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Aims: Bovine respiratory disease (BRD) has serious impacts on dairy production and animal welfare. It is most commonly diagnosed based on clinical respiratory signs (CRS), but in recent years, thoracic ultrasonography (TUS) has emerged as a diagnostic tool with improved sensitivity and specificity. This study aimed to assess the alignment of BRD diagnoses based on a Clinical Respiratory Scoring Chart (CRSC) and weekly TUS findings throughout the progression of BRD of variable severity in preweaned Holstein dairy heifers. Methods: A total of 60 calves on two farms were followed from the 2nd week of life through the 11th week of life and assessed on a weekly basis for CRS and lung consolidation via TUS. The alignment of BRD diagnoses based on CRSC scores and TUS findings was evaluated across disease progression (pre‐consolidation, onset, chronic, or recovered) and severity (lobular or lobar lung consolidation) using receiver operator curves and area under the curves combined with Cohen's kappa (κ), sensitivity, and specificity. Results: The diagnosis of BRD using CRSC scores ≥5 aligned best with the onset of lobar lung consolidation (>1 cm in width and full thickness). This equated to an acceptable level of discrimination (AUC = 0.76), fair agreement (κ = 0.37), and a sensitivity of 29% and specificity of 99%. Similarly, there was acceptable discrimination (AUC = 0.70) and fair agreement (κ = 0.33) between CRSC ≥5 and the onset of a less severe threshold of disease based on lobular (1–3 cm2 but not full thickness) or lobar consolidation. Discrimination remained acceptable (AUC = 0.71) with fair agreement (κ = 0.28) between CRSC scores ≥2 for nasal discharge and/or cough (spontaneous or induced) and the onset of lobar consolidation. However, sensitivity was <40% across comparisons and outside of the onset of disease there tended to be poor discrimination, slight agreement, and lowered sensitivity between CRS and TUS diagnoses of lobular or lobar consolidation (pre‐consolidation, chronic, or recovered). Conversely, specificity was relatively high (≥92%) across comparisons suggesting that CRSC diagnoses indicative of BRD and associated lung consolidation tend to result in few false positive diagnoses and accurate identification of healthy animals. Conclusions and clinical relevance: Although we found the specificity of clinical signs for diagnosing lung consolidation to be ≥92% across all methods of TUS evaluations, the low levels of sensitivity dictate that clinical assessments lead to many false negative diagnoses. Consequently, depending on clinical signs alone to diagnose BRD within populations of dairy calves will likely result in overlooking a substantial proportion of subclinically affected animals that could inform the success of treatment and prevention protocols and guide management decisions. [ABSTRACT FROM AUTHOR]

Little is known about shifts in the fecal microbiome of dairy calves preceding and following the incidence of gastrointestinal disease. The objective of this cohort study was to describe the fecal microbiome of preweaned dairy calves before, during, and after gastrointestinal disease. A total of 111 Holstein dairy calves were enrolled on 2 dairies (D1 and D2) and followed until 5 weeks old. Health assessments were performed weekly and fecal samples were collected every other week. Of the 111 calves, 12 calves from D1 and 12 calves from D2 were retrospectively defined as healthy, and 7 calves from D1 and 11 calves from D2 were defined as diarrheic. Samples from these calves were sequenced targeting the 16S rRNA gene and compared based on health status within age groups and farms: healthy (0-1 week old) vs. pre-diarrheic (0-1 week old), healthy (2-3 weeks old) vs. diarrheic (2-3 weeks old), and healthy (4-5 weeks old) vs. post-diarrheic (4-5 weeks old) calves. Healthy and diarrheic samples clustered together based on age rather than health status on both farms. Based on linear discriminant analysis, a few species were identified to be differently enriched when comparing health status within age groups and farm. Among them, Bifidobacterium sp. was differently enriched in pre-diarrheic calves at D1 (0-1 week old) whereas healthy calves of the same age group and farm showed a higher abundance of Escherichia coli . Bifidobacterium sp. was identified as a biomarker of fecal samples from healthy calves (2-3 weeks old) on D1 when compared with diarrheic calves of the same age group and farm. Feces from diarrheic calves on D2 (2-3 weeks old) were characterized by taxa from Peptostreptococcus and Anaerovibrio genera whereas fecal samples of age-matched healthy calves were characterized by Collinsella aerofaciens and Bifidobacterium longum . After resolution of uncomplicated diarrhea (4-5 weeks old), Collinsella aerofaciens was more abundant in D2 calves whereas Bacteriodes uniformis was more abundant in D1 calves. Taken together, these findings suggest that the age of the preweaned calf is the major driver of changes to fecal microbiome composition and diversity even in the face of uncomplicated gastrointestinal disease., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Claus-Walker, Slanzon, Elder, Hinnant, Mandella, Parrish, Trombetta and McConnel.)

Bovine respiratory disease (BRD) is a leading cause of calf morbidity and mortality, and prevalence remains high despite current management practices. Differential gene expression (DGE) provides detailed insight into individual immune responses and can illuminate enriched pathways and biomarkers that contribute to disease susceptibility and outcomes. The aims of this study were to investigate differences in peripheral leukocyte gene expression in Holstein preweaned heifer calves 1) with and without BRD, and 2) across weeks of age. Calves were enrolled for this short-term longitudinal study on two commercial dairies in Washington State. Calves were assessed every two weeks throughout the pre-weaning period using clinical respiratory scoring (CRS) and thoracic ultrasonography (TUS), and blood samples were collected. Calves were selected that were either healthy (n = 10) or had BRD diagnosed by CRS (n = 7), TUS (n = 6), or both (n = 6) in weeks 5 or 7 of life). Three consecutive time point samples were analyzed for each BRD calf consisting of PRE, ONSET, and POST samples. Nineteen genes of interest were selected based on previous gene expression studies in cattle: ALOX15, BPI, CATHL6, CXCL8, DHX58, GZMB, HPGD, IFNG, IL17D, IL1R2, ISG15, LCN2, LIF, MX1, OAS2, PGLYRP1, S100A8, SELP, and TNF. Comparisons were made between age and disease time point matched BRD and healthy calves as well as between calf weeks of age. No DGE was observed between diseased and healthy calves; however, DGE was observed between calf weeks of age regardless of disease state. Developmental differences in leukocyte gene expression, phenotype, and functionality make pre-weaned calves immunologically distinct from mature cattle, and early life shifts in calf leukocyte populations likely contribute to the age-related gene expression differences we observed. Age overshadows disease impacts to influence gene expression in young calves, and immune development progresses upon a common trajectory regardless of disease during the preweaning period., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Elder et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)