Abstract
Eight conventionally reared, 1- to 11-week old Ayrshire calves were naturally infected by a strain of Mycoplasma dispar (M. dispar). The colonisation was quantitatively followed by nasal swab samples, transtracheal aspiration samples and by the examination of the whole of the respiratory tract for mycoplasmas at slaughter after a follow-up period of 7–10 months.
The fairly uniform pattern of the colonisation by M. dispar was revealed: A high degree of colonisation, measuring 105–108 colour change units (ccu) per nasal sample, lasted for a period of 2–5 months and was followed by a slow decrease in titres. Seven of the calves still harboured M. dispar in their respiratory tracts at slaughter. Intermittently obtained transtracheal aspiration samples were all positive for M. dispar and the titres were regularly higher than those for the simultaneously taken nasal samples indicating a high ability of M. dispar to continuously colonize the more distal parts of the respiratory tract. It was demonstrated that the sensitivity of nasal swabbing in the detection of M. dispar infection largely depended on the phase of colonisation : The method was good for the detection of a fairly recent infection of M. dispar, but inadequate for detection of low grade carriers.
In various phases, the calves also became infected by Mycoplasma bovirhinis and Acholeplasma laidlawii. Their ability to colonize the whole respiratory tract was lower than that of M. dispar.
Keywords: disease recording, slaughter-house, bacon pigs, antiparasitics
Sammanfattning
Åtta konventioneilt uppfödda 1 tili 11 veckor gamla Ayrshire kalvar besmittades på naturlig väg med en stam av Mycoplasma dispar.
Den kvantitativa kolonisationen studeras genom odling av nässekret, transtrakeala aspirationsprov och genom undersöknig av hela andningsvägarna med avseende på förekomst av mycoplasmer vid slakten efter en uppföljningsperiod på 7–10 månader.
M. dispar uppvisade ett rätt regelbundet mönster vid kolonisationen. En höggradig kolonisation, vid vilken 105–108 colour change units per näsprov uppmättes, varade i 2–5 månader och åtföljdes av en längsam titersänkning. Sju av kalvarna hyste fortfarande M. dispar i andningsvägarna vid slakten.
Suoradiska transtrakeala aspirationsprov var alla positiva med avseende på M. dispar, och titrarna var i regel högre än i de prov som samtidigt tagits frän näsan, vilken tyder på en kontinuerlig kolonisation av M. dispar i de lägre delarna av andningsvägarna. Tillförlitligheten av nässekretodlingar vid M. dispar infektioner visade sig tili stor del bero på kolonisationsfasen. Metoden var bra för att påvisa en rätt färsk infektion av M. dispar, men olämplig för att påvisa långvariga infektioner.
Kalvarna infekterades också vid olika tillfällen med Mycoplasma bovirhinis och Acholeplasma laidlawii. Deras förmåga att kolonisera hela andningsvägarna var sämre än M. dispar.
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Footnotes
This work was supported by grants from The Finnish Academy and The Finnish Veterinary Science Foundation.
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