Travis Mulliniks, Range Cattle Nutritionist
In the last few years, we have been conducting studies using indwelling heart rate loggers (Figure 1) and GPS collars on young, range cows. Heart rate monitoring is common in the equine industry, where animal stress response, recovery, and training intensity are of high importance. Heart rate has been used to monitor changes in activity level of the sympathetic nervous system in cattle, and an increased heart rate is a good indication of short-term stress. In addition to indicating stress, heart rate can give us an idea of how much energy is used during grazing. Energy use, or expenditure, of range cows has been determined mostly under controlled, confined conditions. These conditions do not necessarily reflect those of free-ranging animals or of commercial cattle in feedlots. Environmental conditions, feeding level, time spent eating and digesting, tissue and hair conductance, production level, and season of the year may affect the energy expenditure of animals. Combining other technologies like GPS have also enabled researchers to combine information on various activities with data such as locomotion speed and traveling distance, to measure energy expenditure over short intervals, and to calculate the energy cost of each specific activity and of distance traveled under diverse grazing conditions.
Figure 1. Indwelling heart rate logger
So why does all this matter?
Measuring efficiency in extensive cow-calf production systems is either unattainable or measured after the fact (i.e., open cows). Identifying range cows in better fitness may indicate overall production efficiencies. While a thorough investigation of this concept is still incomplete for range livestock, there are strong indicators that this may be true. Preliminary data has shown cows with increased adaptive metabolism are more resilient to environmental stress like drought and are still reproductively competent. Previous research has indicated heifers grazing rangeland exhibit a lower resting heart rate and experience an increase in average daily gain compared with heifers fed in confinement. In the future, continuous monitoring of heart rate might provide producers with a sensitive tool for identifying changes in the energy status or energy efficiency of their cows.
Figure 2. Heart rate of a May 2-year-old range cow grazing upland range durig the breeding season.