Efeito de diferentes fontes de carboidratos associadas à ureia em dietas para ruminantes

Abstract

The objective was to evaluate the impact of diets containing different carbohydrates sources associated with urea on ruminal fermentation in vitro and the ruminal microorganism population profile (experiment 1); and the effect of these diets on intake and digestibility of nutrients, performance, nitrogen utilization and blood metabolic profile of finishing lambs (experiment 2). In the two experiments, four diets were tested: having Tifton-85 hay (580 g/kg dry matter) as forage and corn + soybean meal; corn + urea; cassava scraping + urea; cactus pear + urea. In the experiment 1 two tests were carried out, using the semi-automatic in vitro gas production technique. In the first assay the final incubation time was 24 h and in the second assay the final incubation time was 96 h. The experimental design was in randomized blocks, with four treatments (diets) and five blocks (inoculum). The diet containing cassava + urea resulted in greater (P<0.05) total gas production, higher methane (CH4) production and lower partitioning factor. The diets containing urea affected (P<0.05) the concentrations of isobutyrate, isovalerate and valerate in the two trials. After 96 h of incubation, the diets cassava + urea and cactus + urea reduced (P<0.05) the Ruminococcus flavefaciens population, compared to the corn + urea diet. There was also a reduction in the Streptococcus bovis population compared to the corn + soybean meal diet. In the experiment 2, 40 lambs, Santa Inês, uncastrated males, with average initial body weight of 22.8 ± 2.1 kg were used, distributed in a completely randomized design. The lambs fed with cactus + urea had lower intake (P<0.05) of dry matter (DM), organic matter (OM), lignin, total carbohydrates (TCH), non-fibrous carbohydrates and energy; lower (P<0.05) apparent digestibility of DM, OM and TCH, as well as lower final body weight and average daily gain (g/day). The lambs fed with cactus + urea also had higher (P<0.05) serum magnesium concentration, higher (P<0.05) urinary volume and higher microbial efficiency (relation between microbial N flow and the digestible organic matter fermented in the rumen). Diets containing corn resulted in higher (P<0.05) nitrogen retention and higher serum cholesterol, triglycerides and phosphorus concentration. The cassava containing diet leads to higher CH4 production, reducing fermentation efficiency. Diets containing urea in total substitution to soybean meal alter the production of short chain fatty acids and the populations of S. bovis and R. flavefaciens. The carbohydrates sources corn, cassava scraping or cactus pear, in association with urea, in finishing lambs diets, do not allow the same performance of animals intake corn + soybean meal. Diets containing corn + urea provide a gain rate in body weight of 200 g/day.