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Mycobacterium bovis Survivability in Salt/MineralsFed to Cattle
John B. Kaneene, DVM, MPH, PhD
Joseph Hattey, MS
Carol Bolin, DVM, PhD
James Averill, DVM, PhD
2
Introduction
The discovery of bovine tuberculosis (TB) in a wildlife reservoir (free-ranging white-tailed deer) in 1995, and subsequent discovery of TB-infected cattle herds in northeastern lower Michigan, have raised questions as to how the disease is being transmitted between deer and cattle.
3
Introduction (cont.)
Research by Michigan State University, the USDA, and the Michigan Department of Agriculture (MDA) has implicated contaminated feedstuffs as possible vehicles for the transmission of Mycobacterium bovis, the causative agent of TB.
4
Introduction (cont.)
This research has been limited to plant-based feed materials (hay, carrots, grass, etc.), but has not been expanded to other possible substrates, such as salt/mineral blocks.
5
Introduction (cont.)
Salt blocks may pose a greater risk for disease infection in that they are not immediately consumed by a single animal at one time, but are used by several different animals, and can remain in place for weeks.
6
Introduction (cont.)
Whether or not salt is an inhospitable substrate for the survival of M. bovis is debatable.
7
Objective
To determine the survivability of M. bovis on
salt and mineral blocks over time under normal
weather conditions over a 12 month period
8
Experimental Design
Longitudinal Experimental Design
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Collection of Samples
Samples are taken from the top face of the salt block using sterilized scouring pads on a specified schedule.
10
Collection of Samples (cont.)
Sample Collection Schedule
Within 1 hour after inoculation, and twice a day for the first week and once a day there after.
Three replicate pads were taken from each salt block at each sampling time.
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Methods
Four Plain Salt and Four Mineral Blocks were used
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Methods (cont.)
Pure cultures of M. bovis and M. fortuitum were applied to the surfaces and kept outdoors in BL-3 confinement cages for a year
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Methods (cont.)
Samples from the block surfaces were collected at specified intervals and tested for the presence of the organisms
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1. Percent of samples able to recover M. bovis from salt blocks over time, by season
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Summer (n=78)
Winter (n=84)
Hours
Perc
en
t o
f S
am
ple
s
Results
15
2. Percent of samples able to recover M. bovis from salt blocks over time, by sun/shade
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Sun (n=81)
Hours
Perc
en
t o
f S
am
ple
s
Results
16
3. Percent of samples able to recover M. bovis from mineral blocks over time, by season
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Summer (n=78)
Hours
Perc
en
t o
f S
am
ple
s
Results
17
4. Percent of samples able to recover M. bovis from mineral blocks over time, by sun/shade
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Sun (n=80)
Hours
Perc
en
t o
f S
am
ple
s
Results
18
5. Percent of samples able to recover M. fortuitum from salt blocks over time, by season
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Summer (n=78)
Hours
Perc
en
t o
f S
am
ple
s
Results
19
6. Percent of samples able to recover M. fortuitum from salt blocks over time, by sun/shade
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Sun (n=81)
Hours
Perc
en
t o
f S
am
ple
s
Results
20
7. Percent of samples able to recover M. fortuitum from mineral blocks over time
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Summer (n=77)
Hours
Perc
en
t o
f S
am
ple
s
Results
21
8. Percent of samples able to recover M. fortuitum from mineral blocks over time, by sun/shade
1 5 24 30 48 54 72 780
2.5
5
7.5
10
Sun (n=81)
Hours
Perc
en
t o
f S
am
ple
s
Results
22
Conclusions
1. M. bovis can survive on shaded mineral blocks for over 3 days during the winter and still be viable.
2. The sunlight appears to shorten the viability of the M. bovis to 48 hrs on mineral blocks.
3. The salt blocks, both sun and shade, have a shorter survivability for the M. bovis than the mineral blocks.
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Implications of the Results of This Study to Bovine TB Control Strategies
1. Demonstrates salt/mineral as potential source
2. Will be included as potential risk with infected herds
3. Use caution in how you administer salt/mineral during winter months
24
Acknowledgments
Michigan Department of Agriculture and Rural
Development
Center for Comparative Epidemiology, Michigan State
University
