Serum thromboxane generation by platelets in calves and adult cows

Abstract

Baseline values for platelet numbers and thromboxane A₂ generation during clotting were established in three age groups of cattle. In phase I when a small number of animals (n=9−11 per group) were sampled mean platelet numbers were significantly lower in adult cows (322.2 ± 21.3 × 10⁹/l) compared to yearling heifers and newborn calves (479.4 ± 31.1 and 529.0 ± 58.1 × 109/l, respectively). Thromboxane A₂ generation, as reflected by the concentration of its stable metabolite thromboxane B₂ (TxB₂), was not significantly different among groups after 1 h of clotting. However, mean serum TxB₂ concentrations after 2 h of clotting were significantly higher in yearling heifers and calves compared to adult cows, suggesting that the time of maximal ex vivo generation of thromboxane may be affected by the age of the animal. No linear correlation between platelet number of TxB2 production was detected. These initial data indicated that platelet numbers may be greater and TxB2 production per unit number of platelets following 1 or 2 h of clotting lower in bull calves than in heifer calves, yearling heifers and cows. Sampling of a larger number of young calves (10 heifers, 11 bulls) in phase II, however, failed to confirm an effect of sex on platelet numbers. The data suggest that age and sex have little overall effect on platelet number or ex vivo generations of thromboxane after 1 h of clotting. Therefore, measurement of serum thromboxane concentrations after clotting is a useful and relatively non-invasive method in cattle of assessing arachidonic acid metabolism in platelets and possibly the effects of drugs which modulate this process.