Chronic Stress in Cattle and Lameness as a Possible Chronic Stressor
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There is a close relationship between animal welfare and stress. A good indicator of animal welfare can be the absence of stress. Chronic stress is associated with a long-term condition were the animal cannot fully recover, maladaption. Lameness, as an often painful situation can cause chronic stress. The aim of this thesis is to review the concept of stress focusing on chronic stress and lameness as a chronic stressor. Several measures (physiological and behavioral parameters, performance and health indices, endocrine indicators, biochemical indicators, immune indices etc.) of chronic stress have been proposed as chronic markers. Special attention has been paid to heart rate variability (HRV) used in an experiment I got to be a part of were behavior and HRV of chronically stressed (lame) cows at feed bunk during feeding were examined. 52 dairy cows divided into two groups of lame (locomotion score:3-5) and non-lame (locomotion score: 1-2) was compared. Heart rate (HR) and HRV were measured when the cows were standing at the feed bunk eating and dominance score (DS) was calculated for each animal based on aggression rate (AR). Fecal cortisol concentration was also measured. Result showed a higher HR (beats/min) in lame cows and the HRV indicated a higher parasympathetic tone in lame cows (increase in rMSSD(ms), HF(normalized units) and SD1(ms)). The dominance score was lower in lame cows compared to non lame. The result suggest that the effect of lameness can be manifested in HRV confirmed by the observed differences in aggression levels of lame and non lame cows.