How are distances between grazing cows determined: A case study

抄録

Although cows are protected from their natural enemies, they form herds when grazing in a manner that is similar to protective aggregations of wild animals such as insect swarms, fish schools, bird flocks, and other mammal herds. This study examined how distances between individual grazing cows are determined. In a herd of cows, complicated interrelationships operate between individuals. We assumed that the distance between any two individuals was based on the following five factors: the behavior of the entire herd (measured as the distance between the leftmost and rightmost cows: the herd length effect); repulsive and attractive forces operating directly between two individuals within the herd (direct effect); the effect of third individuals on the distance between two individuals (half-indirect effect); the effect of unconnected pairs on the distance between two individuals (indirect effect); and residual effects that cannot be explained by the other four factors (random/involuntary movement effect). These five factors were analyzed using regression analysis. We applied our model to a grazing herd of cattle. The coordinates of six cows in a one-dimensional, fenced grassland were recorded every 5 min. For each pair of cows, the contribution of each of the five effects was calculated using the sum of squares of data, based on the temporal changes in the distances between individuals. Overall, the random movement effect made the largest contribution (38.8%) to the temporal variation in the distance between two cows, followed by herd length (25.6%), direct (21.0%), and half-indirect (12.5%) effects. The contribution of the indirect effect was negligible. The results revealed that one of the six cows was persecuted by the other cows.