NUTRITIVE-VALUE OF THERMOAMMONIATED AND STEAM-TREATED MAIZE STOVER .2. RUMEN METABOLITES AND RATE OF PASSAGE

Chopped maize stover, ammoniated at ambient and elevated temperatures or steam treated, was evaluated with four Cheviot crossbred wethers fitted with permanent rumen fistulae in a 4 × 4 Latin square design. Treatments were: (i) control, 60% H2O, ensiled for at least 40 days; (ii) 3% NH3, 60% H2O for 30 days at 21°C; (iii) 3% NH3, 60% H2O for 12 h at 90°C; (iv) steamed at 16.2 kg/cm2 and 213°C for 4 min. The sheep received two meals per day at a restricted level of 90% of lowest ad libitum intake. The markers 51Cr-EDTA (100 μ ci) and 103Ru-phenanthroline complex (10 μ ci) were used for the liquid and particulate phases, respectively. Samples for rumen metabolites were collected in each period at 0, 0.5, 1.0, 2.0, 3.0, 4.0, 6.0 and 8.0 h after the morning meal. On the following day, a mixture of the markers in 200 ml of demineralized water was infused into the rumen in a single dose and rumen fluid was sampled at specific times for 4 days. Rumen fluid pH tended to be lower with ammoniated stovers. High NH3-N levels were maintained with ammoniated stovers, indicating gradual release of nitrogen. Total VFA tended to increase more with the thermoammoniated stover. Molar proportions of propionate increased (P < 0.05) and butyrate decreased (P < 0.05) with ammoniation. In contrast, steam treatment increased (P < 0.05) molar proportions of acetate and butyrate. The largest decrease (P < 0.05) for C2 : C3 acids occurred with thermoammoniated stover. Treatments with NH3 or steam increased (P < 0.05) dilution rate. Mean retention time of particulate matter was decreased (P < 0.05) by treatment, being shortest with steamed material. © 1979.