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Microbial Protein Synthesis Low Quality Roughage Rations: Level and Source of Nitrogen

Agricultural Experiment Station, Oklahoma State University⁴, Stillwater 74074

Abstract

Four 350 kg steers, fitted with permanent rumen and abomasal cannulas, were fed cottonseed hulls with soybean meal (SBM) or urea supplements to study the influence of level and source of nitrogen on microbial protein production. Protein levels on a dry matter basis were 11.1, 8.5, 10.8 and 12.6% for S-100, U-75, U-100 and U-115, respectively. Total daily feed intake was 5 kg/day. Steers were fed hourly to maintain relatively steady state ruminal conditions. Mean ruminal ammonia-nitrogen concentrations were 8.1, 3.7, 12.4 and 22.2 mg NH3 -N/100 ml rumen fluid for steers fed the four rations, respectively. SBM was superior to any level of urea for total apparent dry matter (DM), organic matter (OM) and cellulose digestion. The DM, OM and cellulose digestibilities were improved by the addition of urea above the lowest level (P<.01); a negative nitrogen balance was noted with this ration, also. Microbial protein synthesis per 100 g OM apparently digested in the rumen was 18.9, 17.9, 19.9 and 19.3 for S-100, U-75, U-100 and U-115, respectively. An estimated 20% of the SBM-nitrogen escaped ruminal degradation. No significant differences were noted among rations for di-gesta passage, dilution rate or rumen turnover time. Microbial protein production per 100 g DM digested in the rumen appeared to plateau at dilution rates of 5.5 to 6% per hour.

² Present address: Head, Department of Animal Science, University of Tennessee, Knoxville, 37901.

³ Present address: Department of Animal Science, Southern Illinois University, Carbondale, 62901.

⁴ Department of Animal Sciences and Industry.

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