Abstract :
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/(kgBW0.75 ×h)). The ratio of EE:HRwas 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 forW, 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.
© 2005 Elsevier B.V. All rights reserved.
