Synchronization of carbohydrate and protein sources on fermentation and passage rates in dairy cows

Four ruminally cannulated Holstein cows in midlactation were randomly assig ned to a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of tr eatments to evaluate two nonstructural carbohydrate sources (corn or barley ) with two sources of ruminally undegradable protein (soybean meal or extru ded soybean meal) on milk production, ruminal fermentation, and digesta pas sage rates. Milk production (25.1, 27.5, 23.8, and 23.5 kg/d for the corn a nd soybean meal, corn and extruded soybean meal, barley and soybean meal, a nd barley and extruded soybean meal, respectively) and dry matter intake pe r unit of body weight (3.9, 4.1, 3.7, and 3.7%) were greater for cows fed c orn than for cows fed barley and were similar for cows fed soybean meal or extruded soybean meal. Concentrations of ruminal NH3-N were greater for cow s fed the corn and soybean meal diet than for cows fed other diets (15.0, 1 0.4, 9.0, and 11.3 mg/dl). Rumen volatile fatty acid concentrations were gr eater for cows fed corn than barley (133, 139, 121, and 118 mu mol/ml). Fra ctional passage rates of solids from the rumen were greater for cows fed th e barley and soybean meal diet than cows fed the corn and soybean meal diet (3.4, 3.9, 4.2, and 3.8%/h), and ruminal liquid dilution rates were simila r for cows fed all diets (11.2, 11.0, 11.1, and 11.9%/h). The attempt to sy nchronize ruminal nonstructural carbohydrate and crude protein degradabilit y produced minimal benefits for midlactation dairy cows.