Affiliative group size influences grazing and recumbency behaviors in heifers immediately after beginning grazing and in high‐density grazing situations

Abstract We compared grazing and recumbency behaviors of grazing heifers in affiliative groups of two and five immediately after beginning grazing and in high‐density grazing situations in a pasture. Fourteen heifers were divided into two experimental groups of two individuals and two groups of five individuals that were familiar with each other. These heifers were then grazed with unfamiliar cattle in a pasture. Four heifers from each affiliative group (eight heifers in all) were selected as focal animals in three grazing situations: (i) treatment 1, immediately after beginning grazing (0.5 ha animal unit [AU]−1); (ii) control, 1 month after beginning grazing (0.3 ha AU−1); and (iii) treatment 2, high‐density grazing (0.1 ha AU−1). Each focal animal was followed by an individual observer for 12 h beginning at sunrise. Posture and maintenance behaviors at 1‐min intervals were recorded continuously. The mean duration and total time spent grazing during the 12‐h observation period were significantly affected by group size and grazing situation (P < 0.001) and the interaction between these factors (P < 0.01). The mean duration of grazing behavior in the group of two was considerably (P < 0.05) reduced in treatment 2 compared to control, whereas there was no significant difference in the group of five. Although the total time spent in maintenance behavior (grazing and recumbency) in the groups of two and five was the same in each treatment in the former, the difference between the total time spent grazing and recumbency behaviors was greater than that in the latter (P < 0.05). Our results suggest that an affiliative group size may provide a calming effect for cattle in a pasture and contribute to the stability of their lives in a socially competitive situation. An affiliative group of five may be better adapted behaviorally to a changing grazing environment compared to a group of two.