Replacement of Corn Silage with Wheat Middlings and Calcium Chloride or Sodium Bicarbonate for Lactating Dairy Cows1,2

Abstract

Five Holstein cows with ruminal cannulas were used in a 5×5 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% NaHCO3 arranged in a 2×2 factorial. Diets averaged about 34% NDF. Addition of CaCl2 to wheat middling diets generally doubled Ca concentration but decreased pH at 9h postfeeding and decreased acetate:propionate ratio in the rumen; thus, milk fat decreased from 3.70 to 3.50%. The acidic effects of CaCl2 appeared to negate any beneficial responses of increased Ca concentration. Because few interactions were noted for the combination of CaCl2 and NaHCO3, CaCl2 would not likely be a more effective source of Ca than traditional sources. Cows fed wheat middling diets with NaHCO3 had slightly higher ruminal acetate:propionate ratios, but milk fat percentage was unaffected compared with the ratios of cows fed wheat middling diets without NaHCO3. Ruminal pH was below 6.0 for all treatments for at least 9h postfeeding. Therefore, production of VFA probably exceeded buffering capacity for much of the feeding period and limited potential beneficial effects of addition of NaHCO3 on fiber digestion and milk production. On average, cows fed wheat middling diets tended to have lower ruminal pH and acetate:propionate ratios but had higher DMI and FCM production than did those fed the high forage control diet. Results are interpreted to suggest that wheat middlings at 15% of DM are an effective substitute of corn silage for lactating cows.