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

Bovine digital dermatitis (DD) is an infectious claw disease with a negative effect on animal welfare and production. Treponema spp. is the main causative agent, and infected animals produce specific antibodies. Our aim was to estimate sensitivity (Se) and specificity (Sp) of 2 ELISA research tests, Medicago's ELISA test and GD Animal Health's in-house ELISA test, for detection of DD-associated Treponema antibodies in bulk tank milk. We used bulk tank milk samples from 154 Nor-wegian dairy cattle herds, 96 from an expected high-prevalence region and 58 from a low-prevalence region. Both tests were evaluated separately against herd-level (aggregated) claw-trimming records extracted from the Norwegian Dairy Herd Recording System using latent class models in a Bayesian analysis. Cutoff values were selected using an explorative approach, and both non-informative priors for all parameters and informative beta priors for distribution of Se and Sp of claw trimming were explored. The estimated (median) true herd-level prevalence of digital dermatitis varied between 24 and 30% in the high-prevalence region and between 3 and 6% in the low-prevalence region. For Medicago's ELISA test, an Se (95% posterior credible interval) of 0.57 (0.32; 0.94) could be achieved without compromis -ing Sp, and for GD Animal Health's in-house ELISA test, an Se of 0.60 (0.37; 0.92) was achieved. Our study showed that both ELISA tests can detect antibodies against DD-associated Treponema spp. in bulk tank milk. However, neither of the 2 ELISA tests produced satisfactory sensitivity without compromising specific-ity. Based on these results, inspection at claw trimming in a chute is necessary for surveillance and control of DD at the herd level in Norway, although these ELISA tests of bulk tank milk might be a useful supplement

Prevalence of udder pathogens in milk samples from Norwegian dairy cows recorded in a national database in 2019 and 2020

Abstract Background Identification of aetiological agents of mastitis in dairy cattle is important for herd management of udder health. In Norway, results from mastitis diagnostics are systematically recorded in a central database, so that the dairy industry can follow trends in the recorded frequency of udder pathogens and antimicrobial resistance patterns at national level. However, bacteriological testing of milk samples is based on voluntary sampling, and data are therefore subject to some bias. The aim of this study was to examine the prevalence of udder pathogens in Norwegian dairy cows by analysing data from the national routine mastitis diagnostics and to explore how routines for sampling and diagnostic interpretations may affect the apparent prevalence of different bacterial pathogens. We also assessed associations between udder pathogen findings and the barn- and milking systems of the herds. Results The most frequently detected major udder pathogens among all milk samples submitted for bacterial culture (n = 36,431) were Staphylococcus aureus (24.5%), Streptococcus dysgalactiae (13.3%) and Streptococcus uberis (9.0%). In the subset of samples from clinical mastitis (n = 7598); Escherichia coli (14.5%) was the second most frequently detected pathogen following S. aureus (27.1%). Staphylococcus epidermidis (10.0%), Corynebacterium bovis (9.4%), and Staphylococcus chromogenes (6.0%) dominated among the minor udder pathogens. Non-aureus staphylococci as a group, identified in 39% of the sampling events, was the most frequently identified udder pathogen in Norway. By using different definitions of cow-level bacterial diagnoses, the distribution of minor udder pathogens changed. Several udder pathogens were associated with the barn- and milking system but the associations were reduced in strength when data were analysed from farms with a comparable herd size. S. aureus was associated with tiestall housing, E. coli and S. dysgalactiae were associated with freestall housing, and S. epidermidis was associated with automatic milking systems. Only 2.5% of the 10,675 tested S. aureus isolates were resistant to benzylpenicillin. Among the 2153 tested non-aureus staphylococci, altogether 34% were resistant to benzylpenicillin. Conclusions This study presents the recorded prevalence of udder pathogens in Norway over a two-year period and assesses the possible impact of the sampling strategies, diagnostic methods and diagnostic criteria utilized in Norway, as well as associations with different housing and milking systems. The national database with records of results from routine mastitis diagnostics in Norway provides valuable information about the aetiology of bovine mastitis at population level and can reveal shifts in the distribution and occurrence of udder pathogens

Salivary IgG levels in neonatal calves and its association to serum IgG : An observational pilot study

Johnsen, Julie; Chincarini, Matteo ; Sogstad, Åse Margrethe; Sølverød, Liv; Vatne, Marie; Mejdell, Cecilie; Hänninen, LauraThe diagnosis of inadequate transfer of colostrum Immunoglobulin G (IgG) to calf serum, often known as failure of passive transfer (< 10 g/L IgG1 at 24-48 h), necessitates blood sampling from the calf and in some instances the presence of a veterinarian. Sampling saliva is both less invasive and easy for the producer. Previous research has shown that quantification of saliva IgG is possible in juvenile and adult cattle. The objectives of this observational pilot study were to investigate whether IgG can be quantified in neonatal calf saliva, if it is correlated to serum IgG concentrations, and if the indirect quantification of saliva IgG is achievable by use of a digital refractometer. Paired blood and saliva samples were collected from 20 healthy dairy calves aged 1-3 d. In these samples, IgG was quantified directly with Single Radial Immunodiffusion (SRID) and indirectly by use of a digital refractometer indicating Brix % (a subsample of n=12 saliva samples). A strong positive correlation (r = 0.7, P<0.001) between saliva IgG (mean ± SD; 0.2 ± 0.11 g/L) and serum IgG (32.1 ± 11.94 g/L) was found. Saliva IgG ranged from the lowest detectable value, 0.1 g/L (n = 6 samples), to 0.6 g/L. Saliva Brix (1.2 ± 0.69%) was not significantly correlated to serum IgG (n = 12, r = 0.43, P = 0.155), however it was significantly correlated to saliva IgG (n = 12, r = 0.7, P = 0.018) and Brix in serum (n = 12, r = 0.7, P = 0.013). We conclude that IgG was quantifiable in most of the saliva samples. For saliva IgG to be of any value with regards to detecting failure of passive transfer, future studies should investigate methods that can detect IgG <0.1 g/L. The results indicate that saliva IgG can be used to predict serum IgG at levels above 10g/L, which may warrant further exploration of the use of saliva in the surveillance of failure of passive transfer. The results of the current pilot study did not support the potential usage of a Brix % refractometer to quantify saliva IgG.Peer reviewe