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

R Gardinal,C S Takiya,J E Freitas Jr,F P Rennó,H N Souza,N R B Cônsolo,J R Gandra,G D Calomeni,T H A Vendramini

doi:10.5713/ajas.16.0058

Abstract

ObjectiveTwo 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.MethodsExp 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).ResultsExp 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.ConclusionFeeding 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.

Highlights

Non-protein nitrogen is an alternative to partially replace true protein sources in ruminant diets, decreasing feed cost and maintaining animal performance [1]
Despite the lower (p = 0.05) CP intake of animals fed SRB2 compared to those fed SRA2, animals fed SRB2 showed higher total tract apparent digestibility of DM, non-fiber carbohydrate, and CP compared to those fed SRA2
Authors suggested that feed grade urea could decrease DM intake when feeding at levels above 20 g/kg DM due to its low acceptability by cattle [23]

Summary

Introduction

Non-protein nitrogen is an alternative to partially replace true protein sources (i.e. soybean meal) in ruminant diets, decreasing feed cost and maintaining animal performance [1]. Among the non-protein nitrogen sources, urea is the most used in cattle diets to achieve N requirements of rumen microorganisms [2]. Urea can be rapidly hydrolyzed to ammonia in rumen and exceeds the capacity of its conversion into microbial N, because the rate of carbohydrate fermentation is slower than the rate of urea hydrolysis [3].

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Results

Conclusion