The effects of group size on the ingestive and social behaviour of grazing dairy cows

An experiment was conducted with 48 dairy cows grazed in treatment groups of four, eight or 16 cotes per group, whose grazing, social and resting behaviour was recorded over a 53-day period. Cows in groups of four stayed closer to their nearest neighbour, moved their head move vapidly from side to side during grazing and spent move time ruminating than cows in larger groups, suggesting that they were more vigilant against a perceived predation risk. Cows in the group of 16 were more aggressive, maintained a greater distance to their nearest neighbour and had a faster rate of stepping while they grazed, compared with cotes in smaller groups, suggesting increased inter-cow competition. They also spent longer grooming themselves, which normally acts as a displacement activity and may indicate increased stress. Cows in groups of eight had a faster biting rate when grazing than cows in small or large groups and they spent the longest time lying down. There were no effects of group size on milk production but across treatment groups the high yielding cows were the first to initiate grazing and to enter the milking parlour.