Associations of serostatus upon arrival with clinical respiratory disease, lung consolidation and growth in veal calves

Abstract

Respiratory tract infections remain a major problem during calf rearing, especially among milk (formula) fed veal. Preconditioning of calves through appropriate colostrum management and vaccination could be helpful to address this issue. The objective of this study was to investigate whether the presence of serum antibodies against major respiratory tract pathogens (Bovine Respiratory Syncytial virus, Parainfluenza 3 virus, Bovine coronavirus, Mycoplasmopsis bovis, Histophilus somni, Pasteurella multocida and Mannheimia haemolytica) and total serum immunoglobulin G (IgG) concentration in calves upon arrival at the veal facility were associated with the occurrence of clinical bovine respiratory disease (BRD) or lung consolidation in the first 3 weeks, as assessed by both the Wisconsin BRD scorecard (based on 5 clinical signs: cough, rectal temperature, ear position, nasal-and ocular discharge) and by quick thoracic ultrasound scanning (qTUS). Additionally, the association between calves' serostatus production parameters were explored. A prospective cohort study was conducted among 442 male dairy calves on a large veal calf facility in Belgium. Both clinical scoring and qTUS were performed on all calves at 4 key moments in the production cycle: arrival at the facility, initiation of first metaphylactic antimicrobial treatment at peak incidence of BRD (wk 1), end of the first metaphylactic treatment (short-term evaluation) and at wk 10 (long-term evaluation). Mixed effects logit regression models were fitted to quantify relationships. The outcomes of interest were clinical respiratory disease (Wisconsin BRD scorecard positive), lung consolidation (≥1cm or ≥ 3cm), average daily weight gain and cold carcass weight. In the first week of production, incidence of lung consolidation (≥1cm) quickly increased from 14.9% upon arrival to 43.0% at the peak of the BRD incidence, while clinical BRD increased from 3.6% to 16.1%. The main finding of this study was that calves who were seropositive for bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCoV) at arrival had reduced odds of developing lung consolidation at the peak of the outbreak, 0.58 OR (95% CI: 0.38 - 0.89) and 0.37 OR (95% CI: 0.20 - 0.69), respectively. No relationships between serum IgG concentration at arrival and the development of lung consolidations or clinical respiratory disease were found. Nevertheless, on average, throughout the first 10 weeks of the fattening cycle, calves with failed transfer of passive immunity (FPT, serum IgG < 7.5 g/L) gained 40 g/day (95% CI: 10-70g/day) less weight (ADG). Hence, ensuring that calves have a positive serostatus for these respiratory tract pathogens before entering the facility may help lower the incidence of lung consolidations, subsequently reducing treatment incidence and the adverse effects on primary economic outcomes.

Keywords: bovine respiratory disease; failed transfer of passive immunity; pneumonia; quick thoracic ultrasonography.