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

摘要

Hot-iron disbudding, the process of cauterizing thehorn buds of calves or goat kids at an early age toprevent horn growth, is routinely practiced in dairyproduction. The wounds take weeks to heal and arepainful to touch throughout this time. Possible strategiesto hasten the healing of disbudding wounds arenot well understood, but the type of iron used maybe an important factor to consider. When evaluatingstrategies to hasten healing, a within-subjects designmay be preferable, but laterality effects might act asa potential source of variation and confounding in thistype of experiment. Our objectives were to comparehealing after disbudding with 2 commercially availableirons, and to determine whether wounds healed differentlyon the left versus the right side of the head. TenHolstein calves 4 to 10 d of age were disbudded usingthe Rhinehart X50A electric disbudder (RhinehartDevelopment Corp., Spencerville, IN) on one horn budand the Portasol gas disbudder (Portasol USA, Elmira,OR) on the other; side (left vs. right) was balancedbetween treatments. We scored wounds daily for thepresence of 6 tissue types: attached necrotic tissue,detached necrotic tissue, exudate, granulation, crust,and epithelium. Surface temperature and size of thewound were measured twice-weekly using thermal anddigital photographs, respectively. The type of ironused did not affect latency to re-epithelialize, whichtook on average (mean ± standard deviation) 53 ± 3d and 55 ± 3 d for Portasol and Rhinehart wounds,respectively (range: 40–70 d). However, compared withPortasol wounds, those from the Rhinehart had fewerdays of granulation tissue and tended to have moredays of detached necrotic tissue. The Portasol tip hada smaller total surface area than the Rhinehart, whichmay have resulted in a less severe burn, causing thenecrotic tissue to fall off sooner. The left side tendedto re-epithelialize faster than the right side (mean ±standard error: left 51 ± 3 d; right 57 ± 3 d) and havefewer days of crust. Left-sided wounds were also coolerand tended to be smaller than those on the right. Toassess the external validity of these laterality effects inour primary experiment (experiment A), we analyzedwound healing data from 2 other disbudding studies,one on calves (experiment B) and one on goat kids(experiment C). We observed laterality effects in theopposite direction in Experiment B, but negligible effectsin experiment C, indicating that the differencesin laterality had low external validity; the biologicalmeaning of this asymmetry is unclear. Nonetheless, ifusing a within-subjects design, asymmetries in woundhealing should be considered to avoid confounding effects.In conclusion, wounds from both irons took 7 to8 wk to heal, on average; other strategies to acceleratehealing should be explored.