Oven and stack ammoniation of grass hays. 1. Changes in chemical composition in relation to digestibility in vitro and cell-wall degradability

Abstract

Medium-quality crops of cocksfoot, tall fescue, perennial ryegrass and timothy grasses were cut, wilted, baled and barn-dried. They were then stored without additive (control), or following exposure to anhydrous ammonia (35 g kg −1 dry matter) at ambient temperatures for 10 weeks (stack treatment) or at c. 90°C for 15 h (oven treatment). Ammoniation lowered the content of water-soluble carbohydrate (WSC) and cellulase-undegradable cell walls (CUCW) in hay dry matter, but raised the contents of total nitrogen (TN), neutral-detergent-insoluble nitrogen (NDIN), acid-detergent-insoluble nitrogen (ADIN), hot-water-insoluble nitrogen (HWIN), soluble non-ammonia nitrogen (SNAN) and 4-methylimidazole (4-MeI). A significant relationship was found between the increases in SNAN and the losses of WSC, suggesting synthesis of Maillard products. The oven and stack processes gave similar improvements in cell-wall degradability (CWD) and in organic-matter digestibility in vitro (OMD (vt)), but oven ammoniation caused the greater modification and/or release of cell-wall phenolic acids and other aromatics. Increases in CWD were significantly related to losses of ferulic acid from cell walls but OMD (vt) was most accurately predicted from the proportion of CUCW in hay dry matter.