The influence of chemical form on the effects of supplementary malate on serum metabolites and enzymes in finishing bull calves

This study investigated the effects of free malic acid and a commercial malate salt on serum metabolic parameters in finishing-stage Belgian Blue bull calves maintained in a commercial feedlot. Serum levels of glucose, non-esterified fatty acids (NEFA), β-Hydroxibutirate (BHBT) urea nitrogen (SUN), creatinine, total protein (TSP), L-lactate, aspartate aminotransferase (AST) and gamma glutamyl transferase (GGT) were monitored over 86days in 38 animals randomly allotted to three groups: MA (supplementation of feed with 4-g DL-malic acid per kg on a dry mass (DM) basis; 14 animals), MS (supplementation of feed with 4g of a commercial disodium/calcium DL-malic acid salt per kg DM; 14 animals), and C (controls with no malate supplement; 10 animals). All the parameters considered except SUN lay within the physiological ranges for intensively reared beef, possibly due to the high crude protein (CP) content of the diet and the forage fiber source (barley straw). However, animals fed either form of malate had lower serum L-lactate and creatinine levels than those that did not receive this supplement, and their NEFA levels fell over time instead of rising. The only parameters differing between the free acid and salt groups were SUN and BHBT, which for unknown reasons, were higher in group MA than in either controls or group MS. That SUN was higher in group MA than in group C is attributed to its favoring CP-degrading ruminal flora. That BHBT was higher in group MA than in groups MS and C could be due to that the acid form can promote butyrate synthesis in rumen.