Removing dietary sodium bicarbonate increases rumination time but does not affect intake or milk yield

We investigated the effect of adding 3 levels of sodium bicarbonate (SB: 0, 0.74 and 1.47% of total mixed ration (TMR) dry matter) to a low-roughage TMR (20.8% wheat silage, 9% wheat hay and 2.3% clover hay) on feed intake, production (milk and milk-component yields), whole-tract apparent digestibility, rumen pH and rumination time. After 2 wk of receiving the same TMR, 42 mid-lactation multiparous cows were blocked into groups of 3 according to their dry matter intake and energy-corrected milk (ECM) yield and divided into 3 treatment groups. The experimental rations were fed for 7 wk while monitoring intake, production and rumination. Rumen pH was measured after 6 h without access to feed and 6 h after feeding (at 0600 and 1500 h) every other week, and feces samples were taken for whole-tract apparent digestibility at wk 7. Dietary SB level did not affect intake, ECM yield, digestibility or efficiency. Dietary SB concentration negatively correlated with daily rumination time but did not affect rumen pH measured before or after feeding. Lactating cows may, therefore, increase their rumination time to compensate for lack of buffer but overall, removing SB from a wheat-based, low roughage TMR does not impair intake or milk or milk-component yields.