Effect of milk by-products on forage in vitro fermentation by ruminal microflora

The effect of milk-based by-products containing lactose and sucrose on alfalfa (ALF) and tall fescue (TF) hay fermentation by ruminal microflora was studied using a single-flow, continuous-culture and batch-culture procedure. Continuous-culture fermentation used only ALF as a forage source and tested buttermilk (BM) and ice cream by-product with cone (ICBPWC). Levels of by-products were 0, 50, and 100% of total DM. For the batch-culture experiment (n = 5) 5 levels of ALF or TF (0, 10, 20, 50, and 75% of DM) were combined with BM, ICBPWC, or ice cream by-product without cone (ICBP). In continuous culture, addition of BM increased apparent OM digestibility and true OM digestibility linearly (P < 0.05), whereas addition of ICBPWC increased true OM digestibility and NDF digestibility linearly (P < 0.05). Total VFA was increased quadratically (P = 0.05) with addition of BM and tended (P = 0.06) to increase linearly with addition of ICBPWC. The addition of BM linearly decreased (P < 0.05) acetate and linearly increased (P < 0.05) butyrate, but propionate levels did not change (P > 0.05). The addition of ICBPWC quadratically decreased (P < 0.05) acetate and quadratically increased (P < 0.05) propionate. The addition of ICBPWC tended (P = 0.09) to quadratically increase grams of microbial N per kilogram of OM truly digested. Dry matter digestibility increased (P < 0.05) linearly in batch culture when by-products were added to both ALF and TF, with DM digestibility response greater (P < 0.05) for TF than for ALF. Addition of milk-based by-products was not detrimental to forage NDF digestibility and increased DM digestibility of the diet.