Valor nutricional do capim-elefante verde em diferentes idades de corte

Abstract

This study was undertaken to evaluate the nutritional value of fresh elephant grass harvested with different regrowth ages (56, 84 and 112 days). To achieve this objective three experiments were carried out: in situ digestion kinetics (experiment I), semi-automated in vitro gas production technique (experiment II), and indirect calorimetry assay (experiment III). The elephant grass harvested with 56 days of regrowth had higher values of dry matter (22.52%) and crude protein (45.09%) readily digested fraction. The rates of dry matter digestion were 4.08, 3.29 and 2.25%/hour for 56, 84 and 112 days of regrowth, respectively. The crude protein potentially digestible fraction ranged from 56.52 to 84.80% for the grass harvested with 56 and 112 days, respectively. The neutral detergent fiber rate of digestion decreased with maturity, ranging from 3.89 to 2.03%/hour. Maturity of the grass affected negatively rumen fermentation kinetics evaluated through the semi-automated in vitro gas production technique. The grass harvested with 56 days had higher cumulative gas production (210.50 ml/g dry matter) and dry matter disappearance (63.8%) at 96 hours of incubation, and the other regrowth ages of the grass did not differ between themselves. The maximum potential of gas production varied between 187.98 and 200.13 ml/g of dry matter. Sheep fed elephant grass with 56 days of regrowth had higher dry matter and gross, digestible and metabolizable energy intakes, and the other regrowth ages did not differ between themselves. Net energy intake ranged from 88.07 to 137.35 Kcal/BW0.75/day. The energy balances of the sheep from all treatments were positive. Sheep fed elephant grass harvested with 56 days of regrowth had the lowest energy loss in feces; however had the greatest energy losses as methane and heat. The energy losses as feces, urine, methane and heat varied from 29.89 to 42.03%, 1.78% to 2.33, 4.21 to 6.11% and 6.83 to 19 53% of gross energy intake, respectively. The highest values of gross energy metabolizability (0.62) and net energy use efficiency for maintenance (0.86) was obtained for elephant grass harvested with 56 and 112 days of regrowth. The sheep fed elephant grass harvested with 56 days of regrowth had higher oxygen consumption and produced more carbon dioxide and methane. Methane emissions by sheep in g/kg of digestible dry matter (27.2 g / kg) and digestible neutral detergent fiber (22.4 g / kg) did not differ with increasing grass regrowth age. Due to higher total potentially digestible fraction and energy digestibility elephant grass harvested with 56 days of regrowth had a higher nutritional value. In conclusion, elephant grass should be harvest with 56 days of regrowth for better nutrient use as fresh forage.