Abstract
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.
Keywords: Sarcocystis grueneri, life cycle, definitive hosts, dog, silver fox, blue fox
Sammendrag
Forekomsten av mage-tarmnematoder hos ungfe i sin første beitesesong ble studert i relasjon til klima og geografisk lokalisasjon ved undersøkelse av grasprøver og faeces fra dyr fra 8 forskjeilige gårder i 7 ulike deler av landet i løpet av tre beitesesonger. De vanligste artene var Ostertagia spp. og Cooperia spp. De infektive trichostrongylidelarvene var i stor utstrekning i stand til å overleve vint eren i beltet på alle stedene som ble undersøkt, og Ostertagia i større grad enn Cooperia. Det var store variasjoner i antall larver ved begynnelsen av beitesesongen, både fra sted til sted og fra år til år, men de lå ofte på et relativt høyt nivå. Undersøkelsen bekrefter tidligere observasjoner, om at larver som har overvintret i beitet ofte kan vaere en vesentlig årsak til tap. Klinisk utbrudd av parasittær gastroenteritt ble imidlertid bare observert en sommer på ett sted i denne undersøkelsen.
De høye larvetallene som ofte ble funnet om høsten syntes i mindre grad å forårsake klinisk sykdom på den årstiden, da de antagelig opptrer for sent. De er imidlertid av stor betydning som kilde for den smitten som overvintrer i beitet og som angriper ungfe neste vår.
Det var ingen tydelig sammenheng mellom larvetall i beitet og klimaet, bort sett fra at det synes å være høyere tall i de varmere delene av landet, der også beitesesongen er lengre. Det eneste stedet der både egg- og larvetall var gjennomgående lave alle 3 årene i denne undersøkelsen var helt i nord, i Finnmark.
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