Lipid microspheres containing urea for slow release of non-protein N in ruminant diets

Abstract

Context Urea is widely used in ruminant diets as a source of non-protein nitrogen (NPN), partially substituting for true protein in feed, but high levels of urea in the diet may cause toxicity. Aims This study investigated the microencapsulation of urea in carnauba wax for slow release in the rumen to improve the N efficiency and growth of sheep. Methods Two microencapsulated systems were developed with urea:carnauba wax ratios (w/w) of 1:2 (U12) and 1:4 (U14). Based on the initial characterisation, only U12 was examined in an in vivo experiment with Santa Ines crossbred male sheep (n = 40) initially weighing 28 ± 0.6 kg at 270 days of age. The experimental arrangement was a completely randomised design, and the animals were distributed into four treatments; i.e. four levels of inclusion (0, control; 15; 30; and 45 g/kg DM) of microencapsulated urea in the diet. Key results The dietary inclusion of microencapsulated urea was associated with linear increases (P = 0.05) in the intake of DM and metabolisable energy, the digestibility of crude protein, non-fibrous carbohydrates and fibre fractions, and N balance. Additionally, liveweight gain and feed efficiency increased quadratically (P < 0.001). There were also linear reductions (P < 0.001) in blood urea and urinary urea concentrations. Conclusions The study demonstrated that the inclusion of up to 30 g/kg U12 microencapsulated urea can be recommended as a source of slow-release urea in sheep diets since it improved the performance and feed efficiency and promoted lower concentrations of blood urea and urinary urea. Implications The use of urea microencapsulated in carnauba wax can reduce the risk of urea toxicity and provide a safer way to supply NPN to ruminants and improve N utilisation.