Digital dermatitis in Norwegian dairy cattle - a contagious foot disease threatening the animal welfare

Digital dermatitis (DD) is a contagious bovine foot disease characterized by infection of the digital skin with erosions, ulcerations and /or chronic hyperkeratosis/ proliferation. The disease often causes lameness with consequences for animal welfare and production of milk and beef. The objectives of this project were to generate knowledge about the incidence, dissemination, etiology, and the immune response against the disease in Norwegian dairy herds. Digital dermatitis is multifactorial with interactions between the infectious agent, the host, and the environment. Foot- associated Treponema spp. is the most important infectious agent. Data from the Norwegian Animal Health Recording System (DHP) show that altogether 1361 Norwegian cattle herds have had at least one cow with DD from 2014 to September 2022. Lina Ahlén performed a questionnaire among all dairy herds recorded with DD in the Norwegian Dairy Herd Recording System (NDHRS) and a random sample of farmers with no DD recordings in their herds in 2019, in total 380 positive and 1530 negative herds. Analyses of the questionnaire including analyses of data from NDHRS made it possible to identify differences between DD positive and negative herds. The paper «A case-control study regarding factors associated with digital dermatitis in Norwegian dairy herds» is published in Acta Vet Scand https://doi.org/10.1186/s13028-022-00635-0. Digital dermatitis was far more frequent in herds housed in free stalls versus tie stalls. In the free-stall herds purchase of cattle was associated with increased risk for DD. Other factors associated with DD in free stalls were increasing trimming frequency, use of certified professional trimmer, cleaning of the feet in the chute, and solid flooring in the alleys. Some of these are risk factors while others increase the possibility for detection of the disease. This knowledge will be important to control DD and to reduce the dissemination of the disease to naïve herds. Bulk tank milk (BTM) samples from 154 dairy herds, 96 from an expected high (Rogaland) and 58 from a low prevalence county (Sogn & Fjordane) were analyzed with two ELISA tests, Medicago's research test, and GD Animal Health's in-house test, for detection of DD-associated Treponema antibodies. The sensitivity (Se) and specificity (Sp) of both tests were evaluated against herd-level claw trimming records extracted from the NDHRS. The paper «Evaluation of test characteristics of 2 ELISA tests applied to bulk tank milk and claw-trimming records for herd level diagnosis of bovine digital dermatitis using latent class analysis» is published in J. Dairy Sci. https://doi.org/10.3168/jds.2020-19804. The study showed that both ELISA tests can detect antibodies against DD-associated Treponema spp. in BTM, but none of them produced satisfactory Se for surveillance of DD in Norwegian dairy herds, probably because few animals are diseased within each herd and the lesions usually are mild. Currently, diagnostics and recording at claw trimming has higher Se and is necessary even though these ELISA tests may be a useful supplement. Lina Ahlén swabbed the trimming equipment and chutes on nine selected locations at routine claw trimming in 22 herds. The swabs were collected at five different time points, before trimming at arrival on the farm, immediately after trimming of the last animal, after cold water washing, after warm water washing, and after disinfection. The aim was to evaluate the risk for passive transfer of Treponema spp. between herds and to investigate the effect of washing and disinfection. All swabs were analyzed by quantitative PCR analyses of DNA to determine the total amount of Treponema spp. (viable or not). The swabs collected immediately after trimming were also analyzed by a qPCR to identify T. phagedenis, T. pedis, and T. medium/vincentii. Additionally, biopsies of DD lesions from cows in the same herds were analyzed by fluorescens in situ hybridization (FISH) to identify Treponema phylotypes. The DD-associated phylotype T. phagedenis was detected on all nine locations and in the biopsies from 20 of the 22 herds. In two herds T. phagedenis was neither identified in swabs from the trimming equipment and chutes nor from the biopsies. These results verified that DD probably may be transferred with the equipment and chutes. The study showed that washing and disinfection usually were effective to reduce the total amount of treponemes, but with big differences between the locations. No Treponema spp. (viable or not) was detected on the hoof knife after disinfection, whereas the bacteria were detected in high numbers on the trimming chute and occasionally on the disc of the grinder. The paper «Bovine digital dermatitis: Treponema spp. on trimming equipment and chutes and effect of washing and disinfection» is submitted to BMC Veterinary Research for publication. Knowledge from this study will be useful to reduce the passive transfer of DD to naïve herds.

