Iron and laterality effects on healing of cautery disbudding wounds in dairy calves

Hot-iron disbudding, the process of cauterizing the horn buds of calves or goat kids at an early age to prevent horn growth, is routinely practiced in dairy production. The wounds take weeks to heal and are painful to touch throughout this time. Possible strategies to hasten the healing of disbudding wounds are not well understood, but the type of iron used may be an important factor to consider. When evaluating strategies to hasten healing, a within-subjects design may be preferable, but laterality effects might act as a potential source of variation and confounding in this type of experiment. Our objectives were to compare healing after disbudding with 2 commercially available irons, and to determine whether wounds healed differently on the left versus the right side of the head. Ten Holstein calves 4 to 10 d of age were disbudded using the Rhinehart X50A electric disbudder (Rhinehart Development Corp., Spencerville, IN) on one horn bud and the Portasol gas disbudder (Portasol USA, Elmira, OR) on the other; side (left vs. right) was balanced between treatments. We scored wounds daily for the presence of 6 tissue types: attached necrotic tissue, detached necrotic tissue, exudate, granulation, crust, and epithelium. Surface temperature and size of the wound were measured twice-weekly using thermal and digital photographs, respectively. The type of iron used did not affect latency to re-epithelialize, which took on average (mean ± standard deviation) 53 ± 3 d and 55 ± 3 d for Portasol and Rhinehart wounds, respectively (range: 40-70 d). However, compared with Portasol wounds, those from the Rhinehart had fewer days of granulation tissue and tended to have more days of detached necrotic tissue. The Portasol tip had a smaller total surface area than the Rhinehart, which may have resulted in a less severe burn, causing the necrotic tissue to fall off sooner. The left side tended to re-epithelialize faster than the right side (mean ± standard error: left 51 ± 3 d; right 57 ± 3 d) and have fewer days of crust. Left-sided wounds were also cooler and tended to be smaller than those on the right. To assess the external validity of these laterality effects in our primary experiment (experiment A), we analyzed wound healing data from 2 other disbudding studies, one on calves (experiment B) and one on goat kids (experiment C). We observed laterality effects in the opposite direction in Experiment B, but negligible effects in experiment C, indicating that the differences in laterality had low external validity; the biological meaning of this asymmetry is unclear. Nonetheless, if using a within-subjects design, asymmetries in wound healing should be considered to avoid confounding effects. In conclusion, wounds from both irons took 7 to 8 wk to heal, on average; other strategies to accelerate healing should be explored.