Peripheral B lymphocyte percentage as an indicator of subclinical progression of bovine leukemia virus infection.

The relationship between percentage of B cells in peripheral blood and subclinical bovine leukemia virus infection was examined in a herd of 240 Holstein-Friesian cows. Absolute leukocyte count and absolute lymphocyte count were significantly positively correlated with B cell percentage in cows that were seropositive to bovine leukemia virus envelope glycoprotein, but these parameters were not correlated in seronegative cows. The B cell percentage was not affected by age. Cows that had persistent lymphocytosis and hematologically normal seropositive cows had greater mean B cell percentages (78 and 45%, respectively) than did seronegative herdmates (37%). To evaluate B cell percentage as a means of detecting subclinical progression of bovine leukemia virus infection, an index was developed based upon the distribution of B cell percentages in seronegative cows. When this index was compared with a standard hematological key (the European Community's Leukosis Key), which is based on absolute lymphocyte count and age, 29% of seropositive, hematologically normal cows had B cell percentages two standard deviations above the mean of their seronegative herdmates. The B cell percentage was thus shown to be more effective than absolute lymphocyte count for detecting subclinical progression of bovine leukemia virus infection in individual cows.