Nutritive Value And In Vitro Methane Production Of Urochloa Brizantha Cv. Marandu Under Fixed Time Or Variable Stocking Cycles

The aim of this study was to evaluate the chemical composition, digestibility, gas production kinetics and in vitro methane (CH4) production of Urochloa brizantha cv. Marandu under two stocking methods over three consecutive stocking cycles. The stocking methods were (1) a fixed-time stocking cycle of 33 days (33-SC) with a 30-day rest period and a 3-day grazing period, and (2) a variable stocking cycle, with the end of the rest period when the canopy intercepted 95% of the light and a 3-day grazing period (95-LI). The average rest period was 24.5-day (standard deviation of 5.2-day) for 95-LI. The in vitro dry matter digestibility (IVDMD) was higher (p < .01) for 95-LI (646 g/kg) relative to 33-SC (628 g/kg). Crude protein concentration was higher (p < .01) for 95-LI (154 g/kg) relative to 33-SC (136 g/kg). The ADF (303 g/kg DM) and aNDF (623 g/kg) were higher (p < .01) for 33-SC compared to 95-LI (287 and 605 g/kg respectively). The gas production potential from non-fibrous carbohydrates was 9.4% higher for 33-SC. The in vitro CH4 production per unit of degraded dry matter (DDM) was higher (p < .01) for 33-SC (19.9 CH4 ml/g), compared to 95-LI (17.9 CH4 ml/g). The 33-SC management resulted in rest periods that were too long for the time needed for optimal regrowth. The variable SC based on the 95-LI was more favourable, because it resulted in maximum yield of dry matter with improved forage nutritive value, while decreasing CH4 yield.