Table 1.
Tested animals and ambient temperature at the study sites.
Fig 1.
The position of the accelerometer and the electrodes for the heart rate monitor.
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.
Fig 2.
Flowchart of the data analysis.
The equation numbers in the figures correspond to those in the text.
Fig 3.
An example data plot of overall dynamic body acceleration (ODBA) and heart rate per minute over a 24-h recording.
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.
Table 2.
The coefficients of determination (R2) by GLM analysis for all data and for each group when the effects of activity indices on heart rate were analyzed.
Fig 4.
The linear regressions between overall dynamic body acceleration (ODBA) and heart rate for all tested animals.
The lines with the same colors correspond to those in the same groups of species and breeds.
Table 3.
Multiple comparisons of the intercept and slope of linear regression equations between overall dynamic body acceleration (ODBA) and heart rate in the species and breeds tested.
Fig 5.
The energy expenditure of grazing ruminants estimated in the present study and in previous reports.
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 [35–37]); 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 [41] and Brosh et al. [52], 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. [53]; 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. [54], 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. [9], 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.
Fig 6.
Relationships between the rate of oxygen consumption and overall dynamic body acceleration (ODBA) for a range of bipedal and quadrupedal species.
Data other than those for ruminants in the present study were obtained from Halsey et al. [23]. To compare the rate of oxygen consumption (VO2, ml/min) between a wide range of animals with different body weights, VO2 (ml/min) was converted to VO2 per metabolic body weight (ml/ M0.75∙min). The VO2 of the animals in the present study was estimated by converting eEE derived from Eq 10 into VO2 using the heat production per unit of VO2 for ruminants (20.46 J/ml of VO2) given by McLean [56]. The lines for Japanese Black cows and Japanese Brown cows seem to overlap because the body weights were almost identical for these two animals. The line for humans is presented only in the same range of ODBA for the other species.