Dairy calves' time spent in the cow herd in a calf-driven cow-calf contact system during two-step separation with a nose flap

Although originally developed for weaning of beef calves, nose flaps are also used on dairy farms nowadays to wean calves which are reared with contact to their dam or a foster cow. These calves are often weaned younger than beef calves and the time they wear nose flaps is highly variable, since it is unknown for how long younger calves need to wear the nose flap in order to induce an effective weaning. The aim of our study was therefore to track changes in dam-contact initiated by dairy calves after insertion of a nose flap in order to determine the minimum duration a nose flap needs to be worn to effectively reduce suckling motivation of calves. The study was conducted in two sequential experiments using 3-month-old dairy calves that were reared with full-time dam contact. Calves were weaned with a nose flap over either 14 (experiment I, 9 calves in herd A and 9 calves in herd B) or 7 days (experiment II, 11 calves in herd A and 12 calves in herd B) before they were fence-line separated from their dams. The total time a calf spent within the cow herd (TIC) per day was determined from continuous video recordings during 7 days before nose flap insertion (baseline), as well as during the 7 or 14 days in which calves had free access to the cow area while wearing the nose flap. Statistical analysis was conducted using linear mixed effects models. Results from both experiments showed that calves reduced their TIC at the fourth day of wearing the nose flap compared to their individual baseline (p=0.03 and p=0.001 respectively). In experiment I, calves showed a further numerical reduction in TIC from day 4 to day 5, while in experiment II, calves showed no further reduction in TIC after the 4 days of wearing the nose flap. After these 4 or 5 days respectively, TIC of calves in both experiments stayed at a constant low level of several hours per day. Taken together, these results indicate that in 3-month-old dairy calves it needs at least 4 days until the motivation to spend time with the cow decreases after insertion of a nose flap, while there seems to be no further decrease in motivation when using a nose flap longer than this time. However, results were subject to considerable inter-individual variability already during the baseline week and need replication in a pasture-based setting with less space-restrictions.