Abstract
This study was undertaken to investigate the significance and the adequate level of urea supplementation as a source of nitrogen for fully attaining potential digestibility in the ensiled NaOH-treated rice straw. Either untreated or NaOH 6%-treated ensiled rice straw was supplemented with two levels of urea, namely 0 or 2% of the straw dry matter, and with these four rations a digestion and nitrogen balance trial was conducted with four goats in a 4×4 Latin square design in the experiment 1. In the experiment 2, the ensiled NaOH 6%-treated rice straw was supplemented with four levels of urea, namely 0, 1, 2 or 2.5% of the straw dry matter and a digestion and nitrogen balance trial was conduted in the same way as in the experiment 1. In the experiment 1, for the untreated non-supplemented, the untreated 2% urea-supplemented, the NaOH-treated non-supple mented and the NaOH-treated 2% urea-supplemented straws, the dry matter digestibilities were 37.0, 37.7, 53.0 and 59.0%, respectelviy, the TDN contents were 34.7, 36.4, 46.6 and 52.6% on a dry matter basis, respectively and the dry matter intakes were 1.15, 1.15, 0.86 and 1.26% of live weight, respectively. In the experiment 2, for the 0, 1, 2 and 2.5% urea-supplemented NaOH-treated straws, the dry matter digestibilities were 43.4, 55.1, 56.2 and 58.7%, respectively, the TDN contents were 38.6, 48.4, 51.9 and 53.8% on a dry matter basis, respectively and the dry matter intakes were 0.95, 1.26, 1.26 and 1.52% of live weight, respectively. These results indicated that although the treatment of rice straw with NaOH resulted in increased energy digestibility, nitrogen was a limiting nutrient, namely an adequate supply of nitrogen was necessary to increase the rate of microbial digestion and thus the voluntary consumption of the NaOH-treated straw by the animal.
