Effects of polymer coated slow-release urea on ruminal fermentation and nutrient total tract digestion of beef steers

Rodrigo Gardinal,Gustavo Delfino Calomeni,Caio Seiti Takiya,Thiago Henrique Annibale Vendramini,Francisco Palma Rennó,Jefferson Rodrigues Gandra,José Esler De Freitas Júnior,Heraldo Namorato De Souza

doi:10.1590/s1806-92902016000200004

Abstract

The objective of this study was to evaluate the effects of polymer coated slow-release urea (SRU) in high-forage diets of beef steers on nutrient intake and digestibility, ruminal fermentation, microbial protein synthesis, and energy balance. Eight 24-mo-old rumen-fistulated castrated Nellore steers (average body weight = 418.0±40.0 kg) were used in a replicated 4 × 4 Latin square design. Animals were randomly distributed to receive one of the following diets: no urea inclusion; 1.0% inclusion of feed grade urea in the diet (dry matter [DM] basis); 1.0% inclusion of slow-release urea 1 in the diet (DM basis); and 1.0% inclusion of slow-release urea 2 in the diet (DM basis). Slow-release urea 2 had a similar composition to that of slow-release urea 1 and differed in that it contained 2.95% sulfur. A high-forage diet was provided (75% of total DM) and corn silage was used as the forage source. Diets with urea had increased crude protein (CP) intake, and CP and total digestible nutrients total tract digestion. Urea sources increased ruminal concentrations of ammonia nitrogen and acetate, and decreased butyrate concentrations. The polymer coated urea did not alter ruminal fermentation when compared with feed grade urea. Diets did not affect the energy balance of steers. Feed grade urea presented greater microbial protein synthesis than polymer coated slow-release urea. The partial replacement of soybean meal by 1% slow-release urea in a diet with 75% forage does not improve ruminal fermentation and microbial protein synthesis, and shows similar results as feeding feed grade urea to beef steers.

Highlights

Urea is the most common source of non-protein nitrogen (NPN) and is widely used in ruminant feeding because of its lower cost compared with true protein sources, representing an important source of rumen degradable protein (RDP)
The objective of this study was to evaluate the effects of polymer coated slow-release urea (SRU) in high-forage diets of beef steers on nutrient intake and digestibility, ruminal fermentation, microbial protein synthesis, and energy balance
Steers were randomly assigned to the following diets: Control, no urea inclusion; Urea, 1.0% inclusion of feed grade urea (Reforce N®, Petrobras Distribuidora S.A., Rio de Janeiro, RJ, Brazil) in the diet (DM basis); Slow-release urea 1 (SRU1: polymer coated urea synthetic polymer®, Petrobras, Distribuidora S.A., Rio de Janeiro, RJ, Brazil), 1.0% inclusion of SRU1 in the diet (DM basis); and Slow-release urea 2 (SRU2: polymer coated urea synthetic polymer®, Petrobras, Distribuidora S.A., Rio de Janeiro, RJ, Brazil), 1.0% inclusion of SRU2 in the diet (DM basis)

Summary

Introduction

Urea is the most common source of non-protein nitrogen (NPN) and is widely used in ruminant feeding because of its lower cost compared with true protein sources (e.g., soybean and cottonseed meal), representing an important source of rumen degradable protein (RDP). Urea supplementation is a common practice to meet the nitrogen requirement of animals fed high-forage diets. Dietary urea is rapidly hydrolyzed and metabolized into ammonia and CO2 by urease, which increases ruminal ammonia concentrations during the first hour after feeding. Including feed grade urea in ruminant diets has potential negative effects due to the increased level of blood ammonia, and even death by ammonia toxicity if the diet is not appropriately mixed

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