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

Abstract

ContextUrea 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.AimsThis study investigated the microencapsulation of urea in carnauba wax for slow release in the rumen to improve the N efficiency and growth of sheep.MethodsTwo 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±0.6kg 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 45g/kg DM) of microencapsulated urea in the diet.Key resultsThe 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.ConclusionsThe study demonstrated that the inclusion of up to 30g/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.ImplicationsThe 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.