Influence of buffering early lactation rations with sodium bicarbonate and magnesium oxide and subsequent withdrawal or addition effects.

Eighty animals (16 first lactation) were assigned alternately at calving to one of four treatments: A) corn silage, B) corn silage + 1.5% sodium bicarbonate and .5% magnesium oxide in the grain mix, C) 50% hay crop silage and 50% corn silage, and D) 50% hay crop silage and corn silage plus 1.5% sodium bicarbonate and .5% magnesium oxide. All rations contained 50% forage and 50% concentrate (dry) fed as a total mixed ration. During the first 8 wk of lactation no differences were detected in mean performance or in weekly patterns for forage programs alone or buffer treatments alone on average daily intake of dry matter, body weight loss, milk yield, or composition. Addition of buffers to hay crop silage and corn silage rations resulted in a milk yield profile with a smaller increase beyond wk 3 postpartum. Cows fed all corn silage rations yielded more milk on the average than cows on hay crop silage and corn silage, regardless of buffer treatments. From wk 9 through 12 of lactation, buffers either were added or withdrawn. Addition or withdrawal of buffers did not alter significantly patterns of milk yield or composition.