Nasal shedding of bovine coronavirus during commingling is associated with reduced average daily gain and lung lesions in weaned seropositive calves.

Authors

Joanna Urbaniec, Alkiviadis Anagnostopoulos, Peers Davies, Federico G Hoffmann, Noelle Noyes, Joseph Neary

Published in

Journal of dairy science. Jun 23, 2026. Epub Jun 23, 2026.

Abstract

Bovine coronavirus (BCV) is a common calf pathogen and has been proposed as a potential contributor to bovine respiratory disease (BRD); however, little is known about its epidemiology and genetic diversity on UK farms. The aim of this study was to model the relationship between mixing duration and intensity, BCV shedding, BRD development, and production outcomes during a controlled commingling event designed to mimic conventional farming conditions. Three cohorts of weaned Angus × Holstein calves (8-10 weeks old; n = 120) sourced from 10 British source farms (SFs) were enrolled and quasi-randomly assigned to mixing groups of varying intensity. Mixing intensity (MI) was defined by 'Richness', i.e., the number of SFs contributing to each pen and evenness, i.e., the relative proportion of calves from each SF. MI ranged from low richness/low evenness (all calves in a pen originating from a single SF) to high Richness/high Evenness (2 calves from 5 different SFs in a single pen). Nasal swabs and fecal samples were collected on source farms on animal collection day (SF collection), d 0, 3, 7 and 21 post-mixing, and analyzed by BCV qPCR and Sanger sequencing. Serum samples were taken upon SF collection, d 0 and 21 post-mixing, and tested for BCV-specific IgG using ELISA. Calves were monitored daily for signs clinical respiratory disease using a modified University of Wisconsin-Madison system, and presence of lung lesions was assessed by thoracic ultrasonography on SF collection and d 0 and 21 post-mixing. Calves were weighed on SFs, and at the beginning and end of mixing to determine average daily gain (ADG). Associations between MI, BCV shedding, clinical respiratory disease, lung lesions, and ADG were investigated using mixed-effect models appropriate to the outcome type, with calf defined as the experimental unit. High serum BCV IgG titers were detected in all calves at enrolment and declined steadily over the study period. Seropositivity did not prevent BCV shedding, and overall genetic diversity among isolates was low (∼2%). However, distinct genetic variants were identified between source farms and, in one case, within the same animal at the beginning and end of the study period. Nasal BCV shedding was not associated with clinical disease within 7 d of recorded clinical respiratory disease. On the other hand, high-shedders were significantly more likely (∼4.5 times; (95%CI: 1.21; 6.8)) to have concurrent lung lesions and grew slower (- 0.36 kg/day; 95%CI: -0.62; -0.14) when compared with non-shedders. Concurrently, the odds of clinical BRD increased with both commingling duration and MI; however clinical BRD was not meaningfully associated with ADG. Overall, these findings suggest that in BCV seropositive commingled calves, BCV infection is widespread but largely subclinical; importantly, high levels of virus shedding are associated with measurably worse production outcomes whereas BRD risk is primarily influenced by the duration and intensity of mixing.

PMID:
42336052
Bibliographic data and abstract were imported from PubMed on 24 Jun 2026.

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