Effect of Ruminal Ammonia-Nitrogen Concentration on Protein Degradation in Situ

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Abstract
Two experiments were conducted to determine the effect of ruminal ammonia-N concentration on rate of ruminal protein degradation. In experiment 1, 4 Holstein steers were fed a basal diet of corn grain and corn silage at hourly intervals. Continuous intraruminal infusion of solutions containing NaHCO3 and NaCl or ammonium chloride resulted in ruminal ammonia-N concentrations that averaged 4.8 and 17.3 mg/dl. Ruminal fluid pH, fluid volume and turnover rate of fluid and molar percentage of acetate, propionate and butyrate were similar across treatments, reflecting steady-state conditions. Rates of N and dry matter diappearance from polyester bags containing soybean protein supplements with 10.2 or 50.1% soluble N were not affected by increase of ruminal ammonia-N concentrations from 4.8-17.3 mg/dl. In experiment 2, Holstein steers sere fed twice daily a basal diet of urea-supplemented corn grain and corn silage. Polyester bags containing soybean protein supplements were placed in the rumen at -4, 0 or 4 h with reference to feeding and incubated 1-12 h. Peak ruminal ammonia-N concentrations occurred during different periods of incubation for each treatment. Ruminal ammonia-N concentrations ranged from 3 mg/dl at 6 h postfeeding to 46 mg/dl at 1 h postfeeding. N and dry matter disappearance rates during 0-1 and 1-12 h of incubation did not differ among treatments.
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