Cardiac autonomic responses to transrectal examination and parlor milking of lame and non-lame dairy cows

Abstract

We studied the changes in the heart rate variability of lame and non-lame dairy cows in response to transrectal examination and parlor milking. We hypothesized that lame cows experience greater stress, manifested in heart rate variability parameters, which would serve as an argument to promote more caution in the everyday handling of lame animals. In the study, we selected 55 lame (with lesions on at least one hoof, otherwise clinically healthy, with locomotion scores 4 and 5 of 5 point scores) and 55 non-lame (clinically healthy, with locomotion scores 1 and 2 of 5 point scores) cows. The heart rate (HR), root mean square of successive beat-to-beat intervals (RMSSD), the normalized unit of the high-frequency component (HF) of the spectral analysis and Poincaré measures (SD2/SD1) were compared between lame and non-lame cows during five distinct stages of transrectal examination (TRE) and seven stages of parlor milking. HR, RMSSD, and SD2/SD1 showed similar patterns during TRE and milking, while HF remained fairly constant during the studied phases. No distinct RMSSD, HF or SD2/SD1 changes were observed during the phases expected to elicit a stress response. Between-group differences were only observed in terms of HF. Baseline HF was higher in lame cows than in non-lame ones, and such a difference in direction was observed throughout the whole procedure. During milking and TRE, the HR, RMSSD, and SD2/SD1 values showed temporal changes in times of higher physical activity: moving to and waiting in the holding pen and moving into the milking stalls in the parlor for preparation in both lame and non-lame cows. The differences in baseline HF (normalised units) between lame and non-lame cows can not be fully explained based on available information. The lack of a distinct, stress-related change in heart rate variability parameters in both groups can originate in methodological challenges inherent in animal heart rate variability measurements in field conditions.