Effects of treatment with ammonia or fibrolytic enzymes on chemical composition and ruminal degradability of hays produced from tropical grasses

In the first of two experiments, effects of applying NH₃ or a fibrolytic enzyme (Promote®, Pr) on the fiber concentration, and dry matter (DM) and fiber digestibility of two tropical grass hays was measured. In Experiment 2, effects of applying NH₃ or 3 fibrolytic enzymes, Biocellulase X-20® (X-20), CA® (CA), and Biocellulase A-20® (A-20) on the same variables as in the previous experiment were measured. In situ rumen degradability responses were also measured in Experiment 2. The forages were 12-week regrowths of Coastal bermudagrass hay (Cynodon dactylon; BE) and Pensacola bahiagrass hay (Paspalum notatum; BA). The NH₃ was applied at 40g/kg DM and the enzymes were applied at 0 (Control) 0.5, 1, and 2 times the rates recommended by the respective manufacturers. In vitro DM (IVDMD), neutral detergent fiber (NDF, IVNDFD) and acid detergent fiber (ADF, IVADFD) digestibilities were calculated after digesting the hays in buffered-rumen fluid for 6 or 48h in 2 ANKOMII Daisy Incubators. In Experiment 1, Pr and NH₃ application to BA resulted in hydrolysis of NDF into water-soluble carbohydrates (WSC). Whereas, application of both additives to BE resulted in less ADF and higher 6h IVDMD. Ammoniated hays consistently had more CP than Pr-treated or Control hays, and only NH₃ treatment increased 6 and 48h IVNDFD and IVADFD of both hays. In Experiment 2, all additive treatments decreased the NDF concentration and increased 6h IVDMD of BE. Enzyme X-20 increased the 48h IVDMD of both hays and CA and A-20 had similar tendencies. Ammonia treatment increased the 6h IVDMD of BA, the CP concentration of both hays, the 6 and 48h IVNDFD of BE, and the 48h IVNDFD of BA. The 6h IVADFD of BE hay was improved by X-20, A-20, and NH₃ treatment. Treatment with X-20 and NH₃ increased the washing loss ('a') fraction of BE, but only NH₃ treatment increased that of BA. Only ammoniation increased the insoluble, but potentially degradable ('b') fraction, the total degradable fraction (a + b) and potential degradability (P) of both forages. Therefore, these fibrolytic enzymes had negligible effects on the extent of fiber digestion and in situ DM degradation of the hays, but X-20 and A-20 treatment increased the initial and later phases of DM digestion. Ammoniation was more effective than any enzyme treatment at improving DM and fiber digestibility, and in situ degradability.