Slow-rfifase urea in the l amr rumfn ry mtrosphfrfs vegetable fat

Abstract

This study characterized and defined the optimal ratio of low-trans vegetable fat (LTVF) and urea that enables protection of urea for slow-release in rumen by evaluating the physicochemical properties of the material, and the effect of inclusion of levels of the best ratio compared to conventional urea in sheep diets. In the first experiment, three LTVF ratios of 30:70 (SRU30), 40:60 (SRU40) and 50:50 (SRU50). All formulations showed microencapsulation yields above 80%, but the proportion SRU40 showed higher microencapsulation efficiency (85.5%), retaining the highest percentage of urea with 115% crude protein (CP) and higher thermal stability (P <0.05). In the second experiment, the SRU40, just named SRU was included in the diets of lambs, evaluating five treatments: a control treatment with 0.5% free urea (U0.5) in DM and four treatments with SRU40 levels added in the diets at the proportions of 1.25% (SRU1.25), 2.0% (SRU2) and 3.0% (SRU3) of total diet DM. To evaluate the N metabolism, 24 uncastrated Santa Inês lambs with a mean age of six months and mean body weight of 16 ± 2.2 kg were distributed in a randomized block design with two blocks, four treatments and six replications. To evaluate rumen parameters, four Santa Ines sheep with approximately 40 ± 0.5 kg body weight, fistulated and cannulated in the rumen, were distributed in a double 4 × 4 Latin square. The different forms of urea offered (free and protected) and levels of SRU inclusion did not change the intake of DM and N. SRU linearly reduced (P <0.05) N-urinary excretion, impacting on the linear increase of N retention and microbial protein. The inclusion of SRU linearly reduced (P <0.05) the rumen pH at 1 h, 4 h, and 6 h after feeding, but not at 2 h (P = 0.25) after feeding. The inclusion of SRU linearly increased the concentration of BUN and tended to linearly increase the concentration of total proteins and AST (P <0.05). SRU1.25 promoted lower BUN concentration (P <0.05) compared to U0.5, and SRU1.25 diets tended (P = 0.059) to have lower serum magnesium in sheep compared to U0.5. BUN in lambs linearly decreased in relation to offer time and treatments, with the highest BUN concentrations for U0.5 at 0, 4 and 6 h after feeding (P <0.05). SRU diets promoted BUN peak after 2 h of feeding, with the same concentration compared U0.5 (P = 0.117). Rumen pH decreased linearly 1 h after feeding as well as 415 h and 6 h (P <0.05), however, it did not vary at 2 h (P = 0.246). There was a linear increase at 1, 2, 4 and 6 h after the first hour pos-feeding (P <0.05). Low-trans vegetable fat was efficient in encapsulating urea, especially the formulation in the proportion of 40% urea and 60% vegetable fat (SRU40). SRU40 is recommended in sheep’s diets with up to 3% as DM, replacing soybean meal, as it improves N metabolism of animals.