Peripheral lymphocyte counts in Holstein-Friesian cattle infected with bovine leukemia virus in Korea

Bovine leukemia virus에 감염된 우리 나라 젖소의 말초혈액 내 림프구 수

Hematologic investigations were made on the blood samples taken from bovine leukemia virus (BLV)-seropositive Holstein-Friesian cattle in Korea, and their absolute lymphocyte count was compared with that of BLV-seronegative cattle. The incidence of persistent lymphocytosis (PL) was also determined. The normal bovine lymphocyte count was established on the basis of studies of 656 blood samples taken three times from 297 seronegative animals aged from 0~6 months to over 5 years at 5~6-month intervals. The data were examined according to 7 age groups of samples placed into their respective age groups. A peak in average total count was reached at 6~12 months ($5.36{\times}10^3/{\mu}l$) and thereafter the count declined continuously until over 5 years ($3.17{\times}10^3/{\mu}l$). From the results, 99.74 percent limits were calculated, and the upper limit of the range was chosen as the cutoff point for lymphocytosis. A PL was defined as a lymphocyte count that exceeded the above 99.74 percent limits and persisted over an interval of at least three months. The criterion for PL was applied to classifying 515 blood samples obtained four times from 189 seropositive animals without clinical signs at 5~7-month intervals. It was found that 54 (28.5%) of seropositive animals were with PL; cattle with PL were in age groups of 2~3 years to over 5 years.