Studies on enzootic bovine leukosis I. The changes of antibodies against bovine leukemia virus and peripheral blood lymphocyte on Holstein cattle in a dairy farm

축우의 유행형 (지방병성) 백혈병에 관한 연구 I. 한 유우군의 우백혈병 바이러스 항체와 혈중 임파구의 변동에 관하여

To investigate bovine leukosis virus (BLV) infection in the cattle rearing in a dairy farm where a case of bovine lymphosarcoma had been identified several years ago, the 196 Holstein cattle including newborn calves to 12 years of age were tested. The BLV antibody test and peripheral lymphocyte count for bovine leukosis were carried out by the immunodiffusion (ID) test and Bendixen's Kep. These tests were performed 2 to 4 times at the interval of 3 to 5 months. The observed results were as follows: 1. The positive rates of BLV-antibody in the 1st, the 2nd, the 3rd and the 4th tests were 23.3%, 28.1%, 49.0% and 55.7%, respectively. The conversion rates from negative to positive in the 2nd, the 3rd and the 4th tests were 8.9%, 41.4%, and 20.0%, respectively. Results showed that the highest conversion rate was observed at the 3rd test which was conducted after winter. The highest positive rate by ID test were observed in 4 year old cattle in the 1st and 2nd tests, and in 2 year old herd in the 3rd and 4th tests. 2. In hematological test by Bendixen's Key, the positive and suspicious rates in the 1st, the 2nd, the 3rd and the 4th tests were 5.8 and 7.8%, 8.3 and 6.6%, 8.7 and 10.1%, 10.8 and 19.6% respectively. Results showed that the positive and. suspicious rates increased in course of time. 3. 70 to 100% of the positive cattle in hematological test were positive for BLV-antibody test. All of 13 cattle with persistent lymphocytosis (PL) were also positive for BLV-antibody, indicating the high relationship between PL and BLV-antibody. 4. The number of total leukocytes and absolute lymphocytes in the BLV-antibody positive cattle appeared significantly higher than those of the negative cattle. The markedly increased cell counts were observed in the cattle over one year old. 5. The mean of total leukocytes and absolute lymphocytes in the negative cattle for BLV-antibody increased slightly after sero-conversion into positive. 6. In the clinical examinations during experimental periods, none of the 72 positive cattle for BLV-antibody showed any lesions for bovine leukosis.