Cross-sucking by dairy calves may become a habit or reflect characteristics of individual calves more than milk allowance or weaning

To examine the effects of milk allowance and weaning age on cross-sucking, 45 dairy calves were housed in groups of nine and fed milk and grain-based starter feed from automated feeders and allocated to three treatment groups: (A) Low-Milk Early-Weaned (fed 6 L/d of milk until weaned at 47 d of age), (B) High-Milk Early-Weaned (fed 12 L/d of milk until weaned at 47 d of age), (C) High-Milk Later-Weaned (fed 12 L/d of milk until weaned at 89 d of age). We observed all instances of cross-sucking another calf during 12 h/d over 18 d between wk 5 and wk 21. When all calves were drinking milk, little cross-sucking occurred and was not related to milk allowance (P > 0.10). There was no significant change in the duration of cross-sucking when calves were weaned at either age (P > 0.10). There were large differences between individual calves in the duration of cross-sucking performed and these were stable over time, with positive correlations between the duration of cross-sucking in consecutive weekly periods (0.33 < r < 0.57; P < 0.05). When the calves were moved to a second barn for weaned animals, most calves stopped cross-sucking but some calves increased their duration of cross-sucking. These calves performed much of their cross-sucking (43.6–99.1%) on a single calf, and the cross-sucking was often mutual with both calves sucking each other at the same time. Cross-sucking was not strongly affected by milk allowance or weaning and may reflect characteristics of individual calves or be the result of habit formation.