Influence of malic acid supplementation on ruminal pH, lactic acid utilization, and digestive function in steers fed high-concentrate finishing diets

Two trials were conducted to evaluate the influence of malic acid supplemen tation on ruminal fermentation. In Trial 1, six Holstein steers (300 kg) wi th ruminal cannulas were used in a crossover design experiment to study the influence of malic acid (MA) on ruminal metabolism during glucose-induced lactic acidosis. Treatments consisted of a 77% steam-flaked barley-based fi nishing diet supplemented to provide 0 or 80 g/d of MA. After a 13-d dietar y adjustment period, I kg of glucose was infused into the rumen 1 h after t he morning feeding. Ruminal pH was closely associated (R-2 = .70) with rumi nal DL-lactate concentration. Malic acid supplementation increased (P < .01 ) ruminal pH 3 h after the glucose infusion. However, there were no treatme nt effects (P > .10) on ruminal VFA molar proportions or ruminal and plasma DL-lactate concentrations. In Trial 2, four Holstein steers (150 kg) with cannulas in the rumen and proximal duodenum were used in a crossover design experiment to evaluate the influence of MA supplementation on characterist ics of digestion. Treatments consisted of an 81% steam-flaked barley-based finishing diet supplemented to provide 0 or 80 g/d of IMA. There were no tr eatment effects (P > .10) on ruminal and total tract digestion of OM, ADF, starch, and feed N or on ruminal microbial efficiency. Malic acid supplemen tation increased(P < .05) ruminal pH 2 h after feeding. As with Trial 1, th ere were no treatment effects (P > .10) on ruminal VFA and DL-lactate conce ntrations. We conclude that supplementation of high-grain finishing diets w ith MA may be beneficial in promoting a higher ruminal pH during periods of peak acid production without detrimental effects on ruminal microbial effi ciency or starch, fiber, and protein digestion. There were no detectable be neficial effects of MA supplementation on ruminal and plasma lactic acid co ncentrations in cattle fed high-grain diets.