Lipid microspheres of different waxes containing urea enriched with a sulfur source for slow release in the rumen

Abstract

The objective of this study was to obtain and characterize slow-release urea microspheres (SRU) from carnauba wax (CW) and beeswax (BW) with and without enrichment of sulfur source (S). In the 1st experimental stage, we obtained and characterized slow-release urea (SRU) microspheres with a fixed ratio of 2:1(wax:urea), enriched or not of sulfur (magnesium sulfate heptahydrate) from the emulsification/lyophilization technique using urea as core into carnauba wax matrix added (CWUS) or not (CWU) of S source, and urea into beeswax matrix added (BWUS) or not (BWU) of S source. All formulated microencapsulated systems showed high yield values, raging 92.9–107% for BWU and CWU, respectively, with the highest SRU yields (P < 0.001) from CW compared to BW, and higher yields on materials without the presence of sulfur (S). The highest (P < 0.001) microencapsulation efficiency was observed in the SRU using BW, while the lowest yield occurred in the SRU-CWUS, where there was sulfur in the particle (P < 0.001). As for the determination of water activity, with values ranging 0.47–0.72, for BWU and CWUS, respectively. Thermal analyses (TG and DSC) indicated that the presence of the S source reduced the effectiveness of urea protection, and beeswax as an encapsulant showed higher thermal stability. In the 2nd experimental stage, five rumen-fistulated sheep with average body weight 48.9 ± 5.23 kg and age of 24 ± 2 months were assigned in a 5 × 5 Latin square design, with five consecutive 18-day periods divided into 13-day adaptation and five treatments [Urea free (U) as control and four SRU (BWU, BWUS, CWU, and CWUS)]. The SRU showed smooth surfaces with little cavities mainly for BW particles. The use of free urea provided lower concentrations of total proteins and creatinine and higher (P < 0.05) concentrations of BUN and AST compared to animals receiving SRU regardless of the type of encapsulant or the presence of S. However, the serum concentrations of albumin, AST, cholesterol, creatinine, total protein, and triglycerides showed no significant effect comparing only SRU. The sheep show higher concentrations of serum urea 8 h after feeding in comparison to the collection before (0 h) of feeding. Although all microparticles showed potential for SRU in the rumen, the system without added S and with beeswax showed higher encapsulation efficiency and is the most suitable for the diet of adult sheep.