The Effect of Age on Pain Sensitivity during Burn Wound Healing in Dairy Calves

Introduction: Hot-iron disbudding, a husbandry procedure performed in dairy calves in which horn bud growth is prevented through tissue cauterization, produces third-degree burns. Little is known about how long pain persists following disbudding or factors that may influence sensitivity (e.g., age at disbudding). Our objective was to compare mechanical nociceptive thresholds for 3 weeks after disbudding/sham-disbudding and to understand how age affects this response.

Materials and Methods: Forty-eight calves were disbudded or sham disbudded at a younger (3–4 days) or older (34–36 days) age (n = 12/treatment). Nociceptive thresholds were measured with a pressure algometer on days 3, 7, 14, and 21 after disbudding/sham-disbudding. We assessed the effects of procedure (disbudded vs. sham), age of disbudding (younger vs. older), days since disbudding, and their two-way interactions on nociceptive thresholds using linear mixed models with calf fitted as a random effect.

Results: Disbudded calves were more sensitive to pressure applied to the head than sham calves throughout the 3 weeks (mean ± SE: disbudded: 1.37 ± 0.04 N; Sham: 1.96 ± 0.05 N; X² ₁  = 28.1; p < 0.0001). Older calves were more sensitive overall (mean ± SE: older: 1.49 ± 0.04 N; younger: 1.84 ± 0.06 N; X² ₁  = 9.50; p = 0.002), which may reflect lower pain tolerance and/or more developed motor abilities.

Conclusions: Burn wounds from disbudding remain painful for at least 3 weeks, regardless of whether they are inflicted at an early or late age.

Acknowledgement: This study was supported by USDA Multistate Research Project NC1029, a National Sciences and Engineering Research Council PGS-D to SJJA and a Henry A. Jastro Research Scholarship Award to SJJA. We gratefully acknowledge the infrastructure support of the Department of Animal Science, College of Agricultural and Environmental Sciences, and the UC-Davis California Agricultural Experiment Station.