Livestock grazing in arid rangelands often exhibits uneven grazing distribution patterns. Cattle tend to select areas of highly palatable forages in close proximity to water, which may result in soil erosion and degradation of vegetation, leading to reduced economic returns, and increased feed costs. Although many studies have explored important abiotic (e.g. slope, distance to water) and biotic (e.g. forage abundance and quality, animal breed) factors that influence cattle movement, more information is needed on the explicit spatio-temporal configuration of a cattle herd during both active and rest periods. The objective of this project is to evaluate the seasonal pattern of herd spread and its relationship to cattle activity and periods of the day. Location and activity information of eleven free-ranging Bonsmara cows were obtained at five minute intervals using GPS collars coupled with motion sensors. Eight trials of three weeks duration were conducted from September 2007 to August 2008 in a 457 ha pasture in South Texas. The spread of the herd was determined using Euclidean distances from the center of gravity of the group.

Results/Conclusions

Results show that herd spread was greatest during late summer and late autumn and was the least during late winter and early spring (p < 0.01). These results contrast with previous studies where in periods of low forage availability (e.g. winter, dry season) cattle tend to form smaller subgroups and extend their home ranges to forage in new areas. Our results suggest that during warm season the herd is more dispersed, possibly forming a larger number of subgroups, and during the cold season the herd stays closer together. We hypothesize that during the cold dry season when availability is low the herd congregates in supplemental feeding and water areas. On a daily basis, cattle showed a significantly smaller spread during the midday period than early morning, late afternoon, and midnight periods. This could be explained by thermoregulatory actions in which individuals will congregate in shade areas to escape the heat during the hottest periods of the day. Lastly, the traveling activity showed a smaller spread (p < 0.01) during summer and autumn than the grazing and resting activities which exhibited similar spread patterns. These results suggest that cattle traveled close to each other and then dispersed or formed subgroups during resting and grazing activities.