Chemical composition and digestion in vitro of orchardgrass hay ammoniated by different techniques

Abstract

Two experiments were conducted to assess how various treatment conditions affect the quality of ammoniated orchardgrass ( Dactylis glomerata L.) hay. In the first, ammonia was applied at a rate of 36 g kg −1 dry weight (DW) either in anhydrous or aqueous form to a mature orchardgrass hay that had been reconstituted to 150 or 300 g water kg −1 wet weight (WW). The hay was treated in 2-1 glass containers that were either enclosed, or open at the top to allow gaseous exchange with the atmosphere. Increases in total nitrogen (N) and non-exchangeable N (NEN) were greatest for the higher moisture hay treated in closed containers. Ammonia treatment under these conditions increased total N and NEN by 19.4 and 11.1 g kg −1 DW, respectively, for hay treated with anhydrous NH 3, and 17.4 and 9.2 g kg −1 DW, respectively, for hay treated with aqueous NH 3. Concentrations of free NH 3 in the containers decreased exponentially with respect to time during the week following treatment and were lower for hay treated in open containers. For hay treated with anhydrous NH 3 in closed containers, free NH 3 concentrations were lower for high-moisture hay throughout the measurement period, indicating the importance of moisture for NH 3 absorption by hay. Increases in the digestibility in vitro of dry matter and fibre constituents were greatest for high-moisture hay treated in closed containers. Average increases in the digestibility of dry matter, neutral detergent fibre (NDF), hemicellulose and cellulose were 182, 244, 198 and 230 g kg −1 DW, respectively, for hay treated under these conditions. There were no differences in digestibility due to the form in which ammonia was applied. In the second experiment, anhydrous NH 3 was applied to orchardgrass hay from the same lot as that used in Exp. 1 at rates of 18, 36, 72, 108 and 144 g kg −1 DW in either enclosed or open ammoniation containers. The moisture concentration of this hay was 200 g kg −1 WW. Increases in total N and NEN occurred nonlinearly with respect to treatment rate with the largest increases occuring for hay treated in closed containers. Maximum increases in total N and NEN in the closed system were 17.2 and 15.1 g kg −1 DW, respectively, as compared to 11.2 and 9.1 g kg −1 DW in the open system, respectively. Increases in the digestibility in vitro of NDF were nonlinear and largest for hay treated in closed containers. Ammoniation of hay in closed containers at 18, 36, 72, 108 and 144 g kg −1 DW increased NDF digestibility by 111, 204, 214, 204 and 212 g kg −1 DW, respectively.