Combination Effect of Allyl Isothiocyanate and Hoof Trimming on Bovine Digital Dermatitis

Introduction
Digital Dermatitis is a localized infectious dermatitis caused by Treponema- like spirochetes. Antibiotics, such as lincomycin, are currently used for treatment, but their use imposes a withdrawal period. This study investigated the therapeutic effect of topical application of the natural component allyl isothiocyanate, in combination with maintenance hoof trimming, on bovine Digital Dermatitis (stage M2 DD lesions based on Döpfer classification). 

Materials and Methods
Study cows were divided into two groups, the Trimming Group and Non-Trimming Group. The day when allyl isothiocyanate was applied, along with hoof trimming, was set as Day 0. Lesion scores, pain, and the presence of Treponema-like spirochetes on the surface of hooves and in biopsy samples of the tissues were evaluated until Day 6. Assessment of pain was based on a Force Gauge when applying pressure to the lesion. 

Results
One of the microscopic observations of direct smear specimens to detect spirochetes is shown in Fig. 1. These long and coiledstained microorganisms are likely Treponema-like spirochetes related with the DD. On the surface of the lesions in the Trimming Group, the percentage of Treponema-like spirochete positive cows was 83.3% on Day 0, but spirochetes were not detected from Day 2 onward. On the surface of the lesions in the Non-Trimming Group, the percentage of Treponema-like spirochete positive cows was 87.5% on Day 0, but decreased to 25.0% on Day 2 and 12.5% on Day 4. On Day 6, it was 50%, which was significantly higher than it was on Day 4. In addition, the percentage of positive cows in the Trimming Group was significantly lower than that in the Non-Trimming Group on Day 6 (Table 1). Both groups showed improvement of lesion scores. And photos of the DD stained with Warthin-Starry show numerous Treponema-like spirochetes that were detected in the keratin layer on Day 0 (Fig. 2), but were not detectable in any of the cows on Day 6 (Fig. 3) in both groups.  On the surface of the interdigital clefts in the Trimming Group, the percentage of Treponema-like spirochete positive cows was 16.7% on Day 0, 0% on Day 2 and Day 4, and 16.7% on Day 6, which were not significant changes. In the Non-Trimming Group, the percentage of Treponema-like spirochete positive cows was 37.5% on Day 0 and 50.0% on Day 2. On Day 4 and Day 6, the percentage was 0%, which was significantly lower than the percentage on Day 2. Additionally, the percentage of positive cows in the Trimming Group was significantly lower in the Non-Trimming Group on Day 2 (Table 2). 

Conclusions
These results suggest that allyl isothiocyanate has therapeutic effects on Digital Dermatitis, when combined with hoof trimming, and may prevent a relapse of dermatitis and a re-infection of Treponema-like spirochetes.