Nutritive value of thermoammoniated and steam-treated maize stover. I. Intake,digestibility and nitrogen retention

Chopped maize stover, ammoniated at ambient and elevated temperatures or steamed, was evaluated with eight wether lambs in a 4 × 4 double 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. Ammoniated materials were aerated prior to feeding. All rations were equally supplemented with molasses and soya bean meal while urea was added to treatments (i) and (iv) to increase the crude protein content to at least 12%. Ammoniation at ambient and elevated temperatures increased (P < 0.05) organic matter intake by 30 and 39%, respectively. No difference in intake occurred between the control and steam-treated stovers. However, apparent digestibility of dry matter, organic matter, neutral detergent fibre, acid detergent fibre and cellulose increased (P < 0.05) with all treated stovers. Thermoammoniation produced the greatest (P < 0.05) improvements in digestibility. Improvements in nitrogen retention were slight and non-significant with ammoniated stovers.Thermoammoniation of maize stover with 3% NH₃ and 60% H₂O for 12 h at 90°C increased the extent of digestion over ambient ammoniation and steam treatment, and is a rapid and effective method of improving the feeding value of low quality roughages.