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) when malic acid was supplemented at 100 g per cow per day compared to 0 g per cow per day; 50 g per cow per day supplemental malic acid was intermediate. Malic acid supplementation did not affect (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) with either 50 or 100 g of supplemental malic acid. Based on the in vitro results, it appeared that 50 g supplemental malic acid per cow per day would be effective in vivo in altering ruminal fermentation and microbial efficiency. In experiment 2, milk yield was higher (P<0.05) for cows fed supplemental malic acid at a calculated amount of 50 g per cow per day. There was no effect (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) for cows fed supplemental malic acid because of higher milk yield. Total tract digestibility of dry matter (DM), OM, crude protein (CP), ADF, aNDF, hemicellulose, cellulose, ether extract, starch, and nonfiber carbohydrate (NFC) was not affected (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.