Abstract
The effect of different larval dose evels and dosing regimens on the course of Cooperia oncophora infection in calves was studied. Four groups each of 4 calves were experimentally infected either with 50,000 or 200,000 C. oncophora larvae (L3) given either as single infections or as daily trickle infections. An additional group of calves remained as uninfected controls. The animals were necropsied on week 4 after infection.
Mild to moderate clinical signs of parasitic gastroenteritis developed among calves given high doses of larvae, but liveweight gains were not significantly different from those of the uninfected controls. Serum pepsinogen levels of dosed animals were within normal ranges but rose slightly, and on day 14 p.i. they differed significantly from those of the controls. On that occasion, the levels of serum pepsinogen in the trickle infected groups significantly exhibited the levels of the single infected groups. Hypoalbuminaemia was not a feature on any occasion.
The various groups did not differ significantly with regard to total worm counts and adult worm counts, but the groups receiving high larval doses harboured significantly more fourth stage larvae than the group receiving low doses of larvae, both in terms of absolute counts and in terms of percentages of total worm burdens. Within the same dose level, there was a tendency of a more even distribution of worms along the small intestine when the infection was given as a single infection compared with a trickle infection.
The results indicate that C. oncophora larval dose and dosing regimens may influence the pathogenic effects and to some extent the distribution of the parasite in the small intestine.
Keywords: cattle, larval dosing regimen, larval dose size
Sammendrag
Konsekvenserne af 2 forskellige dosisniveauer og 2 forskellige infektionsprocedurer med Cooperia oncophora i kalve blev undersøgt. Fire grupper, bestående af hver 4 kalve, blev eksperimentelt inficeret med hhv. 50.000 og 200.000 C. oncophora larver (L3), doseret enten på én gang eller som “trickle”-infektioner. En femte gruppe fungerede som uinficerede kontroldyr. Dyrene blev aflivet og undersøgt 4 uger efter infektionernes start.
Hos grupperne, som modtog de højeste larvedoser, observeredes lette til moderate symptomer på parasitær gastroenteritis, men dyrenes tilvækst adskilte sig dog ikke signifikant fra kontroldyrenes. De inficerede gruppers serum pepsinogen koncentrationer lå hele tiden i normalområdet, men steg dog noget, og fra dag 14 var de signifikant højere end i kontrolgruppen. Tilmed udviste de “trickle”-inficerede grupper signifikant højere koncentrationer end de éngangsdoserede. Ved intet tilfælde observeredes hypoalbuminæmi.
De inficerede grupper adskilte sig ikke fra hinanden, hverken hvad angik det totale antal parasitter eller det totale antal adulte parasitter, men de 2 grupper, som blev doseret med flest larver, viste sig at have flere 4. stadium larver end de lavt doserede grupper, både udtrykt som absolut antal og som procentvis andel. Inden for samme infektionsniveau, sås hos de éngangsinficerede en tendens til en mere jævn fordeling af parasitterne i tyndtarmen hos de “trickle”-inficerede.
Resultaterne viser, at såvel dosisniveau som infektionsprocedure får indflydelse på C.oncophora’s patogenitet, og i nogen grad også på fordelingen af parasitten i tyndtarmen.
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