Hot-iron disbudding is a common management procedure to prevent horn growth in calves. The study objective was to examine effect of age, breed and sex on horn bud size of dairy-bred and suckler-bred calves at time of disbudding. The left and right horn bud size (diameter and height in mm) of 279 calves, including dairy-bred Holstein-Friesian (Male (M) = 88) and 191 suckler-bred (86 Charolais, CH; (M = 39, Female (F) = 47), 67 Limousin, LM; (M = 32, F = 35) and 38 Simmental, SI; (M = 22, F = 16) sired)) was measured using a digital calliper at time of disbudding. Calves were retrospectively assigned to two age categories at time of disbudding: 1), 14 to 28 days (d) old and 2), 29 to 60 d old. Holstein-Friesian M calves had a greater horn bud diameter (16.97 v.14.45 mm) and height (7.79 v. 5.00 mm) compared to suckler-bred M calves (P < 0.01), with no difference (P > 0.05) among the suckler-bred calves. Suckler-bred M calves had a greater horn bud diameter (14.46 vs 13.29 mm) and height (5.01 vs 3.88 mm) compared to suckler-bred F calves (P < 0.05). The slopes of the lines of best fit show that horn bud diameter and height increased with age (P < 0.05) for HF, SI male and CH female calves while there was no relationship with age (P > 0.05) for CH and LM male calves, or for SI and LM female calves. Linear regression of age with diameter and with height for each breed and sex showed high variability in the data as indicated by R-squared values ranging from 0.003–0.41 indicating that in the case of the diameter and the height, the weight of the fitting effect was poor. Calf age is not a good predictor of horn bud size and recommendations for the disbudding of calves should be based on horn bud size and not on age. The implications of these findings are that calves should be disbudded while horn development is still at the bud stage and when the bud is large enough to be easily palpable/visible, but not so large that disbudding could lead to severe tissue trauma.

中文翻译：

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脱芽时奶牛和乳牛犊的角芽大小

热铁拔芽是防止犊牛角生长的常见管理程序。研究目的是检验年龄、品种和性别对乳牛和乳牛犊在脱芽时角芽大小的影响。279 头小牛的左右角芽大小（直径和高度以毫米为单位），包括奶牛饲养的荷斯坦-弗里斯兰（雄性 (M) = 88）和 191 头乳牛饲养的（86 Charolais, CH；（M = 39，雌性） (F) = 47), 67 Limousin, LM; (M = 32, F = 35) 和 38 Simmental, SI; (M = 22, F = 16) sired)) 在脱芽时使用数字卡尺测量。小牛在出芽时被追溯分配到两个年龄类别：1)、14 至 28 天 (d) 大和 2)、29 至 60 天大。与母乳喂养的 M 小牛相比，荷斯坦-弗里斯兰 M 小牛的角芽直径（16.97 对 14.45 毫米）和高度（7.79 对 5.00 毫米）更大（P < 0.01），母乳喂养的犊牛之间没有差异（P > 0.05）。与母乳喂养的 F 犊牛相比，母乳喂养的 M 犊牛具有更大的角芽直径（14.46 对 13.29 毫米）和高度（5.01 对 3.88 毫米）（P < 0.05）。最佳拟合线的斜率表明，HF、SI 雄性和 CH 雌性小牛的角芽直径和高度随着年龄的增长而增加（P < 0.05），而 CH 和 LM 雄性小牛的角芽直径和高度与年龄无关（P > 0.05） ，或用于 SI 和 LM 雌性小牛。每个品种和性别的年龄与直径和高度的线性回归显示数据的高度可变性，如 R 平方值所示，范围为 0.003-0.41，表明在直径和高度的情况下，拟合效应的权重很穷。犊牛年龄不是角芽大小的良好预测指标，对犊牛去芽的建议应基于角芽大小而不是年龄。这些发现的含义是，当角发育仍处于萌芽阶段时，小牛应该去芽，并且当芽足够大以易于触及/可见时，但不要大到去芽可能导致严重的组织损伤。