Effects of walking speed and forage consumption on energy expenditure and heart rate by Alpine does

Eight nonlactating Alpine does (2.5–6.5 year of age; 46 ± 2.9 kg BW) were used to determine effects of standing versus walking at different speeds and interactions between walking speed and forage ingestion on energy expenditure (EE), heart rate (HR), and their ratio. Coarsely ground alfalfa hay was fed at a maintenance level of intake, and measures were performed in a head-box respiration calorimetry system. In experiment 1, measures occurred at least 3 h after feeding for 20 min after the plateau in EE sequentially, while standing (0 m/s) on a treadmill and thereafter walking at 0.14, 0.28, and 0.42 m/s at a +5% slope. HR and EE ranked (P < 0.05) 0 < 0.14 < 0.28 < 0.42 m/s (HR: 79, 95, 108, and 125 beats/min; EE: 20.6, 25.8, 29.6, and 34.1 kJ/(kg BW0.75 × h)). The ratio of EE:HR was lowest among treatments (P < 0.05) for 0 m/s (6.26, 6.54, 6.58, and 6.56 (kJ/(kg BW0.75 × day)/(beats/min) for 0, 0.14, 0.28, and 0.42 m/s, respectively). In experiment 2, EE and HR were first determined while standing, followed by measures when walking at 0.07, 0.14, or 0.21 m/s at a +5% slope; measurements also occurred while consuming 50% of the daily allocation of forage when standing or walking at the different speeds immediately after measures without forage ingestion. Differences between values for forage consumption plus walking or standing and walking or standing without forage were calculated to determine the origin of, or factor responsible for, change in EE (i.e., walking (W) versus forage consumption (F)), with the previous standing estimate without forage used as a covariate. There was an interaction (P < 0.05) between walking speed and origin of EE. EE due to W ranked (P < 0.05) 0 < 0.07 < 0.14, and 0.21 m/s (−0.3, 3.4, 4.8, and 5.9 kJ/(kg BW0.75 × h)). Conversely, EE attributable to F was lower (P < 0.05) for 0 than for 0.07 and 0.21 m/s (9.0, 10.7, 10.3, and 10.7 kJ/(kg BW0.75 × h) for 0, 0.07, 0.14, and 0.21 m/s, respectively). Differences in HR were generally similar in magnitude to those in EE (−1, 9, 17, and 20 beats/min for W, and 35, 51, 40, and 42 beats/min for F, at 0, 0.07, 0.14, and 0.21 m/s, respectively (S.E. = 2.1)). In summary, these results suggest potential use of HR to predict EE while grazing. Forage consumption increased EE to a greater extent than walking and may lessen effects of walking and walking speed on the grazing activity energy cost.