Effect of time related to calving and rumen protected choline (RPC) supplementation on blood analytes and on liver lipid and glycogen

Lactate dehydrogenase (LDH), an enzyme of the anaerobic glycolytic pathway with several isoforms, is found intracellularly in most tissues. Increased LDH is frequently used in human medicine to distinguish pleural exudates from transudates (Light’s criteria), and therefore may also be useful to help differentiate body cavity effusions in animals. Because LDH is a large molecule that does not pass readily though intact endothelial surfaces, concentrations in pleural or peritoneal fluid do not equilibrate rapidly with plasma values, and high effusion LDH is therefore likely to originate from inflammatory or damaged cells in that cavity. We tested pleural, peritoneal and pericardial effusions from dogs, cats and horses (n=50) using three different LDH tests – RANDOX wet chemistry testing both the lactate-to-pyruvate (L-P) and pyruvate-to-lactate (P-L) reaction and dry chemistry (IDEXX) measuring P-L. Although there is a good correlation between all the tests (r2= 0.98), there are significant differences between their absolute values. IDEXX chemistry produces the highest values (approximately 4x Daytona L-P) followed by Daytona P-L (approximately 2x L-P values) and Daytona L-P usually the lowest. Therefore it is necessary to establish different cut-off values for differentiating between transudates and exudates depending on which method is used. Results to date show that LDH activity tends to be highest in exudates and modified transudates in all methods evaluated and lowest in transudative effusions. This test may be useful for general practice where fluid analysis is not immediately available