Forages and Pastures: Grazing and Forage Management

Pastures located on southern Iowa cow/calf farms, from 8 to 125 ha in size, were used to evaluate the effects of microclimate, shade, botanical composition, and other pasture characteristics influencing the temporal/ spatial distribution of cattle within and outside streamside zones of pastures. Cows were Angus and Angus-cross on 4 of the farms, and Mexican Corriente on the remaining farm. During spring, summer, and fall of 2007–2009, 2 to 3 cows on each farm were fitted with Global Positioning Systems (GPS) collars and used to record location within a pasture at 10 min intervals for periods of 5 to 14 d. One hundred 39 data sets were obtained throughout the 2007–2009 grazing seasons. Data loggers recorded microclimate variables at 10 min intervals. Water sources and fence lines were referenced on a geospatial map and used to establish zones within the pastures; in the stream or pond (water source), closer or further than 30.5 m (Uplands) from the water source. Farm and seasonal effects on cow distribution in pastures were analyzed using the GLM procedure of SAS using years as replicates. LOGISTIC procedure of SAS tested microclimate variables effects on the probability of cattle being in or within 30.5 m of the water. Mean proportions of observations when cattle were in the water source differed (P < 0.0001) between seasons. Mean proportion of cattle observations within the streamside zone (defined as being in the water source or within 30.5 m of the water source) differed (P < 0.0001) between farms. The proportion of time cattle were within the streamside zone increased with decreasing pasture size (r2 = 0.40, 0.55, 0.59) and increasing the proportion of streamside zone within a pasture (r2 = 0.40, 0.64, 0.39) for the spring, summer, and fall seasons, respectively. Proc LOGISTIC determined the probability of cattle located in the streamside zone increased with increasing ambient temperatures. Implementation of grazing management practices for the protection of pasture streams will likely be most effective on small and/or narrow pastures in which cattle have less opportunity to locate in upland locations.