A Highly Effective Protocol for the Rapid and Consistent Induction of Digital Dermatitis in Holstein Calves

Abstract

Bovine Digital Dermatitis (DD) is a leading cause of lameness in dairy cattle. DD is reportedly increasing in prevalence in beef cattle feedlots of the US. The exact etiologic agent(s) responsible for the disease have yet to be determined. Multiple studies have demonstrated the presence of a variety of Treponema spp. within lesions. Attempts to reproduce clinically relevant disease using pure cultures of these organisms has failed to result in lesions that mirror the morphology and severity of naturally occurring lesions. This manuscript details the systematic development of an experimental protocol that reliably induces digital dermatitis lesions on a large enough scale to allow experimental evaluation of treatment and prevention measures. In total, 21 protocols from five experiments were evaluated on their effectiveness in inducing DD lesions in 126 Holstein calves (504 feet). The protocols varied in the type and concentration of inoculum, frequency of inoculation, duration the feet were wrapped, and type of experimental controls need to validate a successful induction. Knowledge gained in the first four experiments resulted in a final protocol capable of inducing DD lesions in 42 of 44 (95%) feet over a 28 day period. All induced lesions were macroscopically and microscopically identified as clinical DD lesions by individuals blinded to protocols. Lesions were also located at the site of inoculation in the palmer aspect of the interdigital space, and induced clinically measurable lameness in a significant portion of the calves. Collectively these results validate the model and provide a rapid and reliable means of inducing DD in large groups of calves.

Missing pieces of the puzzle to effectively control digital dermatitis

“…Although the exact route of transmission for DD is not fully elucidated, DD presents itself as a highly infectious disease, consistent with the experimental model of Krull, Cooper et al. (), in which the negative controls could be infected by being commingled with experimentally infected animals despite the feet of both animals being completely wrapped in bandages for the duration of the study. Another experimental model was used by the Liverpool research team, using sheep affected with DD lesions to induce DD in healthy animals by just mixing and intermingling in a normal farm environment with standard herd management and then chronic lesion development over time (SD Carter, personal communication).…”

“…Potential hypotheses include (i) intrinsic differences in the host anatomy or genetics allow for differences in disease manifestation, (ii) despite similarities in the treponemal species isolated, the clones involved in these diseases differ in their genetics or virulence attributes and (iii) the presence of the treponemes in these cases is more of an opportunistic infection with other organisms in the bacterial consortium driving the lesion pathogenesis. These differences in host response to the organisms along with the development of disease induction models in both cattle (Gomez et al., ; Krull, Cooper et al., ) and sheep (Wilson‐Welder, Nally, Alt, & Plummer, ) provide a good foundation for experimental approaches designed to address and test these hypotheses. By utilizing similar inoculums in both species and observing the differences in clinical disease combined with multi‐omic approaches, we can start to dissect the importance of host differences in the disease process.…”

“…The outcomes of these studies clearly demonstrate that transmission can occur when susceptible animals are housed in the same environment as those with active DD lesions. However, the fact that transmission occurred in the presence of foot wraps could suggest that direct physical contact with lesions is not required (Krull, Cooper et al., ). The literature has also evaluated the role that early or active host‐associated DD lesions play as a primary reservoir of infectious organisms.…”

“…Robust and efficient experimental models of infection are critical to research efforts focused on better understanding the pathogenesis and aetiology of DD. Several induction models have been described for use in the induction of DD lesions in both cattle and sheep (Gomez et al., ; Krull, Cooper et al., ; Wilson‐Welder, Nally et al., ). The most obvious benefit of an experimental model would be to evaluate the aetiology of the disease; however, efforts to use the models in this manner have thus far been underwhelming.…”

“…The most obvious benefit of an experimental model would be to evaluate the aetiology of the disease; however, efforts to use the models in this manner have thus far been underwhelming. Both bovine models have attempted to induce lesions using pure culture of DD‐associated Treponema phagedenis ‐like bacteria (Gomez et al., ; Krull, Cooper et al., ). While both studies observed some degree of lesion formation, the size and severity of the lesions were considerably less than observed when macerated lesion material was used as the inoculum (Gomez et al., ).…”