Influence of polymer-coated slow-release urea on total tract apparent digestibility, ruminal fermentation and performance of Nellore steers

Objective: Two experiments were performed to evaluate the effects of coated slow-release urea on nutrient digestion, ruminal fermentation, nitrogen utilization, blood glucose and urea concentration (Exp 1), and average daily gain (ADG; Exp 2) of steers.Methods: Exp 1: Eight ruminally fistulated steers [503±28.5 kg body weight (BW)] were distributed into a d 4×4 Latin square design and assigned to treatments: control (CON), feed grade urea (U2), polymer-coated slow-release urea A (SRA2), and polymer-coated slow-release urea B (SRB2).Dietary urea sources were set at 20 g/kg DM.Exp 2: 84 steers (350.5±26.5 kg initial BW) were distributed to treatments: CON, FGU at 10 or 20 g/kg diet DM (U1 and U2, respectively), coated SRA2 at 10 or 20 g/kg diet DM (SRA1 and SRA2, respectively), and coated SRB at 10 or 20 g/kg diet DM (SRB1 and SRB2, respectively).Results: Exp 1: Urea treatments (U2+SRA2+SRB2) decreased (7.4%, p = 0.03) the DM intake and increased (11.4%, p<0.01) crude protein digestibility.Coated slow-release urea (SRA2+-SRB2) showed similar nutrient digestibility compwared to feed grade urea (FGU).However, steers fed SRB2 had higher (p = 0.02) DM digestibility compared to those fed SRA2.Urea sources did not affect ruminal fermentation when compared to CON.Although, coated slow-release urea showed lower (p = 0.01) concentration of NH 3 -N (-10.4%) and acetate to propionate ratio than U2.Coated slow-release urea showed lower (p = 0.02) urinary N and blood urea concentration compared to FGU.Exp 2: Urea sources decreased (p = 0.01) the ADG in relation to CON.Animals fed urea sources at 10 g/kg DM showed higher (12.33%, p = 0.01) ADG compared to those fed urea at 20 g/kg DM.Conclusion: Feeding urea decreased the nutrient intake without largely affected the nutrient digestibility.In addition, polymer-coated slow-release urea sources decreased ruminal ammo nia concentration and increased ruminal propionate production.Urea at 20 g/kg DM, regardless of source, decreased ADG compared both to CON and diets with urea at 10 g/kg DM.