Prosjektet har allerede gitt nyttige virkninger for flere målgrupper: Forskerne som har deltatt, har fått økt innsikt i forekomsten, diagnostikken, spredningen og årsakene til digital dermatitt (DD) blant norske melkekyr. Forskningsmiljøer i Norge, Danmark, Sverige og Nederland har deltatt i prosjektet, både mht laboratorieanalyser, epidemiologiske og statistiske analyser og publisering av materialet. Prosjektet var medvirkende til at det ble utarbeidet en søknad til Norges forskningsråd, som ble innvilget, for prosjektet «Diginostics – A novel diagnostic test for digital dermatitis in ruminants (NFR project no. 310067)». Prosjektleder Terje Fjeldaas har vært medforfatter og PhD stipendiat Lina Ahlén har bidratt med bilder av ulike M-stadier av DD til det Nordiske klauvatlaset som ble oppdatert i 2020 https://www.animalia.no/contentassets/55b0d5ad415445a1addb077dc86de1a4/nordicclawatlas_updated-june2020_norsk-oversettelse-002_tora4aug2020_ams_endelig.pdf og det internasjonale ICAR atlaset med Appendix 1 og 2 https://www.icar.org/index.php/publications-technical-materials/technical-series-and-prooceedings/atlas-claw-health-and-translations/. Veterinærstudenter, veterinærer, rådgivere og bønder har fått betydelig mer kunnskap om årsakene til sjukdommen, diagnostikk og risikofaktorer for spredning av sjukdommen mellom besetninger og faktorer som påvirker spredningen innad i besetningene. Denne ervervete kunnskapen fra prosjektet har fortløpende blitt inkludert i undervisningen av studenter ved NMBU Veterinærhøgskolen og har vært formidlet til praktiserende veterinærer, rådgivere og bønder på utallige eksterne fagdager, seminarer og kurs. Sertifiserte klauvskjærere og andre profesjonelle klauvskjærere har på kurs og fagdager fått oppæring i diagnostikk av DD. De har også blitt informert om at deres diagnostikk og rapportering ved rutinemessig klauvskjæring er den beste måten å overvåke sjukdommen på og at lokalbehandling med salicylsyre er et av de beste kurative og preventive tiltakene for å kontrollere sjukdommen. Studien av forekomsten av DD-assosierte Treponema bakterier på klauvskjæringsutstyr og klauvbokser og effekten av vask og desinfeksjon har gitt verdifull kunnskap som er helt vesentlig for å redusere passiv overføring av smitte mellom besetningene. Effekter for norsk storfehold: Samarbeidet med TINE, Animalia og Helsetjenesten for storfe har bidratt til at den ervervete kunnskapen fra prosjektet har blitt omsatt i bransjeretningslinjer og anbefalinger for smittesikker omsetning av storfe https://www.animalia.no/no/Dyr/storfe/nye-helsekrav-ved-livdyromsetning-av-storfe/. Besetninger som har fått påvist DD på ett eller flere dyr, blir nå klassifisert som røde, og for disse besetningene blir "digital dermatitt" skrevet med rødt i buskapsattesten. Alt dette bidrar til å redusere spredningen av digital dermatitt med de gevinstene det har for dyrevelferden og økonomien både i norske melke- og ammekubesetninger.

Digital dermatitis is a contagious foot disease characterized by infection of the digital skin with erosions, painful ulcerations and /or chronic hyperkeratosis/ proliferation. The disease causes lameness with consequences for animal welfare and production of milk and beef. Losses are due to reduced milk production, reduced feed efficiency, reduced fertility, early culling, treatment and not being able to sell animals. Digital dermatitis is multifactorial with interactions between the infectious agent, the host and the environment. Foot- associated Treponema spp. is the most important infectious agent, but other bacteria also seem to be involved in the pathogenesis and a synergy between Treponema spp. and D. nodosus has been suggested. Digital dermatitis has until recently been seen quite sporadic in Norwegian dairy herds, but according to the recordings from professional claw trimmers in June 2016, 138 dairy herds have one or more cows diagnosed with DD. These recordings show that DD has increased rapidly during the last years. The disease is six times more prevalent in free-stall herds compared to tie-stall herds, and considering the Norwegian legislation, which demands only free-stall housing for cattle from 2034, a rapid increase in DD is expected. The planned clinical, serological, bacteriological, histopathological and molecular studies will generate knowledge about the incidence, etiology and pathogenesis of DD and the immune response against Treponema phagedenis under Norwegian conditions. The knowledge gained will support the Cattle Health Services in preventing DD, provide a basis for identifying herds that are free from the disease and for establishing regulations on trade and movement of cattle. We will be able to give recommendations that will reduce the incidence and spread of DD, to farmers whose cattle are affected. One PhD-student will cooperate with researchers in Norway and other Nordic countries.