Oral and Poster Abstracts

loss in milk production and reproductive performance. Results from
studies investigating the relationships between BLV and health, milk
production and reproductive performance have been controversial.The
aim of this study was to investigate the effect of sub-clinical BLV
infections on milk production, reproductive performance and survival in
high producing dairy cows, while taking the point of time at which seroconversion
occurred into account. A prospective cohort study was
conducted in a commercial dairy herd consisting of 300 Israeli Holstein
cows. From January 2006 until November 2007, serum samples were
collected from all first lactation heifers (n=101) calving in 2006.
Collection started 4 weeks before calving and continued every 3 months
until the end of the study or until sero-conversion occurred. Samples were
checked for antibodies against BLV using the agar gel immuno diffusion
test. In total, 422 samples were collected. We used a discrete-time
proportional odds model to investigate the association between the
probability of undergoing sero-conversion and time or season. Health and
reproduction data were analyzed using chi-square tests and Kaplan-Meier
tests. Milk production and somatic cell counts were analyzed using
marginal models for repeated measurements.By the end of the study, 59
(58%) cows experienced sero-conversion. There was no difference in
culling percentage (7%) between sero-positive and sero-negative cows.
No particular risk period could be found for sero-conversion, nor was
sero-conversion associated with season. No significant differences were
found between the two groups in the proportion of cows suffering from
post-partum diseases, unobserved heat, first insemination pregnancy rate
and cumulative probability of conception. No effect of sero-conversion or
of time of sero-conversion on milk production could be demonstrated.Our
results indicate that the risk of BLV sero-conversion in an endemic herd is
more or less constant in the 2 years following first calving and does not
necessarily occur rapidly after introduction of heifers into the lactating
herd. Within our study period, no negative associations between seropositivity
for BLV and survival, health, reproductive performance, and
milk production were found.
328 Epidemiological Studies of Vampire Bats (Desmondus
Rotundus) Attacks in a Brazilian Beef Cattle Herd
E. Ortolani 1 , C. Maruta 2
1 College of Veterinary Medicine, University of Sao Paulo,
Department of Clinical Studies, Sao Paulo, Brazil
2 Vallée S.A., Sao Paulo, Brazil
The predation of cattle by vampire bats is quite common in Brazilian
herds. The most important loss due to vampire bats is cattle rabies, but
also low weight gain occurs by the bloodsucker habits of these animals.
An epidemiological study was carried out throughout the year of 2007 in
a beef cattle herd raised extensively in the State of Sao Paulo, Brazil. In
order to know the distribution of the attacks throughout the year the
number of recent bitten cattle was counted every fortnightly in the herd
that varied from 187 to 205 animals during the year. On day July 2 nd it was
counted the number of cattle (total 205) with recent bites to evaluate the
influence of the category, sex, breed of the animal, the number of
bites/head, the anatomical region attacked on the vampire bat predation.
The complications of the bites in the wounds were also recorded. The herd
was vaccinated against rabies twice a year. The percentage of cattle
recently bitten throughout the months of the year was similar. The attacks
were higher (53%) on weaned calves (5 m to 1 y old) than cows (11.8 %),
steers & bulls (19.5%), and heifers (31.2 %) (P < 0.03); cows were less
bitten than lactating calves (33.3%) (P < 0.04). There was no distinction
between sex (P > 0.8). The Simmental cattle (52.9 %) were much more
bitten than Zebu (14.1%) and Charolais (23.7%) crossbred cattle. Most of
the cattle had a single recent bite (53 %) followed by two (23.5 %) or more
than two (3 up to 6) bites (23.5 %). The most frequently anatomical area
attacked was the neck (60.2 %), followed by the tail (21.5 %), dorsal (9.7
%), head and ears (4.3%), members (3.2%) and shoulders (1.1%). Three
weaned calves had to be treated during the year against myiasis and two
for abscesses that developed in the wounds.
Key words: epidemiology, vampire bats, bites, breeds, cattle
329 Difference in Virus Excretion and Transmission between
Calves and Dairy Cows in the Course of an Acute FMDV
Infection
K. Orsel 1 , A. Dekker 2 , A. Bouma 1 , J. Stegeman 1 , M. De Jong 3
1
Utrecht University, Farm Animal Health, Utrecht, The Netherlands
2
Central Institute for Animal Disease Control CIDC, Lelystad, The
Netherlands
3 Wageningen University and Research Centre, Quantitative
Veterinary Epidemiology, Wageningen, The Netherlands
Objective: The aim of this study was to determine differences in virus
excretion and virus transmission between calves and dairy cows after
infection with FMDV.
Material and Methods: In two experiments, one with groupd of calves
of 10 weeks old and one with lactating dairy cows. Half of each group
was inoculated with FMDV isolate ONET/2001 and the other half of
each group was exposed by direct contact to these animals. Clinical
inspection, virus titration and serological tests were performed. To
quantify virus transmission the reproduction ratio R was estimated with
a maximum likelihood estimate using an S-I-R model.
Results: In the calves mild clinical signs were observed and not all
contact exposed calves became infected. Dairy cows showed severe
clinical signs and all in-contact animals became infected. The total
amount of excreted virus differed significantly between inoculated and
contact-infected animals and also between infected calves and cows.
Inoculated cattle shed virus for a longer time compared to contact
exposed cattle. The transmission ratio for calves Rcalves was estimated
2.52 [1.13;52.1], and for dairy cows R cows= Inf [1.3; Inf]. Both R
values were significantly above 1 (p