Effects of dietary supplementation with slow-release urea coated with carnauba wax on intake, ingestive behavior, selectivity, ruminal parameters, performance and carcass traits of lambs

Abstract

This study developed slow-release urea microparticles coated by carnauba wax (SRU_WAX), and evaluated their effect on intake, ingestive behavior, selectivity, ruminal parameters, performance, and carcass traits of lambs. Firstly, a completely randomized design with three SRU formulations through fusion-emulsification was adopted. Three SRU were produced [SRU_50:50, SRU_60:40 and SRU_70:30 based on shell (carnauba wax) and core (urea) ratios] and characterized. SRU_70:30 and SRU_60:40 showed the highest yields averaging 96 and 94 %, also exhibiting the highest coating efficiencies with values close to 99 %. Among the formulations evaluated, SRU_50:50 showed the highest urea retention percentage when compared to SRU_60:40 and SRU_70:30. The crude protein (CP) content of SRU_60:40 was 13 % higher than that of SRU_70:30. Microscopic analysis revealed similar characteristics among SRU formulations. Differential Scanning Calorimetry indicated that the melting points were similar. Therefore, the formulation 60:40 presented better traits, and it was used in the lamb’s diet. Fifty male lambs (Santa Ines × Dorper) weighting an average 31.2 ± 4.8 kg, were assigned to a completely randomized design consisting of five treatments with ten replications. The experiment included a control treatment containing 4.0 g of free urea (U_FREE), and four SRU_WAX inclusion levels: 10, 20, 30, and 40 g/kg of total dry matter (DM). SRU_WAX did not affect (P > 0.05) the DM intake and its nutritional fractions. Diet selectivity estimates from the nutrients effectively consumed OM, EE, and _aNDF_om and dietary particle size were not influenced by the form of urea supply (P > 0.05). However, there was a linear increase on the concentrations of TDN and NFC and a linear reduction in the concentrations of CP effectively consumed due to the inclusion of SRU_WAX (P < 0.05). The form of urea supply (U_FREE × SRU_WAX) did not affect (P > 0.05) the ingestive behavior, performance and carcass traits of the lambs. However, SRU_WAX addition linearly increased (P = 0.032) the number of boli chewed/day. There was interaction effect (P < 0.05) between treatment and time after feeding to ruminal pH and N-NH₃. Including SRU_WAX at 40 g stabilized ruminal pH closer to neutrality compared to other treatments. U_FREE resulted in higher peak NH₃-N concentrations compared to SRU_WAX, without difference to SRU_WAX levels. SRU_WAX inclusion in the diet linearly reduced (P < 0.01) the final weight, average daily gain (ADG), hot carcass weight, and feed efficiency of the lambs. Carnauba wax was confirmed as an excellent shell for urea protection, and the best proportion was 60:40 (shell: core). However, the addition of SRU_WAX at levels up to 40 g/kg of DM to lamb diets did not result in significant improvements in weight gain or carcass characteristics compared to the use of free urea. Therefore, the selection of a urea-release controlled for lamb feedlot finishing should prioritize economic return.