The association of lung consolidation in beef × dairy cattle at weaning with feedlot growth performance, carcass characteristics, liver health, and liver microbiome diversity.

Bovine respiratory disease (BRD) is the costliest disease in the cattle industry and often compromises the immune system. The objective of this observational cohort study was to evaluate the impact of lung consolidation (LC) diagnosed at weaning (61 plus/minus 14 days of age) on feedlot growth performance, carcass characteristics, and liver health and microbiome in beef × dairy cattle. At 4 d post-weaning, LC was assessed by thoracic ultrasonography. The cattle (n = 139) either had ≥ 1 cm2 LC in at least one lung lobe and were BRD positive (35 calves; BRD) or did not (< 1 cm2) and were negative (104 calves; CONTROL). Cattle were moved to the feedlot at 353 ± 53 d of age, where individual feed intake and body weights (BW) were recorded. Cattle were sent to slaughter when they reached a target final BW (steers = 680 kg and heifers = 635 kg). Liver scores and carcass data were collected. A subset (n = 29; 18 BRD cattle vs. 11 CONTROL cattle) had healthy liver tissue analyzed to investigate the association of LC at weaning with the liver microbiome diversity at slaughter. Only cattle with edible livers and no lung lesions were included in the microbiome analysis subset. Liver tissue samples were collected at slaughter and subsequently sequenced for microbiome analysis using an Illumina platform through targeted sequencing of the V4 region of the 16S rRNA gene. Mixed linear models were used to assess the effects of LC on growth performance and carcass characteristics with calf ranch, sex, and breed as fixed effects in the model. Generalized linear mixed models were used to assess the distributions of lung scores, liver scores, and quality grade at slaughter between LC and CONTROL cattle. To assess the effect of LC at weaning on the liver microbial communities at slaughter, the beta diversity (ADONIS) test was run, and the relative abundance of taxa is presented. There were no differences between BRD and CONTROL cattle for growth performance or most carcass traits (P > 0.05). However, the marbling score was greater (P = 0.05) in carcasses from CONTROL cattle (495 ± 7.82; LSM ± SEM) when compared with carcasses from BRD cattle (462 ± 13.84). The beta diversity in the liver did not differ (P > 0.05) between BRD and CONTROL cattle. Staphylococcus was the most abundant genus among the liver samples, regardless of health status at weaning. A diagnosis of BRD by LC in beef × dairy cattle at weaning (57 ± 14 d of age) reduced marbling and impacted quality grade.