CRC for Sheep Industry Innovation and School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
Vet Parasitol. 2012 Feb 10;183(3-4):274-83. doi: 10.1016/j.vetpar.2011.07.033. Epub 2011 Jul 23.
This study aimed to quantify production loss due to larval challenge in sheep administered a controlled release albendazole capsule (CRC) and thus determine the suitability of CRC treated sheep as a proxy for worm-free sheep in grazing experiments. The experiment used an incomplete 2 × 3 latin square design with 81 Merino wethers. Sheep were either infected (INF) with mixed oral infection of albendazole-susceptible Haemonchus contortus, Trichostrongylus colubriformis, and Teladorsagia circumcincta (initial bolus then thrice weekly maintenance) or remained uninfected (UINF). Worm control treatments were with a CRC (CRCT), threshold treatment with a short-acting anthelmintic when worm egg count (WEC) exceeded 1500 epg (TT) or untreated (UT). The experiment was conducted in two 63-day periods (separated by a 14 day washout period) with infection treatments swapped between periods. A subset of animals was killed at the end of each period for worm counts and tissue sampling. Faecal worm egg count in UINF-UT reached 10,204 and 6078 epg at day 63 in periods 1 and 2, respectively, and remained 0 throughout in the CRT treatments. There was no difference in live weight gain or wool growth of INF-CRCT sheep (67 and 70 g/d) relative to UINF-CRCT (67 and 76 g/d). Live weight gain was significantly lower in INF-UT (27 g/d) and INF-TT (55 g/d) than UINF-UT (88 g/d) or UINF-TT (81 g/d) treatments. During the first infection period, greasy fleece weight growth was significantly lower in INF-UT (6.33 g/d) and INF-TT (6.37 g/d) than UINF-UT (7.80 g/d) or UINF-TT (7.32 g/d) treatments. The effects of infection on production persisted in INF-UT, but not INF-TT sheep for several weeks after termination of infection. Eosinophil counts were elevated in all infected groups and the antibody response to T. colubriformis was greater in INF-CRCT and INF-TT groups compared to uninfected sheep. Together, these results indicate that larval challenge in sheep with a CRC is mildly immunogenic but is not associated with production loss. The results also showed that the CRC itself reduced live weight gain and that anthelmintic treatment at a WEC threshold of 1500 epg reduces production loss during infections and prevents persistence of adverse effects following infection.
本研究旨在量化绵羊幼虫感染导致的生产损失，从而确定使用控释阿苯达唑胶囊（CRC）处理的绵羊作为放牧实验中无蠕虫绵羊的替代物的适宜性。该实验采用不完全 2×3 拉丁方设计，共有 81 只美利奴羊。绵羊要么被感染（INF），即口服感染阿苯达唑敏感的捻转血矛线虫、奥斯特线虫和毛圆线虫（初始弹丸然后每周三次维持），要么保持未感染（UINF）。蠕虫控制处理是使用 CRC（CRCT）、当虫卵计数（WEC）超过 1500 epg 时用短效驱虫药进行阈值处理（TT）或未处理（UT）。实验分为两个 63 天的周期（间隔 14 天清洗期），感染处理在两个周期之间交换。每个周期结束时，一小部分动物被处死进行蠕虫计数和组织取样。UINF-UT 组的粪便虫卵计数在第 1 周期和第 2 周期分别达到 10204 和 6078 epg，而 CRT 处理组在整个周期中均为 0。与 UINF-CRCT 相比，INF-CRCT 绵羊的体重增加（67 和 70 g/d）和羊毛生长（67 和 70 g/d）没有差异。与 UINF-UT（88 g/d）或 UINF-TT（81 g/d）处理相比，INF-UT（27 g/d）和 INF-TT（55 g/d）的体重增加显著较低。在第一个感染周期中，INF-UT（6.33 g/d）和 INF-TT（6.37 g/d）的油腻羊毛生长显著低于 UINF-UT（7.80 g/d）或 UINF-TT（7.32 g/d）处理。感染对生产的影响在 INF-UT 中持续存在，但在感染终止后数周内，INF-TT 绵羊中没有这种影响。所有感染组的嗜酸性粒细胞计数均升高，与未感染绵羊相比，INF-CRCT 和 INF-TT 组对奥斯特线虫的抗体反应更大。这些结果表明，绵羊幼虫感染 CRC 是轻度免疫原性的，但与生产损失无关。结果还表明，CRC 本身会降低体重增加，而在 WEC 阈值为 1500 epg 时使用驱虫药进行阈值处理可减少感染期间的生产损失，并防止感染后不良影响的持续存在。
