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Dietary Buffering Requirements of the Lactating Dairy Cow: A Review¹

Animal Sciences Department, University of Maryland, College Park 20742

ABSTRACT

Requirements for buffering agents in dairy cow diets are a function of salivary buffer secretion, feedstuff buffering capacity, and feed acidity. Decreasing diet ADF by one percentage unit results in a .0564 unit decline in rumen pH. Reduction in rumen pH below 6.3 in dairy cows results in a 3.6 percentage unit decline in ADF digestion per .1 pH unit decrease and 5result in depressed feed intake. Effects of decreased rumen pH on whole animal acid-base balance and metabolism are less well-defined. Although salivary buffer flow is not well-defined because of inadequate methodology available for measurement of saliva flow, the estimates of 108 to 308 L/d in beef and dairy cows is equivalent to 390 to 1115 g/d disodium phosphate and 1134 to 3234 g/d NaHCO₃ secretion, making saliva the predominant source of rumen buffering. Where buffer flow from saliva is inadequate, added dietary buffers 5be justified. Data from a total of 82 experiments were summarized by buffering material and basal diets. Published experiments documented that the use of NaHCO₃, MgO, KHCO₃, K₂CO₃, and other buffering agents in low forage diets, are effective in increasing rumen pH, rumen acetate:propionate molar ratio, and milk fat percent. In diets containing at least 30% DM from forages, effects of dietary buffers on rumen pH and milk fat percent are less pronounced. In 17 studies where corn silage was the sole forage, addition of dietary NaHCO₃ increased feed intake by .5 kg/d and FCM by 1.1 kg/d. However, when alfalfa haylage or hay crop silage was included as all or part of the forage portion of the diet, responses were less. There is no justification for use of dietary buffers in alfalfa hay-based diets from a summary of eight experiments. Regression analysis of milk fat percent responses to dietary ADF, NaHCO₃, and MgO suggest that in diets containing 14% ADF, 44 g NaHCO₃, or 20 g MgO are equivalent to increasing dietary fiber by one percentage unit with responses to added buffers diminishing as dietary fiber increases.

¹ Scientific Article A-4761, Contribution Number 7765 of the Maryland Agricultural Experiment Station.

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