EpiVets, Te Awamutu, New Zealand.
VetSouth Ltd., Winton, New Zealand.
N Z Vet J. 2024 May;72(3):123-132. doi: 10.1080/00480169.2024.2321180. Epub 2024 Mar 11.
To undertake a survey of the prevalence of tail deviations, trauma and shortening on a representative selection of New Zealand dairy farms, and to assess whether sampling based on milking order could be used instead of random sampling across the herd to estimate prevalence.
This was a cross-sectional observational study, with 200 randomly selected farms enrolled across nine regions of New Zealand via selected veterinary practices (one/region). Veterinary clinics enrolled 20-25 farms each depending on region, with 1-2 trained technicians scoring per region. All cows (n = 92,348) present at a milking or pregnancy testing event were tail scored using a modified version of the New Zealand Veterinary Association Industry Scoring System. Palpated lesions were recorded as deviated (i.e. non-linear deformity), shortened (tail shorter than normal) or traumatic (all other lesions). The location of lesions was defined by dividing the tail into three equal zones: upper, middle and lower. A cow could have more than one lesion type and location, and/or multiple lesions of the same type, but for the prevalence calculation, only the presence or absence of a particular lesion was assessed. Prevalence of tail damage calculated using whole herd scoring was compared to random sampling across the herd and sampling from the front and back of the milking order. Bootstrap sampling with replacement was used to generate the sampling distributions across seven sample sizes ranging from 40-435 cows.
When scoring all cows, the median prevalence for deviation was 9.5 (min 0.9, max 40.3)%; trauma 0.9 (min 0, max 10.7)%, and shortening was 4.5 (min 1.3, max 10.8)%. Deviation and trauma prevalence varied between regions; the median prevalence of deviations ranged from 6% in the West Coast to 13% in Waikato, and the median prevalence of all tail damage from 7% in the West Coast to 29% in Southland. Sampling based on milking order was less precise than random sampling across the herd. With the latter and using 157 cows, 95% of prevalence estimates were within 5% of the whole herd estimate, but sampling based on milking order needed > 300 cows to achieve the same precision.
The proportion of cows identified as having damaged tails was consistent with recent reports from New Zealand and Ireland, but at 11.5%, the proportion of cows with trauma or deviation is below acceptable standards. An industry-wide programme is needed to reduce the proportion of affected cows.
在新西兰的一个有代表性的奶牛场样本中，对尾部偏斜、创伤和缩短的发生率进行调查，并评估基于挤奶顺序的抽样是否可以代替整个牛群的随机抽样来估计发生率。
这是一项横断面观察性研究，通过选定的兽医诊所（每个地区一个），在新西兰的九个地区随机选择了 200 个农场。兽医诊所根据地区每区招募 20-25 个农场，每个地区有 1-2 名经过培训的技术员进行评分。在挤奶或妊娠检测活动中出现的所有奶牛（n=92348）都使用新西兰兽医协会行业评分系统的改良版进行尾部评分。触诊到的病变被记录为偏斜（即非线性畸形）、缩短（尾巴比正常短）或创伤（所有其他病变）。病变的位置通过将尾巴分为三个相等的区域来定义：上、中、下。一头奶牛可能有多种病变类型和位置，和/或同一种病变的多个部位，但在计算发生率时，只评估特定病变的存在或不存在。使用整个牛群评分计算的尾部损伤发生率与整个牛群的随机抽样和挤奶顺序的前后抽样进行了比较。使用带替换的自举抽样，对 7 种不同样本大小（40-435 头牛）的抽样分布进行了生成。
对所有奶牛进行评分时，偏斜的中位数发生率为 9.5%（最小 0.9%，最大 40.3%）；创伤为 0.9%（最小 0%，最大 10.7%），缩短为 4.5%（最小 1.3%，最大 10.8%）。偏斜和创伤的发生率在各地区之间有所不同；偏斜发生率的中位数范围从西海岸的 6%到怀卡托的 13%，而所有尾部损伤的中位数发生率从西海岸的 7%到南地的 29%。基于挤奶顺序的抽样不如整个牛群的随机抽样精确。在后一种情况下，使用 157 头牛，95%的发生率估计值在整个牛群估计值的 5%以内，但基于挤奶顺序的抽样需要超过 300 头牛才能达到相同的精度。
被确定为尾部受损的奶牛比例与新西兰和爱尔兰最近的报告一致，但在 11.5%的情况下，创伤或偏斜的奶牛比例低于可接受的标准。需要一个全行业的计划来减少受影响奶牛的比例。
