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- Author or Editor: Kelly F. Lechtenberg x
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Summary
Five strains of Actinobacillus pleuropneumoniae serotype 1 were used to intranasally infect 5 groups of pigs. Using each bacterial strain, infected pigs (termed seeder pigs) were commingled for 48 hours with 5 groups of noninfected test pigs, then were removed. Seeder and test pigs were maintained in isolation and were observed for 14 days. Seeder pigs had mortality that was threefold greater than that of test pigs (24% vs 8%). Rectal temperature in excess of 40.3 C was achieved for 84% of test pigs and 88% of seeder pigs. Neither of these 2 variables was statistically different between the 2 groups of pigs. Clinical impression scores ≥ 2 (on a 0 to 3 scale) were threefold (64% vs 20%) greater for seeder than for test pigs (P < 0.05). The total number of bacterial isolations or nonrecoverable isolates was tabulated for test and seeder pigs’ lungs at necropsy, irrespective of the amount of lesions. The number of A pleuropneumoniae isolations was not statistically different between test and seeder pig populations. Recovery of Pasteurella multocida or other bacteria was greater from the seeder pigs (P < 0.05), whereas the number of non-recoverable isolates was greater from test pigs than from seeder pigs (P < 0.05). Assessment of lung lesions at necropsy by either visual estimation or on a weight basis were in agreement. Fewer test pigs had lung lesions in excess of 5% of total lung volume than did seeder pigs (40% vs 84%) and, according to the odds ratio estimation, seeder pigs were 7 times more likely than test pigs to have such lesions. These results indicate a predictable, moderate intensity, natural exposure model for use in the study of Actinobacillus pleuropneumoniae-induced pneumonia. The seeder pig model appears to mimic field infection in development of clinical illness, febrile response, lung lesions, mortality, and low potential for secondary pneumonic bacterial involvement, thus providing a useful tool for preliminary evaluation of anti-infective modalities.
Abstract
Objective
To determine the effective dosage of tilmicosin phosphate when fed to pigs for the control of pneumonia attributable to Actinobacillus pleuropneumoniae.
Design
Randomized complete block design, with initial weight as the blocking factor.
Animals
Seeder pigs were used to infect clinically normal male and female pigs weighing between 13.6 and 36.3 kg at each of 4 trials.
Procedure
Five doses of tilmicosin phosphate (0, 100, 200, 300, and 400 µg/g) were fed to pigs for 21 days. Pigs received experimental feeds 7 days before the seeder pigs were placed into pens. Feeding continued for an additional 14 days, with seeder pigs removed 3 to 8 days after placement. All pigs were euthanatized and necropsied, with lung bacterial flora and percentages of pneumonic involvement determined.
Results
Improvement in clinical impression score, daily rectal temperature, and weight gain were seen for all doses of tilmicosin, compared with controls. For the same variables, tilmicosin administered at 200 to 400 µg/g resulted in improvements over the 100 µg/g dose.
Conclusions
Data indicate that tilmicosin phosphate fed to pigs at 200 to 400 µg/g is effective in controlling and preventing A pleuropneumoniae-induced pneumonia, when administered in feed for 21 days.
