Evaluation of an IgG Enzyme-Linked Immunosorbent Assay as a Serological Assay for Detection of Mycoplasma bovis Infection in Feedlot Cattle.

Mycoplasma bovis is a pathogen of emerging significance in cattle throughout the world that is causing a range of diseases, including mastitis, arthritis, and pneumonia. The limited availability and efficacy of current diagnostic and prophylactic tools for its control and its increasing antimicrobial resistance are contributing to its increasing importance in beef and dairy cattle. We have developed an indirect IgG enzyme-linked immunosorbent assay (ELISA) based on a recombinant fragment of the MilA protein and have shown its potential as an effective diagnostic tool. To more comprehensively estimate the diagnostic sensitivity and specificity of this IgG ELISA for detection of infection with M. bovis in cattle and to define a suitable cutoff for use in the field, we further assessed its performance in experimentally infected calves in a closed beef herd and by applying Bayesian latent class modeling to laboratory testing results from 7,448 cattle entering Australian feedlots. The most effective cutoff points were estimated to be 68.6 antibody units (AU) for experimentally infected calves and to be 58.7 AU for a closed adult herd. Under field conditions, in feedlot cattle the globally optimal cutoff was estimated to be 105 AU. At this cutoff, the diagnostic sensitivity was 94.3% (95% probability interval [PI], 89.9% to 99.6%) with a diagnostic specificity of 94.4% (95% PI, 90.3% to 99.6%). Applying this 105 AU cutoff, 13.1% of cattle were seropositive for infection with M. bovis on entry into feedlots, and 73.5% were seropositive when followed up approximately 6 weeks later suggesting a high risk of infection shortly after entry into feedlots.

A systematic review and meta-analysis of impact of strongyle parasitism on growth rates in young cattle.

BACKGROUND: To identify any universal impact of strongyle parasite burden on the growth rate of young cattle. METHODS: A meta-analysis and meta-regression of the relationship between differences in strongyle parasite burden between cohorts and average daily weight gain was conducted. Publications were identified from a search of databases applying PRISMA 2020 principles. Eligible studies had at least two groups of growing cattle on the same farm that were identical in composition, management and diet except for parasite exposure and were subject to body weight gain or average daily gain and faecal egg count measurements across the common growing period. The reference group had the lowest growth-period faecal egg count. A meta-regression estimated the impact of strongyle parasitism. The dependent variable was the log of the ratio of average daily gain between comparison groups and the reference group with the predictor variable as the common logarithm of the difference in average faecal egg count (plus 1) between the comparison and the reference groups. RESULTS: 26 publications containing 85 groups and 59 comparison ratios were analysed. Papers included representatives from dairy and beef industries and from pasture and feedlot production systems and from all cattle-producing continents. The comparison group average daily growth rate was 0.89 (95%CI 0.81-0.97) that of the reference group. Meta-regression identified a 0.131 linear reduction in average daily weight gain ratio for every log10 increase in the difference between comparison and reference group faecal egg count. Direction of effect was consistent across all subset analyses (continent, class of stock and production system). Whilst small faecal egg count differences between the comparison and reference groups often provided similar rates of daily weight gain, the trend was negative with most comparison groups having lower daily weight gains than their reference group. CONCLUSIONS: Strongyle parasitism of growing cattle as measured by faecal egg count is associated with reduced growth across all production systems, geographies and classes of cattle.