Effects of delayed food distribution on the behaviour and cortisol levels of dairy cows

The aim of this study was to assess whether there were behavioural, hormonal and productive effects in dairy cows subjected to a mild unpredictable management stressor. Twelve healthy Holstein dairy cows, aged 33 to 81 months, were used. They were loose housed indoors with cubicles in two groups of six, with access to an outdoor pen. They were fed concentrate by automatic feeders, unifeed at 7.30 and 13.30, and milked at 5.30 and 17.00. The stressor consisted of a delay of one and a half hour in the distribution of the morning unifeed meal either for one (Tuesday, “short stress”) or for 3 consecutive (Tuesday to Thursday, “long stress”) days. All other management procedures were kept constant. The cows were observed by instantaneous scan sampling every 2 minutes at 7.00-8.00, 9.00-10.00, 11.00-12.00, 13.00-14.00 on Tuesday, Thursday and Saturday. Blood samples were taken at 14.30 on Tuesday and Thursday and cortisol levels analysed by RIA. Data on activity and production were automatically recorded. Behavioural data were analysed (alpha=0.01) by Kruskal-Wallis, milk yield by two-way ANOVA and cortisol by GLM. In the “long stress” period the cows showed a significant increase of activities (sniffing, licking, nibbling) towards the trough, other structures and other cows and decreased unifeed feeding time. They showed also significantly increased intraspecific agonistic behaviour (butting, displacement). No significant difference was found, on the contrary, between the “short stress” and the control period except for an increase in activities towards the trough. Neither general activity levels nor milk yield were affected. Cortisol levels show a significant individual difference in response to the stressor (P<0.05). The data suggest that a three-day delay in feeding could be stressful for dairy cows.