The association of lung consolidation and respiratory pathogens identified at weaning on the growth performance of beef on dairy calves

This observational study evaluated the relationship between lung consolidation observed at weaning and calf ADG, and the association of pathogen shedding at weaning on ADG in beef × dairy calves up to 238 d. Beef × Holstein calves (n = 143) were sourced from 2 dairies. Calves were managed in 3 cohorts and fed milk replacer and calf starter preweaning. Calves were transported to another facility after weaning and raised in one group where they were fed calf starter with oat hay and transitioned to a corn silage-based total mixed ration diet. Calf ADG was calculated from arrival to weaning at 61 ± 14 d (period 1), from weaning to 83 ± 21 d (period 2), and from 83 d to 238 ± 21 d (period 3). Thoracic ultrasonography (TUS) was performed at weaning to evaluate if a calf had lung consolidation (characterized as TUS+ ≥ 1 cm² in one lobe) and to categorize the degree of lung consolidation found (LC = none, 1 to 2 cm², or 3 cm²). Nasopharyngeal swabs were taken from the TUS+ calves and from pair-matched TUS- calves (n = 35 pairs) for pathogen identification by culture at a diagnostic laboratory. A mixed linear regression model assessed the association of LC with calf ADG with LC, period, period × LC, and sire breed as fixed effects, arrival weight as a covariate, and calf nested within the cohort as a random effect. Another mixed linear regression model assessed the association of pathogen shedding with calf ADG from weaning to 238 d with period, and sire breed as fixed effects, pair was nested within cohort as a random effect. A logistic regression model was used to evaluate the likelihood of a TUS+ calves shedding a pathogen with pair as a fixed effect. There was an LC × period interaction affecting ADG over period 2 (P = 0.03) where TUS- calves had increased ADG (1.18 ± 0.02 kg/d) compared with calves with LC = 3 cm² (1.03 ± 0.04 kg/d, P = 0.01). However, TUS- calves had similar ADG to calves with LC = 1 to 2 cm² in period 2 (P > 0.05). Calf ADG was not associated with LC in period 3 (P > 0.05), and calves weighed 324 ± 37 kg (mean ± SD) at 238 d. In addition, 57% (20/35) of TUS+ calves and 26% (9/35) TUS- calves shed Pasteurella multocida. There was no association of pathogen shedding with calf ADG (P > 0.05), but TUS+ calves were more likely to shed a pathogen. These findings suggest that calves with pneumonia experienced poor growth up to 20 d post-weaning, but compensatory gain occurred by 238 d. Furthermore, P. multocida was not associated with growth performance up to 238 d in beef × dairy calves.