Sward structure driven by light interception controls grazing efficiency in BRS Zuri guinea grass pastures

The hypothesis was that variations in pre-grazing light interception (LI) would result in distinct pasture structures, directly affecting the frequency and severity of defoliation by grazing animals. This study evaluated the effects of four LI levels (80, 85, 90, and 95%) on the structural characteristics of zuri grass and on defoliation dynamics during grazing. Sixteen paddocks were grazed for 24 h, and defoliation was assessed in 18 tillers per paddock at 4, 8, and 24 h. The evaluated variables included grazed area, frequency (FD) and severity of defoliation (SD) by morphological component, bite rate (TB), and number of steps between feeding stations (PE). Both FD and SD increased linearly with increasing LI, particularly for expanded and expanding leaves. Conversely, TB and PE decreased linearly as LI increased, with reductions of 4.74 bites min⁻¹ and 0.15 steps, respectively, indicating lower foraging effort under higher LI. Pastures managed at 90 and 95% LI promoted greater forage mass above the post-grazing residue target and supported higher instantaneous stocking rates, resulting in greater forage utilization efficiency. In contrast, LI levels of 80 and 85% induced more intense foraging behavior and reduced utilization efficiency. Managing zuri grass at 90-95% LI is recommended to optimize pasture structure and maximize forage utilization efficiency in grazing systems.