Zinc toxicosis has been reported with increasing frequency in livestock species. This report describes changes in haemograms, prothrombin time, activated partial thromboplastin time (APTT), fibrinogen concentration and antithrombin III activities in zinc-toxic calves (706 μg zinc/g diet), compared to control calves (100 μ zinc/g diet). When comparing differential leucocyte counts in calves before and during exposure to high zinc, there was a significant increase in segmented neutrophils and unclassified cells, and a reduction in eosinophils; there was no change in the number of band neutrophils, lymphocytes, monocytes, basophils and the ratio of neutrophils to lymphocytes. Measures of coagulability were compared between zinc-toxic calves, 13 days after reduction of their diet from 706 μg to 150 μg zinc/g diet, and control calves. Significantly lower (p <0.01) prothrombin time in zinc-toxic calves (mean = 13.3 s), compared to control calves (mean = 15.9 s), and significantly lower (p <0.01) APTT in zinc-toxic calves (mean = 27.8 s), compared to control calves (mean = 36.6 s) indicated that clot generation was more active in zinc-toxic calves. These findings, when combined with the observed pathological lesions of thrombosis, supported a state of hypercoagulability. Fibrinogen concentration in zinc-toxic calves (231 mg/ dl) did not differ from controls (199 mg/dl). Similarly, antithrombin III activities in zinc-toxic calves (107.5%) did not differ from controls (103.5%). Possible mechanisms responsible for these alterations are discussed.
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