Application of Overall Dynamic Body Acceleration as a Proxy for Estimating the Energy Expenditure of Grazing Farm Animals: Relationship with Heart Rate

<div><p>Estimating the energy expenditure of farm animals at pasture is important for efficient animal management. In recent years, an alternative technique for estimating energy expenditure by measuring body acceleration has been widely performed in wildlife and human studies, but the availability of the technique in farm animals has not yet been examined. In the present study, we tested the potential use of an acceleration index, overall dynamic body acceleration (ODBA), as a new proxy for estimating the energy expenditure of grazing farm animals (cattle, goats and sheep) at pasture with the simultaneous evaluation of a conventional proxy, heart rate. Body accelerations in three axes and heart rate for cows (n = 8, two breeds), goats (n = 6) and sheep (n = 5) were recorded, and the effect of ODBA calculated from the body accelerations on heart rate was analyzed. In addition, the effects of the two other activity indices, the number of steps and vectorial dynamic body acceleration (VeDBA), on heart rate were also investigated. The results of the comparison among three activity indices indicated that ODBA was the best predictor for heart rate. Although the relationship between ODBA and heart rate was different between the groups of species and breeds and between individuals (<i>P</i><0.01), the difference could be explained by different body weights; a common equation could be established by correcting the body weights (<i>M</i>: kg): heart rate (beats/min) = 147.263∙<i>M</i>^-0.141 + 889.640∙<i>M</i>^-0.179∙ODBA (<i>g</i>). Combining this equation with the previously reported energy expenditure per heartbeat, we estimated the energy expenditure of the tested animals, and the results indicated that ODBA is a good proxy for estimating the energy expenditure of grazing farm animals across species and breeds. The utility and simplicity of the procedure with acceleration loggers could make the accelerometry technique a worthwhile option in field research and commercial farm use.</p></div

The energy expenditure of grazing ruminants estimated in the present study and in previous reports.

<p>1) (Gray bars) The estimated energy expenditure of Japanese Black cow (JBL), Japanese Brown cow (JBR), Saanen goat (SA) and Corriedale sheep (CO) with accelerometry in the present study (in combination with the relationship between heart rate and energy expenditure derived from the previous reports [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref035" target="_blank">35</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref037" target="_blank">37</a>]); 2) and 3) The whole energy cost of grazing cows estimated from the heart rate in combination with oxygen consumption per heart beat (O₂ pulse) by Aharoni [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref041" target="_blank">41</a>] and Brosh et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref052" target="_blank">52</a>], respectively; 4) The estimated energy expenditure of grazing goats during different seasons (winter, summer and monsoon) in India by collecting the expired air in short periods (5–10 min), reported by Shinde et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref053" target="_blank">53</a>]; 5) and 6) The estimated energy expenditure of grazing sheep and goats at different stocking rates from heart rate measurements with O₂ pulse by Animut et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref054" target="_blank">54</a>], respectively; and 7) and 8) The estimated energy expenditure of goat bucks and wethers in open range by the doubly labeled water method by Toerien et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0128042#pone.0128042.ref009" target="_blank">9</a>], respectively. The low standard deviations in the present study might be attributed to the condition of experiments (i.e., the use of one breed at a similar stocking rate under thermoneutral conditions) in each animal group.</p

The position of the accelerometer and the electrodes for the heart rate monitor.

<p>The position of the accelerometer is at the top of the animal’s back (behind the withers), and the positions of the two electrodes connected to a transmitter of the heart rate monitor are at the animal’s right shoulder and left anterior thorax, which are known to be the appropriate points for heart rate measurements for ruminants.</p

An example data plot of overall dynamic body acceleration (ODBA) and heart rate per minute over a 24-h recording.

<p>The interruptions in the recording indicate the temporal interruptions of the heart rate recording, whereas ODBA was recorded continuously throughout the experiment. The interruptions in ODBA occurred due to the synchronization of the heart rate and ODBA for the data analysis.</p

Flowchart of the data analysis.

<p>The equation numbers in the figures correspond to those in the text.</p

The linear regressions between overall dynamic body acceleration (ODBA) and heart rate for all tested animals.

<p>The lines with the same colors correspond to those in the same groups of species and breeds.</p

Tested animals and ambient temperature at the study sites.

<p>The age, body weight and ambient temperature data are means ± SD.</p><p>Tested animals and ambient temperature at the study sites.</p