Relations between oral stereotypies, open-field behavior, and pituitary-adrenal system in growing dairy cattle.

The aim of this study was to investigate possible differences between calves with or without stereotypies concerning their behavioural reaction to an acute stress situation such as an open field and their behavioural and pituitary-adrenal responses to long-term tethering. Behavioural observations, open field tests, sampling for baseline adrenocorticotropic hormone (ACTH), and adrenocortical response tests after synthetic ACTH administration were made on 48 4- to 7-months-old dairy calves housed in tether stalls. Behavioural observations and blood sampling for baseline ACTH and cortisol determination after synthetic ACTH were repeated a year later in the same animals. Individual stereotypy levels showed a high correlation between calf values and heifer values (p < 0.001). Baseline ACTH in the calves was related to individual stereotypy levels (p < 0.05) in that the calves with higher stereotypy levels had lower ACTH values. The release of cortisol after injection of synthetic ACTH was considerably higher in the animals as heifers than when they were calves (p < 0.001). There was a relation between adrenocortical response to ACTH and stereotypy level in the heifers, showing that the higher the stereotypy level, the lower the cortisol response (p < 0.05). In the open field tests, the calves with the highest stereotypy levels moved around least but explored most. In conclusion, this study shows that growing dairy cattle with relatively high levels of oral stereotypies differ from individuals devoid of, or with low stereotypy levels, in behavioural response patterns to a short-term stressor such as an open field in adreno-cortical responses to exogenous ACTH and in baseline ACTH after 2 weeks of tethering.