Evaluation of the prophylactic potential of an immunomodulator against respiratory disease in calves.

The prophylatic effect against respiratory disease in feedlot calves of an immunomodulator, based on an inactivated avipox virus preparation, was evaluated in a double blind, placebo controlled field trial. The effect of the immunomodulator on phagocytosis and on the reactivity of the lymphocytes was also tested. On the day of arrival at the feedlots and 3 days later 257 calves were injected with either the immunomodulator or with placebo. All calves were then observed for respiratory disease and treatments were recorded. The immunomodulator did not reduce the frequency of disease, compared to the placebo. Thirty percent of the calves treated with the immunomodulator and 27 % of the controls were treated with antibiotics for respiratory disease. The cell mediated immune reactivity of 7 calves treated with the immunomodulator and of 7 untreated calves was tested. Monocytes isolated from the animals were examined for their ability to ingest latex beads and lymphocytes from the animals were examined for their response to different mitogens. Sera from each of the two groups were also investigated for the effect on phagocytosis. No difference in these parameters was observed between the two groups.