Tharaldsen J, Helle O
Acta Vet Scand. 1984;25(2):164-86. doi: 10.1186/BF03547262.
The occurrence of trichostrongylid nematodes in young cattle was studied in relation to climate and geographical location, by examination of herbage and faecal samples from 8 farms in 7 different regions in Norway, during 3 consecutive summers. Species of Ostertagia and Cooperia were dominant. Infective larvae, especially those of Ostertagia, were able to survive the winter in the pasture to a great extent in all the areas studied. The spring larval counts varied considerably from place to place, and from year to year, but were often at fairly high levels. This confirms previous findings that the larvae which overwinter on the pasture may be a major cause of losses. Overt clinical disease, however, was only seen at 1 farm during this investigation. The large number of larvae often seen in the autumn seems to be of less significance as a cause of disease, due to the late appearance, but is of major importance as a source of the larvae which survive the winter in the pasture and infect young cattle the following spring. There was no obvious correlation between pasture larval counts and the climate, except that there seemed to be higher counts in the warmer parts of the country, where the grazing season is also longer. The only place were both faecal egg counts and larval counts in the herbage were consistently low, was in the very far north.
在连续三个夏天里，通过对挪威7个不同地区8个农场的牧草和粪便样本进行检测，研究了气候和地理位置与幼牛体内毛圆科线虫发生情况之间的关系。奥斯特他线虫属和古柏线虫属为优势种。在所有研究地区，感染性幼虫，尤其是奥斯特他线虫属的幼虫，在很大程度上能够在牧场越冬。春季幼虫数量在不同地点和年份差异很大，但通常处于相当高的水平。这证实了之前的研究结果，即牧场越冬幼虫可能是造成损失的主要原因。然而，在本次调查中，仅在1个农场发现了明显的临床疾病。秋季常见的大量幼虫，由于出现较晚，作为疾病病因的重要性似乎较低，但作为牧场越冬并在次年春季感染幼牛的幼虫来源却至关重要。除了该国较温暖地区（放牧季节也较长）的幼虫数量似乎较多外，牧场幼虫数量与气候之间没有明显的相关性。唯一粪便虫卵计数和牧草幼虫计数一直较低的地方是最北部地区。
