Effects of proanthocyanidins, dehulling and removal of pericarp on digestion of barley grain by ruminal micro-organisms

The effects of proanthocyanidins (PA), dehulling, and removal of the pericarp on the rate and extent of barley digestion by ruminal micro-organisms were studied using a control barley (cv Harrington) and three PA-free barley lines (Caminant, Ca5043l6 and Ca802711). Each barley was studied in five preparations: whole grain (W); dehulled kernels (DH); kernels with pericarp removed (DP); dry-rolled grain (DR), and the pericarp-testa fraction (PT) produced during preparation of DP. Vanillin-HCl staining and chemical analysis confirmed that PA were present only in the Harrington barley, and localised in the pericarp-testa layer. Whole kernels, DH and DP were incubated with diluted ruminal fluid in vitro, and all five preparations were incubated in situ (nylon bag technique). Harrington DR and all four PT fractions were also incubated in vitro in the presence (0.074% w/v) and absence of polyethylene glycol (PEG), which specifically binds PA. The four barleys did not differ in in vitro dry matter disappearance (DMD) or gas production from W, DH or DP preparations, nor in in situ DMD rates from W, DH or DP (P > 0.05). In vitro DMD and gas production among PT fractions from the four barleys were also similar (P > 0.05), as were in vitro DMD from PEG-present and PEG-absent DR Harrington. With Harrington PT, in vitro ammonia concentrations were higher (P < 0.05) with PEG than without. For each barley line, in vitro DMD rates were highest (P < 0.01) with DP, followed by DH, and then by W (P < 0.01). In in situ incubations also, DMD rates and effective degradabilities of DR samples exceeded (P < 0.05) those of DH samples. It was concluded that the presence of proanthocyanidins did not affect ruminal digestion of barley grain, and that abrasive milling to breach the hull and pericarp may be a promising method by which to regulate the rate of barley digestion in the rumen.