Effects of malic acid on microbial efficiency and metabolism in continuous culture of rumen contents and on performance of mid-lactation dairy cows

Two experiments were conducted to determine the effect of malic acid supplementation on: (1) nutrient digestibility and metabolism of ruminal microorganisms in continuous culture of rumen contents and (2) lactation performance of mid-lactation dairy cows and total tract nutrient digestibility. In experiment 1, digestibility of acid detergent fiber (ADF) and neutral detergent fiber (aNDF) was higher (P 0.05) the production of total volatile fatty acids, propionic acid, butyric acid, and isobutyric acid, the ratio of acetic to propionic acid, or pH. Microbial nitrogen (N) production and efficiency of organic matter (OM) and total carbohydrate use for microbial N production increased (P 0.05) of malic acid supplementation on content of fat, true protein, or lactose in milk. However, yield of true protein and lactose was higher (P 0.05) by malic acid supplementation. In conclusion, malic acid supplementation in lactating cow diets was effective at increasing microbial N production and microbial efficiency measured in vitro and milk yield.