Studies on ammonia treatment of wheat straw: Effects of level of ammonia, moisture content, treatment time and temperature on straw composition and degradation in the rumen of sheep

Abstract

The effect of 144 different treatment conditions (NH 3 level: 0, 15, 30 and 45 g kg −1 dry matter (DM); moisture content: 120, 300 and 450 g kg −1; temperature: 20, 40, 60 and 80°C; duration: 7, 14 and 28 days) on nitrogen (N), neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin content and the rumen DM degradability of wheat straw was examined in a 4 × 3 × 4 × 3 factorial experiment. The N content of the straw was increased by ammoniation, depending on NH 3 level, moisture and temperature. Compared with untreated straw (6 g kg −1 DM0, a maximum value was reached at 29.1 g kg −1 DM (45 g NH 3 kg −1 DM, 450 g moisture kg −1 straw, 20°C). Significant NH 3 level × moisture, NH 3 level × temperature, moisture × temperature and moisture × time interactions were observed. In the straw, 89, 67 and 51% of the added N was recovered when 15, 30 and 45 g NH 3 kg −1 DM, respectively, were applied. Ammoniation (30 g NH 3 kg −1 DM) decreased NDF content from 834 to 771 g kg −1 DM on average, whereas ADF content remained almost unaffected (577 vs. 573 g kg −1 DM). The mean lignin content was 96 and 86 g kg −1 DM in untreated and NH 3-treated samples. At the higher temperature (80°C), an increase in the lignin content compared with that at 20°C in both untreated (from 78 to 115 g kg −1 DM) and ammonia-treated straw (from 74 to 99 g kg −1 DM) was observed. Rumen DM degradability of treated straw samples ranged from 36.7% (without NH 3, 120 g moisture kg −1 straw, 80°C, 28 days) to 74.4% (45 g NH 3 kg −1 DM, 450 g moisture kg −1 straw, 60°C, 7 days). Increasing the NH 3 level from 15 to 45 kg −1 DM resulted in improved DM degradability, but the dose-related additional effect became smaller. The best results were obtained with 30–45 g NH 3 kg −1 DM and a moisture content of 300 g kg −1 straw, indicating optimum conditions for ammonia treatment. Temperatures of 40–60°C enhanced the effect of treatment, whereas extending the duration of treatment did so below a temperature of ∼55°C only. The change in the in sacco DM degradability was correlated to the change in the nitrogen content by r=0.58.