Slow-releasing urea coated with low-trans vegetable lipids: Effects on lamb performance, nutrient digestibility, nitrogen balance, and blood parameters

Abstract

The objective of this study was to produce slow-release urea (SRU) coated with low-trans vegetable fat (LTVF) and compare it to uncoated urea (U) in the diet of lambs. The first experiment evaluated LTVF-coated U produced in three different ratios (U: LTVF), 30:70 (SRU30), 40:60 (SRU40), and 50:50 (SRU50). SRU40 had higher (P < 0.05) coating yield (85.5 %) and efficiency (98 %) in comparison to SRU30 (82.9 and 96 %) and SRU50 (83.7 and 96.6 %). SRU40 maintained better thermal stability for retention and slower release of urea (P < 0.05). A second experiment tested SRU40 in 32 intact male Santa Inês lambs (average age: 6 months; average body weight: 17.9 ± 2.01 kg). The lambs were allocated in four treatments: one control diet with 0.5 % U (U0.5 %) and three levels of SRU40 [1.25 % (SRU1.25); 2.0 % (SRU2); 3.0 % (SRU3); dry matter (DM) basis] in a randomized block design to evaluate performance and ingestive behavior. A third experiment evaluated apparent digestibility, nitrogen (N) metabolism, rumen, and blood parameters of 24 intact Santa Inês lambs (average age: 6 months; average body weight: 16 ± 2.2 kg) in a randomized block design with six replications. Including SRU linearly increased ether extract (EE), and non-fiber carbohydrates intake (P < 0.05) but did not change DM, organic matter, crude protein (CP), and neutral detergent fiber assayed with heat stable amylase and expressed excluding residual ash (aNDFom), intake and performance of the lambs (P >0.05). Lambs tended to spend less time ruminating (P = 0.052) and more time eating (P = 0.078) when SRU was included in the diet. The inclusion of SRU in the diet of lambs tended to linearly increase the apparent total tract digestibility of CP (P = 0.078). There was no effect of SRU on N-intake, however, including SRU linearly reduced N-urinary excretion and linearly increased N-retention (P < 0.05). Feeding SRU1.25 % resulted in higher N-retained and lower N-urinary and N-fecal than feeding U0.5 %. Blood urea nitrogen (BUN) and rumen pH decreased linearly with the inclusion of SRU, while NH3-N concentration increased linearly (P < 0.05). Lambs fed SRU1.25 % presented higher BUN and lower NH3-N compared to lambs fed U0.5 % (P < 0.05). N-retained, microbial nitrogen and protein supply linearly increased (P < 0.05) due to the inclusion of SRU in the lambs’ diet. Lambs fed U0.5 % presented the highest (P < 0.05) BUN concentrations at all times after feeding. There was a linear decrease of BUN in lambs fed SRU at 0, 4, and 6-h post-feeding (P < 0.05). LTVF was efficient in coating urea, especially the formulation with 40 % urea and 60 % vegetable fat (SRU40). It is recommended the inclusion of SRU40 in the diet of lambs up to 3 % (total DM basis) as it improves the use of N in the rumen, reducing N-excretion and increasing N-retention, without affecting the performance of the lambs.