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Manipulation of the Ruminal Fermentation. III. Effect of Nitrate on Ruminal Volatile Fatty Acid Production and Milk Composition

Department of Dairy Science, University of Wisconsin, Madison 53706

ABSTRACT

The ability of nitrate to alter ruminal fermentation by acting as an alternate electron acceptor was investigated. Sodium and potassium nitrate were either incorporated into the concentrate portion of a high grain ration fed to a nonlactating Jersey cow or were infused intraruminally in progressively larger amounts until nitrate (NO-₃) intake equaled 5 to 6% of total feed intake. Feed intake was reduced above 4% dietary nitrate, and methemoglobinemia appeared at higher nitrate intake. As per cent dietary nitrate increased from 0.7 to 4%, ruminal acetate increased from 62.3 to 80.2 molar per cent, propionate decreased from 19.6 to 14.7%, and butyrate from 16.1 to 5.0%. At times butyrate was lowered to 0.9 molar per cent. Nitrate-adapted ingesta reduced added nitrate in vitro more rapidly and caused greater alterations in ruminal acid production than nonadapted ingesta.

A lactation study with eight cows receiving a high grain, fat depressing ration determined if feeding nitrate would alter ruminal acetate and propionate production enough to increase fat test. Feeding nitrate at 2% of total feed intake increased molar per cent of ruminal acetate from 51.5 to 65.7 and decreased propionate from 33.6 to 20.9%. Molar per cent of butyrate was not affected. Ruminal ammonia increased with nitrate supplementation. Other than reduced feed intake, no toxic symptoms were noted. Milk composition was not significantly altered.

Nitrate is effective as an electron sink in ruminal fermentation, thus lowering the amount of relatively reduced acids such as propionate and butyrate and increasing acetate. Because of reduced palatability and the potential for toxicity, nitrate is probably not a desirable agent for manipulating ruminal fermentation.

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