An experimental model to induce digital dermatitis in beef calves

Abstract

Background: Digital dermatitis (DD) is a multifactorial infectious disease affecting the skin on feet of cattle causing erosion and inflammation above the heel bulbs. Some cases of DD cause lameness and significantly impact animal welfare and productivity. While DD has emerged as a concern for the beef industry, key information regarding early detection and its impact on cattle behaviour is lacking. The primary objective of this study was to determine if an established DD experimental model for dairy calves could be used to induce DD lesions in beef calves. A secondary objective was to describe changes in behaviour and pain associated with induction of DD lesions. Eight beef calves acquired from a single cow-calf operator were enrolled in the study. Upon enrolment, calves were evaluated and determined to be free of foot lesions. Within the experimental environment, calves were housed in individual pens and assigned to two groups (mock-inoculated and inoculated). Both hind feet of each calf were enrolled. Within calf, inoculation protocol was consistent, and a 28-day experimental protocol was employed. Two days prior to inoculation, both hind feet of each calf were abraded (area above the heel bulbs and below the dewclaws), moistened, and wrapped to facilitate an anaerobic condition. Feet were inoculated with macerated DD lesion material or mock inoculum and remained wrapped until clinical signs of DD or protocol endpoint.

Results: After a period of 14 to 18 days post inoculation, three of five inoculated calves developed clinical signs (lameness), and upon close inspection, DD lesions were present on at least one hind foot. Two of five inoculated calves did not develop lesions within 28 days. Zero of three mock-inoculated calves developed DD. Treponema spp. were detected by quantitative polymerase chain reaction from biopsies of induced lesions. Measurements of behaviour prior to disease induction were numerically different between DD affected and mock-inoculated calves.

Conclusions: An experimental infection model established for dairy cattle was used to successfully induce acute DD lesions in three of five inoculated beef calves. This model can provide a framework to study intervention protocols and to evaluate the impact of DD on behaviour and pain.

Keywords: Behaviour; Cattle; Experimental infection; Hairy heel warts; Induction model; Pain.

Fig. 1

Representative lesions from digital dermatitis (DD) experimental model. ID = calf identification; MI = mock-inoculated calves (no DD lesions); IN-NDD = inoculated calves (no DD lesions); IN-DD = inoculated calves with a clinical case of DD (red arrows); Blue arrows = location of abrasion sites (four regions: two above the heel bulbs, above the medial and lateral claws, and two below the dewclaws on each side of the pastern area. Colour version available online

Fig. 2

Absolute abundance of each bacterial species isolated from the inoculum and biopsies taken from experimentally induced DD calves. Species copy numbers were standardized by the weight of the biopsy tissue. A pseudocount of 1 was added before log transforming bacterial copy numbers. Inoculum_A = inoculum at the start of the induction protocol; Inoculum_B = inoculum at the end of the induction protocol; ID = calf identification; LH = left hind foot; RH = right hind foot; HE = heel bulbs; DC = dewclaws. Colour version available online

Fig. 3

Mechanical nociceptive threshold (MNT) in hind feet of beef cattle experimentally induced with digital dermatitis (DD). MNT = mechanical nociceptive threshold in Newtons (N); ID = calf identification; Mock-inoculated = no DD lesions; Inoculated No DD = no DD lesions; Inoculated DD = calves with a clinical case of DD; Observations = observation number where 1 is acute DD lesion at diagnosis, 3 is healing lesion (IN-DD) or abrasion site (MI; IN-NDD), and 5 is healed lesion (no sign of pre-existing lesion) or healed abrasion (no sign of abrasion site); LH = left hind foot; RH = right hind foot. Colour version available online

Fig. 4

Timeline of the experimental induction of beef calves with digital dermatitis (DD). Periods of acclimatization, abrasion (including attachment of ear accelerometers), inoculation, evaluations 1 and 2 (re-moistening; foot warp reinforcement), evaluation 3 (foot wrap removal; clinical appraisal for DD; pain assessment; treatment), interval days between events, and when DD diagnosis was made