Saliva is the free buffer

Walk a freestall after the second delivery and you can hear the difference before you see it. Quiet pens that still have full bunks often have cows that ate fast and then stopped chewing. The mixer ticket may look balanced. The free buffer may already be thin.

Saliva is free and manageable — alkaline fluid that arrives mostly when she chews. Most of it arrives when she chews; resting rates are much lower. Penn State’s From Feed to Milk puts farm units around six to eight hours of chewing a day and tens of gallons of saliva, rich in bicarbonate and phosphate. Beauchemin’s Journal of Dairy Science review puts lactating cows nearer about 4.5 hours eating plus about 7 hours ruminating (roughly 11.5 hours chewing total). Use both as ranges, not a duel: the practical point is that chewing drives salivary buffer flow, and fine, wet, or pelleted feeds cut saliva per pound of dry matter.

That does not make saliva the primary proton sink in the rumen. Aschenbach and related work (including OSU summaries of ruminal pH regulation) put the larger share of acid removal on absorption of short-chain fatty acids across the rumen wall. Saliva is the free lever you can still manage with particle size, bunk access, heat abatement, and water. Bagged sodium bicarbonate (or sesquicarbonate) is an aid for high–corn-silage or low-fiber diets, not a replacement for the endogenous stream.