VALIDATION OF A HEART-RATE MONITOR FOR MEASURING A STRESS-RESPONSE IN DAIRY-COWS

In three experiments, a commercial non-invasive heart-rate monitor, Polar(R) Sport Tester (PST), was validated for use with dairy cows. First, 10 monitors were tested using a pulse generator, which produced pulses at levels between 30 and 240 bpm. PST values and generated beats were highly correlated (r = 0.97) but with varying delay (5-55 s), depending on pulse-rate level. In a second experiment, 10 dairy cows were quietly standing or exercising on a treadmill while their heart rates were recorded by direct-wire electrocardiograph (ECG) as well as the PST. Correlations between ECG and PST values during standing (0.88) and exercising (0.72) were significant and differed between cows. During standing, inter-beat interval and PST standard deviations were significantly correlated (R(sp) = 0.76), as were their coefficients of variation (R(sp) = 0.89). The third experiment showed that the heart rate of 10 dairy cows increased rapidly immediately after an individual was isolated from the herd. Cows showed no obvious signs of being hampered by the equipment during the 1-h trials. Change in heart rate may be a relevant parameter for studying an animal's response to a stressor. As heart-rate variability is thought to serve as an important mechanism for adaptability in humans, this aspect needs further attention in farm animals. The PST is suitable for measuring both heart rate and heart-rate variability in dairy cows.