Grazing Relations — Abstract of Paper


The Effect of Topography, Vegetation and Weather on Cattle Distribution at the San Joaquin Experimental Range, California
Norman R. Harris,¹ Douglas E. Johnson,¹ Melvin R. George,² Neil K. McDougald³


In this study livestock distribution on the landscape was mapped during two seasons, summer and winter, for two years to determine where livestock congregate and to model factors that influence livestock distribution. Two small herds of cows were observed in separate range units on the San Joaquin Experimental Range for a total of twenty-four 24-hour observation periods to ascertain daily movements and activities. Treatments involving water placement and the use of supplemental feeding sites were implemented to judge the effects of these management techniques on cattle distribution. Animal distribution during daylight hours was determined by videotaping all visible animals in the herd every 15 minutes, then positioning cows on rectified digital orthophotographs. The location of the videographer was determined to an accuracy of one meter using a differential global positioning system (DGPS) to facilitate placement of animals. During nighttime hours, the location of the herd was determined every 15 minutes using the DGPS. Night animal activities were observed using night-vision binoculars and recorded for each time period. Our study identified topographic, vegetative and environmental forces that affected cattle distribution patterns. The effects of these factors varied between seasons and years. Water treatments varied in effect with seasons and size of range unit. They showed little effect in winter when free water was available on the forage. The feeding of supplement also had a variable effect. Animals consumed some supplement at all times, but the amount of supplement consumed varied with supplement placement, as well as with the quantity and quality of available forage. Thermal environment was an important factor in determining cattle location and activity. The social interactions of individual animals were important in determining subgroups that formed the herd units. A probabilistic model was developed from this research and will be tested in future studies.