Modulation of ruminal pH, milk fat secretion, and biohydrogenation intermediates by alkalizing agents in dairy cows fed starch-rich diets

Abstract We aimed to evaluate the effects of magnesium-based supplements and NaHCO3 on ruminal fermentation parameters, milk fatty acid (FA) profile, and milk fat synthesis in dairy cows fed high-starch diets. Eight second-lactation Holstein dairy cows (4 ruminally-cannulated) averaging 97 ± 12 days in milk and 33 ± 2.5 kg/d of milk were assigned to a replicated 4 × 4 Latin square design with 21-d periods. Cows were fed the following isoenergetic diets (1.64 Mcal/kg DM): (1) the control [342 g/kg starch on dry matter (DM) basis] without any buffering or alkalizing agent, (2) the control plus 8 g/kg DM NaHCO3, (3) the control plus 4 g/kg DM MgO, and (4) the control plus 8 g/kg DM CaMg(CO3)2. Ruminal pH was continuously measured for 72-h in each period using indwelling pH electrodes. Mean ruminal pH was not affected by treatments, but the duration of ruminal pH below 5.8 was shorter (P