Xaraés Palisadegrass Forage Under Rotational Grazing Strategies: Physical Characteristics and Nutritive Value.

The objective of this research was to ascertain whether defoliation frequency based on fixed calendar days would generate variable sward structure over grazing events and try to establish the relative importance of physiological versus chronological age in the determination of nutritive value indicators of Xaraes palisadegrass (Brachiaria brizantha cv. Xaraés). The experimental design was completely randomized, with three treatments: two grazing frequencies defined by canopy light interception (LI) at initiation of grazing (95% or 100%) and one based on chronological time (28 days), each replicated three times. Forage produced with 95% LI was mostly leaves (92.5%), with high concentration of crude protein (CP; 141 g/kg in leaves, 89 g/kg in stems and 138 g/kg in whole forage), low concentration of neutral detergent fiber (NDF) in stems (740 g/kg), and higher in vitro dry matter digestibility (IVDMD) of leaves (690 g/kg) and stems (660 g/kg). Lower grazing frequency treatments (100% LI and 28 days) resulted in forage with higher proportion of stems (9.8 and 9.1%, respectively). Concentrations of CP were lower in forage grazed every 28 days (71 g/kg in stems and 114 g/kg in whole forage) and the higher concentrations of NDF in stems were obtained from forage harvested with 100% LI (769 g/kg) and 28 days (764 g/kg). Shearing resistance of stems was lower in forage produced with 95% LI (9 kgf), and higher resistance for the 100% LI (10.5 kgf) and 28 day (11.2 kgf) treatments. The hypothesized structural and physiological uniformization of treatments based in LI across grazings did not result in a corresponding uniformization of qualitative determinants of the forage on offer, because both LI-based treatments resulted in variation across grazing events. The treatment based on fixed days of rest, as expected, did not result in uniformity either.