Williams J C, Knox J W, Barras S A, Hawkins J A
Department of Veterinary Science, LSU Agricultural Center, Baton Rouge 70803.
Am J Vet Res. 1990 Dec;51(12):2034-43.
Four groups of 18 beef calves each were used to evaluate effects of different treatments on parasite control and weight gains. The investigation extended from November 1986 (weaning) to October 1987. Group-1 calves were treated with ivermectin (200 micrograms/kg of body weight, SC) at approximately 6-week intervals for a total of 8 treatments; group-2 calves were given the same dosage of ivermectin by the same route of administration as group-1 calves in November, March, and July; group-3 calves were given fenbendazole paste (5 mg/kg, PO) at the same times as group-2 calves; and group-4 calves served as untreated controls with provision for ivermectin salvage treatment. All groups grazed on individual pairs of larval-contaminated, 1.6-ha pastures. Highest (P less than 0.05) initial worm counts in fall tracer calves were found in group 3 (Ostertagia ostertagi and Trichostrongylus axei adults) and group 4 (O ostertagi and Haemonchus adults). Fecal egg counts of group-1 calves were low throughout the experiment and pasture larval counts remained negligible after July. Egg counts and larval counts of other groups remained higher into summer. Worm counts, including O ostertagi inhibited early fourth-stage larvae (EL4), were highest (P less than 0.05) in groups-3 and -4 spring tracer calves; numbers of O ostertagi EL4 were similarly high in groups 2, 3, and 4; and T axei counts were highest (P less than 0.05) in groups-3 and -4 yearlings slaughtered in spring. Liveweights of group-1 calves were greater (P less than 0.05) than in other groups from March 2 to October, and by July 2, group-2 calves had a liveweight advantage over group-4 calves. Group-3 calves had the lowest rate of gain from March to July and mean liveweight of the group was less (P less than 0.05) than in all other groups from April to October. Only minimal worm numbers were recovered from groups-1 or -2 calves in October. Large numbers of O ostertagi and T axei were recovered from group-4 calves and O ostertagi from group-3 calves. A few calves in groups 3 and 4, but particularly in group 4, were affected by type-II disease (chronic to acute gastritis caused by maturation and emergence of previously inhibited larvae) from August to October. Final mean liveweights in descending order were 365 kg in group 1, 328 kg in group 2, 316 kg in group 4, and 281 kg in group 3.
四组实验，每组18头肉用犊牛，用于评估不同处理对寄生虫控制和体重增加的影响。研究从1986年11月（断奶）持续到1987年10月。第1组犊牛每隔约6周皮下注射伊维菌素（200微克/千克体重），共注射8次；第2组犊牛在11月、3月和7月按与第1组相同的给药途径给予相同剂量的伊维菌素；第3组犊牛在与第2组相同的时间给予芬苯达唑糊剂（5毫克/千克，口服）；第4组犊牛作为未处理的对照，但预留伊维菌素挽救治疗。所有组在单独的一对受幼虫污染的1.6公顷牧场上放牧。秋季追踪犊牛中，第3组（奥氏奥斯特线虫和阿氏毛圆线虫成虫）和第4组（奥氏奥斯特线虫和血矛线虫成虫）的初始蠕虫计数最高（P<0.05）。在整个实验过程中，第1组犊牛的粪便虫卵计数较低，7月后牧场幼虫计数仍可忽略不计。其他组的虫卵计数和幼虫计数在夏季仍较高。包括奥氏奥斯特线虫早期第四期幼虫（EL4）在内的蠕虫计数，在第3组和第4组春季追踪犊牛中最高（P<0.05）；第2组、第3组和第4组的奥氏奥斯特线虫EL4数量同样较高；第3组和第4组春季屠宰的一岁龄牛的阿氏毛圆线虫计数最高（P<0.05）。从3月2日至10月，第1组犊牛的活重比其他组更大（P<0.05），到7月2日，第2组犊牛的活重超过第4组犊牛。从3月到7月，第3组犊牛的增重率最低，从4月到10月，该组的平均活重比所有其他组都低（P<0.05）。10月时，从第1组或第2组犊牛中仅回收了极少数量的蠕虫。从第4组犊牛中回收了大量的奥氏奥斯特线虫和阿氏毛圆线虫，从第3组犊牛中回收了奥氏奥斯特线虫。8月至10月，第3组和第4组的一些犊牛，特别是第4组的犊牛，受到II型疾病（由先前受抑制幼虫的成熟和出现引起的慢性至急性胃炎）的影响。最终平均活重从高到低依次为：第1组365千克，第2组328千克，第4组
