PhD: Identifying infection reservoirs of digital dermatitis in dairy cattle

 

  Research Partner: University of Liverpool

  Start and end date: October 2013 - September 2017

  PhD Student: Jennifer Bell

 

 

 

 

 

Digital dermatitis (DD) is an infectious disease that forms ulcerative lesions usually found between the bulbs of the heel on the hind feet of dairy cattle.  The lesions can be very painful often resulting in lameness, making the disease an important welfare concern. Furthermore DD has significant economic implications for the dairy industry, particularly with regards to treatment costs. Bactria belonging to the Treponema genus are considered to be integral in disease initiation and progression. There is currently little known about how transmission of DD occurs which limits methods available for controlling the disease. My project aims to identify the infection reservoirs of DD and thus identify possible transmission routes of the disease; by understanding the relationship between dairy cows, DD associated treponemes and the dairy farm environment.

 

The project was split into four different studies:

  1. Development of an optimised DNA extraction technique to enable possible detection of DD associated treponemes in bovine faeces
  2. Survey of  dairy cow tissues and the dairy farm environment for the presence of DD associated treponemes
  3. Studies into the association of DD associated treponemes with tissue other than the lesions themselve
  4. Understanding the survival and growth of DD associated treponemes under different host and environmental conditions

 

Results:

When considering within host infection reservoirs other than within the foot lesion, the DD treponemes were identified in the bovine gastro-intestinal (GI) tract, primarily the gingiva and recto-anal junction (RAJ) and they do not appear to cause damage to the host in these locations. Furthermore for the first time the ability to culture/isolate DD treponemes from faeces was demonstrated adding to evidence for faecal shedding as one route of transmission of DD. Survival studies in the laboratory demonstrated that DD treponemes have the ability to survive in sterile faeces for a median of 1 day and a maximum of 6 days which would enable transmission of viable bacteria to another animal’s foot. Given involvement with the GI tract and faeces, increasing hygiene on farm should help to reduce DD on farm.

The DD treponemes were detected in dairy cattle fomites (surfaces touched by affected feet/lesions) including hoof trimming knives, trimming equipment and gloves as well as surface footprints made on crush and parlour floor surfaces. These fomites should be considered important infection reservoirs in addition to DD lesions themselves and the GI tract. Improving biosecurity and foot trimming practices should help reduce disease spread. Further research is needed into protocols for disinfecting hoof trimming equipment and to mitigate on farm infection sources.

In the laboratory, the best farm beddings to use to reduce the presence of DD treponemes were 1) straw or 2) sand containing 5% (w/w) lime as the DD bacteria were not viable in these beddings. The straw bedding data corresponds with several epidemiological studies suggesting straw is lower risk for DD. Field trials are now needed to gage how this knowledge may be applied to control DD and to verify the effectiveness of these bedding types on actual farms. In contrast, DD treponemes can remain viable in recycled manure solids (RMS) for five days, in sawdust for six days and in sand for at least seven days.

From a broader perspective, in order to effectively tackle DD in the future, further research should investigate (but not be limited too) the development of novel antimicrobials and/or disinfectants as well as alternative novel methods to reduce transmission of the disease. Further research into effective vaccines is also needed.

 Final Report