The effect of early burn injury on sensitivity to future painful stimuli in dairy heifers

Abstract

Animals that experience painful procedures as neonates are more sensitive to pain later in life. We evaluated whether disbudding with a heated iron at 3 (n = 12), 35 (n = 9), or 56 (n = 20) d of age affected heifers' pain responses to vaccine injections at 11 mo of age. Heifers responded to the injection procedure with struggling and changes in eye temperature and heart rate variability compared to a sham procedure the day before, and still had a heightened response 6 d later, regardless of disbudding age. However, some heart rate variability indices suggested increased sympathetic dominance in heifers disbudded at 35 d, compared to the other 2 age groups, independent of the injection procedure. We also found that heifers disbudded at 3 or 35 d had a higher mean heart rate after the injection procedure compared to those disbudded at 56 d. We conclude that: (1) heifers find injections aversive; and (2) there is some evidence that disbudding age influences autonomic nervous system activity later in life.

Fig 1. Estimated marginal mean ± SE count of struggling behaviour in 11-mo-old heifers receiving 2 consecutive injections, one on each side of the neck (I0), while restrained in a headlock.

Heifers were also observed in a sham procedure the day before (C-1) and 6 d after (C6) the injections. Behaviours were scored for 60 s following the start of the procedure. Heifers were previously disbudded at 3 (n = 12), 35 (n = 9), or 56 (n = 20) d of age. Data are back-transformed from the log scale.

Fig 2. Estimated marginal mean ± SE change in maximum eye temperature (°C) from baseline (-5-0 min) to 0–1 min, and from 0–1 min to 2–5 min post-treatment.

Heifers received 2 consecutive injections, one on each side of the neck (I0), as well as a sham procedure the day before (C-1) and 6 d after (C6) the injections. The injection procedure began at 0 min and took approximately 30 s. Different superscripts indicate trial differences (P < 0.05) within time intervals.

Fig 3. Estimated marginal mean ± SE maximum eye temperature (°C) at baseline (-5-0 min), and 0–1 to 2–5 min post-treatment.

Heifers received 2 consecutive injections, one on each side of the neck (I0), as well as a sham procedure the day before (C-1) and 6 d after (C6) the injections. The injection procedure began at 0 min and took approximately 30 s.

Fig 4. Mean heart rate during the 10-min sampling period for 11-mo-old heifers receiving 2 consecutive injections, one on each side of the neck (I0), while restrained in a headlock.

Heifers were also observed in 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. The injection procedure began at 0 min and took approximately 30 s.