Managing respiratory disease in finisher pigs: Combining quantitative assessments of clinical signs and the prevalence of lung lesions at slaughter.

This study aimed to assess the relationship between quantitative assessments of clinical signs of respiratory disease (recorded manually and automatically) and the prevalence of lung lesions at slaughter to validate the use of both in the management of respiratory disease on farm. This was an observational study where pigs (n = 1573) were monitored from 25 ± 5.3 kg (week 12) to slaughter at 114 ± 15.4 kg (week 24). Pigs were housed in eight rooms divided into six pens on a wean-to-finish farm. A manual pen-based coughing (CF) and sneezing (SF) frequency was recorded weekly, for ten consecutive weeks, and a SOMO box (SoundTalks®) was installed in each room, issuing a daily respiratory distress index (RDI) for 13 weeks. Lungs were individually scored for pneumonia, scarring and dorsocaudal (DC) and cranial (CP) pleurisy lesions at slaughter. Relationship between prevalence of lung lesions and weekly RDI and CF and SF was assessed using Spearman's rank correlations and multivariable linear and logit-normal models. Both coughing and lung lesions were largely pen-specific, which fit the disease presentation of Mycoplasma hyopneumoniae. Results showed agreement between RDI and CF (rs = 0.5, P < 0.001), measuring higher levels of coughing at the beginning (weeks 13-14) and end (weeks 21-24, and weeks 21-22, respectively) of the finisher period. Positive associations were found between the prevalence of pneumonia and CF on week 21 and 22 (P < 0.001 and P = 0.011, respectively) and RDI on week 21-24 (r > 0.70; P < 0.050); the prevalence of DC and CP, and CF on week 22 (P < 0.001); and prevalence of scar lesions and CF on week 17 and 21 (P = 0.013 and P = 0.004, respectively), and RDI on week 21-24 (r > 0.70; P < 0.050). In the earlier weeks of the finisher stage, coughing was recorded but was not reflected in a higher prevalence of lung lesions at slaughter. These findings highlight the benefit of including measurements of coughing frequency to complement post mortem findings, to improve the management of respiratory disease on farm.