Exploring a novel method for inoculation to experimentally induce digital dermatitis in dairy calves

Area of Science:

• Veterinary Dermatology
• Bovine Medicine
• Infectious Disease Modeling

Background:

• Digital dermatitis (DD) is a significant bovine hoof disorder with unknown causes.
• Current animal models are insufficient for rapid, standardized DD infection.
• Optimizing inoculation methods is crucial for developing effective DD models.

Purpose of the Study:

• To explore and optimize bacterial inoculation techniques for a standardized digital dermatitis infection model in cattle.
• To evaluate the efficacy of tattoo needles for enhanced bacterial skin penetration in a bovine model.
• To identify key factors influencing DD pathogenesis through inoculation trials.

Main Methods:

• A pilot study identified tattoo needles as effective for skin penetration in calf feet.
• Two animal trials involved inoculating calves with DD lesion macerates or pure isolates using tattoo needles.
• Pre-treatment protocols, including foot wrapping and water application, were tested.
• Bacterial presence was monitored via swabbing and confirmed through skin biopsies and silver staining.

Main Results:

• Tattoo needle inoculation successfully delivered bacterial inoculum into calf skin.
• Neither trial successfully induced digital dermatitis lesions in inoculated calves.
• DD-associated Treponema spp. were detected early post-inoculation, while other anaerobes persisted longer in the pure isolate group.
• DD-Treponema spp. were identified in biopsies, confirming spirochete presence, but lesion development was absent.

Conclusions:

• While tattoo needles facilitate bacterial skin penetration, this method alone does not induce digital dermatitis.
• The failure to develop lesions suggests critical, yet unidentified, factors are missing for DD pathogenesis in this model.
• Further research is needed to elucidate the complete etiology of digital dermatitis and refine infection models.