Effect of different sources of nitrogen on in situ degradability and feed intake of Zebu cattle fed sugarcane tops (Saccharum officinarum)

Research projects were conducted to determine the amount of nitrogen needed to maximize the dry matter intake (DMI) and degradability in steers consuming sugarcane tops (SCT). Four Zebu steers were allocated in four experiments under a 4×4 Latin square design and fed SCT as basal forage. The nitrogen sources were Taiwan grass (TG) at 0, 100, 200 and 300 g/kg; poultry manure (PM) 0, 100, 200 and 300 g/kg; urea at 0, 8, 16, and 24 g/kg of DM and high-nitrogen/energy supplement (HNES) 0, 500, 1000 and 1500 g fresh matter/(animal day). The addition of nitrogen increased the total DMI and SCT intake in all experiments, except in experiment 1, where, TG had a substitution effect on SCT intake. The intake of PM was 100 g/kg DM in all treatments in experiment 2, regardless the quantity of PM offered. Organic matter intake (g/kg W0.75) increased with supplementation in all experiments (P<0.05). The fractional degradation rate increased with nitrogen supplementation; however, there were no effect on the higher levels of supplementation in all experiments. The addition of a source of nitrogen increased the rumen ammonia concentration in all experiments. The fractional degradation rate of King grass as well as DMI of SCT were optimized when NH3 concentration was in the range of 90–110 mg/l in experiments with PM, urea and HNES. These trials confirmed that SCT are a potential source of forage for cattle, but as sole food were deficient in nitrogen. However, it is possible to supply this nitrogen by 100 g PM/kg DM, 8 g urea/kg DM or 500 g of HNES to satisfy the needs of rumen microorganisms for fermentable nitrogen in SCT diets.