Table 2. Heart rate and heart rate variability (HRV) parameters (estimated marginal mean ± SE) in 11-mo-old heifers restrained in a headlock during the 5-min period before the injection procedure.
| HRV parameter | Disbudding age | C-1 | I0 | C6 |
|---|---|---|---|---|
| Heart rate (bpm) | 3 | 90 ± 4 | 94 ± 4 | 84 ± 4 |
| 35 | 97 ± 5 | 97 ± 4 | 91 ± 4 | |
| 56 | 90 ± 3 | 91 ± 3 | 85 ± 3 | |
| RMSSD (ms) | 3 | 81 ± 9 | 55 ± 10 | 52 ± 9 |
| 35 | 28 ± 15 | 30 ± 11 | 46 ± 11 | |
| 56 | 48 ± 8 | 46 ± 7 | 48 ± 8 | |
| HFnorm | 3 | 64 ± 7a | 58 ± 7 | 48 ± 7 |
| 35 | 23 ± 11b | 33 ± 8 | 47 ± 8 | |
| 56 | 45 ± 6ab | 45 ± 5 | 57 ± 6 | |
| LF/HF ratio | 3 | 0.6 ± 1.7b | 0.7 ± 1.8b | 3.5 ±1.7 |
| 35 | 15.3 ± 2.8aB | 8.9 ± 2.1aB | 2.0 ± 2.1A | |
| 56 | 2.4 ± 1.4b | 2.7 ± 1.4b | 2.1 ± 1.4 | |
| SD2/SD1 ratio | 3 | 2.0 ± 0.6 | 1.9 ± 0.6 | 2.6 ± 0.6 |
| 35 | 4.0 ± 0.9 | 3.9 ± 0.7 | 3.1 ± 0.7 | |
| 56 | 2.4 ± 0.5 | 2.7 ± 0.5 | 2.6 ± 0.5 | |
| Sample entropy | 3 | 0.45 ± 0.08 | 0.37 ± 0.08 | 0.59 ± 0.08 |
| 35 | 0.42 ± 0.11 | 0.44 ± 0.09 | 0.37 ± 0.09 | |
| 56 | 0.58 ± 0.06 | 0.46 ± 0.06 | 0.54 ± 0.06 | |
| Sample size | 3 | 10 | 9 | 10 |
| 35 | 4 | 7 | 7 | |
| 56 | 15 | 16 | 15 |
The procedure consisted of 2 consecutive injections, one on each side of the neck (I0), or a sham procedure the day before (C-1) and 6 d after (C6) the injections. Heifers were previously disbudded at 3, 35, or 56 d of age. Different lower-case superscripts indicate differences between ages within trial (P < 0.05). Different upper-case superscripts indicate differences between trials within age group. Pairwise contrasts within a trial or age group were only calculated when an interaction effect between trial and disbudding age was observed (P < 0.10). RMSSD = root mean square of successive differences; HF = high frequency; LF/HF = low-frequency to high-frequency ratio.