Wound healing and pain sensitivity following caustic paste disbudding in dairy calves

Abstract

Caustic paste disbudding is increasing in popularity on commercial dairy farms in the US, but little research has explored the pain and welfare implications beyond the acute period of this procedure. Researchers have reported it takes 7 to 9 wk, on average, for hot-iron disbudding wounds to re-epithelialize in dairy calves. Our objective was to describe wound healing and sensitivity following caustic paste disbudding. Jersey and Holstein female calves were disbudded using Dr. Naylor's caustic paste at 3 d of age (n = 18) while control calves received a sham procedure (n = 15). Before disbudding, calves received a local block and an NSAID. Calves ≥34 kg and <34 kg at birth had 0.3 or 0.25 mL of paste applied per unshaved horn bud, respectively. Following disbudding, wounds were scored 2x/wk for the presence/absence of 8 tissue categories including the final stages: new epithelium and fully healed. Control calves were removed from the experiment after 6 wk to be hot-iron disbudded and avoid more invasive procedures. Mechanical nociceptive threshold (MNT) measures were collected weekly to evaluate wound sensitivity until calves were removed from the study or wounds were healed. Wounds were slow to re-epithelialize (16.2 ± 5.7 wk, mean ± SD; range: 6.2-32.5 wk) and contract to be considered fully healed (18.8 ± 6 wk, mean ± SD; range: 8.7-34.1 wk). Compared with non-disbudded controls, paste calves exhibited lower MNT values for all 6 wk (mean ± SE, Control:1.46 ± 0.16; Paste:1.18 ± 0.12 N). These data indicate that wounds from caustic paste disbudding are more sensitive than undamaged tissue for at least 6 wk and take twice as long to heal compared with cautery methods described in the literature. In conclusion, caustic paste disbudding wounds took 18.8 wk to fully heal and were more sensitive than intact horn buds for 6 wk. Future work should examine if aspects of paste application (e.g., amount, time rubbed in, age, pain mitigation), could improve healing time and sensitivity.