Validation and design of a wearable harness for monitoring remote heart rate variability in dairy cows under grazing conditions

In veterinary medicine, heart rate variability (HRV) has emerged as a valuable tool for assessing welfare, comfort, stress responses, and overall physiological status. This study aimed to design and validate a harness/vest wearable system for remote HRV measurement and monitoring in dairy cows managed under rotational grazing conditions in the high tropics. The harness/vest was developed to protect and stabilize Holter-type measurement devices under field conditions, ensuring that it did not interfere with animal comfort and allowed proper HRV signal acquisition. For HRV measurements, a Polar H10® Heart Rate Sensor paired with a Polar Unite® watch was used. To evaluate the practical application of the harness/vest and its impact on animal comfort, lactating Holstein and Holstein x Jersey crossbreed dairy cows (n = 74) were monitored. The behavior of the animals was observed, and these observations were subsequently compiled into an ethogram, used as an outcome measure to verify whether the harness/vest altered natural behaviors. Behavioral and physiological responses were compared between cows wearing the harness/vest and those without it. The observed behavioral patterns, including posture, locomotion, feeding behavior, and social interactions, were similar between groups, indicating that the harness/vest did not interfere with comfort or routine activities. Comfort was assessed through: (1) comparison of frequencies and durations of key behaviors, (2) evaluation of any avoidance or agitation responses at fitting, and (3) continuous observation for signs of mechanical interference, rubbing, or restraint. Based on these evaluations, Holter-type devices can be reliably integrated into the harness/vest system developed in this study, representing an innovative and effective tool for continuous, remote, and noninvasive HRV monitoring in grazing dairy cows in the high tropics, while preserving comfort and welfare.