Effects of aerosolized endotoxin in feedyard dust on weanling goats

Abstract

Weanling female Spanish goats ( n=36) were randomly allotted to four treatment groups (each group, n=9): principal dust group with antibiotic; principal dust group without antibiotic; control group with antibiotic; and control group without antibiotic. The principals were exposed to twenty-two 4 h dust treatments in a closed tent. Dust treatments occurred as follows: one dust treatment, 18-day rest, seven daily dust treatments, 7-day rest, seven daily dust treatments, 7-day rest, and seven daily dust treatments. All principals and six controls were euthanatized and necropsied at the end of the experiment. There was an interaction between dust and tilmicosin antibiotic for feed intake and average daily gain following the first dust treatment. The interaction occurred because control goats not exposed to dust nor receiving tilmicosin protection had lower ( P<0.05) feed intake than those principals exposed to dust without tilmicosin protection (996 g per head per day versus 1131 g per head per day, respectively). Consequently, these goats also gained more ( P<0.02) weight than the control goats without tilmicosin protection (57 g per head per day versus 42 g per head per day). Contrary to the hypothesis that dust might reduce the efficiency of feed utilization, it tended to improve it. After the first dust treatment, the mean rectal temperatures of the four groups with and without antibiotics were significantly different ( P≤0.0003). Four hours ( P≤0.0016) after dust treatment, the mean rectal temperature of the two principal groups was higher than the controls. On the first 7-day dust treatment series there was a significant ( P≤0.0006) difference between the groups. The mean rectal temperatures of the two principal groups at 8 h on day 1 were significantly ( P≤0.02) higher than the control groups. On the second 7-day dust treatments, there were no significant differences in mean rectal temperature between the groups. On the third 7-day treatment series there were significant ( P≤0.0001) differences among the four groups. On the first day of the dust treatment series, at 8 h, the trend of the principal groups’ mean rectal temperature was higher than the controls. It appears that repeated endotoxin/dust exposures induces a state of tolerance for increased rectal temperatures that are characteristic after one dust exposure. There were no gross observable differences between the controls and principal respiratory tracts. The following histologic changes were observed in the principal goats: a mild alveolar septal hypercellularity, moderate multifocal airway exudation of neutrophils and macrophages containing foreign particulate material, and there was a marked increase in bronchial associated lymphoid tissue compared to controls. The diagnosis was mild acute exudative bronchointerstital pneumonia. No significant microscopic lesions were observed in the control goats.