Proceedings of the 10th International Colloquium on Paratuberculosis

#154 Effect <strong>of</strong> Mycobacterium avium subsp. paratuberculosis infection on time to calving
and time to culling in dairy
Rebecca Lee Smith, Robert Lee Strawderman, Ynte Hein Schukken, Scott J Wells, Yrjo Tapio Grohn
College <strong>of</strong> Veterinary Medicine, Cornell University, USA; College <strong>of</strong> Veterinary Medicine, University <strong>of</strong> Minnesota, USA
Among <strong>the</strong> costs attributed to Mycobacterium avium subsp. paratuberculosis (MAP) infection in dairy cattle, <strong>the</strong>
impacts on reproduction and culling are <strong>the</strong> least documented. In order to properly estimate <strong>the</strong> cost <strong>of</strong> MAP
infections in a dairy herd, <strong>the</strong> rates <strong>of</strong> conception and culling were calculated for cows in each stage <strong>of</strong> MAP
infection relative to uninfected cows. Two well-defined databases, each consisting <strong>of</strong> culling and reproduction
data from 3 commercial dairy herds, were used for analysis, consisting <strong>of</strong> 2,856 cows with 6,380 calvings
and 1,696 cullings. Every cow in each study herd was tested regularly for MAP, and herds were followed for
between 4 and 7 years. Infection status (uninfected/latent vs. low- or high-shedding) was defined as a time-dependent
variable for all cows with at least one positive test result. Cox’s proportional hazards model, stratified
on herd and controlling for <strong>the</strong> time-dependent variable was used to analyze time to culling. Latent and uninfected
animals were significantly less likely to be culled in comparison with animals in <strong>the</strong> low- and high-shedding
categories. Time to conception was analyzed using a proportional means model, an analog to <strong>the</strong> Cox
regression model suitable for recurrent event data, stratifying on herd and weighted to adjust for <strong>the</strong> dependent
censoring caused by <strong>the</strong> culling effects describe above. Low- and high-shedding animals had longer calving intervals
in comparison with latent and uninfected animals, but <strong>the</strong>se results were non-significant using a robust
variance estimate. These results can be incorporated into economic models for <strong>the</strong> cost <strong>of</strong> MAP in dairy herds.
#164 Diagnosis <strong>of</strong> paratuberculosis in slaughtered calves in <strong>the</strong> Northwest <strong>of</strong> Castilla y León
(Spain) by pathological methods
Valentin Perez, Oscar Moreno, Maria Muñoz, Carlos Garcia-Pariente, Julio Benavides, Laetitia Delgado, Jorge
Gonzalez, Mencia Luis, Miguel Fuertes, J Francisco Garcia-Marin, M Carmen Ferreras, Universidad de Leon, Spain
Objectives: To assess <strong>the</strong> prevalence <strong>of</strong> Map infection in calves from extensive herds in <strong>the</strong> slaughterhouse,
using histopathological and PCR methods .
Materials and Methods: A total <strong>of</strong> 15,546 slaughtered calves between 8-12 months-old and different
breeds, from 137 extensive herds in <strong>the</strong> Northwest <strong>of</strong> Castilla y León region (Spain) were examined between
2001 and 2008. Samples <strong>of</strong> ileocaecal lymph were examined microscopically for <strong>the</strong> presence <strong>of</strong> lesions
characteristic <strong>of</strong> Map infection and <strong>the</strong> presence <strong>of</strong> acid-fast organisms by Ziehl-Neelsen (ZN) Selected
sections were examined immunohistochemically using a polyclonal anti-Map antibody. Lesions were classified
as focal, multifocal and diffuse according to <strong>the</strong> number <strong>of</strong> granulomas. Lesions with 1-3 granulomas formed
by less than 20-25 macrophages, containing a yellow granular pigment were considered as doubtful. A PCR for
detection <strong>of</strong> Map DNA was performed in 182 paraffin wax embedded tissue samples.
Results: Lesions associated with paratuberculosis infection, including doubtful lesions, were observed in
440 calves. Diffuse lesions appeared in 1 case, multifocal lesions in 8 calves, focal lesions in 137 and doubtful
lesions in 294. Diffuse lesions were positive by ZN, immunohistochemistry and PCR. Seven multifocal lesions
were PCR positive and one case only was positive by immunohistochemnical methods. PCR gave positive
results in 60.8% and 24.7% <strong>of</strong> calves with focal and doubtful lesions respectively.
Conclusions: A remarkable percentage <strong>of</strong> <strong>the</strong> calves from extensive herds in this study (2.83%) had
lesions associated with paratuberculosis. This prevalence was higher if considering herds with at least one
infected animal (49.63%).
The sampling and technical methods used have demonstrated to be efficient in <strong>the</strong> detection <strong>of</strong> lesions in
<strong>the</strong> early stages <strong>of</strong> paratuberculosis infection (subclinical cases).
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