It has been established that heart rate is a reliable indicator of energy expenditure and stress in livestock and wildlife. It has also been explored to see if it is feasible to use overall dynamic body acceleration (ODBA) as a proxy for heart rate, due to the simplicity of attaching a collar to an animal and transmitting data to a remote receiver. This reduces the need to implant heart rate and body temperature loggers, especially in many wildlife species. 

Connection of ODBA and heart rate studied in free-ranging cows
In a recent study, cattle in Norway were studied while grazing free-ranging in the woods of the mountains with the aim to see if ODBA could be used this way. Free-range grazing in the woods is practiced in many places in Norway due to low rugged landscapes, maximizing the utilization of fields to grow winter feed. Under these grazing circumstances, the cattle face similar environmental pressures as wildlife does, through changing weather conditions, predators, and injuries. Using ODBA could be more feasible as non-invasive welfare monitoring on a large scale, especially in remote places where capture and handling of wild species is difficult.

One minute resolution used to compare heart rate and ODBA
In the spring of 2022, a group of scientists from the University of Inland, Norway, implanted 14 cows with Star-Oddi DST centi-HRT. Three farms participated in the study where 4-5 cows from each farm were implanted with a heart rate logger and fitted with an external activity collar. The cows were all adults and were accompanied by their calves. The loggers measured the heart rate every 15 minutes throughout summer for three-week period (maintenance period) followed 48h where temperature and heart rate were sampled every minute, called the intensive period. During the intensive period, ECGs were stored during the first 12 hours (6 am - 6 pm). This raw ECG data was verified by using the free Star-Oddi HRT Analyzer software and used for ODBA comparison, where 12495 1-min averaged observations were compared.

Low OBDA and heart rate can be associated with static behaviours
Behaviours as resting lying, resting standing, suckling of calves, ruminating standing or lying and vigilance showed a correlation to low ODBA values and heart rate. As expected, high ODBA values were in correlation with more active behaviour like foraging, walking, and other activities like running. However, scratching with teeth also showed high ODBA values due to rigorous head movements. The linear relationship between ODBA and heart rate is solid when the ODBA values are low, this gets more challenging with high ODBA values and heart rate and the risk of under or overestimating energy expenditure increases. It interested the scientists that heart rate prediction revealed a circadian pattern seen in low-intensity grazing conditions.

The article was published in Conservation Physiology and can be found here.

Photo at top borrowed from the Fjords in Western Norway