Replacement of Corn Silage with Wheat Middlings and Calcium Chloride or Sodium Bicarbonate for Lactating Dairy Cows

Five Holstein cows with ruminal cannulas were used in a 5 x 5 Latin square design in which one diet contained 50% corn silage (high forage control) and four diets contained 38 to 39% corn silage and 15% wheat middlings with or without addition of .45%CaCl2 or .9%NaHC03 arranged in a 2 x 2 factorial.Diets averaged about 34% NDF.Addition of Ca02 to wheat middling diets generally doubled Ca concentration but decreased pH at 9 h postfeeding and decreased acetate:propionate ratio in the rumen; thus, milk fat decreased from 3.70 to 3.50%.The acidic effects of CaCI2 appeared to negate any beneficial responses of increased Ca concentration.Because few interactions were noted for the combination of CaCl2 and NaHC03, CaCI2 would not likely be a more effective source of Ca than traditional sources.Cows fed wheat middling diets with NaHC03 had slightly higher ruminal acetate:propionate ratios, but milk fat percentage was unaffected compared with the ratios of cows fed wheat middling diets without NaHC03.Ruminal pH was below 6.0 for all treatments for at least 9 h postfeeding.Therefore, production of VFA probably exceeded buffering capacity for much of the feed-