The epidemiology of trichostrongylid infections in young cattle in Norway
Tharaldsen, J.
Acta Veterinaria Scandinavica. Supplementum 1976(61): 1-21
1976
ISSN/ISBN: 0065-1699 PMID: 1065208 Document Number: 101142
Field experiments were carried out from 1972-1974 to study the occurrence of the free-living stages of trichostrongylid nematodes and their effect on calves during their first grazing season. The effect of artificial irrigation on the herbage contamination was followed in 1973 and 1974. The last year a group on parasite-free pasture was included for comparison. Half of the animals on irrigated and unirrigated pasture and on parasite-free ground were given anthelmintics 20 days after they were turned out in 1974. Pasture larvae counts indicated that the number of infective trichostrongylid larvae in the spring were about 1/5 to 1/3 of those seen at the end of the previous grazing season. The number fell gradually to a minimum in the beginning of July, followed by a rapid build-up in Aug., then a new decrease, and a rise towards the end of the grazing season. The counts at the end of the season can be extremely high. The larvae were mainly of Ostertagia ostertagi and Cooperia oncophora. Clinical ostertagiosis was obvious only in 1972; the symptoms occurred in June/July, when the mean fecal counts were > 1100 eggs/g in the 33 animals observed. The weight gain in calves on parasite-free pasture in 1974 was significantly better than in those on both permanent pastures, where the reduced growth was most pronounced during the first part of the grazing season. In the climate of Norway a sufficient number of infective larvae seems to survive the winter in the pasture to produce varying degrees of parasitic gastroenteritis in young, susceptible cattle during the first part of the grazing season. Treatment with an anthelmintic about 20 days after the animals were turned out did not effectively control the infection due to the overwintering larvae. There was no improved weight gain and no reduction in the production of nematode eggs. Artificial irrigation did not seem to influence the occurrence of infective larvae in the pasture.