Suarez V H, Lorenzo R M, Busetti M R, Santucho G M
Estación Experimental Agropecuaria Anguil, Instituto Nacional de Tecnología Agropecuaria, Anguil, La Pampa, Argentina.
Vet Parasitol. 1999 Feb 25;81(2):137-48. doi: 10.1016/s0304-4017(98)00183-6.
The epidemiology of nematode infection was studied in fattening grazing cattle from weaning (April 1994) to market at the end of their second autumn (July 1995). Sixty Aberdeen Angus calves of seven months of age were randomly allocated by weight to two groups: GT, treated every three weeks with doramectin (200 mcg/kg); and GI, an infected group, only treated with fenbendazole (7.5 mg/kg) at weaning and on the 1st of October. The two groups were grazed together on contaminated lucerne pastures until July, on 'clean' oat pastures until October and again on contaminated lucerne until the end of the trial. Fecal egg counts (epg), herbage larvae (L3), serum pepsinogen (Pep) and blood eosinophils (Eo) were evaluated monthly. Eight steers were slaughtered for worm recovery, three in July 1994, three in December 1994 and two in July 1995. Grazing feed intake was estimated by fecal output (chromic oxide method)/l-diet digestibility and to measure non-specific response, Brucella antibodies were detected at 11 and 40 days post-vaccination in early winter. Fecal egg counts, Pep and Eo of GI increased (P<0.01) from April to July when there was a moderate-to-high level of infection. Ostertagia, Trichostrongylus and Cooperia were the predominant genera. By late winter, all parameters decreased on oat 'clean' pastures and increased again when cattle returned to moderately infected lucerne. During summer, the parameters measured reflected the negligible numbers of L3 on pastures until early autumn. At this time, increased numbers of L3 were followed by a moderate rise (P<0.01) of epg, Pep and Eo values. During winter, GT showed higher (P<0.04) Brucella antibody IgG titers while feed intake of GI was 24.9% depressed (P<0.02). There were total cumulative weight-gain (WG) differences (P<0.001) between groups (GT=263.1 kg; GI=214.3 kg). During the second autumn, the mean WG of GT steers was 16.6 kg greater (P<0.04) than that of GI. Vaccination titres against Brucella suggested non-specific depression of immunity, while higher Pep and Eo levels in second-year steers may have reflected hypersensitivity reactions.
对从断奶（1994年4月）至第二个秋季末（1995年7月）育肥期的放牧牛的线虫感染流行病学进行了研究。60头7月龄的阿伯丁安格斯犊牛按体重随机分为两组：GT组，每三周用多拉菌素（200微克/千克）治疗一次；GI组，即感染组，仅在断奶时和10月1日用芬苯达唑（7.5毫克/千克）治疗。两组在受污染的苜蓿牧场上一起放牧至7月，在“清洁”的燕麦牧场上放牧至10月，然后再次在受污染的苜蓿牧场上放牧至试验结束。每月评估粪便虫卵计数（epg）、牧草幼虫（L3）、血清胃蛋白酶原（Pep）和血液嗜酸性粒细胞（Eo）。宰杀8头公牛以回收蠕虫，1994年7月宰杀3头，1994年12月宰杀3头，1995年7月宰杀2头。通过粪便排出量（氧化铬法）/日粮消化率估算放牧采食量，并为测量非特异性反应，在初冬接种疫苗后11天和40天检测布鲁氏菌抗体。4月至7月感染程度为中度至高度时，GI组的粪便虫卵计数、Pep和Eo升高（P<0.01）。奥斯特他线虫、毛圆线虫和古柏线虫是主要的属。到冬末，在燕麦“清洁”牧场上所有参数均下降，当牛回到中度感染的苜蓿牧场时又再次升高。夏季，所测参数反映出直到初秋牧场L3数量可忽略不计。此时，L3数量增加后，epg、Pep和Eo值适度上升（P<0.01）。冬季，GT组布鲁氏菌抗体IgG滴度较高（P<0.04），而GI组采食量降低24.9%（P<0.02）。两组之间存在总累积体重增加（WG）差异（P<0.001）（GT组=263.1千克；GI组=214.3千克）。在第二个秋季，GT组公牛的平均体重增加比GI组多16.6千克（P<0.04）。针对布鲁氏菌的疫苗接种滴度表明免疫出现非特异性抑制，而第二年公牛中较高的Pep和Eo水平可能反映了过敏反应。
