Abstract
Hereford calves were infested with Psoroptes ovis. Hemograms were evaluated weekly for 7 weeks during progressively extensive dermatitis and compared to uninfested control calves. Calves were treated with ivermectin and weekly hemograms were compared for 4 weeks during regression of clinical disease. They developed extensive dermatitis and marked decreases in total white blood cells, neutrophils, and lymphocytes. Infested calves also had moderate anemia, increased plasma proteins, and increased plasma fibrinogen. Some calves developed marked eosinophilia. Within 1 week after ivermectin treatment, nearly all hematologic parameters returned or began to return to normal values, even though scabs remained on the calves at 4 weeks. Peak eosinophilia in calves which responded occurred 1 to 2 weeks after treatment. The findings indicate that most of the hematologic changes occurring with psoroptic scabies in cattle are associated with living mites and not with toxic substances in the scab on the skin surface.