Effect of prolonged treatment of wheat straw with urea or a urea/caustic soda combination during baling on the nutritional value thereof for sheep.
A study was undertaken to investigate the treatment of wheat straw with urea or urea plus caustic soda (combined treatment) during baling. Wheat straw treated as above, as well as wheat straw ammoniated with urea using a stack method, was evaluated in an intake and in vivo digestibility study with sheep following 2, 4, 8, 12 and 18 weeks of treatment. Untreated wheat straw was evaluated solely for reference purposes. Voluntary intake of all three treatments tended to be at its lowest level after two weeks of treatment. The voluntary intake of the combined treatment straw was higher (P ≤ 0,05) than that of the urea ammoniated straw, whether treated in the stack or in the baler (38,7 and 28,5% respectively). The organic matter digestibility of all three treatments increased by 22,7 to 28,9% after 2 weeks of treatment. The organic matter digestibility was significantly improved (P ≤ 0,05) by increasing the treatment period from 2 to 12 weeks. The combined treatment with urea/caustic soda did not show any additive effect with regard to organic matter digestibility. The neutral detergent fibre, acid detergent fibre and hemicellulose digestibilities tended to improve as the treatment period increased. The crude protein digestibility of the urea ammoniated straw was significantly (P ≤ 0,05) lower after 12 and 18 weeks treatment compared to a treatment period of 2 weeks. The nitrogen balance of sheep fed all three treated straw diets varied around zero, and no significant differences occurred