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