We examined whether separating dominant and subordinate cows affected production or behavior, and the relationships between dominance and production measures, by using grazing cows, some of which were offered forage supplements. In experiment 1, 80 cows were allocated to either pasture only or pasture and a silage supplement offered indoors overnight. Dominance was principally related to body weight, but was also positively correlated with lactation number and negatively correlated with grazing time. In experiment 2, 72 spring-calving cows were classified as dominant or subordinate, on the basis of aggressive interactions, and were divided by two factors; i.e., dominant and subordinate cows grazed together or apart, and with or without a hay supplement, which was offered indoors for 75 min/d. Dominant cows produced more milk than subordinates, probably because of their faster pasture biting rate and hay chewing rate. The hay-supplemented dominant cows produced more milk when kept apart from subordinates, and both dominant and subordinate cows gained more weight and lay down for longer when kept apart. However, when no hay was offered, dominant cows produced more milk and had a faster pasture biting rate when grazed together with subordinates. Cows high in the dominance order were more likely to enter the parlor first, but not to begin grazing first. The results suggest that production can increase when dominant and subordinate cows that are offered forage in a competitive situation are separated, whereas there is no benefit in separating them if they are at pasture all day.
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