Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, PEI, Canada C1A 4P3.
Prev Vet Med. 2013 Aug 1;111(1-2):63-75. doi: 10.1016/j.prevetmed.2013.04.001. Epub 2013 May 4.
Gastrointestinal nematodes, such as Ostertagia ostertagi and several species of Cooperia, are ubiquitous in temperate climates and have been shown to have detrimental effects on production in adult dairy cattle. A published meta-analysis demonstrated that overall, producers lose approximately 0.35 kg of milk per parasitized cow per day. Enzyme-linked immunosorbent assays (ELISAs) have the ability to quantify nematode infections in cattle, and thus, could be used to estimate the amount of milk production loss due to differing levels of parasitism at the individual cow level. ELISA results from individual cow milk samples were used to predict milk production response following a randomized anthelmintic treatment in a large field trial. To increase statistical power, the data collected from this field trial was pooled with data from two other published field trials to form an individual patient data meta-analysis (IPDMA). The ability to predict the effect of anthelmintic treatment on milk production depends on the level of parasitism quantified by an ELISA measuring milk antibodies against O. ostertagi, and reported as optical density ratios (ODRs). Therefore, the estimates from the interaction between ODR and treatment on milk production were used to determine how well the ODR predicted the response of the treatment. It was anticipated that the relationship between milk production and ODR was unlikely to be linear, so fractional polynomials were applied to the continuous ODR values. The interaction in the field trial showed a trend (p=0.138) toward a beneficial treatment effect when the individual ODR values, measured in late lactation and using Svanovir(®), were greater than 0.12. When individual data from two other similar studies were included in an IPDMA, the interaction terms became statistically significant (p=0.009) indicating that there is a beneficial treatment effect when ODR values are slightly elevated. A graph was used to demonstrate the treatment effect (the estimated difference of kg/cow/day of milk yield between the treated and placebo cows), with 95% confidence intervals, as the ODR values increase. It is important to note that the methods of quantifying the ODR values differed between the three studies in the IPDMA, therefore some caution should be used when using these final estimated values. However, the shape and magnitude of the treatment effects, as well as the other fixed model estimates, were very similar between the field trial and the IPDMA suggesting that any bias would likely be minimal.
胃肠道线虫，如奥斯特泰勒线虫和几种库珀线虫，在温带气候中普遍存在，并已被证明对成年奶牛的生产有不利影响。已发表的荟萃分析表明，总的来说，每头受感染的奶牛每天会损失约 0.35 公斤牛奶。酶联免疫吸附测定（ELISA）能够定量牛体内的线虫感染，因此，可以用来估计由于个体牛水平上的不同寄生虫感染程度而导致的牛奶产量损失。ELISA 从个体奶牛奶样中的结果用于预测在大型田间试验中随机驱虫处理后的牛奶生产反应。为了增加统计效力，将从该田间试验收集的数据与来自另外两个已发表的田间试验的数据汇集在一起，形成个体患者数据荟萃分析（IPDMA）。预测驱虫治疗对牛奶生产的影响的能力取决于通过测量针对奥斯特泰勒线虫的牛奶抗体的 ELISA 定量的寄生虫感染程度，并报告为光密度比（ODR）。因此，从 ODR 与治疗对牛奶生产的相互作用中得出的估计值用于确定 ODR 对治疗反应的预测程度。预计牛奶生产与 ODR 之间的关系不太可能呈线性，因此将分数多项式应用于连续的 ODR 值。田间试验中的相互作用显示出一种趋势（p=0.138），即当个体 ODR 值（在泌乳后期使用 Svanovir®测量）大于 0.12 时，治疗效果呈有益趋势。当将另外两项类似研究的个体数据纳入 IPDMA 时，交互项变得具有统计学意义（p=0.009），表明当 ODR 值略有升高时，治疗效果有益。使用图表来演示治疗效果（治疗牛与安慰剂牛的牛奶产量每天每头的估计差异），随着 ODR 值的增加，95%置信区间。需要注意的是，在 IPDMA 中的三项研究中，ODR 值的定量方法有所不同，因此在使用这些最终估计值时应谨慎。然而，田间试验和 IPDMA 之间的治疗效果的形状和幅度以及其他固定模型估计值非常相似，这表明任何偏差都可能很小。
