Social dominance affects intake rate and behavioral time budget in pre-pubertal dairy heifers allocated in continuous competitive situations

In intensive feeding systems, competition may be high and social dominance may affect animal performance by changing dry matter intake (DMI) and behavioral time budgets. If competition level is maintain over time, the strategies developed by heifers of different social status are expected to differ. Thus, the aim of this study was to compare individual DMI, intake rate and eating, ruminating, lying and standing behaviors in dominant (DOM) and subordinate (SUB) pre-pubertal dairy heifers in a model study implying continuous competitive situations. A total of 16 Holstein and Jersey×Holstein pre-pubertal heifers (251±10 days old, weighing 208±14 kg; mean±SEM) were allocated into eight homogeneous dyads. Each dyad was maintained during 120 days (day 0=beginning of measurements) in pens, and received a total mixed ration from one feeder/dyad. The DOM and SUB heifers was determined (day 0, twice during the first month of the experiment and every month afterwards) by observation of the winner in agonistic interactions in each dyad after the feed was supplied. The general activity pattern (eating, ruminating, lying and standing) of each heifer was recorded by direct instantaneous scan-sampling, every 10 min for 12 h, in 7 days (days 1, 21, 35, 60, 75, 100 and 120). Individual DMI was estimated with the double marker technique, in three intervals (I=days 17-26; II=days 78-87 and III=days 112-120), while estimated intake rate (kg/min) was calculated for each interval as the DMI per total eating time. After the experiment was concluded, data of the first 5 and the last 6 h of the 12 h scan-sampling (related to the moment the feed was supplied) was grouped according to the moments of greater and lesser competition for feed on each day. During the first 5 h, where competition was expected to be highest, no differences in eating behavior were found between heifers of different social status, but DOM heifers spent more time ruminating and lying than SUB heifers, while SUB spent more time standing than DOM heifers. No differences were found on DMI between DOM and SUB, but SUB ate at a faster rate on interval II compared with DOM heifers. In conclusion, in this model study of heifer dyads, SUB heifers had greater intake rate with no differences in feed intake, spent less time ruminating and lying, and more time standing than DOM heifers during the first hours after feed delivery.