Social hierarchy and feed supplementation of heifers: Line or piles?

Cattle on pasture may have unequal access to grain supplement due to the effect of social dominance. Subordinate animals are known to have less access to resources when competition exists. This trial was designed to test if distributing feed supplement (corn meal) along and under the fence in individual piles would affect heifers feeding behaviour and grant better access to all animals compared to supplement offered in a continuous line. Four groups of nine heifers were used in a 2 × 2 cross-over design, and tested in two treatments: LINE (1 linear meter/animal) and PILE (one pile/heifer distant 1 m from each other). Each period had 3 days for habituation followed by 7 days for data collection. Animals were managed under Voisin's rotational grazing system and observed for one hour from the moment they entered the new paddock (8:00 to 9:00). Individual behaviour of the heifers / grazing, eating grain supplement, competing or other) was registered at one-minute interval instantaneous scans. All agonistic interactions were recorded and a sociometric matrix was calculated for each group to define each heifer as dominant, intermediate or subordinate. Feeding behaviour as not affected by treatment, but it affected by social hierarchy status. High and intermediate ranking heifers spent more time eating supplement than low ranking ones (P ≤ 0.03). Subordinate heifers grazed longer than intermediate heifers, which in turn grazed longer than dominant heifers (P ≤ 0.01). Social rank did not affect competitive behaviour, but there was a trend for more competition events when concentrate was distributed in piles (P = 0.09). Dominance score was associated with initial body weight (r= 0.686; P ≤ 0.0001). In summary, distributing the grain supplement in individual piles did not benefit the subordinate heifers, as they had less access to the supplement than the dominant ones. When entering a new paddock with supplement offered, the subordinate heifers seemed to avoid competing for grain and spent more time grazing while the dominant heifers spent more time eating supplement.