Ryan W G, Crawford R J, Gross S J, Wallace D H
University of Missouri, Southwest Research Center, Mt Vernon 65712, USA.
J Am Vet Med Assoc. 1997 Sep 15;211(6):754-6.
To assess parasite control and weight gain after administration of an ivermectin sustained-release bolus over 135 days to calves grazing in the midwestern United States.
Replicated pasture study.
56 Bos taurus calves.
Calves were matched for body weight and randomly allocated to remain untreated or to receive an ivermectin sustained-release bolus before turnout on day 0. Calves were grazed by treatment group on B pastures (4 replicates). Body weights and fecal egg counts were recorded on days- 1 and 28, and then at 28-day intervals until day 168.
Parasitism was not clinically evident prior to or during the study. In treated calves, mean fecal egg counts were at or near 0 at all posttreatment evaluations. Although the mean egg count exceeded 20 ova/g only once in control calves, the cumulative egg output was > 42 million/calf. For the treated group, it was < 0.1% of this number. Mean total weight gain was 33.9 kg (74.6 lb) greater for ivermectin-treated calves than for untreated control calves (P < 0.02): a 34% increase.
Fecal trichostrongyle eggs from calves can accumulate over a grazing season to provide enormous potential for augmenting pasture infectivity. An ivermectin sustained-release bolus (administered to calves being placed on pasture) controls parasitism, limits pasture infectivity, and can substantially influence growth by limiting the impact of subclinical parasitism.
评估在美国中西部放牧的犊牛服用伊维菌素缓释大丸剂135天后的寄生虫控制情况和体重增加情况。
重复牧场研究。
56头荷斯坦犊牛。
犊牛按体重匹配，随机分为未处理组或在第0天放牧前接受伊维菌素缓释大丸剂处理组。犊牛按处理组在B牧场放牧（4次重复）。在第 -1天和第28天记录体重和粪便虫卵计数，然后每隔28天记录一次，直至第168天。
在研究前或研究期间，寄生虫感染在临床上并不明显。在处理过的犊牛中，所有处理后评估的平均粪便虫卵计数均为0或接近0。虽然对照犊牛的平均虫卵计数仅一次超过20个卵/克，但累计产卵量>4200万个/犊牛。对于处理组，这一数字<0.1%。伊维菌素处理的犊牛平均总增重比未处理的对照犊牛高33.9千克（74.6磅）（P<0.02）：增加了34%。
犊牛粪便中的毛圆线虫卵可在一个放牧季节积累，极大地增加牧场的感染性。伊维菌素缓释大丸剂（给即将放牧的犊牛服用）可控制寄生虫感染，限制牧场感染性，并可通过限制亚临床寄生虫感染的影响显著影响生长。
