Endres M I, Lobeck-Luchterhand K M, Espejo L A, Tucker C B
Department of Animal Science, University of Minnesota, St. Paul 55108.
Department of Animal Science, University of Minnesota, St. Paul 55108.
J Dairy Sci. 2014;97(6):3523-30. doi: 10.3168/jds.2013-7464. Epub 2014 Mar 20.
Dairy welfare assessment programs are becoming more common on US farms. Outcome-based measurements, such as locomotion, hock lesion, hygiene, and body condition scores (BCS), are included in these assessments. The objective of the current study was to investigate the proportion of cows in the pen or subsamples of pens on a farm needed to provide an accurate estimate of the previously mentioned measurements. In experiment 1, we evaluated cows in 52 high pens (50 farms) for lameness using a 1- to 5-scale locomotion scoring system (1 = normal and 5 = severely lame; 24.4 and 6% of animals were scored ≥ 3 or ≥ 4, respectively). Cows were also given a BCS using a 1- to 5-scale, where 1 = emaciated and 5 = obese; cows were rarely thin (BCS ≤ 2; 0.10% of cows) or fat (BCS ≥ 4; 0.11% of cows). Hygiene scores were assessed on a 1- to 5-scale with 1 = clean and 5 = severely dirty; 54.9% of cows had a hygiene score ≥ 3. Hock injuries were classified as 1 = no lesion, 2 = mild lesion, and 3 = severe lesion; 10.6% of cows had a score of 3. Subsets of data were created with 10 replicates of random sampling that represented 100, 90, 80, 70, 60, 50, 40, 30, 20, 15, 10, 5, and 3% of the cows measured/pen. In experiment 2, we scored the same outcome measures on all cows in lactating pens from 12 farms and evaluated using pen subsamples: high; high and fresh; high, fresh, and hospital; and high, low, and hospital. For both experiments, the association between the estimates derived from all subsamples and entire pen (experiment 1) or herd (experiment 2) prevalence was evaluated using linear regression. To be considered a good estimate, 3 criteria must be met: R(2)>0.9, slope = 1, and intercept = 0. In experiment 1, on average, recording 15% of the pen represented the percentage of clinically lame cows (score ≥ 3), whereas 30% needed to be measured to estimate severe lameness (score ≥ 4). Only 15% of the pen was needed to estimate the percentage of the herd with a hygiene score ≥ 3, whereas 30% to estimate the prevalence of severe hock lesions. Estimating very thin and fat cows required that 70 to 80% of the pen be measured. In experiment 2, none of the pen subsamples met our criteria for accurate estimates of herd prevalence. In conclusion, we found that both a higher percentage of the pen must be sampled to generate accurate values for relatively rare parameters and that the population measured plays an important role in prevalence estimates.
奶牛福利评估项目在美国农场越来越普遍。基于结果的测量指标，如运动能力、跗关节损伤、卫生状况和体况评分（BCS），都包含在这些评估中。本研究的目的是调查一个农场中围栏内或围栏子样本中的奶牛比例，以准确估计上述测量指标。在实验1中，我们使用1至5级运动评分系统（1 = 正常，5 = 严重跛行；分别有24.4%和6%的动物评分为≥3或≥4）对52个高围栏（50个农场）中的奶牛进行跛行评估。奶牛还使用1至5级的BCS进行评分，其中1 = 消瘦，5 = 肥胖；奶牛很少消瘦（BCS≤2；0.10%的奶牛）或肥胖（BCS≥4；0.11%的奶牛）。卫生状况评分采用1至5级，1 = 清洁，5 = 严重肮脏；54.9%的奶牛卫生状况评分≥3。跗关节损伤分为1 = 无损伤，2 = 轻度损伤，3 = 严重损伤；10.6%的奶牛评分为3。通过随机抽样的10次重复创建数据子集，分别代表每个围栏测量奶牛数量的100%、90%、80%、70%、60%、50%、40%、30%、20%、15%、10%、5%和3%。在实验2中，我们对12个农场泌乳围栏中的所有奶牛进行相同的结果测量，并使用围栏子样本进行评估：高；高且新；高、新且住院；高、低且住院。对于这两个实验，使用线性回归评估从所有子样本得出的估计值与整个围栏（实验1）或牛群（实验2）患病率之间的关联。要被认为是一个好的估计值，必须满足3个标准：R²>0.9、斜率 = 1和截距 = 0。在实验1中，平均而言，记录围栏内15%的奶牛代表临床跛行奶牛（评分≥3）的百分比，而要估计严重跛行（评分≥4）则需要测量30%。仅需测量围栏内15%的奶牛即可估计卫生状况评分≥3的牛群百分比，而估计严重跗关节损伤的患病率则需要30%。估计极瘦和极胖的奶牛需要测量围栏内70%至80%的奶牛。在实验2中，没有一个围栏子样本满足我们对准确估计牛群患病率的标准。总之，我们发现对于相对罕见的参数，必须抽取更高比例的围栏样本才能得出准确值，并且所测量的群体在患病率估计中起着重要作用。
