Scherpenzeel C G M, den Uijl I E M, van Schaik G, Riekerink R G M Olde, Hogeveen H, Lam T J G M
GD Animal Health, PO Box 9, 7400 AA Deventer, the Netherlands.
GD Animal Health, PO Box 9, 7400 AA Deventer, the Netherlands.
J Dairy Sci. 2016 May;99(5):3753-3764. doi: 10.3168/jds.2015-9963.
The goal of dry-cow therapy (DCT) is to reduce the prevalence of intramammary infections (IMI) by eliminating existing IMI at drying off and preventing new IMI from occurring during the dry period. Due to public health concerns, however, preventive use of antimicrobials has become questionable. In this study, we evaluated the effects of 8 scenarios for selecting animals for DCT, taking into account variation in parity and cow-level somatic cell count (SCC) at drying off. The aim of this study was to evaluate udder health, antimicrobial usage, and economics at the herd level when using different scenarios for selecting cows for DCT. To enable calculation and comparison of the effects of different scenarios to select cows for DCT in an "average" herd, we created an example herd, with a virtual herd size of 100 dairy cows to be calving during a year. Udder health, antimicrobial usage, and economics were evaluated during the dry period and the first 100 d in lactation, the period during which the greatest effect of DCT is expected. This leads to an estimated 13,551 cow-days at risk during a year in a 100-cow dairy herd. In addition to a blanket DCT (BDCT) scenario, we developed 7 scenarios to select cows for DCT based on SCC. The scenarios covered a range of possible approaches to select low-SCC cows for DCT, all based on cow-level SCC thresholds on the last milk recording before drying off. The incidence rate of clinical mastitis in the example herd varied from 11.6 to 14.5 cases of clinical mastitis per 10,000 cow-days at risk in the different scenarios, and the prevalence of subclinical mastitis varied from 38.8% in scenario 1 (BDCT) to 48.3% in scenario 8. Total antimicrobial usage for DCT and clinical mastitis treatment varied over the scenarios from 1.27 (scenario 8) to 3.15 animal daily dosages (BDCT), leading to a maximum reduction in antimicrobial usage of 60% for scenario 8 compared with BDCT. The total costs for each of the scenarios showed little variation, varying from €4,893 for scenario 5 to €5,383 for scenario 8. The effect of selective DCT compared with BDCT on udder health, antimicrobial usage, and economics is influenced by the SCC criteria used to select cows for DCT. Scenario 2 resulted in the lowest increases in clinical and subclinical mastitis compared with BDCT. The greatest reduction in antimicrobial usage was achieved under scenario 8. From an economic perspective, lowest costs were achieved with scenario 5. Drying off dairy cows with antimicrobials has an effect on udder health, antimicrobial usage, and economics.
干奶期治疗（DCT）的目标是通过在干奶时消除现有的乳房内感染（IMI）并防止在干奶期发生新的IMI，来降低IMI的发生率。然而，出于公共卫生方面的考虑，预防性使用抗菌药物已变得存在疑问。在本研究中，我们评估了8种为DCT选择动物的方案的效果，同时考虑了胎次差异以及干奶时牛群水平的体细胞计数（SCC）。本研究的目的是在使用不同方案为DCT选择奶牛时，评估牛群水平的乳房健康、抗菌药物使用情况和经济效益。为了能够计算和比较在一个“平均”牛群中为DCT选择奶牛的不同方案的效果，我们创建了一个示例牛群，虚拟牛群规模为100头奶牛，一年内产犊。在干奶期和泌乳的前100天评估乳房健康、抗菌药物使用情况和经济效益，这是预计DCT产生最大效果的时期。这导致在一个100头奶牛的奶牛场中，一年估计有13551个风险牛日。除了全面干奶期治疗（BDCT）方案外，我们还制定了7种基于SCC为DCT选择奶牛的方案。这些方案涵盖了一系列为DCT选择低SCC奶牛的可能方法，所有方法均基于干奶前最后一次牛奶记录时的牛群水平SCC阈值。在不同方案中，示例牛群中临床乳腺炎的发病率为每10000个风险牛日11.6至14.5例临床乳腺炎病例，亚临床乳腺炎的发生率从方案1（BDCT）的38.8%到方案8的48.3%不等。DCT和临床乳腺炎治疗的总抗菌药物使用量在不同方案中从1.27（方案8）到3.15动物每日剂量（BDCT）不等，与BDCT相比，方案8的抗菌药物使用量最多可减少60%。每个方案的总成本变化不大，从方案5的4893欧元到方案8的5383欧元不等。与BDCT相比，选择性DCT对乳房健康、抗菌药物使用情况和经济效益的影响受用于为DCT选择奶牛的SCC标准影响。与BDCT相比，方案2导致临床和亚临床乳腺炎的增加最少。方案8实现了最大程度的抗菌药物使用减少。从经济角度来看，方案5成本最低。用抗菌药物对奶牛进行干奶对乳房健康、抗菌药物使用情况和经济效益有影响。
