Effect of Ammoniation Treatment of Wheat Straw on in Vitro and in Vivo Digestibility

Ammoniation treatment of wheat straw (WS) was evaluated with in vitro and in vivo digestibility trials. The WS used in the in vitro trial was treated with either anhydrous ammonia (NH3, saturated) or ammonium hydroxide (NH4OH, 5% of as fed WS). Both treated straws were stored at 29 C for 21 d. Crude protein (CP) content and in vitro dry matter digestibility increased (P<.05) from 3.6 to 9.8% and from 13.8 to 31.8%, respectively, with the NH3 treatment, and from 3.6 to 11.9% and from 13.8 to 32.9%, with the NH4OH treatment. The WS used in the in vivo trial was treated with NH3 under ambient conditions (mean temperature: 6.1 C for 44 d) with 50 g NH3/kg WS. Five crossbred wether lambs (average weight 35 kg) were allotted to each of the following treatments: (1) untreated WS + feather meal (FM; 7.9% CP); (2) NH3-treated WS (8.1% CP); (3) untreated WS + FM (13.5% CP) and (4) NH3-treated WS + FM (12.1% CP). Daily CP intake/head for lambs on treatment 1, 2, 3 and 4 were (grams): 39.1, 38.0, 72.5 and 71.1, respectively. Apparent dry matter (DM) and acid detergent fiber (ADF) digestibilities were higher (P<.05) in treatments that contained NH3-treated WS, with coefficients of (1) 50.0, 45.2; (2) 52.1, 52.3; (3) 51.5, 46.4 and (4) 55.0, 52.5%, for treatments 1, 2, 3 and 4, respectively. Organic matter (OM) digestibility was lowest (P<.05) in treatment 1, and there were no differences among the other treatments. Apparent crude protein and acid detergent lignin digestibilities were higher (P<.05) in treatment 3 than for the other treatments. Gross energy digestion coefficients were not different (P>.05) among treatments. Results suggest that treatment of WS with NH3 will improve digestibilities of DM, OM, CP and ADF, and that anhydrous ammonia is as effective as NH4OH in improving digestibility of WS.