Effect of subclinical infection with Actinobacillus pleuropneumoniae in commingled feeder swine.

Sequential serologic analysis for Actinobacillus pleuropneumoniae was done on 240 commingled feeder swine at 1 and 21 days after purchase and at slaughter. At the beginning of the experiment, mean weight of the pigs was 18.6 kg, and the pigs were maintained to a mean slaughter weight of 109.95 kg. A fourfold increase in antibody titer against Actinobacillus pleuropneumoniae was demonstrated in 28 (12%) pigs. Mean adjusted rate of gain for infected pigs was 0.74 +/- 0.10 kg/d and 0.77 +/- 0.09 kg/d for uninfected pigs. Differences in feed efficiency were not detected between infected and uninfected pigs. Our findings suggested that 5.64 additional days are required for pigs with subclinical infection to reach market weight of 113.6 kg, compared with that for uninfected herdmates. A vaccination program to prevent subclinical infection may not be cost effective.