title: Influence of polymer-coated slow-release urea on total tract apparent digestibility, ruminal fermentation and performance of Nellore steers.
abstract: 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 NH3-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.
  
  
  CONCLUSIONS
  Feeding urea decreased the nutrient intake without largely affected the nutrient digestibility. In addition, polymer-coated slow-release urea sources decreased ruminal ammonia 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.
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: R
authors.initials: R
authors.lastname: Gardinal
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: G D
authors.initials: GD
authors.lastname: Calomeni
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: N R B
authors.initials: NR
authors.lastname: Cônsolo
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: C S
authors.initials: CS
authors.lastname: Takiya
authors.affiliation: Department of Animal Sciences, Federal University of Bahia, Salvador, BA 40170-110, Brazil.
authors.forename: J E
authors.initials: JE
authors.lastname: Freitas
authors.affiliation: Department of Animal Sciences, Universidade Federal da Grande Dourados, Dourados, MS 79804-970, Brazil.
authors.forename: J R
authors.initials: JR
authors.lastname: Gandra
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: T H A
authors.initials: TH
authors.lastname: Vendramini
authors.affiliation: Petrobrás, CENPES, 21040-000, Rio de Janeiro, RJ, Brasil.
authors.forename: H N
authors.initials: HN
authors.lastname: Souza
authors.affiliation: Department of Animal Nutrition and Production, School of Veterinary Medicine and Animal Science, University of Sao Paulo (USP), Pirassununga, SP 13635-900, Brazil.
authors.forename: F P
authors.initials: FP
authors.lastname: Rennó
keywords: Ammonia; Average Daily Gain; Non-protein Nitrogen; Slow-release Urea