Ammonia and sulfur dioxide treated wheat straw as a feedstuff for cattle

Abstract

Wheat straw was treated with anhydrous NH 3 at 0, 1.75 or 3.50% of dry matter (DM) and then with SO 2 (0, 2, 3, 4 and 5% DM) for either 3 or 7 days. Dry matter degradability (DMD) was measured using an in situ nylon bag technique. Nitrogen retention and DMD of the wheat straw was increased by the ammoniation ( P < 0.001, linear and quadratic) with a significant NH 3 × SO 2 interaction ( P < 0.05). Main effects for SO 2 also showed increased DMD and crude protein (CP) at 0, 2, 3, 4 and 5% levels ( P < 0.001). The 7 day treatment with SO 2 resulted in increased DMD (62.0% vs. 59.7%, P < 0.001). Two feeding trials were conducted with wheat straw treated with either NH 3 alone or a combination of NH 3 and SO 2. In Study 1, growing beef heifers were fed: (a) untreated straw (US); (b) ammoniated straw (AS); (c) NH 3 + SO 2 treated straw; (d) NH 3 + SO 2 treated straw (43% DM) and hay (57% DM); (e) bromegrass hay (H) alone fed ad libitum. All heifers received 1.3 kg of supplement in two daily meals. Intake of NH 3 + SO 2 treated straw for the first 28 days was very low compared with AS (1.8 kg vs. 3.8 kg), resulting in severe weight loss (−600 g day −1). This treatment was replaced by a mixture of NH 3 + SO 2 treated straw (43% DM) and haylage (57% DM) for the rest of the trial (10 weeks). Ammoniation of wheat straw did not significantly increase DM intakes (DMI) compared with US (5.99 kg day −1 vs. 5.12 kg day −1, P > 0.05) but improved average daily gain (ADG) (510 g vs. 347 g, P < 0.02). Heifers fed NH 3 + SO 2 treated straw and either haylage or hay consumed more feed (7.27 kg day −1 and 8.07 kg day −1 vs. 5.99 kg day −1) and gained more weight (833 g day −1 and 816 g day −1 vs. 510 g day −1) than animals fed AS. Animals fed H had DMI and ADG values similar to those fed NH 3 + SO 2 treated straw and hay ( P > 0.05). The second trial was done to determine the effects of chemical treatment of straw on ruminal function and fiber digestion. The diets, offered ad libitum with a supplement, were US, AS, NH 3 + SO 2 treated straw alone and with hay. There was no effect of diet on ruminal dilution rate. The DMD values of the US, AS, NH 3 + SO 2 treated straw, and H were 48%, 58%, 68% and 62%, respectively. When fed as the only forage, NH 3 + SO 2 treated straw resulted in anorexia and weight loss; however, when fed at 43% of diet DM, feed intakes and weight gains of heifers were better than AS and similar to H. In summary, the combined use of NH 3 and SO 2 at ambient temperatures has potential as a practical method for treatment of wheat straw.