Effects of chemical pretreatments on the composition and In vitro digestibility of crop by-products

Abstract

Samples of barley straw, pea straw, sugar cane bagasse and sunflower hulls were treated with sodium hydroxide, calcium hydroxide, ammonium hydroxide, anhydrous ammonia, urea, sodium chlorite, sodium chlorite plus ammonia, sulphur dioxide and chlorine gas. Different levels of the chemicals and different methods of application were used. Responses were assessed in terms of changes in chemical composition and in vitro organic matter digestibility (IVO MD) values. Treatment with anhydrous or aqueous ammonia increased the nitrogen contents of the materials; with urea-ammonia treatment the highest amount of nitrogen was retained when the samples were ensiled for 1 day, compared with those ensiled for 7, 14 or 28 days. With increases in the levels of the chemicals used the hemicellulose contents decreased, thereby decreasing the neutral detergent fibre contents. Treatment with chlorine gas resulted in higher acid detergent fibre values compared with their corresponding neutral detergent fibre values, resulting in apparently negative hemicellulose values. With barley straw (IVO MD, untreated 38%), treatment with sodium hydroxide, calcium hydroxide (by the soaking method), anhydrous ammonia, urea or sodium chlorite plus ammonia increased the IVO MD values by 18, 15, 18, 14 and 23 digestibility units, respectively. In pea straw and bagasse the maximum increases of 13 (42 versus 55) and 23 (33 versus 56) digestibility units, respectively, were obtained by treating with sodium hydroxide. In sunflower hulls (IVO MD untreated 17%), the highest IVO MD of 41% was obtained by treating with sodium chlorite followed by ammoniation.