Effect of slower nitrogen releasing additive on the quality of napiergrass (Pennisetum purpureum Schumach.) silage

Urea is commonly used as a feed additive to improve the quantity of nitrogen (N) and digestibility in ruminants. Supplementation of urea increases crude protein but decreases the fermentation quality of silage with increasing pH by releasing ammonia N. Thus, oxalic acid diamide (oxamide, O) and guanyl urea sulfate (GU), N slow-release compounds, were used as additives in the present study. As much as 650 grams of the napiergrass were ensued into a laboratory silo (1.0 liter polyethylene container). The treatments were: no additive (control), O, O+glucose (OG), GU and GU+glucose (GUG). O and GU were added at the level of 0.23% N on the napiergrass fresh weight basis, and glucose was added at 1%. Silage was incubated for 7, 15, 30 and 60 days at room temperature (28°C). After the silo was opened, pH, contents of dry matter, total nitrogen (TN), volatile basic nitrogen (VBN) and organic acids were determined. Compared with the control, OG, GU and GUG treatments significantly decreased pH value, VBN/TN, acetic acid and butyric acid contents, and significantly increased contents of dry matter, TN and lactic acid after 60 days of fermentation. The length of storage did not affect dry matter, lactic acid and TN contents and VBN/TN. In conclusion, without glucose addition GU may be a good N supplement for silage making of napiergrass, but glucose is necessary to improve fermentation quality when ensiled with O additive.