放牧牛のピロプラズマ病人工感染免疫における毒血接種から免疫獲得までに要する期間についての一観察例 Observation on the Interval between Virulent Blood Inoculation and Acquisition of Immunity to Piroplasmosis in Grazing Cows

Thirty-one Holstein cows were placed in pasture in Shimane Prefecture over a period from April to August, 1970. Each of them was inoculated with 1ml of defibrinated blood of indigenous cattle infected with piroplasrnas to a severity of -H-F, in April, 1970. As a result, piroplasmas were detected from all the cows by 45 days after inoculation. Finally, 13 cows (41.9%) were proved to have acquired immunity to the protozoa, without receiving any treatment during the proper period of grazing. In general, 70 days seemed to be insufficient and at least 4 months required for effective immunity to be established.