Avaliação agronômica e nutricional de híbridos de sorgo com Capim-sudão, normais e mutantes BMR - Portadores de nervura marrom

Abstract

The aim of this study was to evaluate and compare the forage potential, chemical composition, voluntary intake, digestibility, net energy and kinetics of degradation of sorghum and sudangrass hybrids, normal and mutant BMR (brown midrib). In Chapter III, the agronomic characteristics and chemical compositions of 13 sorghum and sudangrass normal hybrids and 12 mutant BMR hybrids were evaluated and compared in two successive cuts, at 51 days after planting and 31 days regrowth. The values of green matter (GM) and dry matter production (DM) ranged, respectively, from 18.6 to 51.2 t/ha and 1.6 to 5.1 t/ha. Comparing the pairs of hybrid strains, the GM and DM productions of normal hybrids were respectively 16.25% and 24.64% higher than the average production of mutant BMR hybrids. The values of dry matter in vitro digestibility (DMIVD) ranged from 61.81% to 76.02%. Comparing the six pairs of isogenic hybrids, the average of DMIVD of mutants BMR hybrid was 6.75% higher than the average of their normal pair. In Chapter IV, the agronomic characteristics and chemical compositions of 3 sorghum and sudangrass, two normal (BR 800 and CMSXS156A * Tx2785) and one mutant BMR (CMSXS156Abmr * Tx2785bmr) were evaluated and compared in two successive cuts, at 64 days after planting and 60 days of regrowth. The values of GM and DM productions, respectively, ranged from 15.1 to 32.3 t/ha and 1.67 to 5.43 t/ha. The coefficient of DMIVD had a high negative correlation (P<0.05) with the accumulation of fibrous fractions in the whole plant and stem, and plant height. The DMIVD of the whole plant ranged from 56.23% to 69.83%. For the whole plant, leaf and stem fractions, DMIVD coefficients observed for the mutant BMR hybrid were higher (P<0.05) than those observed for their normal isogenic pair. In Chapter V, it was evaluated the apparent digestibility of the nutritional components of sorghum and sudangrass, and two normal and one mutant BMR. No significant difference (P>0.05) was observed between hybrids for dry matter digestibility, however, for dry matter intake and dry matter digestible per unit of metabolic weight, the hybrid mutant CMSXS156Abmr * Tx2785bmr was better (P<0.05) than normal hybrids. The NDF and ADF digestibilitiy, and NDF and ADF digestible intake were higher (P<0.05) for the mutant hybrid CMSXS156Abmr * Tx2785bmr compared to their normal isogenic pair. The hybrid mutant CMSXS156Abmr * Tx2785bmr also presented values higher (P<0.05) than their normal isogenic pair for digestible, metabolizable and net energy intake. In Chapter VI, it was evaluated the kinetics of rumen fermentation of sorghum and sudangrass, normal and mutant BMR, by the in vitro semi-automated gas production, using inocula of cattle. For the total gas production (TGP) at 96 hours of incubation, the average value of the mutants BMR materials was 234.56 mL/g DM, while the average value of standard materials was 169.32 mL/g DM. For the DM degradability (DMD) at 96 hours of incubation, the average value of the mutants BMR materials was 82.23% while the average value of standard materials was 75.68%. For the model of France et al. (1993) parameters, average value of the mutant BMR materials was 234.56 mL/g DM, while the average value of standard materials was 169.32 mL/g DM. The gas production rates ranged from 0.042 to 0.064 mL/h, respectively for the average hybrid in normal and mutant BMR version. The colonization time ranged from 4hrs and 16min to 5hs and 23min, respectively for the average of the hybrids in mutant BMR and normal versions. The results of this study demonstrate the potential use of sorghum and sudangrass BMR production systems of ruminants with high performance.