Effects of progressive grazing of a pasture on the spatial distributions of herbage mass and utilization by cattle: A preliminary study

Spatial distributions of herbage mass and utilization were investigated at a small patch scale in a bahia grass (Paspalum notatum Flügge) pasture progressively grazed with beef cows, using a method combining sward and animal measurements. For a 6-day grazing period, pre-grazing herbage mass (M_pre) and rate of defoliation (D) were non-destructively estimated every day, using an electronic capacitance probe, at 91 fixed locations (50 cm x 50 cm each) along a permanent line transect. At the same time, ingestive behavior by cows at the individual locations was measured every day, in terms of the number of visits (N_V), total residence time (T_R), total number of bites (N_B), residence time per visit (T_RV), number of bites per visit (N_BV) and biting rate (R_B). Spatial distribution patterns of herbage mass and utilization variables clearly illustrated which locations of the pasture were highly available, frequently visited, grazed longer, received more or faster bites and heavily defoliated during the progressive grazing. The mean and CV values of the spatial distributions showed that cows visited more locations more evenly by shifting from one location to another more frequently as the grazing progressed. The study also revealed that M_pre became more heterogeneous and D tended to be more homogeneous with the progression of grazing. The relationships between the herbage utilization variables and herbage mass showed that locations with lower herbage mass were more frequently visited, grazed longer and received more bites on the first 5 days, although the rate of defoliation was usually lower. Thereafter, neither locations with lower herbage mass nor those with higher herbage mass were preferred by cows. These results showed how vegetation patchiness and patch utilization by cows changed with decreasing feed resources in a pasture.