Potencial forrageiro de um híbrido de sorgo com capim-sudão portador da mutação bmr colhido em quatro estádios de maturação

Abstract

The use of sorghum-sudangrass hybrids contributes to the development of systems that produce high-quality forages year-round. The objective of this research was to determine the effect of maturity stage of the brown midrib mutant sorghum-sudangrass hybrid BR007Abmr x TX2785Rbmr on the agronomic traits, chemical composition, ruminal degradation kinetics, intake, digestibility and nitrogen (N) utilization by sheep. The hybrid was evaluated at 77, 84, 91 and 98 days (d) after sowing. Plant height, dry matter yield, digestible dry matter yield, percentage of stems and percentage of panicles increased linearly over time whereas the percentage of leaves decreased linearly. Whole plant dry matter (DM) content ranged from 12.3 to 15.2% with quadratic effect. Whole plant neutral detergent fiber (NDF) ranged from 59.1 to 68.4% and increased linearly. Mean acid detergent fiber (ADF) content of the whole plant, stems and leaves were 36.8, 40.4 and 31.5%, respectively. Acid detergent lignin content of the whole plant and stems varied from 2.9 to 4.4% and 3.2 to 4.4%, respectively, and increased linearly. Whole plant and leaves mean crude protein (CP) content were 10.2% and 17.4%, respectively. In vitro DM digestibility of the whole plant, stems and leaves ranged from 64.9 to 75.9, 60.6 to 73.7 and 63.5 to 68.9%, respectively, and decreased linearly over time. The soluble fraction of CP was high (>44%) in all evaluated stages. The undegradable fraction of DM and CP linearly increased with maturity, while ruminal disappearance rate and effective degradability of DM, NDF and CP linearly decreased. DM, digestible DM, CP, digestible CP, NDF and digestible NDF intake ranged from 76.8 to 54.0, 49.0 to 31.6, 9.40 to 6.02, 5.86 to 2.88, 45.5 to 32.1 and 27.1 to 17.0 g kg-1 BW0.75 d-1, respectively, and decreased linearly with advancing maturity. DM, CP and NDF digestibility ranged from 63.5 to 52.3, 61.9 to 45.1 and 59.2 to 47.3%, respectively, and decreased linearly along the harvest ages. The digestible energy content of this hybrid ranged from 2.50 to 2.10 Mcal kg-1 DM and decreased linearly with advancing maturity. N intake, urinary N, retained N and the ratio between retained N and N intake ranged from 23.1 to 15.0 g d-1, 7.25 to 4.14 g d-1, 7.11 to 2.67 g d-1 and 30.7 to 17.6%, respectively, and also decreased linearly along time. Fecal N was not influenced by the maturity stage and presented a mean value of 8.21 g d-1. The hybrid evaluated herein presents high nutritional value and yield potential but the nutritional values decreases and the yield potential increases with advancing maturity.