An autoradiographic study of DNA synthesis in lymphoid cells of leucotic and healthy cattle.

The present study on 3H-thymidine incorporation using the histouatoradiographic method showed that spontaneous DNA synthesis occurred, on average, in 0.526 (+/- 0.233) per cent of lymphoid cells in 19 cattle with the normal blood picture (6,355+/-1,866 leucocytes/cu. mm). In 17 leucotic cattle with persistent leuco- and lymphocytosis (19,138+/-8,817 leucocytes/cu. mm) the proportion of these cells was insignificantly different, hovering about 0.554 (+/-0.191) per cent. The present sample did not include cases with marked changes in the blood picture (50,000-600,000 leucocytes/cu. mm) which occur in only 5-10 per cent of leucotic animals. This fact, however, could not influence the conclusion that even when used in conjunction with other methods, the determination of spontaneous DNA synthesis in peripheral lymphocytes is not a useful tool for the detection of preclinical phases of bovine leucosis.