Ruminal Fermentation Products and Plasma Ammonia of Fistulated Steers Fed Apple Pomace-Urea Diets

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The effects of apple pomace diets on ruminal fermentation products and plasma ammonia (NH3) were studied in two trials with fistulated steers. In trial 1, four fistulated steers were used in a 4 × 4 Latin square designed experiment to compare the addition of starch, trace minerals or both to an apple pomace-urea diet. In trial 2, five fistulated steers were used in a 5 × 5 Latin square designed experiment to compare a corn silage diet, an apple pomace-cottonseed meal diet, an apple pomace-urea diet, an apple pomace-urea diet plus corn starch and an apple pomace-urea diet plus straw. Feeding apple pomace was associated with a slightly reduced ruminal pH, a higher acetic propionic acid ratio, lower proportions of ruminal butyric, isobutyric and isovaleric acids and a noticeable production of ruminal ethanol. After apple pomace diets were fed, ruminal acetic acid increased more rapidly than propionic acid and ruminal ethanol concentration increased to a peak about 2 hr after feeding. The apple pomace-urea diet elevated ruminal NH3 concentrations and tended to delay the normal ruminal NH3 peak with time after feeding; however, plasma NH3 concentrations were not elevated. The addition of starch to apple pomace-urea diets tended to lower the acetic propionic acid ratio and to increase butyric acid. The effect of starch on ruminal NH3 concentration was variable but tended to lower the concentrations. Ruminal NH3 concentration peaked sooner with time after feeding when a mixture of trace minerals was added to the apple pomace-urea diet. The addition of straw to the apple pomace-urea diet did not affect ruminal fermentation products.