Carroll Rebecca I, Forbes Andrew, Graham David A, Messam Locksley L McV
Herd Health and Animal Husbandry, School of Veterinary Medicine, University College Dublin, Dublin, Ireland.
Scottish Centre for Production Animal Health and Food Safety, School of Veterinary Medicine, University of Glasgow, G61 1QH, Scotland.
Prev Vet Med. 2020 Jan;174:104807. doi: 10.1016/j.prevetmed.2019.104807. Epub 2019 Oct 23.
Post-mortem liver inspection results together with production parameters are often used to estimate the impact of liver fluke infection on farm animal populations. However, post mortem liver inspection is an imperfect method of determining the liver fluke infection status of cattle. This work estimates the difference in mean lifetime weight gain at 819 days (ΔLWG) between steers assigned liver fluke negative (LFN) and liver fluke positive (LFP) status at post-mortem meat inspection, quantifies the potential impact of imperfect sensitivity and specificity on these results and estimates the economic impact of these differences. The study population is 32,007 steers that never moved from their birth herd in the Republic of Ireland and were slaughtered in one of two Irish meat processors in 2014. Individual animal-level data are used to generate 46 county - processor level estimates of ΔLWG. Standard errors and confidence intervals for these estimates are derived using bootstrapping. A meta-analytic approach is then used to obtain 3 overall estimates of the effect of liver fluke status on the ΔLWG in all the county - processor combinations, assuming post - mortem liver inspection Se = Sp = 1, 0.99 and 0.95. A random effects model is used and 95% prediction intervals (95% PI) are calculated. Assuming Se = Sp = 1 for post - mortem liver inspection, the random effects summary estimate of ΔLWG (ΔLWG) is 36 kg (95% PI: -1, 73). There is a minor change in ΔLWG (38 kg, 95% PI: -1, 77) when Se = Sp = 0.99 is assumed but this increases to 46 kg (95% PI: -2, 94) assuming Se = Sp = 0.95. The corresponding cost in euros of these differences between the LFN and LFP steers, assuming a price per kg of €3.90, are €77.01 (95% PI: -2.57, 156.37), €80.65 (95% PI: -3.43, 164.74) and €98.67 (95% PI: -5.15, 202.27) respectively. Our results demonstrate an association between liver fluke infection and reduced weight gain. We show that the effect of liver fluke infection on weight gain in cattle is underestimated due to misclassification resulting from imperfection in post mortem meat inspection. These findings will aid researchers, farmers and veterinary practitioners to make informed decisions on the control of liver fluke on farms.
死后肝脏检查结果与生产参数常被用于评估肝吸虫感染对农场动物群体的影响。然而，死后肝脏检查是确定牛肝吸虫感染状况的一种不完美方法。这项研究估计了在死后肉类检查中被判定为肝吸虫阴性（LFN）和肝吸虫阳性（LFP）的阉牛在819天时平均终生体重增加量的差异（ΔLWG），量化了不完美的敏感性和特异性对这些结果的潜在影响，并估计了这些差异的经济影响。研究群体为32007头从未离开其出生牛群的爱尔兰共和国阉牛，于2014年在两家爱尔兰肉类加工厂之一被屠宰。使用个体动物水平的数据生成了46个县 - 加工厂水平的ΔLWG估计值。这些估计值的标准误差和置信区间通过自助法得出。然后采用荟萃分析方法，假设死后肝脏检查的灵敏度（Se）=特异度（Sp）= 1、0.99和0.95，获得所有县 - 加工厂组合中肝吸虫状况对ΔLWG影响的3个总体估计值。使用随机效应模型并计算95%预测区间（95% PI）。假设死后肝脏检查的Se = Sp = 1，ΔLWG的随机效应汇总估计值（ΔLWG）为36千克（95% PI：-1，73）。假设Se = Sp = 0.99时，ΔLWG有轻微变化（38千克，95% PI：-1，77），但假设Se = Sp = 0.95时，这一数值增加到46千克（95% PI：-2，94）。假设每千克价格为3.90欧元，LFN和LFP阉牛之间这些差异对应的成本分别为77.01欧元（95% PI：-2.57，156.37）、80.65欧元（95% PI：-3.43，164.74）和98.67欧元（95% PI：-5.15，202.27）。我们的结果表明肝吸虫感染与体重增加减少之间存在关联。我们发现，由于死后肉类检查不完善导致的错误分类，肝吸虫感染对牛体重增加的影响被低估了。这些发现将有助于研究人员、农民和兽医从业者在农场肝吸虫控制方面做出明智决策。
