability (ADMD; P<0.05). In the bio-assay, grains had increased gas production with PEG addition, and correlations (P<0.05) occurred between CT content and gas increment following PEG addition as well as ADMD. Grain cultivars had as good or better fermentation parameters and ADDM when harvested at 60, 90 and 120 days post-sowing as did forage cultivars at the same maturities.