We compared behavioural and cardiac responses to emotional stresses between familiar and unfamiliar heifers in groups of two or five. Fourteen Japanese Black heifers were divided into two experimental groups of two individuals (F2) and two groups of five individuals (F5) that were familiar with each other. Four additional Holstein heifers were used in forming the unfamiliar groups (UF2 and UF5), in which the focal animals had never been seen. Experimental animals were equipped with heart-rate monitors and led into a test room (5.5 m x 10.0 m) at the experimental station. Each animal was tethered inside a single stall, and the focal animals were monitored by two video cameras. We designed three stress tests for the heifers: (1) a novelty test (encountering a strange object); (2) a surprise test (hearing a loud sound); and (3) a conflict test (trying to eat formula food). In the first test, a red paper doll was presented to the focal animal for 10 min. In the second test, a tin bucket containing several weights was dropped from the ceiling (5 m high) diagonally in front of the focal animal. Three minutes later, the third test was conducted by placing a feed bin containing food pellets covered with wire mesh in front of each animal for 10 min. This series of tests was carried out in the order UF5, UF2, F5, and F2. There were the significant effects of familiarity on behavioural responses in the novelty and conflict test. Moreover, there were not only significant effects of familiarity but also a significant interaction between familiarity and group size on cardiac responses in the surprise and conflict tests. Particularly, changes in the mean heart rate during the two tests were minimal in the group F5. Our results indicate that both familiarity and larger group size may reduce emotional stress, and the calming effect of affiliative groups of five may be higher than groups of two for cattle.
|Publication Title||Applied Animal Behaviour Science|
|Author Address||Graduate School of Agricultural Science, Tohoku University, Kawatabi, Narugo, Miyagi 989-6711, Japan. firstname.lastname@example.org|
|Cite this work||
Researchers should cite this work as follows: