Effects of Leucocyte Extract, Levamisole and Sulphadimidine on Natural Coccidial Infections (Eimeria Spp.) in Young Lambs

Abstract

The efficacy of leucocyte extract (LE) and sulphadimidine in preventing coccidiosis in naturally infected lambs on pasture was evaluated in 3 separate experiments, whereas the prophylactic effect of levamisole was studied in 1 of the experiments. LE prepared from ewes immune to coccidia (Eimeria spp.) was administered either intravenously or intraperitoneally to young lambs 7, 5, or 2 days before they were turned out on pastures contaminated with coccidia. In all experiments, LE failed to transfer protective immunity to the lambs against the first coccidial infection on pasture. The LE preparations used apparently had an immunosuppressive effect, which resulted in more severe clinical signs of coccidiosis in the recipients. The lambs given LE showed a higher incidence of diarrhoea, a poorer weight gain, a higher mortality, and a higher oocyst output than the untreated control lambs. In lambs treated with sulphadimidine at 200 mg/kg on days 12, 13, and 14 after turnout there was a reduced severity of the coccidial infections in all experiments. The sulphadimidine-treated lambs had better weight gains and passed fewer oocysts than the controls during the third and fourth week after turnout, but some of them developed diarrhoea. Lambs treated with levamisole at 2 mg/kg 2 days before turnout, at turnout, and 2 days after turnout were more severely affected by the first coccidial infection on pasture than the controls.

To study the lambs’ immunity against a heavy challenge infection with coccidia as compared with their immunity against the natural reinfection on pasture, some of the lambs from the original groups (untreated, sulphadimidine-treated, LE-treated) were each inoculated with 2 mill. Eimeria spp. oocysts about 6 weeks after turnout. The oocyst counts of the challenged lambs, except the LE-treated lambs, increased to a new peak 19–20 days after challenge. The challenge infection caused a softening of the faeces and a marked depression in weight gain in all challenged groups of lambs, mainly between days 10 and 17 after challenge. The lambs were thus only partially immune to coccidia after the first coccidial infection on pasture. The lambs treated with either LE or sulphadimidine in connection with the first coccidial infection on pasture were not appreciably more susceptible to the challenge infection than the untreated lambs.

Sammendrag

I tre forsøk vart leukocyttekstrakt (LE), framstilt frå søyer immune mot koksidiar, gitt til lam like før dei vart sleppte ut på koksidieinfisert beite for å prøva og gjera dei meir resistente mot koksidieinfeksjonar. LE vart gitt anten i.v. eller i.p. til lamma 7, 5 eller 2 dagar før beiteslepp. I alla forsøka synte lamma som fekk LE alvorlegare symptom på koksidiose enn dei ubehandla kontrollane. Samanlikna med dei sistnemnde, hadde dei LE-behandla lamma ein høgare diaréfrekvens, høgare mortalitet, dårlegare tilvekst i 3. og 4. beiteveke, og høgare oocystetal i feces på dei fleste prøvedatoane. Ein reknar det difor som sannsynleg at LE har hatt ein immunosuppressiv effekt på lamma. Behandling med sulfadimidin i ein dose på 200 mg/kg på dag 12, 13 og 14 etter beiteslepp greidde delvis å førebyggja koksidiose, men nokre lam fekk diaré, og nokre få daua. Dei lamma som fekk sulfadimidin hadde likevel i gjennomsnitt ein betre tilvekst enn kontrollane i 3. og 4. beiteveke. Tre dosar av levamisol, kvar på 2 mg/kg, gitt annankvar dag frå dag 2 før beiteslepp, syntest å gjera lamma meir mottakelege for den fyrste koksidieinfeksjonen på beite. Forsøk med kunstig reinfeksjon av lamma med 2 mill. oocyster 6 veker etter beiteslepp synte at dei lamma som tidlegare hadde fått sulfadimidin eller LE, hadde utvikla ein om lag like sterk immunitet mot koksidiar som dei tidlegare ubehandla lamma. Alle lamma var likevel på dette tidspunktet berre delvis immune mot koksidieinfeksjonar, og synte moderate kliniske symptom etter den kunstige reinfeksjonen. Denne immuniteten var likevel sterk nok til å hindra at den naturlege reinfeksjonen på beite resulterte i klinisk koksidiose.