Abstract
Fortytwo calves, 28 to 117 days old, were collected from 23 dairy farms and transported in a lorry, allowing direct contact between the calves, to 8 calf rearing farms. The average transport time per calf was 4.5 h, ranging from 0.3 to 12.8 h. The calves were sampled by nasal swabbing for mycoplasmas first before loading and then immediately after transport. Thirteen of the calves were transferred to farm I. They were placed in individual pens in a separate room to themselves, and were sampled at intervals for a period of 4 weeks.
Ten of the 42 calves (23.8 %) originating from 5 of the source farms were found initially positive for M. dispar with titers > 4 log10 ecu; 3 of these 10 calves were delivered to farm I and 7 calves to 6 others of the 8 receiving farms. Three initially infected calved delivered to farms I continued to be positive throughout the follow-up period; among the 10 initially negative calves the frequency of detected infection, and the geometric mean titer (within parenthesis), developed so that on days 1, 7, 14, and 28 the figures were: 2 (2.5), 8 (4.3), 9 (4.7), and 10 (5.5), respectively.
After transport 3 initially negative calves were found positive with low titers. Two of them were placed on farm I. In one of them positivity proved to be only transient; the case seems to represent a phenomenon of transfer of mycoplasmas without establishment of infection. In contrast, at least 4 (possibly 7) calves, negative both before and after transport–ascribed above to the group of 10 initially negative calves arriving on farm I–had in all likelihood caught the infection during the transport. Two of the 10 calves most likely caught the infection on the farm; for 3 calves the evidence was equivocal as to the 2 alternatives.
Seven of the 42 calves (16.7 %) were found to be initially infected with M. bovir-hinis, 2 of the 42 with Acholeplasma laidlawii. Among the 13 calves transported to an reared on farm I, 8 were found to be positive at least once for M. bovirhinis during the study. Colonisation by this mycoplasma was partly detected only intermittently and the detectable prevalence among the 13 calves at its highest was only 38.5 %.
Keywords: Mycoplasma infections, mycoplasmosis in cattle, respiratory diseases of cattle, epidemiology, disease transmission, calf transport
Sammendrag
Fyrtiotvå kalvar i åldern 28 till 117 dagar samlades från 23 mjölkkobesättningar och fördes i en transportvagn som möjliggjorde direkt kontakt mellan djuren till 8 kalvuppfödningsbesättningar.
Transporttiden var i medeltal 4,5 timmar per kalv och varierade mellan 0.3 och 12.8 timmar. Provtagning med avseende på mykoplasma från nässlemhinnan togs först före lastningen och därefter genast efter transporten. Tretton kalvar flyttades till gård I. Kalvarna placerades i enskilda boxar i ett eget rum och undersöktes med jämna mellanrum under 4 veckors tid.
Tio av de 42 kalvarna (23.8%) som kom från 5 ursprungbesättningar var från børjan positiva för M, dispar med tittrar ≥ 4 log10 ccu; 3 av dessa 10 kalvar fördes till gård I och 7 till 6 andra bland emottagande gårdar. De 3 kalvar som var infekterade från början och som fördes till gård I förblev positiva under uppfödningsperioden; bland 10 från början negativa kalvar var frekvensen av påvisad infektion och den geometriska medeltitern (inom parentes) på dagarna 1, 7, 14 och 28 följande: 2 (2.5), 8 (4.3), 9 (4.7) och 10 (5.5).
Efter transporten blev 3 från början negativa kalvar positiva med låga titrar. Två av dessa placerades på gård I. Hos en av dessa kalvar visade sig posiviteten vara övergående; fallet tycks representere en slags spridning av mykoplasmer utan etablering av infektion. I motsats till detta hade åtminstone 4 (möjligen 7) kalvar, negativa både före och efter transporten – de beskrivs ovan som tillhörande gruppen från början negativa kalvar som anlände till gård I – med all sannolikhet smittats under transporten. Två av de 10 kalvarna smittades sannolikt på gården, för de övriga 3 kalvarna var båda alternativen bevisligen möjliga.
Sju av de 42 kalvarna (16.7%) var från början infekterade med M. bovirhinis och 2 kalvar av 42 med Acholeplasma laidlawii. Bland de 13 kalvarna som transporterades till och födds upp på gård I lyckades isoleringen av M. bovirhinis hos 8 kalvar åtminstone en gång under undersökningen. Delvis påvisades kolonisation med denna mykoplasma endast periodvis. Den påvisade maximal prevalensen bland de 13 kalvarna var endast 38.5 %.
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Acknowledgements
This study received financial support from The Research Council for Medical Sciences of the Academy of Finland and The Finnish Veterinary Science Foundation.
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