Aerosol disinfection from weaning: a pilot study to assess the impacts on clinical signs of Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae (APP) is a respiratory disease causing ill thrift, acute deaths and carcass damage. The pathogen is difficult to control in large populations, with disease severity impacted by numerous factors including the number of pigs in an airspace (Cargill and Banhazi 2001). Previous research suggests that air quality is improved with aerosol disinfection (fogging) (Costa et al. 2014), however the impacts on clinical signs of APP are unclear. This study tested the hypothesis that fogging during the weaner period would reduce coughing, improve survival and decrease carcass pleurisy when pigs were subsequently housed in a fogged finisher facility.

A total of 3829 pigs (Large White x Landrace; PrimeGro™ Genetics) was selected at weaning and housed in one of four weaner rooms (955–957 pigs/room). Weaner rooms were allocated to one of two treatments: Control weaners, no aerosol disinfection during the weaner period (CW); and Fogged weaners, aerosol disinfection during the weaner period (FW). Fogging was achieved using Ozmist Patiomist Pedestal fans, with four fans in each weaner room. Timers were used and the fans were set to fog for 30 min every 2 h, 24 h/day. At 9 weeks of age, 3623 pigs were moved to the one finisher facility, with the CW pigs housed at one end of the facility and the FW pigs housed at the other end. The entire finisher facility was aerosol disinfected using a fixed high-pressure system (750 psi and 10 micron nozzles), with the system running 10 min every 2 h outside of working hours and then on a restricted schedule during the day (10 min on; 10 min off; 10 min on during staff breaks). Virogard (quaternary ammonium compounds; Chemetall Pty Ltd; Bayswater North, Victoria), at a rate of 1 : 1000, was used as the disinfectant in both fogging systems. Pigs were offered ad libitum access to commercial diets from weaning through to slaughter (21 weeks of age). Growth performance was measured on a pen basis (45 pens/treatment) from 9 to 21 weeks of age, while the prevalence of coughing was assessed during this period every 4 weeks on five pens per treatment. The protocol for cough scoring involved waking the pigs and immediately counting the number of coughs per pen in the subsequent 3 min. Pigs were slaughtered in a commercial abattoir and a pleurisy score (increasing scale from 0 to 3) obtained for each carcass. Growth performance, cough score and slaughter data were analysed for treatment effects using ANOVA (Genstat, 16th Edition; UK), with the finisher pen as the experimental unit. The impact of fogging on mortality was analysed using Chi-square.

Individual pedestal fans delivered an average of 17.6 L/d during the weaner period. Weaner mortality and removal rates were similar between treatments to 9 weeks of age (χ² = 0.27, P = 0.60). Post mortems were conducted on 98.5% of all deaths from 9 weeks of age, with lung lesions associated with APP present on 78% of pigs autopsied. Between 9 and 14 weeks of age, the number of deaths and destructions tended to be greater in CW pigs compared to counterparts previously fogged as weaner pigs (3.2% and 2.2% of the population, respectively; χ²= 0.21, P = 0.06). This was primarily due to a 3-week delay in the first APP outbreak in the FW pigs. There was no treatment effect on total deaths and destructions over the entire period (9–21 weeks of age, χ²=0.51, P = 0.48). Cough score during the grower/finisher period was similar between treatments (P = 0.38) as was daily weight gain (P = 0.94). Average pleurisy score at slaughter was similar between treatments (2.62 and 2.56 for the CW and FW respectively, P = 0.12), however pleurisy scores improved in the FW pigs with increased distance in the shed from the CW (P = 0.003).

The delay in the first APP outbreak in the FW treatment group was encouraging, suggesting early fogging may reduce clinical disease. An eventual APP outbreak in the FW was expected considering that half of the pigs in the total finisher airspace were CW. The outcomes from this pilot study suggested that the use of aerosol disinfection from weaning may provide a tool for reducing the clinical impacts of APP in large populations. Further investigations are aimed at quantifying the benefits when whole batches of pigs are fogged from weaning in combination with a tight age spread (<7 d), vaccination and 800–1000 psi fogging systems.