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 40 g/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 48 h 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 6 h IVDMD. Ammoniated hays consistently had more CP than Pr-treated or Control hays, and only NH3 treatment increased 6 and 48 h IVNDFD and IVADFD of both hays. In Experiment 2, all additive treatments decreased the NDF concentration and increased 6 h IVDMD of BE. Enzyme X-20 increased the 48 h IVDMD of both hays and CA and A-20 had similar tendencies. Ammonia treatment increased the 6 h IVDMD of BA, the CP concentration of both hays, the 6 and 48 h IVNDFD of BE, and the 48 h IVNDFD of BA. The 6 h 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.