Mycobacterium bovis Survivability in Salt/Minerals Fed to Cattle

Mycobacterium bovis Survivability in Salt/Minerals Fed to Cattle John B. Kaneene, DVM, MPH, PhD Joseph Hattey, MS Carol Bolin, DVM, PhD James Averill, DVM, PhD

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.

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.

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.

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.

Introduction (cont.) • Whether or not salt is an inhospitable substrate for the survival of M. bovisis debatable.

Objective To determine the survivability of M. bovis on salt and mineral blocks over time under normal weather conditions over a 12 month period

Experimental Design Longitudinal Experimental Design

Collection of Samples Samples are taken from the top face of the salt block using sterilized scouring pads on a specified schedule.

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.

Methods Four Plain Salt and Four Mineral Blocks were used

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

Methods (cont.) Samples from the block surfaces were collected at specified intervals and tested for the presence of the organisms

Results 1. Percent of samples able to recover M. bovis from salt blocks over time, by season

Results 2. Percent of samples able to recover M. bovis from salt blocks over time, by sun/shade

Results 3. Percent of samples able to recover M. bovis from mineral blocks over time, by season

Results 4. Percent of samples able to recover M. bovis from mineral blocks over time, by sun/shade

Results 5. Percent of samples able to recover M. fortuitumfrom salt blocks over time, by season

Results 6. Percent of samples able to recover M. fortuitumfrom salt blocks over time, by sun/shade

Results 7. Percent of samples able to recover M. fortuitumfrom mineral blocks over time

Results 8. Percent of samples able to recover M. fortuitumfrom mineral blocks over time, by sun/shade

Conclusions • M. bovis can survive on shaded mineral blocks for over 3 days during the winter and still be viable. • The sunlight appears to shorten the viability of the M. bovisto 48 hrs on mineral blocks. • The salt blocks, both sun and shade, have a shorter survivability for the M. bovis than the mineral blocks.

Implications of the Results of This Study to Bovine TB Control Strategies • Demonstrates salt/mineral as potential source • Will be included as potential risk with infected herds • Use caution in how you administer salt/mineral during winter months

Acknowledgments Michigan Department of Agriculture and Rural Development Center for Comparative Epidemiology, Michigan State University

Mycobacterium bovis Survivability in Salt/Minerals Fed to Cattle