Studies on ammonia-treated straw. I. The effects of type and level of ammonia, moisture content and treatment time on the digestibility in vitro and enzyme soluble organic matter of oat straw

Abstract

Oat straw containing 2.5, 5.0, 7.5 and 10.0% moisture was treated with anhydrous or aqueous ammonia at 20 and 40 g NH 3/kg dry matter for 3 and 6 weeks at room temperature (17–20° C). Samples were milled and used for determinations of digestibility of dry matter in vitro (IVDMD) and of organic matter (IVOMD) and also enzyme solubility (ESOM). The moisture contents of the straw after treatment corresponded fairly well with those planned. Both types of ammonia improved the IVDMD, IVOMD and ESOM of the straw as compared with the untreated samples. However, aqueous ammonia caused significantly higher improvements than did anhydrous ammonia. The averages of IVDMD, IVOMD and ESOM of the straw were 61.9, 64.2 and 25.6 with aqueous ammonia, and 54.7, 57.4 and 18.9 with anhydrous ammonia. The 40 g kg −1 level of ammonia was more effective than the 20 g kg −1 level; this trend was more clear with aqueous than with anhydrous ammonia. The effects of both types of ammonia were more pronounced at 6 weeks than at 3 weeks. The results showed that treatment with 40 g kg −1 aqueous ammonia for 6 weeks improved the IVDMD, IVOMD and ESOM to 69.4, 71.7 and 33.4, respectively. However, anhydrous ammonia in the same conditions gave values of 58.3, 61.2 and 22.2, respectively. The ammonia treatment was less effective at low than at higher moisture contents, particularly with anhydrous ammonia. It was concluded that maximal improvement in the nutritive value of the oat straw was obtained when straw containing 7.5% moisture was treated with 40 g kg −1 aqueous ammonia for 6 weeks. With this treatment values for IVDMD, IVOMD and ESOM of oat straw were 72.5, 74.5 and 35.5, respectively.