Hematologic and immunologic responses of Holstein calves to a fire ant toxicant

Holstein calves (3 to 5 months of age) were used to develop an animal model sensitive to environmental toxicants. In the present study, the fire ant toxicant AMDRO was fed (113.5 g/day/calf) to weanling castrated calves (9 test and 9 controls) for 7 weeks. As early as 14 days after the start of the AMDRO feeding, leukopenia was observed. Differential counts revealed significant non-transient decreases in lymphocytes and eosinophils. Eosinopenia was observed from days 21 to 49 of AMDRO treatment. Variability in hematocrit and hemoglobin values in treated and control calves precluded making a determination of trends due to toxicant exposure. The AMDRO treatment did not produce significant decreases in primary or secondary antibody responses to keyhole limpet hemocyanin or to Brucella abortus vaccination. It also did not produce suppression of cellular immunity, as determined by delayed-type hypersensitivity response to bacille Calmette-Guérin. Potential effects of AMDRO on thermoregulatory mechanisms were indicated by significant depressions of rectal temperature observed after 25, 32, and 39 days' treatment.