Table 3. 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 after the injection procedure.
| HRV parameter | Disbudding age | C-1 | I0 | C6 |
|---|---|---|---|---|
| Heart rate (bpm) | 3 | 85 ± 3B | 97 ± 3aA | 85 ± 3B |
| 35 | 93 ± 4AB | 100 ± 3aA | 88 ± 3B | |
| 56 | 85 ± 2AB | 89 ± 2bA | 82 ± 2B | |
| RMSSD (ms) | 3 | 66 ± 8 | 61 ± 8 | 72 ± 8 |
| 35 | 31 ± 12 | 61 ± 9 | 59 ± 8 | |
| 56 | 52 ± 6 | 64 ± 6 | 62 ± 6 | |
| HFnorm | 3 | 53 ± 7 | 60 ± 7 | 59 ± 7 |
| 35 | 30 ± 11 | 37 ± 8 | 44 ± 7 | |
| 56 | 46 ± 6 | 54 ± 6 | 54 ± 5 | |
| LF/HF ratio | 3 | 5.4 ± 1.7b | 2.2 ± 1.8 | 0.8 ± 1.7 |
| 35 | 13.6 ± 2.7aA | 2.9 ± 2.0B | 3.0 ± 1.8B | |
| 56 | 2.3 ± 1.4b | 1.6 ± 1.4 | 1.2 ± 1.3 | |
| SD2/SD1 ratio | 3 | 2.7± 0.5b | 2.9 ± 0.5 | 2.3 ± 0.5 |
| 35 | 6.1 ± 0.8aA | 3.2 ± 0.6B | 3.1 ± 0.5B | |
| 56 | 2.7 ± 0.4b | 2.8 ± 0.4 | 2.6 ± 0.4 | |
| Sample entropy | 3 | 0.48 ± 0.06 | 0.28 ± 0.06 | 0.38 ± 0.06 |
| 35 | 0.59 ± 0.09 | 0.25 ± 0.07 | 0.37 ± 0.07 | |
| 56 | 0.55 ± 0.05 | 0.33 ± 0.05 | 0.34 ± 0.05 | |
| Sample size | 3 | 10 | 9 | 10 |
| 35 | 4 | 7 | 9 | |
| 56 | 16 | 16 | 18 |
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.