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

Abstract

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.

Conditioned place preference reveals ongoing pain in calves 3 weeks after disbudding

“…Indeed, it is possible the cornual nerve block was relieving pruritus in the Day 20 disbudded calves as local anesthetics have anti-pruritic actions 44 . The necrotic tissue on all wounds was peeling by 17 days after disbudding, and had started to fall of by 20 days, similar to previous descriptions 4,5 . It would be of interest to know whether calves experience pruritus at this stage in order to provide appropriate medication; antihistamines, for example, are commonly prescribed for pruritus in human burn patients 42 .…”

“…The resulting burns from disbudding remain sensitive to mechanical stimulation until they have re-epithelialized, which takes from 6 to 13 weeks 4,5 . Others reported increased sensitivity for at least 14 weeks, after re-epithelialization had concluded 6 .…”

“…We chose lidocaine as the analgesic agent because it has a quick onset (1-5 min), short duration of action (90 min), negligible side effects, and established antinociceptive efficacy in calves 12 . The selected timepoints after disbudding, 6 hours and 20 days, represent respectively the acute post-operative period and a period of transition when the initial necrotic tissue begins to peel away from the scalp and eventually falls off, leaving an open wound 4,5 . Since wounds vary in healing time 4,5 , we also documented the tissue types present in the wound bed to verify the healing stage at these timepoints.…”

Sensitivity and wound healing after hot-iron disbudding in goat kids

“…Thus, it remains unclear why some locations are more sensitive than others and what relevance this has, if any, for the animal's welfare. As expected, sensitivity did not differ between left and right wounds, as has also been found in calves (Heinrich et al, 2010; but see Adcock et al, 2019).…”

“…Welfare may also be compromised for several weeks during the healing process. In disbudded calves, tissue remains severely damaged for at least 3 or 4 wk (Huebner et al, 2017) and complete re-epithelialization takes from 6 to 13 wk (Adcock and Tucker, 2018b;Adcock et al, 2019). Throughout this time, wounds are more sensitive to pressure algometry than newly re-epithelialized tissue (Adcock and Tucker, 2018b).…”